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SYSTEM OF DIFFERENTIAL CORRECTION AND MONITORING
INTERFACE
CONTROL
DOCUMENT
Radiosignals and digital data structure of
GLONASS Wide Area Augmentation System,
System of Differential Correction and Monitoring
(Edition 1)
2012
Edition 1 2012 ICD SDCM
Joint Stock Company "Russian Space Systems"
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УТВЕРЖДАЮ APPROVED
Командующий Космическими войсками
О.
Head of Federal Space Agency
____________________Vladimir Popovkin
«_______»____________________2012
Interface Control Document
Radiosignals and digital data structure of
GLONASS Wide Area Augmentation System,
System of Differential Correction and Monitoring
(Edition 1)
AGREED
Deputy Head of Federal Space Agency
______________Anatoliy Shilov
«_______»__________2012
First Deputy Director General – Designer
General of Russian Space Systems
__________________Sergey Ezhov
«_______»______________2012
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From Russian Space Systems From Federal Space Agency
Grigoriy Stupak
A.Terekhov
From Center of programs and planes
realization on rocket and space
engineering
Vyacheslav Dvorkin Vladimir Klimov
Sergey Karutin
S. Andrianov
Sergey Kalinchev
N.M. Volkov
Vladimir Kurshin
Vitaliy Sernov
Daniil Visnyakov
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Table of contents
1 Introduction .......................................................................................................... 10
1.1 SDCM purpose .............................................................................................. 10
1.2 SDCM components ....................................................................................... 10
1.3 SDCM interface definition ............................................................................ 11
2 GENERAL ........................................................................................................... 13
2.1 ICD definition ................................................................................................ 13
2.2 ICD approval and revision ............................................................................. 13
3 Space Segment of SDCM ..................................................................................... 14
3.1 Space Segment structure ................................................................................ 14
4 General aspects interaction between SDCM and user ......................................... 15
5 Interface of SDCM radiosignals ........................................................................... 17
5.1 L1 signal structure ......................................................................................... 17
5.2 RF signal characteristics of L1 ...................................................................... 17
5.3 C/A codes in L1 SDCM signal ...................................................................... 20
5.4 Convolutional encoding of transmitted digital data ...................................... 23
6 SDCM data format ............................................................................................... 24
6.1 General format information ........................................................................... 24
6.2 Preamble ........................................................................................................ 24
6.3 Message type identifier .................................................................................. 24
6.4 Data field ....................................................................................................... 26
6.5 Messages and Relationship between Message Types ................................... 26
6.6 Data field M(x) .............................................................................................. 27
6.7 Cyclic Redundancy Check ............................................................................ 27
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7 SDCM data content .............................................................................................. 29
7.1 SDCM testing mode (Message Type 0) ........................................................ 29
7.2 PRN Mask Assignments (Message Type 1) .................................................. 29
7.3 GEO Navigation Message (Message Type 9) ............................................... 33
7.4 GEO Almanac Message Type 17 .................................................................. 34
7.5 Long-term and mixed satellite error corrections (Message Types 24 and 25)37
7.6 Fast corrections Message Types 2-5 ............................................................. 42
7.7 Integrity parameters of fast and long-term corrections (Message Type 6) ... 45
7.8 Ionosphere Grid Point Masks Message Type 18 ........................................... 47
7.9 Ionospheric Delay Corrections Messages Type 26 ...................................... 52
7.10 Degradation parameters (Messages Type 7 and 10) ................................. 54
7.11 SDCM Network Time/UTC/GLONASS Time Offset Parameters
Message Type 12 .......................................................................................... 59
7.12 SDCM Service Message Type 27 ............................................................. 61
7.13 Clock-ephemeris Covariance Matrix Message Type 28 .......................... 64
7.14 Null Message Type 63 and Internal Test Message Type 62 .................... 66
8 Annex А. Definitions of basic a priory and a posteriori parameters for navigation
user equipment accuracy assessment taking into account SDCM data .................. 67
9 Annex B. Basic integrity principles .................................................................... 69
10 Annex C. Tables of SDCM message formats ................................................. 76
11 Annex D. Recommendations on SDCM data use in the navigation algorithm
GLONASS/GPS/SDCM ......................................................................................... 84
12 Annex E. Recommendations on the troposphere model ............................... 102
13 Annex F. Transmission sequence of SDCM messages. ............................... 105
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14 Annex G. Transmission sequence of SDCM messages when changing data
field of used satellites (change of PRN mask) ...................................................... 107
15 Annex I. Definitions of SDCM data application protocols ......................... 108
16 Annnex J. Additional materials and data ...................................................... 124
17 References ..................................................................................................... 127
18 Changes registration list ................................................................................ 128
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List of acronyms and abbreviations
UE – User Equipment
IMO – International Marine Organization
GEO – Geostationary satellite
GNSS – Global Navigation Satellite System
GSO – Geostationary Orbit
GDOP – Geometric Dilution of Precision
ICAO – International Civil Aviation Organization
II – Integrity Information (of GNSS radionavigation field)
SC – Spacecraft
CI – Correcting Information (corrections to ephemeris and time-and
frequency parameters)
CMS – Command-Measuring System
NUE – Navigation User Equipment
NSC – Navigation Spacecraft
NS – Navigation Satellite
OC – Orbital Constellation
ERP – Earth Rotation Parameters
SW – Software
SS – Space Segment
SDCM – System of Differential Correction and Monitoring
RS – Reference Station
SA – Standard Accuracy
RIRV – Russian Institute of Radionavigation and Time
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STS – System Time Scale
CS – Central Synchronizer
MCS – Mission Control Center
TFC – Time-and-Frequency Corrections
ECD – Efemeris and Clock Data
AT – Atomic Time
BPSK – Binary Phase-Shifted Key
CRC – Cyclic Redundancy Check
C/A – Coarse Acquisition
ECEF – Earth-Centered Earth-Fixed
ET – Ephemeris Time
DOP – Dilution of Precision
GDOP – Geometric Dilution of Precision
GIVE – Grid Ionospheric Vertical Error
HAL – Horizontal Alert Limit
HDOP – Horizontal Dilution of Precision
HPL – Horizontal Protection Level
IOD – Issue of Data
JD – Julian Date
PDOP – Position Dilution of Precision
PRN – Pseudorandom Number
RAIM – Receiver Autonomous Integrity Monitoring
RMS – Root Mean Square
RTCA – Radio Technical Commission for Aeronautics
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RTCM – Radio Technical Commission for Maritime Services Special
Committee
SARPs – Standards and Recommended Practices
SBAS – Satellite-Based Augmentation System
SNT – SBAS Network Time
SoL – Safety of Life service
TDOP – Time Dilution of Precision
TTA – Time to Alert
VAL – Vertical Alert Limit
VDOP – Vertical Dilution of Precision
VPL – Vertical Protection Level
UIRE – User Ionospheric Range Error
UERE – User Equivalent Range Error
UDRE – User Differential Range Error
UERRE – User Equivalent Range Rate Error
URA – User Range Accuracy
UT – Universal Time
UTC – Universal Time Coordinated
UTC (SU) – Universal Time Coordinated (SU)
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1 Introduction
1.1 SDCM purpose
1.1.1 The System of Differential Correction and Monitoring
(SDCM) is an SBAS augmentation to the Global Navigation Satellite System
GLONASS for enhancing accuracy and calculating integrity of positioning for
marine, airborne, terrestrial and space users of GLONASS and GPS opened
radiosignals.
1.2 SDCM components
1.2.1 SDCM includes two subsystems:
Constellation of satellites (Space Segment);
Ground-based monitoring and control facilities (Control Segment)
Space Segment includes 3 operating geostationary satellites of multifunctional
Space System Luch, broadcasting SDCM data to users by means of SBAS
radiosignals described in Section 4.
Control Segment includes Center of Differential Correction and Monitoring
(CDCM), ground based facilities transmitting SDCM data to users, Mission Uplink
and Control Center and the network of Reference Stations located worldwide.
Control Segment is responsible for:
Monitoring of opened radionavigation field of GLONASS and GPS
satellites;
continuous correcting (уточнение) of orbits and clocks of GLONASS
and GPS satellites;
generating correcting data and integrity parameters;
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transmitting corrections and integrity data to users via Space Segment
and ground facilities.
1.3 SDCM interface definition
1.3.1 Fig 1 shows General Interface from Space Segment (of
GLONASS, SDCM and GPS systems) to Navigation User Equipment (NUE). It is
formed by L1 radiosignals of SDCM and opened GLONASS and GPS radiosignals of
L1, L2, L3 and L5 frequency bands.
Figure 1. Interface from Space Segment to NUE for SDCM
GLONASS constellation includes GLONASS-M and GLONASS-K satellites.
GLONASS-M satellites radiate opened navigation radiosignals with frequency
division (OF) in two frequency bands: L1 and L2. Satellites located in opposite points
of the same orbit plane (antipodal), can transmit navigation radiosignals on equal
carrier frequencies.
GLONASS-K satellites of the first phase radiate L3OC opened radiosignals in
L3 frequency band, besides L1OF and L2OF.
Interface of L1OF and L2OF signals radiated by GLONASS-M and
GLONASS-K satellites, regulated by GLONASS ICD «Navigation radiosignal in
bands L1, L2 with open access and frequency division », 2010, Edition 5.2.
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Interface of L3OC signal radiated by GLONASS-K satellites, regulated by
GLONASS ICD «Navigation radiosignal in band L3 with open access and code
division», 2011, Edition 1.
L1 signal of SDCM СДКМ radiated by geostationary satellites, is
informational and transmits differential corrections and GNSS integrity data to
navigation users.
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2 GENERAL
2.1 ICD definition
2.1.1 Given Interface Control Document (ICD) specifies
parameters of interface of radiosignals emitted by SDCM Space Segment in L1
frequency band.
2.2 ICD approval and revision
2.2.1 Joint Stock Company “Russian Space Systems” (JSC RSS)
is a developer of ICD and a head responsible for SDCM creation.
JSC RSS is responsible for development, coordination, revision, maintenance
an official distribution of ICD.
ICD shall be approved by duly authorized representatives of Federal Space
Agency (Roskosmos) and enters into effect upon approval by Head of Roskosmos.
In the course of SDCM development its separate parameters can vary. The
developer of ICD bears responsibility for negotiation of the offered modifications
with all responsible sides and for preparation, if necessary, the new edition of the
ICD containing modifications.
Modifications and new editions of the ICD enter into effect upon approval by
Head of Roskosmos.
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3 Space Segment of SDCM
3.1 Space Segment structure
3.1.1 Completely deployed Space Segment includes 3 operating
geostationary satellites (see Table 1).
Table 1. Nominal parameters of SDCM Space Segment
Orbital position Luch-5А Luch -5B Luch -5V
167o E 95
o E 16
o W
PRN 140 125 141
Eccentricity 0 0 0
Inclination (o) 0 0 0
Radius (km) GSO 42164 42164 42164
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4 General aspects interaction between SDCM and user
Requirements for SDCM Time to alert (TTA) are showed in Annex G
‘Recommendations for using SDCM data in the navigation algorithm
GLONASS/GPS/SDCM (accordingly for state functions of GNSS satellites, principal
differential corrections and accurate differential corrections)”. Figure 2 shows
components of total TTA for both ground and space segments.
Figure 2. Time to alert for SDCM
According to Figure 2 ‘initial event’ in GNSS/SDCM and ‘initial event’ at user
equipment which mean satellite failure are considered simultaneous. Actually it is not
so due to different parameters of receivers. There is little difference, due to receiver
processing, between the time of measured pseudorange distortion and the time when
distorted information is displayed. For simplification, it is not shown in the Figure.
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Taking into account the local nature of tropospheric delay, all users calculate
their own delays at troposphere. Recommended model for tropospheric delay
calculation is given in Annex D ‘Recommendations for tropospheric model’ (based
on RTCA/DO-229D) nevertheless, other models can also be used, at discretion and
responsibility of the user.
Multipath contribution into positioning error is considerable and affects both
SDCM ground facilities and user equipment. In SDCM ground facilities multipath
effect is decreased as far as it is possible or suppressed to minimize signal errors.
User equipment also should provide for multipath suppression means.
Special means is used in SDCM preventing any ambiguity when using
corrections. It is described in Section 7.5.
In GPS and GLONASS different coordinate systems are used, WGS-84 and
PZ-90.02 respectively. SDCM generates corrections in WGS-84 by matrix
transformation of GLONASS data from PZ-90.02 (see Annex I “SDCM data
protocols definition”).
In SBAS messages SDCM data for GLONASS and GPS are presented in
single time scale, GPS.
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5 Interface of SDCM radiosignals
5.1 L1 signal structure
5.1.1 L1 signal of SDCM is radiated by three geostationary
satellites, antenna inclination to the north from is 7 o.
5.2 RF signal characteristics of L1
5.2.1 Carrier frequency of L1 signal
Noise –type radiosignal is used at the carrier frequency of 1575,42 MHz with
code division between three geostationary satellites.
5.2.2 Carrier frequency stability
Short-term instability of carrier frequency at the output of the satellite
transmitting antenna shall not exceed 5 × 10-11
when averaging at time intervals of 1-
10 s.
5.2.3 Carrier phase noise
In L1 signal the phase noise spectral density of the non-modulated carrier is
such that in a receiver a phase locked loop of 10 Hz one-sided noise bandwidth
provides the accuracy of carrier phase tracking not worse than 0.1 radian (1σ).
5.2.4 Spurious Transmissions
Spurious transmissions will be at least 40 dB below the unmodulated carrier
power over all frequencies.
5.2.5 Modulation
Transmitted message 250 bps with convolutional encoding at a rate of 500
symbols per second will be added modulo-2 to a 1023-bit pseudo-random noise code.
It will then be bi-phase shift-keyed (BPSK) modulated onto the carrier at a rate of
1,023 Mbps. Symbols of SDCM message (transmission rate of 500 symbols per
second are synchronized with time interval of 1 millisecond of С/А code.
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5.2.6 L1 radiosignal spectrum
Main lobe of L1 signal transmitted by SDCM geostationary satellites will
occupy the bandwidth of 2,046 MHz.
5.2.7 Doppler shift
The Doppler shift of L1 carrier received by stationary user from a SDCM
geostationary satellite, is caused by the satellite motion which in the worst case (end
of life) will be less than 40 meters per second relative to the user and, respectively,
Doppler shift will be less than 210 Hz.
5.2.8 Polarization
L1 signal transmitted by SDCM geostationary satellites will be right-hand
circularly polarized. The ellipticity will be no worse than 2 dB for the angular range
of 9,1 from boresight.
5.2.9 User received signal levels
The power level of the received L1 С/А signal from SDCM geostationary
satellite with the radiated power of 43 3 W, at the output of a 0dBi right-hand
circular polarized antenna will be greater than -158,5 dBW for elevation angle of 5O
or more. The maximum received power level will be greater than -155 dBW in such
an antenna.
Power level response of the received L1 С/А signal for nominal radiated power
and the antenna gain 1 depending from the elevation angle is showed in Table 2 for
ground-based users of north and south latitudes across the meridian of SDCM
geostationary satellite position.
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Table 2. L1 power level response depending from the elevation angle of
geostationary satellite provided that the user and satellite positions have the same
meridian
Elevation angle
(degrees)
Power level
(dBW)
5 -157,0
15 -156,7
25 -156,5
35 -156,3
45 -156,1
55 -156,1
65 -156,1
75 -156,2
85 -156,6
90 -156,9
85 -157,1
75 -157,7
65 -158,5
55 -159,4
45 -160,3
35 -161,1
25 -161,8
15 -162,3
5 -162,7
Estimated coverages of SDCM geostationary satellites are showed in Figure 3.
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ased
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es
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ased
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des
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Figure 3. Estimated coverages of SDCM geostationary satellites
Edge of coverage is determined by signal level (not less than -158,5 dBW) and
by elevation angle.
5.2.10 Correlation loss
Correlation loss of L1 signal resulting from modulation imperfections and
filtering of inside the satellite will be less than1 dB.
5.3 C/A codes in L1 SDCM signal
5.3.1 Requirements
C/A codes used in L1 SDCM signal will belong to the family of 1023-bit Gold
codes.
5.3.2 C/A codes generation
C/A codes are Gold codes generated by Modulo-2 addition of two 1023 bit
pseudo-random sequences, G1 and G2 generated by two 10 trigger resistors having
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different feedbacks (see Figures 4 and 5): for G1 from triggers 3 and 10; for G2 from
triggers 2, 3, 6, 8, 9, 10.
C/A codes are identified in three ways:
1) PRN number;
2) G2 delay in chips (see Figure 4);
3) Initial G2 state (see Figure 5).
5.3.3 SDCM C/A codes
SDCM uses 3 allowable С/А codes with numbers 125, 140 and 141. Table 3
shows G2 delay figures for given codes (code delay).
Figure 4. Programmable G2 delay
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Figure 5. Programmable initial G2 state
Table 3. Allowable SDCM С/А codes
PRN G2 delay
(chips) Initial G2 state First 10 SDCM chips
125 235 1076 0701
140 456 1653 0124
141 499 1411 0366
Comment. Initial G2 state and first 10 chips of SDCM are written in the
following way: first left figure is 0 or 1 for the first chip, next three figures in octal
counting system present other 9 chips. First 10 chips of SDCM are inverse to initial
G2 state and also presented in octal counting system.
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5.4 Convolutional encoding of transmitted digital data
In L1 signal transmitted by a geostationary satellite, digital data transmitted at
a rate of 250 bit per second are continuously convolutional encoded at a code rate of
500 symbols per second.
Figure 6 shows convolutional encoding.
Figure 6. Convolutional encoding
Comment. In the first part of each bit output switch of the convolutional
encoder is fixed in the lower (1) position.
Data Input
250 BPS
Output symbols 500 SPS
1
2
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6 SDCM data format
6.1 General format information
All SDCM messages are transmitted in blocks by 250 bits (Figure 7): 8
bits – preamble, 6 bits – Message Type, 212 bits – data field, 24 bits – Cyclic
Redundancy Check (CRC) for error detection in the data field.
Direction of data flow from satellite . Most significant bit (MSB) transmitted first
250 Bits – 1 Second
8-Bit Preamble 24-Bits Parity
6-Bit Message Type Iidentifier
212-bit Data Field
Figure 7. Data block format
6.2 Preamble
The distributed preamble will be a 24-bit unique word, distributed over three
successive blocks. These three 8-bit words will be made up of the sequence of bits -
01010011, 10011010, 11000110.
6.3 Message type identifier
Message type identifier consists of 6 binary symbols and defines 64 message
types (0…63), as Table 4 shows. Message type identifier is transmitted by most
significant bit ahead.
Table 4 shows SDCM messages transmitted by geostationary satellites. These
data are transmitted in 250-bit blocks. Each block starts with 8-bit heading
(preamble), then 6-bit message type follows defining the type (or number) of the
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message. Data field length is 212 bits. At the end of each block 24 parity bits go
allowing checking the validity of received data and in some cases restore the data.
Table 4. SDCM message types
Type Contents
0 Don’t use for safety applications (for SDCM testing)
1 PRN Mask assignments
2–5 SDCM fast corrections
6 GNSS/SDCM integrity information
7 Fast correction degradation factor
8 Reserved for future messages
9 GEO navigation message
10 Degradation parameters (of fast and long-term corrections, ionospheric
delays)
11 Reserved for future messages
12 SDCM network time /UTC offset Parameters
13 to16 Reserved for future messages
17 GEO satellite almanac
18 Ionospheric grid point masks
19 to 23 Reserved for future messages
24 Mixed fast corrections /long-term satellite error corrections
25 Long-term satellite error corrections
26 Ionospheric delay corrections
27 SDCM Service Message
28 Clock-Ephemeris Covariation Matrix Message
29–61 Reserved for future messages
62 Internal Test Message
63 Null message
Above messages are transmitted with different frequency which depends on
information validity time or message urgency. For instance, if uncertainty of any
SDCM GEO satellite is detected, Message Type 0 with respective PRN code is
transmitted immediately. Table 5 shows data update intervasl and aging time within
which different SDCM data can be used.
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Table 5. Time intervals of SDCM messages
Data Message type
Maximum data
update interval
(seconds)
Data aging
time
(seconds)
Testing 0 6 –
PRN mask 1 60 –
Fast corrections 2-5, 24 60 18 *
Long-term
corrections 24, 25 120 360
GEO data 9 120 360
Modification of
parameters 7,10 120 360
Ionospheric
mask 18 300
Ionospheric
corrections 26 300 600
UTC data 12 300 –
Almanac 17 300 –
* For fast corrections aging time is given taking into account additional
transmission of respective data in Message Type 7.
6.4 Data field
Data field comprises 212 binary symbols (bits). Each parameter in the Data
field is transmitted by most significant bit ahead. Structure of digital data in the Data
field and transmitted parameters are defined by a message type to be transmitted and
presented below.
6.5 Messages and Relationship between Message Types
To associate data in different message types, a number of issue of data (IOD)
parameters are used. These parameters include:
GPS IODClock (IODCk) and GPS IODEphemeris (IODEk) indicate
GPS clock and ephemeris issue of data, where k = satellite;
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GLONASS Data (IODGk) – indicate GLONASS clock and ephemeris
issue of data, where k = satellite;
IOD PRN Mask (IODP) identifies the current PRN mask
IOD Fast Corrections j (IODFj) identifies the current fast corrections,
where j = fast corrections Message Type (Types 2-5);
IOD Ionospheric Grid Point Mask (IODI) – identifies the current
Ionospheric Grid Point Mask;
IOD Service Message (IODS) – identifies the current Service Message
(s) Type 27.
The relationship among the messages is shown in Figure 9.
6.6 Data field M(x)
Data field M(x) of a GEO message (226 bits) is formed by 8-bit preamble, 6-
bit message type identifier and 212-bit data field. Binary bits are arranged in the same
order as transmitted from SDCM satellite, so as to make m1 correspond to the first
transmitted bit of preamble and m226 to the 212 bit of data field.
CRC-code including r bits is arranged so as to make r1 the first transmitted bit
and r24 – the last the first transmitted bit.
6.7 Cyclic Redundancy Check
In each block of transmitted digital data of 250 bits long the last 24 bits are the
bits of Cyclic Redundancy Check (CRC) parity which permits detecting errors during
reception, without correction.
Bits of CRC parity in blocks of digital data are calculated as a remainder, R(x),
from Modulo 2 division of 2 binomials:
mod 2
kx M xQ x R x
G x,
k = 24 – number of redundancy bits in CRC;
M(x) – data field of binary symbols, im presented as the polynomial:
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226226 225 224 0
1 2 226
1
i
i
i
M x m x m x m x m x
G(x) – code seed:
24 23 18 17 14 11 10 7 6 5 4 3 1G x x x x x x x x x x x x x x
Q(x) – quotient from division;
R(x) – remainder from division comprising control symbols ( ir ) of
cyclical redundancy code (CRC):
23 22 0
1 2 24
1
kk i
i
i
R x r x r x r x r x ; 24k .
Data field M x of 226 bits long is made up by 8-bit preamble, 6-bit message
type identifier and 212-bit data field. Binary bits are arranged in the same order as
transmitted from SDCM satellite, so as to make m1 correspond to the first transmitted
bit of the preamble and m226 to the 212 bit of data field.
CRC-code including r bits is arranged so as to make r1 the first transmitted bit
and r24 – the last transmitted bit.
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7 SDCM data content
7.1 SDCM testing mode (Message Type 0)
The first message type, Message Type 0, will be used during testing SDCM
system or a new satellite. The user can not use the signal of this satellite.
Message Type 0 (see Table 4) – is broadcasted by SDCM during testing phase
at the minimum rate of once per minute.
Message Type 0 informs the user that received data should not be used due to
possible degradation of accuracy and integrity. SDCM testing data will not be used
for safety navigation operations.
During testing phase SDCM can exclude certain message types out from the
list of messages and use null field of Message Type 0 for additional transmission of
fast corrections substituting data field of Message Type 2 for null field of Message
Type 0 (see Table 4).
7.2 PRN Mask Assignments (Message Type 1)
In the form of PRN Mask this message contain the information about all
satellites for which SDCM transmits corrections. It consists of 210-ordered slots
following one after another. Table 6 shows data description of this message.
The length of PRN Mask is nominally restricted by 210 slots but permits
message transmission from 1 to a maximum of 51 satellites from the list presented in
Table 6.
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Table 6. SDCM: Message Type 1
PRN Slot Assignment
1-37 GPS/GPS Reserved PRN
38-61 GLONASS (GLONASS Slot Number plus 37)
62-119 Future GNSS (Galileo)
120-138 GEO/SBAS PRN
139-210 Future GNSS / GEO /SBAS/Pseudosatellites
The field of Message Type 1 is made up as follows (see Figure 8).
Direction of data flow from satellite; Most significant bit (MSB) transmitted first250 bits - 1 second
6-Bit Message Type Identifier ()
8-Bit Preamble
24-Bit
Parity
PRN Mask field for indicating satellites (210 Bits)
IODP (2 Bits)
Figure 8. Structure of Message Type 1 – the list of satellites for which digital
data are transmitted
Preamble, message type identifier and 24 parity bits are defined above
(Sections 6.2, 6.3, 6.7). Issue of Data (IODP) fix transmitted digital data to the
number of the satellite in the list of used satellites. IODP definition is given in Annex
B “Basic principles of integrity”.
Binary bits are arranged in the same order as transmitted from SDCM satellite,
so as to make m1 correspond to the first transmitted bit of preamble and m226 to the
212 bit of data field.
The field of PRN Mask in Message Type 1 indicates for which satellites digital
data are transmitted and determines the list of satellites for which corrections are
transmitted.
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Comment. The first transmitted bit of PRN Mask corresponds to PRN-code
number 1 (definition of the term «the number of PRN-code» is given below).
Code rule for 210 bits in PRN Mask:
0 – data do not exist;
1 – data exist.
In SBAS standard mentioned parameters are transmitted in the following
messages:
– the list of satellites comprises 210 bits in Message Type 1;
– the number of satellite in the list – in messages 24, 25 and 28;
– the number of PRN-code – in message Type 17;
– Issue of data (IODP) in Messages Type 1, 2, 3, 4, 5, 7, 24, 25 and 28.
For satellite identification in SBAS standard the term «the number of PRN-
code» of the satellite is used which unambiguously identify each satellite and its
belonging to systems, as Table 5 shows. The number of PRN-code is formed from the
code of PRN Mask and is equal to the number 1 in the code of PRN Mask.
The list of satellites (PRN Mask): this is 210-ordered position binary code for
definition of those satellite numbers for which SDCM transmits corrections in the
SBAS format. Each of 210 code bits shows whether the satellite having the number
equal to this bit is included in the list or not. For instance, if the bit having the
number 5 is equal to 1, it means that for the satellite with PRN 5 corrections are
generated and transmitted in the current portion of digital data. If the bit is equal to 0,
it means that for the satellite corrections are not transmitted in the current stream of
digital data (but SDCM can transmit these data in digital data flow from another GEO
satellite). Due to restrictions to permissible update time in the SBAS channel each
digital data flow can transmit data maximum for 51 satellites (from 210 satellites
given in Table 7).
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Table 7. PRN Slots applicability to systems
PRN Slot Belonging to a system
0 No satellite
1 – 37 GPS
38 – 61 GLONASS Slot Number plus 37
62 – 119 Not reserved
120 – 138 (158)* , including
125, 140, 141
SBAS including
GEO – SDCM
139 (159) – 210 Not reserved
* Comment. Currently authorized international organizations are in the process
of resolving the issue of enhancing the number of SBAS codes from 19 to 39. After
the decision has been approved SBAS PRN Slots will reserve the numbers 120 – 158.
Figure 9 shows the principle of generating actual numbers of satellite PRN
Slots and defining sequence order of data included in digital data with use of PRN
Mask Slot. The numbers of the satellites not taken into account are indicated as
«empty».
Table 8 shows the structure of Message Type 1 fields (PRN Mask and IODP)
Figure 9. Principle of generating the PRN Mask assignments.
Table 8. Structure of message 1 fields (PRN Mask and IODP)
Field contents Bits Numbers Resolution
For each of 210 bits of
PRN Mask
Mask values:
1 0 or 1
1
IODP: 2 0–3 1
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7.3 GEO Navigation Message (Message Type 9)
GEO Navigation Message Type 9 comprises ephemeris and time corrections of
a SDCM satellite. SDCM transmits this message in order to provide compatibility
with WAAS navigation equipment produced previously, it is used only for satellite
signal search but not for navigation measurements.
Figure 10 shows the structure of Message Type 9. Table 9 shows Type 9 GEO
Navigation Message parameters. Following symbols used in Figure 10 and Table 9:
Direction of data flow from satellite; Most significant bit (MSB) transmitted first
250 bits - 1 second
8-Bit Preamble
6-Bit Message Type
Identifier ()
Spare (8 Bits)
XG YG ZG GX GY GZ GX GY GZ aGf0 aGf1
t0,GEO
URA
24-Bit
control
Figure10. Structure of Type 9 GEO Navigation Message
t0,GEO – data lock-on time for the range function of a GEO satellite expressed
as the time interval from the midnight of current day.
GGG ZYX – GEO satellite coordinates at t0,GEO.
GGG ZYX – GEO satellite velocity at t0,GEO.
GGG ZYX – GEO satellite acceleration at t0,GEO.
aGf0 – GEO satellite onboard time scale offset relative to the SDCM network
time (SNT), at t0,GEO.
aGf1 – drift rate of GEO satellite onboard time scale relative to SNT.
User Range Accuracy (URA) –Root-mean-square user range error without
taking into account atmosphere effects.
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Table 9. Navigation Message Type 9
Parameter
No. of
Bits Effective Range
Resolution
Not reserved 8 –– ––
t0,GEO 13 0–86 384 sec 16 sec
URA 4 (see the Comment) ––
XG 30 42 949 673 m 0,08 m
YG 30 42 949 673 m 0,08 m
ZG 25 6 710 886,4 m 0,4 m
17 40,96 m/sec 0,000625 m/sec
17 40,96 m/sec 0,000625 m/sec
18 524,288 m/sec 0,004 m/sec
10 0,0064 m/sec 2 0,0000125 m/sec
2
10 0,0064 m/sec 2 0,0000125 m/sec
2
10 0,032 m/sec 2 0,0000625 m/sec
2
aGf0 12 0,9537 10-6
sec 231
sec
aGf1 8 1,1642 10-10
sec
/ sec
240
sec / sec
Comment. According to the SBAS standard, if URA is equal to 15, range
signal of the satellite can not be used. SDCM does not provide pseudorange
measurements to GEO satellite, therefore in order to provide compatibility with the
equipment produced earlier, URA is defined in SDCM ICD as a constant equal to 15.
7.4 GEO Almanac Message Type 17
Almanac for three satellites will be broadcast in the GEOs Almanac Message
Type 17. These messages will be repeated to include all GEOs. Unused almanacs will
have a PRN number of 0 and should be ignored.
Almanac comprises information about satellite health and state and service
provider ID ensuring uplinking with GEO satellite. Table 10 Service Provider IDs.
GX
GY
GZ
GX
GY
GZ
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Table 10. Service Provider IDs.
ID Service Provider
0 WAAS
1 EGNOS
2 MSAS
3 GAGAN
4 SDCM
5-15 Reserved
Almanac information including status (transmitted parameters) of each GEO is
transmitted by Message Type 17.
Figure 11 shows the structure of Message Type 17 (with additional information
- Figure 12). Message Type 17 permits transmitting data for 3 GEOs simultaneously.
Satellite identification is effected by a PRN number.
Figure 11. Type 17 GEO Almanac Message Format
Figure 12. Information interpretation for one satellite
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Comment.
1. The field «Data identifier» in Message Type 17 is always «002».
2. In order to provide compatibility with navigation equipment produced earlier,
the fields of coordinates components and satellite velocity are kept.
Preamble, message type identifier, parity field and PRN number field are
defined above (Sections 6.2, 6.3, 6.7, 7.2).
Table 11 Health and status bits.
Table 11. Health and status bits of a GEO («0» – data transmitted; «1» – data not
transmitted)
Bit 0 (LSB) Ranging –– 1
Bit 1 Accurate corrections 0 1
Bit 2 Broadcast Integrity 0 1
Bit 3 Not reserved –– ––
Bits 4 – 7 Service Provider ID See Table 11
Comment.
SDCM does not provide pseudorange measurements to GEO satellite, therefore
the bit 0 (LSB) is always equal to «1».
Table 12 shows Service provider IDs (establishing belonging of the transmitter
in SBAS coding)
Table 12. Service Provider ID (in SBAS coding)
Identifier Digital data provider
0 WAAS
1 EGNOS
2 MSAS
3 GAGAN
4 SDCM
5–13 Not reserved
14–15 Reserved
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7.5 Long-term and mixed satellite error corrections (Message Types 24 and
25)
Messages Type 24 and 25 will be broadcast to provide error estimates for slow
varying satellites ephemeris and clock errors. These long-term corrections are mot
applied for GEOs. Instead, the Type 9 GEO Navigation Message will be updated as
required to prevent slow varying GEO satellite errors.
Message Type 24 as well contains information about fast corrections.
Long-term corrections are differential corrections to GEO navigation
ephemeris and clock errors for which update interval shall not exceed 120 sec.
Mixed corrections are the message of SDCM comprising long-term as well as
fast corrections simultaneously (see Section 0) to ephemeris and clock of a navigation
satellite.
Preamble, message type identifier, parity field and PRN number field are
defined above (Sections 6.2, 6.3, 6.7, 7.2).
The structure of Message Type 25 comprising long-term corrections depends
on whether corrections rates-of-change are transmitted or not (in case of their quick
change between received messages). Specific format of transmitted message is
defined in accordance with the code figure in the field “Velocity code”.
Code rule for the field «Velocity code » (1 bit):
0 – corrections ix , iy , iz , , 1i fa are not transmitted (Figure 13 shows the
format of Message Type 25);
1 – corrections ix , iy , iz , , 1i fa are transmitted (Figure 14 shows the
format of Message Type 25).
The following symbols are used when describing Type 24 and 25 Message
formats:
ix – correction to ephemeris for i-satellite along x-axis ;
iy – correction to ephemeris for i-satellite along y-axis;
iz – correction to ephemeris for i-satellite along z-axis;
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, 0i fa – clock correction for i-satellite;
ix – correction to ephemeris (velocity) for i-satellite along x-axis;
iyδ – correction to ephemeris (velocity) for i-satellite along y-axis;
izδ – correction to ephemeris (velocity) for i-satellite along z-axis;
, 1i fa – frequency correction for i-satellite;
,i LTt – time from the midnight of current day until the user has received the
parameters: , 0, , , , , , и ,i i i i f i i i iflx y z a x y z a in seconds;
t0 – reference time transmitted in Message Types 24-25 provided that the
velocity code is equal to 1.
Figure 13 shows Type 25 Message format for the velocity code equal to 0,
Figure 14 – for the velocity code equal to 1.
Figure 15 shows Type 24 Message format comprising fast and long-term
corrections.
Direction of data flow from satellite . Most significant bit (MSB) transmitted first
250 Bits - 1 secondVelocity code = 0
IODi (8 Bits)
PRN mask
number
6-Bit Message type identifier
8-Bit Preamble
24-Bits
parity
IODP (2 Bits)
X ZY 0faX Y Z 0fa S
Second half of message
(Data for SC №3 and SC №4)
S = Spare
Data for SC №1Data for SC №2
Figure 13. Type 25 Message format (the velocity code = 0)
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Direction of data flow from satellite . Most significant bit (MSB) transmitted first
250 Bits - 1 second
Velocity code = 1
IODi (8 Bits)
PRN mask number IODP (2 Bits)
X ZY 0faX Y Z 1fa
Second half of message
(Data for SC №2)
24-Bits parity
6-Bit Message type identifier
8-Bit Preamble
t0
Data for SC №1
Figure 14. Type 25 Message format (the velocity code = 0 – corrections rate-
of-change are transmitted) – long-term corrections (maximum for 2 satellites).
Direction of data flow from satellite . Most significant bit (MSB) transmitted first
250 Bits - 1 second
Block identifier (2 Bits)
Fast corrections FCi
(for 6 satellites, by 12 Bits)IODP (2 Bits)
106-bit long-term satellite error
correction Half Message Type 25
6 4 Bit UDREIs
S
IODF (2 Bits)
S – Spare (4 Bits)
8-Bit Preamble
6-Bit Message type identifier
24-Bits parity
Figure 15. Type 24 Message format – mixed (fast and long-term) corrections
Basic provisions of the present standard concerning the transmission of fast
and long-term corrections are the following:
1) long-term corrections to ephemeris for GLONASS and GPS systems are
transmitted: for GLONASS – in PZ-90.02, for GPS – in WGS-84;
2) The following rules are established for long-term corrections.
Issue of data (IODi): factor connecting long-term corrections for i-th satellite
with ephemeris transmitted by this satellite. It is used differently for GLONASS and
GPS.
For GLONASS IODi defines the time period within which GLONASS data
will be used together with SDCM data. This information is included in its two
subfields as shown in Table 13.
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Table 13. IODi contents for GLONASS satellites
Operation time (V): the time period within which GLONASS ephemeris data
are used (coding step is 30 seconds).
Delay time (L): the time interval starting from the last GLONASS ephemeris
update to the predicted time of receiving the long-term correction by the user
Table 14. Operation time V and delay time L
For GLONASS satellites the user can use long-term corrections only if the time
of receiving last GLONASS ephemeris tr and the time of receiving the long-term
correction by the user tLT meet the following condition:
.LT r LTt L V t t L
For GPS satellites long-term corrections only can be used provided that IODi in
received SDCM corrections coincide with IODE in received GPS ephemeris and with
8 LSB of IODC.
Table 15 shows Type 24 Message format and the effective range within which
its parameters may vary.
Table 16 shows Type 25 Message format and the effective range within which
its parameters may vary for velocity code 0 and Table 17 - for velocity code 1.
5 LSB IODi: identifier V 3 MSB IODi : identifier L
Operation time (see Table 14) Delay time (see Table 14)
Data Bits used Values used Resolution
Operation time (V) 5 30 – 960 sec 30 sec
Delay time (L) 3 0 – 120 sec 30 sec
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Table 15. Type 24 Mixed fast correction/long-term satellite error corrections message
format
Parameter Bits Effective Range Resolution
Fast corrections (FCi)
(for six satellites) 12 256,000 m 0,125 m
User Differential Range
Error UDREIi
(for six satellites)
4 (see Table 19) (see Table 19)
IODP 2 0–3 1
Fast correction type
identifier 2 0–3 1
IODFj 2 0–3 1
Not reserved 4 — —
Half Message Type 25 106 — —
Table 16. Type 25 long-term satellite error corrections message format (velocity
code = 0)
Parameter Bits Effective
Range Resolution
Velocity code = 0 1 0 1
For two satellites:
PRN musk number 6 0–51 1
Issue of data (IODi) 8 0–255 1
xi 9 ±32 m 0,125 m
yi 9 ±32 m 0,125 m
zi 9 ±32 m 0,125 m
ai,f0 10 ±2–22
sec 2–31
sec
IODP 2 0–3 1
Not reserved 1 — —
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Table 17. Type 25 long-term satellite error corrections (velocity code = 1)
Parameter Bits Effective
Range Resolution
For one satellite
Velocity code = 1 1 1 1
PRN musk number 6 0–51 1
Issue of data (IODi) 8 0–255 1
xi 11 ±128 m 0,125 m
yi 11 ±128 m 0,125 m
zi 11 ±128 m 0,125 m
ai,f0 11 ±2–21
sec 2–31
sec
8 ±0,0625
m/sec 2
–11 m/sec
8 ±0,0625
m/sec 2
–11 m/sec
8 ±0,0625
m/sec 2
–11 m/sec
ai,f1 8 ±2–32
sec/sec 2–39
sec/sec
Reference time (t0) 13 0–86 384 sec 16 sec
IODP 2 0–3 1
7.6 Fast corrections Message Types 2-5
Fast corrections contains the information about correction of measured ranges
to navigation satellites. The correction is used as the following expression:
PR t PR t PRC t RRC t tcorrected measured f of of( ) ( ) ( ) ( ),
where:
PRmeasured – measured range to a satellite
PRCf – correction included in Message Types 2-5
t – current time
tof – reference time or time of applicability of the most recent fast correction
( )current previous
of
PRC PRCRRC t
t ,
ixδ
izδ iyδ
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t = (tof – tof,previous).
This correction permits compensating fast errors when measuring range to a
satellite which arise due to inaccurate predictions of satellite onboard clock offset.
Fast correction also permits compensating errors introduced by selective availability.
Apart from corrections SDCM Message Types 2-5 contain accuracy data –
UDRE (User Differential Range Error), which permits to the user to define
navigation accuracy.
SDCM Message Type 2 contains the data sets for the first 13 satellites
designated in the PRN mask, SDCM Message Type 3 – for satellites 14-26, SDCM
Message Type 4 – for satellites 27-39, SDCM Message Type 5 – for satellites 40-51.
Fast correction (FCi) is a correction for fast errors (clocks) of a satellite which
is added to the measured pseudorange of i-th satellite. In order to transmit fast
corrections for the 51-st satellite 4 types of messages are used in sequence:
Message Type 2 contains the data sets for the first 13 satellites designated in
the PRN mask (13 satellites);
Message Type 3 contains the data sets for satellites 14 - 26 designated in the
PRN mask (13 satellites);
Message Type 4 contains the data sets for satellites 27 - 39 designated in the
PRN mask (13 satellites);
Message Type 5 – contains the data sets for satellites 40 - 51 designated in the
PRN mask (12 satellites).
Types 2-5 fast satellite error corrections formats are identical and given in
Figure 16.
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Direction of data flow from satellite . Most significant bit (MSB) transmitted first
250 Bits - 1 second
Fast corrections FC for 13 (12) satellites (by 12 Bits) – seе Table 11
6-Bit Message type identifier
8-Bit Preamble
24-Bits parityIODP (2 Bits)
IODF-j (2Bits)
FC
UDREI errors for 13 (12) satellites (by 12 Bits) – see Table 11
Figure 16. Types 2-5 fast satellite error corrections
Preamble, message type identifier and parity field are defined above (Sections
6.2, 6.3, 6.7).
Fast correction IODFj.
In Messages Type 2, 3, 4 and 5, IODFj is designated respectively IODF2,
IODF3, IODF4 and IODF5. Each 2-bit IODFj sequentially receives the values 010, 110,
210 and 310. When there is no alert condition for any of the satellites in a message
type, sequential change of codes in IODF2, IODF3, IODF4 and IODF5 (each code
sequentially takes on a value: 010, 110 and 210) provides the connection of digital data
from messages type 2-5 with data from Message Type 6 – synchronization method is
presented in Annex B. integrity principles. However, in the case of accuracy
degradation of differential corrections of one or several satellites (digital data for
them are transmitted in Messages Type 2-5, 24), Message Type 6 is also transmitted,
in which the respective value of IODFj; j [2…5] is equal to 3. Code IODFj = 310
indicates that for one or several satellites from the Message Type j the error уi2,UDRE is
sharply risen. Relationship of IODF2, IODF3, IODF4 and IODF5 and satellite numbers
is given in Section 7.7 below.
Table 18. Message Types 2-5 – fast corrections
Parameter Bits Effective Range Resolution
IODFj 2 0–3 1
IODP 2 0–3 1
For 13 satellites (or 12 satellites in Message type 5):
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Parameter Bits Effective Range Resolution
Fast correction (FCi) 12 256,000 m 0,125 m
UDREIi 4 (see Table 19) (see Table 19)
7.7 Integrity parameters of fast and long-term corrections (Message Type 6)
This Message contains range accuracy data – UDRE. Apart from this, Message
Type 6 contains information permitting to define the integrity of all data. When a new
satellite becomes available, Message Type 6 reflects this information.
The value of UDREIi indicating the integrity of fast and long-term corrections
delivered to the user is defined on the basis of Root-mean-square residual errors for i-
th satellite (σi,UDRE) as Table 19 shows.
Dispersion (σ2i,UDRE) of the residual errors file of the satellite (satellite clock
and ephemeris) is defined by pseudorange error after the user has applied fast and
long-term corrections (not taking into account ionosphere corrections). Residual error
is used by the user when assessing integrity parameters, in particular in horizontal
and vertical protection levels evaluations.
Table 19. Evaluation of UDREIi
UDREIi i2,UDRE
0 0,0520 m2
1 0,0924 m2
2 0,1444 m2
3 0,2830 m2
4 0,4678 m2
5 0,8315 m2
6 1,2992 m2
7 1,8709 m2
8 2,5465 m2
9 3,3260 m2
10 5,1968 m2
11 20,7870 m2
12 230,9661 m2
13 2 078,695 m2
14 Not monitored
15 Do not use
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Timeliness of UDREIi delivery provides the reliability of navigation for the
user. Therefore these parameters in addition to the Message Type 6 are also
transmitted with fast corrections (in Messages Type 2-5 and 24).
Figure 17 shows Type 6 Message format comprising integrity parameters.
Direction of data flow from satellite . Most significant bit (MSB) transmitted first
250 Bits - 1 second
UDREI parameters for 51 satellites (by 4 Bitsт)
6-Bit Message type identifier
8-Bit Preamble
24-Bits parityBlock of parameters: IODF2, IODF3, IODF4, IODF5 (by 2 Bits)
IODF (2 Bits)
Figure 17. Type 6 Message format
Preamble, message identifier and parity field are defined above (Sections 6.2,
6.3, 6.7).
UDREIi definition is given above.
IODFj, apart from standard synchronization functions when changing data in
the channel (for this purpose sequential values of IODF equal to 0, 1 and 2 are used
in the manner described in Annex B “Basic integrity principles”), may also be used
for urgent informing the user about the failure of integrity included into the respective
group: for this purpose the value of IODF equal to 3 is used. The following
relationship is taken:
IODF2 = 3 – the failure of integrity for satellites 1 … 13,
IODF3 = 3 – the failure of integrity for satellites 14 … 26,
IODF4 = 3 – the failure of integrity for satellites 27 … 39,
IODF5 = 3 – the failure of integrity for satellites 40 … 51.
The satellite in which integrity is failed is defined after UDREIi parameters
have been received and analyzed completely from Message Type 6.
Table 20 shows Type 6 integrity message content.
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Table 20. Type 6 integrity message content
Parameter Bits Effective Range Resolution
IODF2 2 0–3 1
IODF3 2 0–3 1
IODF4 2 0–3 1
IODF5 2 0–3 1
UDREIi 4 (See Table 19) (See Table 19)
7.8 Ionosphere Grid Point Masks Message Type 18
Message Type 18 simultaneously with Message Type 26 (see Section 7.9),
permits calculating ionosphere propagation delay (at L1) of a navigation satellite and
its accuracy.
Corrections to user equipment pseudoranges (corrections compensating
navigation signal delays in ionosphere) according to the SBAS standard are
transmitted as two parameters: vertical delay and conditional digital codes-indicators
GIVEIi, unambiguously connected with dispersion of vertical ionosphere delay
assessments (see Table 23). These parameters are defined in Ionospheric Grid Point
locations and give the assessment of L1 (1575,42 MHz) vertical ionosphere delay for
the case of signal vertical pass through this location. Using these data the user shall,
according to the methodology described in SDCM ICD, interpolate SBAS message
vertical delay from nearest grid points to the slant delay for the line of sight of
operating satellite.
Aggregate of points on the Earth surface for which zenith (vertical)
ionosphere delays are calculated is designated as IGP – Ionospheric Grid Point.
IGP parameters are defined as follows. The predicated IGPs are contained in
11 bands (numbered 0 to 10):
Bands 0 – 8 are vertical bands on a Mercator projection map, covering the
Equator and middle latitudes;
Bands 9 – 10 are horizontal bands on a Mercator projection map, higher south
and north polar latitudes.
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IGP location coordinates are indicated in Table 18. General spacing of 1808
IGP points for all 11 IGP bands is showed in Figure 18.
Figure 18. Predefined Global IGP Grid
For each indicated IGP point, IGP Band Mask in Message Type 18
defines if there are data about respective point delay in Message Types 26.
Coordination rule:
0 – no data;
1 – data exist.
The number of IGP Band Mask is equal to the maximum number of IGP points
within one band and, according to Table 21, is equal to 201 bits.
Table 21. Ionospheric mask bands
Coordinates of IGP points
Bits in Mask Longitu
de Latitudes for all band points:
1 2 3
Band 0
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Coordinates of IGP points
Bits in Mask Longitu
de Latitudes for all band points:
1 2 3
180 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N,
85N
1–28
175 W 55S, 50S, 45S, ..., 45N, 50N, 55N 29–51
170 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 52–78
165 W 55S, 50S, 45S, ..., 45N, 50N, 55N 79–101
160 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 102–128
155 W 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151
150 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178
145 W 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201
Band 1
140 W 85S, 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N,
75N
1–28
135 W 55S, 50S, 45S, ..., 45N, 50N, 55N 29–51
130 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 52–78
125 W 55S, 50S, 45S, ..., 45N, 50N, 55N 79–101
120 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 102–128
115 W 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151
110 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178
105 W 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201
Band 2
100 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27
95 W 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50
90 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N,
85N
51–78
85 W 55S, 50S, 45S, ..., 45N, 50N, 55N 79–101
80 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 102–128
75 W 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151
70 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178
65 W 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201
Band 3
60 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27
55 W 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50
50 W 85S, 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N,
75N
51–78
45 W 55S, 50S, 45S, ..., 45N, 50N, 55N 79–101
40 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 102–128
35 W 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151
30 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178
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Coordinates of IGP points
Bits in Mask Longitu
de Latitudes for all band points:
1 2 3
25 W 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201
Band 4
20 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27
15 W 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50
10 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 51–77
5 W 55S, 50S, 45S, ..., 45N, 50N, 55N 78–100
0 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N,
85N
101–128
5 E 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151
10 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178
15 E 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201
Band 5
20 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27
25 E 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50
30 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 51–77
35 E 55S, 50S, 45S, ..., 45N, 50N, 55N 78–100
40 E 85S, 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N,
75N
101–128
45 E 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151
50 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178
55 E 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201
Band 6
60 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27
65 E 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50
70 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 51–77
75 E 55S, 50S, 45S, ..., 45N, 50N, 55N 78–100
80 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 101–127
85 E 55S, 50S, 45S, ..., 45N, 50N, 55N 128–150
90 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N,
85N
151–178
95 E 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201
Band 7
100 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27
105 E 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50
110 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 51–77
115 E 55S, 50S, 45S, ..., 45N, 50N, 55N 78–100
120 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 101–127
125 E 55S, 50S, 45S, ..., 45N, 50N, 55N 128–150
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Coordinates of IGP points
Bits in Mask Longitu
de Latitudes for all band points:
1 2 3
130 E 85S, 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N,
75N
151–178
135 E 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201
Band 8
140 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27
145 E 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50
150 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 51–77
155 E 55S, 50S, 45S, ..., 45N, 50N, 55N 78–100
160 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 101–127
165 E 55S, 50S, 45S, ..., 45N, 50N, 55N 128–150
170 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 151–177
175 E 55S, 50S, 45S, ..., 45N, 50N, 55N 178–200
1 2 3
Band 9
60 N 180W, 175W, 170W, …, 165E, 170E, 175E 1–72
65 N 180W, 170W, 160W, …, 150E, 160E, 170E 73–108
70 N 180W, 170W, 160W, …, 150E, 160E, 170E 109–144
75 N 180W, 170W, 160W, …, 150E, 160E, 170E 145–180
85 N 180W, 150W, 120W, … , 90E, 120E, 150E 181–192
Band 10
60 S 180W, 175W, 170W, …, 165E, 170E, 175E 1–72
65 S 180W, 170W, 160W, …, 150E, 160E, 170E 73–108
70 S 180W, 170W, 160W, …, 150E, 160E, 170E 109–144
75 S 180W, 170W, 160W, …, 150E, 160E, 170E 145–180
85 S 170W, 140W, 110W, …, 100E, 130E, 160E 181–192
In Message Types 26 data routing (affixment of transmitted delays to grid
points) is effected by indicating in a message the following features:
A band number, for which delays are transmitted. IGP points locations in bands
are defined in Table 21;
a block ID comprising 15 points inside a band. All initial sequence comprising
201 points is divided by groups of 15 sequential points called the block;
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Transmission of delays for point inside the block strictly in such sequence in
which their respective «1» follow in IGP Band Mask (this identification scheme is
identical to the identification scheme described above – see Section 7.2).
Type 18 Message Format comprising IGP Band Mask data is given in Figure
19.
Preamble, message identifier and parity field are defined above (6.2, 6.3, 6.7).
250 Bits - 1 second
8-bit Preamble
24 Bits Parity
NO.of bands (4 Bits)
Band number (4 Bits)
IODI (2 Bits)
Spare Bit
201-bit Mask Field
6-Bit Message Type Identifier
Figure 19. Type 18 Message Format –IGP Band Mask.
Table 22 shows bits network of Message Type 18.
Table 22. Message Type 18 – IGP field
Parameter
No. of
Bits
Effective
Range Resolution
Number of bands being broadcast 4 0–11 1
Band Number 4 0–10 1
Issue of Data - Ionosphere (IODIk) 2 0–3 1
For 201 band points the following is transmitted:
IGP Mask 1 0 or 1 1
Spare 1 — —
7.9 Ionospheric Delay Corrections Messages Type 26
The Type 26 Ionospheric Delay Corrections Message provides the users with:
Vertical Pseudorange delay relative to an L1 signal (in meters);
Their accuracy 2
,i GIVE at geographically defined IGPs identified by band
number and IGP number in Table 21. The evaluation of the 2
,i GIVE is transmitted in
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the form of 4-bit block ID GIVEIi unambiguously corrected with dispersion value (in
meters), as showed in Table 23.
Table 23. Evaluation of GIVEIi
GIVEIi 2
,i GIVEI Meters2
:
0 0,0084
1 0,0333
2 0,0749
3 0,1331
4 0,2079
5 0,2994
6 0,4075
7 0,5322
8 0,6735
9 0,8315
10 1,1974
11 1,8709
12 3,3260
13 20,787
14 187,0826
15 Not monitored
The data content of this message is given in Table 24 with a format presented
in Figure 20.
Direction of data flow from satellite . Most significant bit (MSB) transmitted first
250 Bits - 1 second
Repeat for 14 more grid points
IGP Vertical delay (9 Bits)
Block ID (4 Bits)
Band Number (4 Bits)
IODI 24 Bits Parity
S – Spare (7 Bits)
2 15141312111098765
43 S
GIVEI (4 Bits)
6-Bit Message Type Identifier
8-Bit Preamble
1
Figure 20. Type 26 Ionosphere Delay Corrections Message Format
Preamble, message type identifier and parity field are defined above (Section
6.2, 6.3, 6.7).
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Table 24. Ionospheric Delay Model Parameters for Message Type 26
Parameter
No. of
Bits Effective Range Resolution
Band Number 4 0–10 1
Block ID 4 0–13 1
For each of 15 grid points:
IGP Vertical Delay
Estimate
9 0–63,875 m 0,125 m
Grid Ionospheric Vertical
Error Indicator (GIVEIi)
4 (see Table 23) (see Table 23)
IODIk 2 0–3 1
Spare 7 — —
7.10 Degradation parameters (Messages Type 7 and 10)
Message Type 7 comprises information about fast corrections ageing time and
fast and long-term corrections change factor.
Message Type 10 transmits a set of additional data to be used for navigation
accuracy definition.
Degradation parameters define SDCM corrections ageing rate and required for
definition of validity period of transmitted data. Degradation parameters are
transmitted in two messages:
- Fast corrections degradation parameters are transmitted in Message Type 7;
- For all the others (ionosphere, long-term corrections) Message Type 10 is
used.
Figure 21 shows Type 7 message format.
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Direction of data flow from satellite . Most significant bit (MSB) transmitted first
250 Bits - 1 secondIODP (2 Bits)
51 4-Bit UDRE degradation factor indicators
1tSpare (2 Bits)
8-Bit Preamble
24- Bits Parity6-Bit Message Type Identifier
(4 Bits)
Figure 21. Type 7 Fast Correction Degradation Factor Message Format
Preamble, message type identifier and parity field are defined above (Section
6.2, 6.3, 6.7).
Specific data of Message Type 7 comprise:
a) System latency time (t1) – time interval between the start of correction
degradation (the time for which the correction is calculated) and the time of data
uplinking to SDCM channel (repeating delay is assumed zero);
b) Fast correction degradation factor indicators (aii) which are
unambiguously connected with corrections change rate (with degradation factor) and
defined according to Table 25.
Table 25. Fast corrections degradation factor
Fast Corrections Degradation
Factor Indicator iai
Fast Corrections Degradation Factor
ia , м/с2
ia
0 0,00000
1 0,00005
2 0,00009
3 0,00012
4 0,00015
5 0,00020
6 0,00030
7 0,00045
8 0,00060
9 0,00090
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Fast Corrections Degradation
Factor Indicator iai
Fast Corrections Degradation Factor
ia , м/с2
ia
10 0,00150
11 0,00210
12 0,00270
13 0,00330
14 0,00460
15 0,00580
Table 26 shows Type 7 message contents.
Table 26. Fast Correction Degradation Factor
Parameter
No. of
Bits
Effective
Range Resolution
System latency (tl) 4 0–15 s 1 s
IODP 2 0–3 1
Spare 2 — —
For each of 51 satellites (according to PRN mask):
Degradation Factor Indicator
(aii) 4 (see Table 25) (see Table 25)
Figure 22 shows Type 10 message format comprising degradation parameters
of long-term corrections and ionosphere delays.
250 Bits - 1 second
8-Bit Preamble
24- Bits Parity
6-Bit Message Type Identifier
Brrc(10 Bits)
Cltc_lsb(10 Bits)
Cltc_v1(10 Bits)
Iltc_v1(9 Bits)
Cltc_v0(10 Bits)
Iltc_v0(9 Bits)
Cgeo_lsb(10 Bits)
Cgeo_v(10 Bits)
Igeo(9 Bits
Cer(6 Bits)
Ciono_step(10 Bits)
Iiono(9 Bits)
Ciono_ramp(10 Bits)
RSSUDRE(1 Bits)RSSiono(1
Bits)
Empty bits (81 Bits)
Figure 22. Type 10 Long-term Correction Degradation Factor Message Format
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Preamble, message type identifier and parity field are defined above (Section
6.2, 6.3, 6.7).
Table 27 shows specific parameters transmitted in Message Type 10.
Table 27. Type 10 Degradation Factors
Parameter No. of Bits Effective Range Resolution
Brrc 10 0–2,046 m 0,002 m
Cltc_lsb 10 0–2,046 m 0,002 m
Cltc_v1 10 0–0,05115 m/sec 0,00005 m/sec
Iltc_v1 9 0–511 sec 1 sec
Cltc_v0 10 0–2,046 m 0,002 m
Iltc_v0 9 0–511 m 1 с
Cgeo_lsb 10 0–0,5115 m 0,0005 m
Cgeo_v 10 0–0,05115 m/sec 0,00005 m/ sec
Igeo 9 0–511 sec 1 sec
Cer 6 0–31,5 m 0,5 m
Ciono_step 10 0–1,023 m 0,001 m
Iiono 9 0–511 sec 1 sec
Ciono ramp 10 0–0,005115 m/ sec 0,000005 m/ sec
RSSUDRE 1 0 or 1 1
RSSiono 1 0 or 1 1
Ccovariance 7 0–12,7 0,1
Spare 81 — —
Where:
rrcB – parameter defining noise and approximation error ranges when
calculating correction to range rate of change.
_ltc lsbC – maximum approximation error defined by definition of transmitted
orbit and time data.
_ltc vlC – is the velocity error bound on the maximum range rate difference of
missed messages due to clock and orbit rate differences derived from Message Type
10
_ltc lsbI –long-term corrections update interval when rate code is equal to «1».
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_ 0ltc vC – parameter defining discrepancy limits between two sequential long-
term corrections for satellites with rate code equal to «0».
_ 0ltc vI – minimum update interval for long-term messages when rate code is
equal to «0».
_GEO lsbC – not used in SDCM.
_GEO vC – not used in SDCM.
GEOI – not used in SDCM.
erC – residual error range connected with data use outside time interval.
_iono stepC – range of differences between sequential delays in ionosphere grid.
ionoI – minimum update interval for messages with ionosphere corrections.
_iono rampC – ionosphere corrections rate of change.
UDRERSS – indication of Root Mean Square addition for differences of fast and
long-term corrections.
The following code rule is used:
0 – correction differences are added linearly;
1 – correction differences squares are added under square root.
ionoRSS – indication of Root Mean Square addition for differences of ionosphere
corrections.
The following code rule is used:
0 – correction differences are added linearly;
1 – correction differences squares are added under square root.
covC – parameter used for compensation of discretization when Message Type
28 is applied.
Comments:
1. Parameters ai and tl, required for application of parameter are to be selected
from Message Type 7.
2. If Message Type 28 is not transmitted parameter covC is not applied.
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7.11 SDCM Network Time/UTC/GLONASS Time Offset Parameters
Message Type 12
Message Type 12 comprises offset between GLONASS and GPS time scales.
Figure 23 shows Type 12 message format.
Figure 23. Type 12 Time Parameters Message Format
Preamble, message type identifier and parity field are defined above (Section
6.2, 6.3, 6.7).
Table 28 shows Type 12 message contents.
Table 28. SDCM Network Time/UTC Parameters
Parameter
No. Of
Bits Effective Range Resolution
1SNTA 24 7,45 10–9
sec/sec 2–50
sec/sec
0SNTA 32 1 sec 2–30
sec
t0t 8 0–602 112 sec 4 096 sec
tWN 8 0–255 weeks 1 weeks
LSDT 8 128 sec 1 sec
LSFWN 8 0–255 weeks 1 weeks
DN 8 1–7 days 1 days
250 Bits - 1 second
8-Bit Preamble
24- Bits Parity
6-Bit Message Type Identifier
A1SNT
(24 Bits)
A0SNT
(32 Bits)
t0t (8 Бит)
WNt (8 Bits)
∆tLS (8 Bits)
WNLSF (8 Bits)
DN (8
Bits)
∆tLSF (8
Bits)
IUTS (3 Bits)
TOW (20 Бит)
WN (10
Bits)
IGLO (1 Bits)
δaGLONASS (32 Bits)
Spare (42 Bits)
DtLSF (8 Bits)
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LSFDt 8 128 sec 1 sec
UTC standard Identifier 3 BIPM, NIST, USNO —
GPS Time-of-Week (TOW) 20 0–604 799 sec 1 sec
GPS Week Number (WN) 10 0–1 023 weeks 1 weeks
GLONASS Indicator 1 0 or1 1
GPS-GLONASS time offset
ai,GLONASS
32 2 10–30
sec 1 sec
Spare 42 — —
Parameters given in Table 25 are defined as follows:
1) UTC standard Identifier – indicates reference source of UTC as
defined in Table 29.
Table 29. UTC standard Identifier
UTC Identifier UTC standard
0 UTC as operated by the Communications Research
Laboratory (CRL), Tokyo, Japan
1 UTC as operated by the National Institute of Standards and
Technology (NIST), USA
2 UTC as operated by the U.S. Naval Observatory
3 UTC as operated by the International Bureau of Weights and
Measures (BIPM)
4 UTC as operated by the European Laboratory
5 UTC as operated by the TBD
6 Not reserved
7 UTC not provided
2) Time count in Time-of-Week (TOW): the number of seconds passed from
transition from previous to current GPS-week.
3) GLONASS Indicator: shows if GLONASS time parameters are transmitted
or not.
Code rule:
0 – GLONASS time parameters are not transmitted;
1 – GLONASS time parameters are transmitted.
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4) Correction ai,GLONASS to GLONASS system time offset relative to GPS
system time: parameter indicating correction to offset between GLONASS and GPS
system time.
5) Parameters A1SNT, A0SNT, t0t, WNt, tLS, WNLSF, DN and tLSF are defined
according to UTC standard.
7.12 SDCM Service Message Type 27
Type 27 messages may be transmitted to increase the σUDRE values in selected
areas. This provides the user with the opportunity of more precise definition of
navigation service quality or the extent of location reliability of position vector. This
message may content the information about integral quality of all SDCM system.
The format of Message Type 27 is given in Figure 24 and Table 30.
250 Bits - 1 second
8-Bit Preamble
24- Bits Parity
6-Bit Message Type Identifier
IODS (3 Bits)
Number of service messages (3 Bits)
Service Message Number (3 Bits)
Number of regions (3 Bits)
Priority Code (2 Bits)
UDRE Indicator – inside (4 Bits)
UDRE Indicator - outside 4 Bits)
Spare (15 Bits)
Region 1
(35 Bits
Region 2
(35 Bits)
Region 3
(35 Bits)
Region4
(35 Bits)
Region5
(35 Bits)
Coordinate1 latitude (8
Bits)
Coordinate 2 latitude
(8 Bits)
Region data (35 Bits)
Coordinate2 longitude
(9 Bits)
Coordinate1 longitude
(9 Bits)
Region shape (1 Bit)
Figure 24. Service Message Type 27
Preamble, message type identifier and parity field are defined above (Section
6.2, 6.3, 6.7).
Table 30. Type 27 Service Message Parameters
Parameter No. of
Bits
Effective
Range Resolution
Issue of Data, Service (IODS) 3 0–7 1
Number of service messages 3 1–8 1
Service message number 3 1–8 1
Number of regions 3 0–5 1
Priority code 2 0–3 1
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Parameter No. of
Bits
Effective
Range Resolution
UDRE Indicator - Inside 4 0–15 1
UDRE Indicator - Outside 4 0–15 1
For each of up to 5 regions:
Coordinate 1 (latitude) 8 90 1
Coordinate 1 (longitude) 9 180 1
Coordinate 1 (latitude) 8 90 1
Coordinate 1 (longitude) 9 180 1
Region Shape 1 — —
Spare 15 — —
The above parameters of Message Type 27 are defined as follows:
A. Issue of Data, Service (IODS): identification of data service from
different Messages Type 27;
B. Number of service messages: number of transmitted Messages Type 27
(value is transmitted with an offset to minus 1; the first transmitted message is zero);
C. Number of service message: message ID which defines present Message
Type 27 in the transmitted sequence of Message Type 27 (from 1 to quantity of
service messages coded with an offset to minus 1);
D. Number of regions: number of service regions for which coordinates are
transmitted in present Message Type 27;
E. Inside UDRE Indicator is a conventional code defining (according to
Table 28) the degradation factor ( UDRE) of regional parameter UDRE. This
conventional code is applicable only when positioning on the territory of regions
coordinates of which are defined in present Message Type 27;
F. Priority code: a code for definition of message priority in positions
belonging to two overlapping regions. Message with higher code has higher priority.
If priority codes are equal, message with lower UDRE has higher priority;
G. Outside indicator UDRE is a conventional code defining (according to
Table 31) the degradation factor ( UDRE) of regional parameter UDRE. This
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conventional code is applicable only when positioning outside the territory of regions
defined in all current Message Type 27;
Table 31 – UDRE Indicator Evaluation
UDRE Indicator UDRE
0 1
1 1,1
2 1,25
3 1,5
4 2
5 3
6 4
7 5
8 6
9 8
10 10
11 20
12 30
13 40
14 50
15 100
H. Multifunctional coordinate 1 (latitude, longitude) {coordinate 2 (latitude,
longitude)}: latitude and longitude of angular point 1 {point 2} of region territory.
Used for definition of region borders which can be square and triangular;
I. Coding of Region Shape: 0 denotes a triangular region, 1 denotes a square
region.
Region borders are defined according to the rules:
- coordinate 3 has always the latitude of coordinate 1 and longitude of
coordinate 2;
- for definition of square region form coordinate 4 is required which has
always the latitude of coordinate 2 and longitude of coordinate 1;
- region border is formed by linking coordinates as 1-2-3-1 (triangle) or 1-2-3-
4-1 (square). The segments of border have either constant latitude or longitude, or
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constant slant in latitude degrees into longitude degrees. Latitude or longitude
variation along any segment of border between two coordinates is less than 180о.
7.13 Clock-ephemeris Covariance Matrix Message Type 28
Message Type 28 may be broadcast to provide the relative covariance matrix
for clock and ephemeris errors. Message Type 28 provides increased availability
inside and increased integrity outside the service area of SDCM Wide Area
Differential System.
Elements of covariance matrix are used taking into account a user position for
definition of degradation factor ( UDRE) required for calculation of User
Differential Range Error (UDRE).
For compression of transmitted data in SBAS format clock-ephemeris
covariance matrix (С) is transmitted as a set of decomposition matrices: SF
coefficient of scale factor (SFi,j;),i,j = 1…4 and triangular matrix (Е4х4) of Cholesky
factorization:
C = (E∙SF)т ∙ E∙SF.
Cholesky factorization elements (Eij) are the elements of upper triangular
matrix (4х4) which together with scale factor matrix SF4х4 minimize digital data
content to be transmitted.
Figure 25 and Table 32 present the contents of the of Type 28 message
representing the Cholesky factor of the clock-ephemeris covariance matrix for two
PRN codes.
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Direction of data flow from satellite . Most significant bit (MSB) transmitted first
250 Bits - 1 secondIODP
Scale Exponent
1,1E 2,2E 2,3E3,3E 4,4E 1,2E 1,4E 2,4E 3,4EFirst satellite
PRN Mask Number24- Bits Parity
6-Bit Message Type Identifier
8-Bit Preamble
E Second satellite
Figure 25. Type 28 Clock-ephemeris Covariance Matrix Message Format.
Table 32. Type 28 Clock-ephemeris Covariance Matrix Message Parameters
Parameter
No. Of
Bits
Effective
Range Resolution
IODP 2 0–3 1
For each of two satellites:
PRN Mask No. 6 0–51 1
Scale exponent 3 0–7 1
E1,1 9 0–511 1
Е2,2 9 0–511 1
Е3,3 9 0–511 1
Е4,4 9 0–511 1
Е1,2 10 512 1
Е1,3 10 512 1
Е1,4 10 512 1
Е2,3 10 512 1
Е2,4 10 512 1
Е3,4 10 512 1
Preamble, message type identifier and parity field are defined above (Section
6.2, 6.3, 6.7).
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7.14 Null Message Type 63 and Internal Test Message Type 62
The null Message Type 63 is used as a filter message if no other message is
available for broadcast for the one-second time slot. The Internal Test Message Type
62 is used for internal testing purposes. The user will continue to use the GEO
broadcast and ranging capabilities.
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8 Annex А. Definitions of basic a priory and a posteriori parameters
for navigation user equipment accuracy assessment taking into account
SDCM data
The following parameters are assumed a priori for user positioning accuracy
assessment:
HAL (Horizontal Alert Limit) – horizontal circle radius (with the center
in the actual user position) meeting integrity requirement: all altitude
positioning reports are within the circle with probability of 1-10-7
[1/hour];1
VAL (Vertical Alert Limit) – half length of vertical distance (in the
actual user position) meeting integrity requirement: all altitude positioning
reports are within the interval {- VAL, + VAL } with probability of 1-10-
7 [1/hour];
1
For navigation user equipment accuracy evaluation taking into account
SDCM data the following a posteriori parameters called the protection levels
are evaluated according positioning results:
HPLSDCM (Horizontal Protection Level) – Horizontal Protection Level.
Equal to distribution model dispersion of horizontal positioning true error
taking into account SDCM data within confidence interval «6 » (expectancy
of hitting – more than 1-10-7
);
VPLSDCM (Vertical Protection Level) – Vertical Protection Level. Equal
to distribution model dispersion of vertical positioning true error taking into
account SDCM data within confidence interval «6 » (expectancy of hitting –
more than 1-10-7
);
Navigation user equipment accuracy taking into account SDCM data
meets integrity requirements (more than 1-10-7
) provided that the following
conditions are met:
1 Given probability is defined by integrity requirements. Here the probability of failure in
GPS /GLONASS/SDCM system is a priory less than 10-4
[1/hour].
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HAL ≥ HPLSDCM;
VAL ≥ VPLSDCM .
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9 Annex B. Basic integrity principles
B.1 Integrity of GLONASS/GPS/SDCM navigation field
B.1.1 Monitoring and integrity maintenance of GLONASS navigation field
and integrity monitoring of GPS navigation field are important features defining the
user positioning quality. GNSS radionavigation field integrity is a final product of
complex interaction of various factors which can be classified as follows:
- errors of monitoring navigation satellites by GNSS ground facilities and
generating data for uplinking to navigation satellites defined by ground facilities
accuracy;
- errors of generating radionavigation signal onboard GLONASS and GPS
satellites;
- residual error of atmosphere effects along navigation signal propagation path.
For GNSS users the errors of first two groups are indistinguishable and appear
as a general error of a range signal. When SDCM system is used the general error of
range signal is range ambiguity (residual discrepancy) generated after the application
of long-term and fast corrections and after the definition of error of atmosphere
effects. Such discrepancy is defined as a variation of centered normal distribution of
measured range difference (normally distributed value) and estimated (geometrical)
difference for each signal source, and designated as UDRE. For the user UDRE
defines the upper limit of pseudorange assessment error and therefore is a criterion of
GNSS field integrity assessment.
B.1.2 For integrity assessment dual frequency user receiver can use only
UDRE parameter because this parameter includes the errors of first two groups (see
Section 7), troposphere errors, and residual ionosphere error is small in dual
frequency measurements.
For integrity assessment single frequency user receiver also requires UIRE
parameter. UIRE is a residual error for taking into account ionosphere effects on the
basis of ionosphere delays map data for SDCM signal. The map is a set of grid
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vertical delays introduced by ionosphere into a navigation signal and, additionally,
GIVE codes unambiguously connected with dispersion of such delays. Basing on
GIVE and its own position, the user defines UIRE parameter, the analogue of GIVE
but for a user position, for example between grid nodes of delays map.
B.1.3 There is the finite probability of non-receiving a regular SDCM
message by a SDCM receiver. In this case for continuing navigation SDCM
transmits message degradation parameters. Said parameters are used in a number of
mathematical models describing additional residual error from long-time and fast
differential corrections appearing as a result of using aged but valid SDCM data. Said
models are used for modification of UDRE and UIRE variations if necessary.
B.1.4 Above parameters UDRE and UIRE vare used by a receiver for
navigation solution error assessment. Navigation solution error is calculated by
projecting pseudorange errors into a user coordinate area. Horizontal Protection Level
(HPL) defines the border of user horizontal positioning error with the probability
obtained from integrity requirements. The same algorithm is assumed for VPL and
Vertical Protection Level. If estimated value of HPL or VPL exceeds HAL or VAL
alert limit, SDCM integrity is not enough for support of this navigation solution.
B.1.5 Clock-ephemeris residual errors ( GIVE)
Clock residual error is described by zero mean and normal distribution.
Ephemeris residual error depends on a user position. At accurate differential
correction the residual error for any user within service area is included in UDRE.
B.1.6 Vertical ionosphere error ( GIVE)
Residual ionosphere error is presented by normal distribution with zero mean.
The errors are the functions of measurement noise of ionosphere map and ionosphere
spatial decorrelation.
B.1.7 Errors of navigation user equipment
Total error due to multipath and receiver contribution is restricted as presented
in Annex C. This error can be divided into the multipath and receiver contribution in
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accordance with Section C 9, here a standard multipath model may be used. The
receiver contribution may be obtained from the accuracy requirements (Annex C) and
extrapolated to typical signal conditions. In particular, it may be assumed that the
following expression is true for navigation user equipment: 2
air = 2
receiver + 2
multypath,
where receiver is assumed to be defined by RMSpr_air, and multypath is defined in Annex
В.
B.1.8 Troposphere model error
A receiver uses the model for troposphere effects correction. The user assess
the residual error of the model ( tropo) according to the formula (E.5) presented in
Annex E .
B.2 SDCM data integrity
B.2.1 Digital data synchronization in the structure of messages transmitted
by SDCM geostationary satellites
Correct use of received SDCM digital data in navigation user equipment
consist in selecting complete set of messages for each operational satellite out from
received digital data flow, and in appropriate application of selected messages that
must belong to the same data validity interval.
SDCM messages delivery must take into account the asynchronous manner of
data transmission and reception. Moreover, the order of transmitted digital data in
SDCM channel is not constant and may vary if necessary in order to quickly correct
current errors of navigation satellites. Main mission of SDCM channel is to provide
transmission of digital data within data update intervals defined by the SBAS
standard. The user must be provided with all necessary information for identification
and affixment of received data, i.e. for “synchronization” of received digital data with
the number of navigation satellite for which it is generated, and with the time to
which these digital data belong.
Digital data identification and synchronization methods defined by the
standard, also consider restrictions from data transmission channel. Digital data
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format described herein provides digital data identification and synchronization for
the user under the following channel restrictions:
а) finite capacity for data transmission in the SBAS standard.
Comments. The SBAS standard permits the transmission of data flow with the
rate of 250 bits/sec for no more than 51 satellites;
б) SDCM assumes SBAS standard extension with maintenance of succession
for navigation user equipment in force.
Comments. For servicing prospective expanded orbital constellation of
navigation satellites under conditions of restricted channel capacity (see above) data
flow “compression” is required, for the sake of which non-relevant digital data (for
antipode satellites) are excluded from transmitted messages. Digital data are
transmitted only for those navigation satellites which are visible for users of present
SDCM satellite – these are the SDCM messages of the SBAS standard necessary for
the user. Here decoding and application algorithm of digital data is not changed
which guarantees return succession (applicability) of current version of the Standard
for actual navigation user equipment.
SBAS standard extension consists in the necessity of transition to the dynamic
model of the mask which now defines not only the list of satellites from all
navigation systems but exactly those satellites for which digital data are transmitted
via present SDCM satellite (for no more than 51 satellites);
в) asynchronous manner of digital data update in a channel.
Comments. Digital data reception in a channel is not synchronized with
transmission, messages in the channel may comprise both new (updated) digital data
and digital data from previous update cycle. It is worth reminding that for the user
digital data are mutually compatible and correct only when they belong to the same
update cycle.
Validity of considering these restrictions follows from the analysis of SBAS
standard parameters, the analysis of total number of satellites in GPS, GLONASS,
Galileo, WAAS, EGNOS and SDCM systems. Considering declared redundancy the
number of satellites will make up 100 (which significantly exceeds SDCM channel
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capacity on the basis of the SBAS standard – channel can transmit digital data only
for 51 satellites), at the same time the total number of satellites in visibility field will
not exceed 43. Moreover, return compatibility is possible: the provisions of present
document are entirely applicable for existing navigation user equipment widely used,
which operate using GPS/WAAS systems on the basis of previous version of the
SBAS standard.
Considering the above channel restrictions the following principles of digital
data synchronization are used in present document (in the order of descending
priority to be observed by users when decoding digital data):
1) beginning of each message is to be defined by the field “Preamble” (see
Section 6.2);
2) content and rules of digital data decoding “Data fields” are to be defined by
the field «Message type identifier» (see Section 6.3);
3) control of reliability of received digital data is effected with use of control
sum (see Section 6.7);
4) Digital data synchronization in accordance with satellites numbers is
effected using one of the following methods:
4.1) By direct indication a number of satellite PRN in a message for which
digital data are intended;
4.2) If there is no data for 4.1 – digital data belonging to specific satellite is
effected via position code PRN Mask (Message Type 1 – see Section 7.2). The
following rule is used: digital data blocks in decoded message follow exactly in the
same order (and comprise digital data for satellites with same numbers), in which
numbers of bits of PRN Mask with code 1 follow (the number of bit in PRN Mask is
numerically equal to the number of satellite). Satellites numbers with the code of
PRN Mask equal to 0, are not presented in transmitted digital data and not considered
in the sequence of digital data blocks.
Comment. For instance, 210-bits code of PRN Mask equal to 1001 1000 1100
0010 0000…0000, in decoded message defines availability of digital data for the
satellites having numbers PRN = 1, 4, 5, 9, 10 and 15, and defines the following
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blocks sequence in this message (digital data for the satellite number N): digital data
1, digital data 4, digital data 5, digital data 9, digital data 10, digital data 15.
5) Digital data time synchronization is effected by selection out from received
data file those data which have the identical code in the field «data identifier».
Mutually compatible digital data have the identical code in the field Issue of
Data. The length of field Issue of Data (no more than 2 bits) provides data division by
the feature «new – old» for not less that two sequential digital data updates in the
SBAS channel (see Section 6.3).
B.2.2 Separation of compatible data from different messages
SBAS standard does not have user requirements for synchronous data reception
and transmission. Therefore, during the time of receiving messages by the user in the
SBAS channel periodical digital data update may occur, in this case received
messages will relate to different time and become incompatible. For correct use all
digital data must be preliminary checked by the user for compatibility. Compatible
data have the same code value in the field Issue of Data. The following Issue of Data
are used in present document: (IOD – Issue of Data):
GPS clocks Issue of Data (GPS IOD Clock – IODCk) – GPS satellite time, k –
satellite number;
GPS ephemeris IOD (GPS IOD Ephemeris – IODEk) – GPS satellites
ephemeris, k – satellite number;
GLONASS Data (IODGk) – GLONASS IOD identifies clocks and ephemeris
of GLONASS satellites, k – satellite number;
IOD PRN Mask (IODP) – identifies data about satellites used. Identifies the
current list of satellites used;
IODFj – identifies data about fast corrections, j - message number (2-5);
Additional functions IODFj: see Section 7.6;
IODI – ionosphere IOD– identifies aggregate of points for which ionosphere
delay is calculated;
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IODS – service IOD– identifies Service Message Type 27.
Figure B.1 shows the correlation diagram provided for compatibility check of
received SDCM messages by the user.
GPS EphemerisLong-term changes
(25)
Fast changes
(2-5,24)
GPS ClocksField of used satellites
(1)
GLONASS Data
Integrity information (6)
Ionospheric corrections
(26)
Ionospheric Mask
(18)
Covariance Matrix
(28)
Service Messages
(27)
Navigation data of
SDCM satellite (9)
Degradation parameters
(7)
IODE
IODPIODC
IODG
IODP
IODP IODP
IODS
IODI
IODP
Figure B.1– Message Correlation Diagram
Before use of digital data message types indicated in the Figure must be
checked for compatibility by the user with application of IODs presented.
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10 Annex C. Tables of SDCM message formats
Each SDCM message is coded in accordance with established message format
defined in Tables C.1 – C.16. All parameters defined in these Tables with digit,
comprise digit bit transmitted in the most significant bit.
Table C.1 – Message Type 0. Do not use for safety applications
Parameter
No. Of
Bits
Effective
Range Resolution
Not reserved 212 — —
Table C.2 – Message Type 1. PRN Mask assignments
Parameter
No. Of
Bits
Effective
Range Resolution
For each of 210 numbers
of PRN-code
Mask value 1 0 or 1 1
IODP 2 0–3 1
Comment. All parameters are defined in Section 7.2.
Table C.3 – Message Type 2–5. Fast corrections
Parameter
No. Of
Bits
Effective
Range Resolution
IODFj 2 0–3 1
IODP 2 0–3 1
For 13 points
Fast correction (FCi) 12 256,000 m 0,125 m
For 13 points
UDREIi 4 (See Table 19) (See Table 19)
Comments:
1. Parameters IODFj and FCi are defined in Section 0.
2. Parameter IODP is defined in Section 7.2.
3. Parameter UDREIi is defined in Section 7.7.
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Table C.4 – Message Type 6. Integrity information
Parameter
No. Of
Bits Effective Range Resolution
IODF2 2 0–3 1
IODF3 2 0–3 1
IODF4 2 0–3 1
IODF5 2 0–3 1
For 51 satellites (defined by the number of PRN Mask)
UDREIi 4 (See Table 19) (See Table 19)
Comments:
1. Parameters IODFj are defined in Section 0.
2. Parameter UDREIi is defined in Section 7.7.
Table C.5 – Message Type 7. Fast correction degradation factor
Parameter
No. Of
Bits
Effective
Range Resolution
System delay (tlat) 4 0–15 sec 1 sec
IODP 2 0–3 1
Not reserved 2 — —
For 51 satellites (defined by the number of PRN Mask)
Degradation indicator (aii) 4 (See Table D.4) (See Table D.4)
Comments:
1. Parameters tlat and aii are defined in Annex D
2. Parameter IODP is defined in Section 7.2
Table C.6 – Message Type 9. GEO navigation message
Parameter
No. Of
Bits Effective Range Resolution
Not reserved 8 –– ––
t0,GEO 13 0–86 384 sec 16 sec
URA 4 (See Table C.7) (See Table C.7)
XG 30 42 949 673 m 0,08 m
YG 30 42 949 673 m 0,08 m
ZG 25 6 710 886,4 m 0,4 m
17 40,96 m/sec 0,000625 m/sec
17 40,96 m/sec 0,000625 m/sec
18 524,288 m/sec 0,004 m/sec
10 0,0064 m/sec2 0,0000125 m/sec
2
10 0,0064 m/sec2 0,0000125 m/sec
2
10 0,032 m/sec2 0,0000625 m/sec
2
aGf0 12 0,9537 10-6
sec 231
sec
aGf1 8 1,1642 10-10
sec/sec
240
sec/sec
Comment: All parameters are defined in Section 7.3
GX
GY
GZ
GX
GY
GZ
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Table C.7 – User range measurement accuracy
URA
Accuracy
(rms)
0 2 m
1 2,8 m
2 4 m
3 5,7 m
4 8 m
5 11,3 m
6 16 m
7 32 m
8 64 m
9 128 m
10 256 m
11 512 m
12 1 024 m
13 2 048 m
14 4 096 m
15 "Do not use"
Table C.8 – Message Type 10. Degradation parameters
Parameter No. Of Bits
Effective
Range Resolution
Brrc 10 0–2,046 m 0,002 m
Cltc_lsb 10 0–2,046 m 0,002 m
Cltc_v1 10 0–0,05115 m/s 0,00005 м/s
Iltc_v1 9 0–511 s 1 s
Cltc_v0 10 0–2,046 m 0,002 m
Iltc_v0 9 0–511 s 1 s
Cgeo_lsb 10 0–0,5115 m 0,0005 m
Cgeo_v 10 0–0,05115 m/s 0,00005 m/s
Igeo 9 0–511 s 1 s
Cer 6 0–31,5 m 0,5 m
Ciono_step 10 0–1,023 m 0,001 m
Iiono 9 0–511 s 1 s
Ciono ramp 10 0–0,005115 m/s 0,000005 m/s
RSSUDRE 1 0 or 1 1
RSSiono 1 0 or 1 1
Ccovariance 7 0–12,7 0,1
Not reserved 81 — —
Comment: All parameters are defined in Section 7.10.
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Table C.9 – Message Type 12. SDCM network time /UTC offset parameters
Parameter
No. Of
Bits Effective Range Resolution
A1SNT 24 7,45 10–9
sec/sec 2–50
sec/sec
A0SNT 32 1 sec 2–30
sec
t0t 8 0–602 112 sec 4 096 sec
WNt 8 0–255 weeks 1 weeks
tLS 8 128 sec 1 sec
WNLSF 8 0–255 weeks 1 weeks
DN 8 1–7 hours 1 hours
tLSF 8 128 sec 1 sec
UTC standard identifier 3 (See Table 25) (See Table 25)
Time in GPS week (TOW) 20 0–604 799 sec 1 sec
Number of GPS week
(WN)
10 0–1 023 weeks 1 weeks
GLONASS indicator 1 0 or 1 1
ai, GLONASS (comment 2) 32 1 sec 2–30
sec
Reserved 42 — —
Comment:
1. All parameters are defined in Section 7.11.
2. To be applied only when the information about GPS/GLONASS time offset
correction is transmitted in Message Type 12.
Table C.10 – Message Type 17. GEO satellite almanacs
Parameter
No. Of
Bits
Effective
Range Resolution
For each of three satellites
Not reserved 2 — —
Number of PRN-code 8 0–210 1
Operability and status 8 — —
Not used 49 — —
Not used 11 — —
Comment: All parameters are defined in Section 7.4.
Table C.11 – Message Type 18. Ionospheric grid point masks
Parameter
No. Of
Bits
Effective
Range Resolution
Number of IGP bands 4 0–11 1
IGP band ID 4 0–10 1
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Parameter
No. Of
Bits
Effective
Range Resolution
Feature of ionosphere data package
(IODIk)
2 0–3 1
For 201 points of IGP
IGP Mask 1 0 or 1 1
Not reserved 1 — —
Comment: All parameters are defined in Section 0.
Table C.12 – Message Type 24. Mixed fast corrections/
long-term satellite error corrections
Parameter
No. Of
Bits Effective Range Resolution
For six points
Fast correction (FCi) 12 256,000 m 0,125 m
For six points
UDREIi 4 (See Table 19) (See Table 19)
IODP 2 0–3 1
Fast correction IOD 2 0–3 1
IODFj 2 0–3 1
Not reserved 4 — —
Half Message Type 25 106 — —
Comment:
1. Parameters " Fast correction type identifier ", IODFj and FCi are defined in Section 8.5.
2. Parameter IODP is defined in Section 7.2
3. Parameter UDREIi is defined in Section 7.7.
Table C.13 – Message Type 25. Long-term satellite error corrections
(Half Message for VELOCITY CODE = 0)
Parameter
No. Of
Bits
Effective
Range Resolution
Velocity Code = 0 1 0 1
For two satellites
PRN Mask number 6 0–51 1
Feature of data package (IODi) 8 0–255 1
xi 9 ±32 m 0,125 m
yi 9 ±32 m 0,125 m
zi 9 ±32 m 0,125 m
ai,f0 10 ±2–22
sec 2–31
sec
IODP 2 0–3 1
Not reserved 1 — —
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Parameter
No. Of
Bits
Effective
Range Resolution
Comments:
1. Parameters " PRN Mask number " and IODP are defined in Section 7.2.
2. All other parameters are defined in Section 7.5.
Table C.14 – Message Type 25. Long-term satellite error corrections
(Half Message for VELOCITY CODE = 1)
Parameter
No. Of
Bits
Effective
Range Resolution
For one satellite
Velocity Code = 1 1 1 1
PRN Mask number 6 0–51 1
Feature of data package (IODi) 8 0–255 1
xi 11 ±128 m 0,125 m
yi 11 ±128 m 0,125 m
zi 11 ±128m 0,125 m
ai,f0 11 ±2–21
sec 2–31
sec
8 ±0,0625 m/sec 2–11
m/sec
8 ±0,0625 m/sec 2–11
m/sec
8 ±0,0625 m/sec 2–11
m/sec
ai,f1 8 ±2–32
sec/sec 2–39
sec/sec
Time-of-Day Applicability (ti,LT) 13 0–86 384 sec 16 sec
IODP 2 0–3 1
Comments:
1. Parameters " PRN Mask number " and IODP are defined in Section 7.2.
2. All other parameters are defined in Section 7.5.
Table C.15 – Message Type 26. Ionosphere delay corrections
Parameter
No. Of
Bits Effective Range Resolution
IGP band identifier 4 0–10 1
IGP block identifier 4 0–13 1
For each of 15 grid points
IGP vertical delay evaluation 9 0–63,875 m 0,125 m
Grid ionosphere vertical error
indicator (GIVEIi)
4 (See Table 23) (See Table 23)
IODIk 2 0–3 1
Not reserved 7 — —
Comment: All other parameters are defined in Section 7.
ixδ
iyδ
izδ
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Table C.16 – Message Type 27. SDCM Service Message
Parameter
No. Of
Bits
Effective
Range Resolution
Feature of service data (IODS) 3 0–7 1
Number of service data 3 1–8 1
Service data number 3 1–8 1
Number of regions 3 0–5 1
Priority code 2 0–3 1
Inside index UDRE 4 0–15 1
Outside index UDRE 4 0–15 1
For each of five regions
Coordinate 1 latitude 8 90 1
Coordinate 1 longitude 9 180 1
Coordinate 2 latitude 8 90 1
Coordinate 2 longitude 9 180 1
Shape of region 1 — —
Not reserved 15 — —
Comment: All other parameters are defined in Section 7.12
Table C.17 – Message Type 63. Null message
Parameter
No. Of
Bits
Effective
Range Resolution
Not reserved 212 — —
Table C.18 – Message Type 28. Clock-Ephemeris Covariance Matrix Message
Parameter No. Of Bits
Effective
Range Resolution
IODP 2 0–3 1
For two satellites
PRN Mask number 6 0–51 1
Scale Exponent 3 0–7 1
E1,1 9 0–511 1
Е2,2 9 0–511 1
Е3,3 9 0–511 1
Е4,4 9 0–511 1
Е1,2 10 512 1
Е1,3 10 512 1
Е1,4 10 512 1
Е2,3 10 512 1
Е2,4 10 512 1
Е3,4 10 512 1
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Parameter No. Of Bits
Effective
Range Resolution
Comments:
1. Parameters including PRN mask number and IOD are defined in Section
7.2.
2. All other parameters are defined in Section 7.13
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11 Annex D. Recommendations on SDCM data use in the navigation
algorithm GLONASS/GPS/SDCM
D.1 General provisions
D.1.1 Required data and transmission intervals
SDCM transmits data required for the functions supported by the system, as
showed in Table D.1. If SDCM data transmitted by the system are not required for
specific function, these data are used for other functions. Maximum transmission
intervals of all data via each type of messages are defined in Table D.1.
D.1.2 Control of SDCM radiofrequencies
SDCM controls SDCM satellite parameters indicated in Table D.2 and
undertake provided actions.
Comment: SDCM can transmit zero messages (Type 63) in each transmission
interval for which there is no any other data to be transmitted.
D.1.3 Message "Do not use"
SDCM transmits the message "Do not use" (Type 0) when it is necessary to
inform users than transmitted SDCM data should not be used.
D.1.4 Almanac
SDCM transmits the almanac of SDCM satellites (defined in Section 7.4) in
which satellites coordinates are defined with the error of less than 150 km. In unused
cells of the almanac in the Message Type 17 zero number of PRN-code is indicated.
Words " health " and "status " indicate the status of a satellite and service provider as
defined in Section 7.2.
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Table D.1 – Data transmission intervals and provided functions
Data type
Maximum
transmissi
on
intervals
Status of
GEO
SDCM
Status of
GNSS
satellites
Standard
differential
corrections
Accurate
differential
corrections
Respe
ctive
messa
ge
types
Clock-ephemeris
covariation matrix 120 sec 28
SDCM in test
mode
6 sec 0
PRN Mask 120 sec R R R 1
UDREI 6 sec R*
R R 2–6,
24
Fast corrections 60 sec R* R R 2–5,
24
Long-term
corrections
120 sec R* R R 24, 25
GEO navigation
data
120 sec R 9
Fast corrections
degradation
120 sec R* R R 7
Degradation
parameters
120 sec R 10
Ionosphere grid
mask
300 sec R 18
Ionosphere
corrections,
GIVEI
300 sec R 26
Time data 300 sec R
(see
Comment
3)
R
(see Comment
3)
R
(see
Comment
3)
12
Almanac 300 sec R R R 17
Service level 300 sec 27
Comments:
1. "R" indicates that present information is transmitted for provision of present function.
2. "R*" indicates special coding as defined in 4.
3. Messages Type 12 are required only for GLONASS satellite data.
D.2 Status of GNSS satellites
If SDCM provides satellite status data, they correspond to the requirements of
present section.
D.2.1 Characteristics of satellite status functions
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Under any reliable combinations of valid information the probability of
horizontal error exceeding HPLSDCM (as defined in Annex I) within more than 8 sec,
shall not exceed 10–7
for any hour provided that the user has zero delay.
Comment: Valid information means the information validity period of which is
not expired in accordance with Table D.1.
D.2.2 PRN Mask and feature of PRN data set (IODP)
SDCM transmits parameters "PRN Mask" and IODP (Message Type 1). The
values of PRN Mask indicate whether data on each GNSS satellite provided or not.
IODP changes when PRN Mask changes. Change of IODP in Message Type 1 take
place before IODP change in any other message. In Messages Type 2–5, 7, 24 and 25
IODP is determined in the same manner as IODP transmitted in Message Type 1 for
PRN Mask, used for indication of satellites for which information is provided in
present message.
When PRN Mask is changed, SDCM repeats Message Type 1 a few times
before transmission to other messages, in order to guarantee reception of a new Mask
by the user.
D.2.3 Integrity data
If SDCM does not provide the required accuracy of differential correction, fast
corrections, long-term corrections and fast corrections degradation parameters for all
visible satellites indicated in the PRN Mask are transmitted in zero coding.
If SDCM does not provide the required accuracy of differential correction and
if the pseudorange error exceeds 150 m, it means that the satellite is not healthy
(feature “Do not use”).
If SDCM does not provide the required accuracy of differential correction and
if the pseudorange error can not be defined, SDCM reports that for given satellite
there is “No monitoring”.
If SDCM does not provide the required accuracy of differential correction and
if no features “Do not use” and “No monitoring” are assigned to the satellite, SDCM
transmits URDEIi 13.
Parameter IODFj in Messages Type 2 5, 6 or 24 is defined equal to 3.
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D.3 Differential correction
If SDCM provide the required accuracy of differential correction, SDCM
meets the requirements contained in this Section, in addition to the information about
SDCM satellites status (Section 7.4).
D.3.1 Differential correction characteristics
Under any combinations of valid data the probability of horizontal error
exceeding HPLСДКМ (as defined in Annex I) within more than 8 sec, does not exceeds
10-7
for any hour, provided that the user has zero delay.
Comment: under valid data the following is assumed: data validity period of
which is not expired in accordance with Table D.1.
D.3.2 Long-term corrections
SDCM defines and transmits long-term corrections for each visible GNSS
satellite (see Comment) indicated in the PRN Mask (PRN Mask is equal to "1"), apart
from SDCM satellites. For each GLONASS satellite SDCM, before definition of
long-term corrections, transforms satellites coordinates into WGS-84 as indicated in
Section 7.5. For each GPS satellite IOD feature transmitted by it coincide
simultaneously with GPS IODE and 8 lower bits of IODC which correspond to clock-
ephemeris data used for calculation of corrections (Section 7.5). When a GPS satellite
transmits new ephemeris SDCM continues using aged ephemeris for long-term and
fast corrections definition within, at least, 2 minutes but no more than 4 minutes. For
each GLONASS satellite SDCM calculates and transmits IOD including delay and
action time, as indicated in Section 7.5.
Comment: Satellites visibility is defined on the basis of reference stations
coordinates and takeoff angle mask (5°).
D.3.3 Fast corrections
SDCM defines fast corrections for each GNSS visible satellite indicated in the
PRN Mask (PRN Mask is equal to "1"). If IODF 3, each time when any data of a
fast correction are changed in Messages Type j (j = 2, 3, 4 or 5), IODFj feature is
changed in the order of "0, 1, 2, 0, ...".
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Comment: In case of irregular operation IODFj feature may be equal to 3 (see
Section 0).
D.3.4 Time data
If the data are provided for GLONASS, SDCM transmits a time message
(Message Type 12) including GLONASS time offset as defined in Table D.8.
D.3.5 Integrity data
For each satellite for which corrections are applied SDCM transmits integrity
data (UDREIi and additionally the data of Message Type 27 or 28 for calculation of
UDRE) in the manner that provides meeting integrity requirements contained in
Annex B. If fast and long-term corrections exceed the limits of their code intervals,
SDCM indicates that the satellite is unhealthy (“Do not use”). If 2
i, UDRE parameter is
not defined SDCM indicates that there is “No monitoring” for the satellite.
If Message Type 6 is used for transmission of 2
i, UDRE than:
Feature IODFj coincide with IODFj for fast corrections assumed in Message
Type j for which 2i,UDRE is applied; or IODFj is equal to 3 if
2i,UDRE is applied to all
reliable fast corrections assumed in Message Type j the validity period of which is
not expired.
D.3.6 Degradation parameters
SDCM transmits degradation parameters (Message Type 7) for indication of
validity period of fast corrections and meeting integrity requirements presented in
Section 7.10.
D.4 Differential correction
SDCM provides differential correction in accordance with requirements
contained in this Section.
D.4.1 Differential correction characteristics
When GNSS errors occur and under any reliable combinations of SDCM data,
when the user is assumed to have zero delay, SDCM data application provides the
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probability of exceeding admissible thresholds of positioning error of less than 2
10-7
within any time interval after SDCM alarm activation (less than 10 second).
Exceeding of admissible threshold is defined as horizontal error exceeding of
HPLSDCM (as defined in Annex I). When exceeding of admissible threshold is
detected a final alarm message is repeated three times (transmitted in Messages Type
2–5 и 6, 24, 26 or 27).
Altogether SDCM alert occurs for times in 4 seconds.
Comments:
А). Under valid data the following is assumed: data validity period of which is
not expired in accordance with Table D.1. This requirement includes failures of
GLONASS, GPS and SDCM.
B). Sequential messages can be transmitted with standard update rate.
D.4.2 Ionosphere grid point model Mask (IGP Mask)
SDCM transmits IGP and IODIk Mask (up to 11 Messages Type 18
corresponding to 11 IGP diapasons). IGP values indicate if data are provided for each
IGP. If the 9-th diapason of IGP is used, IGP values for points located to the north
from 55 N in the diapasons 0–8 are set to "0". If the 10-th diapason of IGP is used,
IGP values for points located to the south from 55 S in the diapasons 0–8 are set to
"0". IODIk feature is changed when IGP Mask values are changed in k-th diapason.
New IGP Mask is transmitted in Message Type 18 before a reference to it in
corresponding Message Type 26 occurs. IODIk feature in Message Type 26 is equal
to IODIk feature transmitted in the message for IGP Mask (Message Type 18) which
is used for indication of IGP points by which data are transmitted in the message.
D.4.3 Ionosphere corrections
SDCM transmits Ionosphere corrections for IGP points indicated in IGP Mask
(IGP Mask values are equal to “1”).
D.4.4 Ionosphere data integrity
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For each IGP provided with ionosphere corrections SDCM transmits GIVEI
data in such manner which provides meeting integrity requirements of D.3.5. If
ionosphere correction of parameter 2
i,GIVE exceed code interval SDCM indicates that
IGP is unhealthy (indicated in correction data). If parameter 2
i,GIVE can not be
defined, SDCM indicates that there is “Mo monitoring” for present IGP (indicated at
coding GIVEI).
D.4.5 Degradation parameters
SDCM transmits degradation parameters (Message Type 10) in such manner
which provides meeting integrity requirements of Table C.8.
D.5 Additional functions
D.5.1 Time data
If UTC time parameters are transmitted they are defined as showed in Table
C.9. (Message Type 12).
D.5.2 Service indication
If service data are transmitted they are defined as showed in Table C.15
(Message Type 27), and Messages Type 28 are not transmitted. IODS parameter in
all Messages Type 27 is increased by one when any change of data occurs in Message
Type 27.
D.5.3 Clock-ephemeris covariation matrix
If covariation matrix data are transmitted they are transmitted for all controlled
satellites as defined in Table C.16 (Message Type 28), and Messages Type 27 are not
transmitted.
D.6 Monitoring
D.6.1 SDCM radiofrequency monitoring
SDCM continuously monitors SDCM satellites parameters indicated in Table
D.2 and undertakes indicated actions.
D.6.2 Data monitoring
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SDCM monitors satellite signal in order to detect conditions which may cause
incorrect function of differential processing in Navigation user equipment, using
tracking characteristics.
D.6.2.1 SDCM monitors all operational GNSS data which may be used by any
user within service area.
D.6.2.2 SDCM gives up an alarm within 10 sec if any combination of valid
data and signals in space radiated by GNSS is out of defined thresholds.
Comment. Monitoring covers all failure cases including the failures of
basic orbital system(s) of satellites of SDCM.
Table D.2 – SDCM radiofrequency monitoring
Parameter Threshold Required action
Signal/noise ratio
of received signal
Less than 34 dBHz
More than 55 dBHz
Cease reception of onboard repeater
Swith off telecommand system (switch to
redundant set)
Carrier frequency
stability
Frequency drift from
nominal more than 6,0
kHz
Swith off telecommand system (switch to
redundant set)
Reliability
Control of
uplinked
information
Invalid data are
detected
Cease data transmission within 2 sec
D.6.3 Robustness to failures of basic orbital system(s)
When a failure occurs at a satellite of the basic orbital system(s) SDCM
continues normal operation using available tracked signals of healthy satellites.
D.7 Recommended receiver parameters
Comments:
1. Parameters referred to in this Section are defined in Section 8.
2. Requirements of this Section are not mandatory for equipment which
includes additional navigation sensors (for example, for a receiver interconnected
with inertial sensors).
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D.7.1 GNSS receiver using SDCM signals
If not defined specially, a GNSS receive capable to receive SDCM signals
process simultaneously SDCM signals and GLONASS and GPS signals. Pseudorange
measurements for each satellite are smoothed using carrier measurements and
smoothing filter which has post-initialization offset of less than 0,1 m for 200 sec
relative to the stable status of filter response defined in Section 8.4, provided that the
drift between the code phase and integrated carrier phase makes up to 0,01m/sec.
D.7.2 Conditions of data use
Reception of Message Type 0 from SDCM satellite cause ceasing operations
with this satellite and all data received from it during at least 1 minute. For GPS
satellites a receiver applies long-term corrections only when IOD coincides with
IODЕ and 8 lower-order bits of IODС. For GLONASS satellites a receiver applies
long-term corrections only when GLONASS ephemeris reception time (tr) is within
the following IOD validity time:
LT r LTt L V t t L
Comments: This requirement does not assume that a receiver cease tracking
SDCM satellite.
D.7.2.1 Receiver uses integrity or correcting data only when IODP for this
information coincides with IODP for PRN Mask.
D.7.2.2 Receiver uses ionosphere data provided by SDCM (assessment of
IGP and GIVEIi vertical delay) only when IODIk connected with these data in
Message Type 26 coincides with IODIk, connected with respective mask of IGP
diapason transmitted Message Type 18.
D.7.2.3 Receiver uses the latest received integrity data for which: IODFj is
equal to 3 or IODFj coincides with IODFj connected with applied fast corrections (if
any transmitted).
D.7.2.4 Receiver uses any regional degradation to parameters 2
i,UDRE as
defined by service Message Type 27. If Message Type 27 with new IODS contains
higher UDRE for a user position, this higher UDRE is to be applied without delay.
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Lower UDRE in a new Message Type 27 is not used until a complete message set
has not been received with a new IODS.
D.7.2.5 Receiver uses satellite degradation to parameters i,UDRE2 as defined
by Message Type 28 about Clock-Ephemeris Covariation Matrix. Parameter UDRE
received from Message Type 28 is to be applied without delay.
D.7.2.6 For GPS satellites a receiver applies long-term corrections only when
IOD coincides with IODE and 8 lower-order bits of IODC.
D.7.2.7 Receiver does not use transmitted parameter of data if it is expired.
Table D.3 shows data validity intervals.
D.7.2.8 Receiver does not use a fast correction if t for respective correction
to range rate (RRC) exceeds a validity interval for fast corrections of if RRC age
exceeds 8 t.
D.7.2.9 RRC calculation is renewed if for given satellite the features “Do not
use” and “No monitoring” are assigned.
D.7.2.10 Receiver uses only satellites with elevation angle not less than 5 .
D.7.2.11 Receiver uses signals of given satellite if received UDREIi is less
than 12.
Table D.3 – Data validity intervals
Data
Respective
message types Validity period
Clock-Ephemeris Covariation
Matrix 28 360
SDCM in the test mode 0 No
PRN Mask 1 600 sec
UDREI 2–6, 24 18 sec
Fast corrections 2–5, 24 See Table D.4
Long-term corrections 24, 25 360 sec
Degradation of fast corrections 7 360 sec
Degradation parameters 10 360 sec
Ionosphere grid mask 18 1 200 sec
Ionosphere corrections, GIVEI 26 600 sec
Time 12 86 400 sec
GLONASS time offset 12 600 sec
Almanac 17 No
Service level 27 86 400 sec
Comment. Validity intervals are counted from the message reception time.
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Table D.4 – Definition of fast corrections validity interval
Degradation factor of fast
corrections (aii)
Validity interval of fast
corrections
0 180 sec
1 180 sec
2 153 sec
3 135 sec
4 135 sec
5 117 sec
6 99 sec
7 81 sec
8 63 sec
9 45 sec
10 45 sec
11 27 sec
12 27 sec
13 27 sec
14 18 sec
15 18 sec
D.7.2.12 SDCM satellites status
D.7.2.12.1 Definition of GEO satellite status. Receiver decodes Message
Type 9 and defines status of SDCM satellite.
D.7.2.12.2 SDCM satellites identification. Receiver identifies SDCM
satellites.
D.7.2.12.3 SDCM satellites status. Receiver excludes the satellites from
navigation solution if SDCM gave up the "Do not use". If integrity data provided by
SDCM are used, the receiver has no need to exclude GPS satellites on the basis of
unhealthiness feature provided by GPS or GLONASS satellites on the basis of
unhealthiness feature provided by GLONASS.
Comments:
1. If a satellite is indicated as unhealthy by GLONASS or GPS, SDCM can not
generate clock and ephemeris corrections which allow to the user to use the satellite.
2. If SDCM indicated a satellite by the feature “No monitoring” and it is used
in navigation solution, SDCM provides no integrity data.
D.7.2.13 Differential functions realized in the receiver
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D.7.2.13.1 Range measurement accuracy of the basic orbital system(s). Root
Mean Square (1 ) of onboard error total contribution into the error of corrected
pseudorange for a GPS satellite under the minimum received power and the worst
interference conditions shall not exceed 0,4 m without taking into account multipath
effects, troposphere and ionosphere residual errors.
Root Mean Square (1 ) of onboard error total contribution into the error of
corrected pseudorange for a GLONASS satellite under the minimum received power
and the worst interference conditions shall not exceed 0,8 m without taking into
account multipath effects, troposphere and ionosphere residual errors.
D.7.2.13.2. Receiver calculates and applies long-term corrections, fast
corrections, corrections to the range rate (single frequency receiver additionally
applies transmitted ionosphere corrections). For GLONASS satellites ionosphere
corrections received from SDCM are multiplied by a squared ratio of GLONASS and
GPS frequencies (fGLONASS/fGPS)2.
D.7.2.13.3 Receiver applies technique of least squares for navigation solution.
D.7.2.13.4 Receiver applies troposphere model the average residual error of
which ( ) is less than 0,15 m and standard deviation (1 ) is less than 0,07 m.
Recommendations for troposphere delay calculation are given in Annex E.
D.7.2.13.5 Receiver calculates and applies horizontal and vertical protection
levels as defined in Section 8.4. Here parameter tropo is defined as follows:
2
i
10,12 м,
0, 002 sin (θ )
where iθ – elevation angle of i-th satellite.
In addition, parameter air meets the condition of normal distribution with zero
mean, and the standard deviation equal to air restricts the distribution error for
residual pseudorange errors in navigation user equipment as follows:
ny
yyf x dx Q для всех 0
σσ , and
y
n
yyf x dx Q для всех 0
σσ,
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where
fn(x) – the function of probability density of residual pseudorange errors.
2t
2
x
1e dt.
2πQ x
Comment. Standard multipath attenuation for navigation user equipment can
be used for restricting multipath error.
D. 7.2.14 Error in the form of continuous wave (CW)
D.7.2.14.1 GPS and SDCM receivers
D.7.2.14.1.1 GPS and SDCM receivers correspond to the required
characteristics over disturbing signals in the form of continuous wave the power of
which at antenna input is equal to interference threshold indicated in Table D.5, and
presented in figure D.1, and the useful signal level of which at antenna input is equal
to –164,5 dBW.
Figure D.1 – Threshold of interference in the form of continuous wave (CW)
for GPS and SDCM receivers
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D.7.2.14.2 GLONASS receivers
D.7.2.14.2.1 GLONASS receivers correspond to the required characteristics
over disturbing signals in the form of continuous wave the power of which at antenna
input is equal to interference threshold indicated in Table D.6, and presented in figure
D.2, and the useful signal level of which at antenna input is equal to –165,5 dBW.
Figure D.2 – Threshold of interference in the form of continuous wave (CW)
for GLONASS receivers
Table D.5 –Threshold of interference in the form of continuous wave (CW) for
GLONASS receivers
Interference frequencies fi (MHz) Interference thresholds for receivers (dBW)
fi 1315 –4,5
1 315 <fi 1 525 Linearly decrease from –4,5 to –42
1 525 <fi 1 565,42 Linearly decrease from –42 to –150,5
1 565,42 <fi 1 585,42 –150,5
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Interference frequencies fi (MHz) Interference thresholds for receivers (dBW)
1 585,42 <fi 1 610 Linearly decrease from –150,5 to –60
1 610 <fi 1 618 Linearly decrease from –60 to –42
1 618 <fi 2 000 Linearly decrease from –42 to –8,5
1 610 <fi 1 626,5 Linearly decrease from –60 to –22
1 626,5 <fi 2 000 Linearly decrease from –22 to –8,5
fi> 2 000 –8,5
Table D.6 – Threshold of interference in the form of continuous wave (CW) for
GLONASS receivers
Interference frequencies fi (MHz) Interference thresholds for receivers (dBW)
fi 1 315 –4,5
1 315 <fi 1 562,15625 Linearly decreases from –4,5 to –42
1 562,15625 <fi 1 583,6525 Linearly decreases from –42 to –80
1 583,65625 <fi 1 592,9525 Linearly decreases from –80 to –149
1 592,9525 <fi 1 609,36 –149
1 609,36 <fi 1 613,65625 Linearly decreases from –149 to –80
1 613,65625 <fi 1 635,15625 Linearly decreases from –80 to –42
1 613,65625 <fi 1 626,15625 Linearly decreases from –80 to –22
1 635,15625 <fI 2 000 Linearly decreases from –42 to –8,5
1 626,15625 <fi 2 000 Linearly decreases from –22 to –8,5
fi> 2 000 –8,5
D.7.2.15 Noise-type interference with restricted spectrum
D.7.2.15.1 GPS and SDCM receivers
D.7.2.15.1.1 After transition in the navigation solution mode GPS and SDCM
receivers correspond to the required characteristics over the noise-type disturbing
signals in the bandwidth of 1575,42 MHz Bwi/2 with the power levels at antenna
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input equal to interference threshold indicated in Table D.7 and presented in figure
D.3, and the useful signal level at antenna input equal to –164,5 dBW.
Figure D.3 – Relation of interference threshold from a bandwidth for GPS and
SDCM receivers
Comment: Bwi – equivalent bandwidth of noise-type disturbing signal.
Table D.7 – Noise-type interference thresholds for GPS and SDCM receivers
Interference bandwidth Interference threshold (dBW)
0 Hz <Bwi 700 Hz –150,5
700 Hz <Bwi 10 kHz –150,5 + 6 log10(BW/700)
10 kHz <Bwi 100 kHz –143,5 + 3 log10(BW/10000)
100 кГц <Bwi 1 MHz –140,5
1 MHz <Bwi 20 MHz Linearly increases from –140,5 to –127,5*
20 MHz <Bwi 30 MHz Linearly increases from –127,5 to –121,1*
30 MHz <Bwi 40 MHz Linearly increases from –121,1 to –119,5*
40 MHz <Bwi –119,5 *
* Interference threshold does not exceed–140,5 dBW / MHz in the bandwidth of
1575,42 10 MHz.
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D.7.2.15.2 GLONASS receiver
D.7.2.15.2.1 After transition in the navigation solution mode GLONASS
receivers correspond to the required characteristics over the noise-type disturbing
signals in the bandwidth of fk Bwi/2 with the power levels at antenna input equal to
interference threshold indicated in Table D.8, and the useful signal level at antenna
input equal to –165,5 dBW.
Comment: fk is the central frequency of the GLONASS channel equal to
fk = 1602 MHz + k 0,6525 MHz, where k may vary from–7 to +6, and Bwi –
equivalent bandwidth of the noise-type disturbing signal.
D.7.2.15.2.2 Pulse interference. After transition in the navigation solution
mode the receiver correspond to the required characteristics over the pulse disturbing
signal having the parameters of Table C.9 in which interference threshold at antenna
input are indicated.
D.7.2.15.2.3 SDCM receivers do not provide incorrect data over an
interference including the interference with the level exceeding the value defined in
Sections D.10 and D.11.
Table D.8 – Noise-type interference thresholds for GLONASS receivers
Interference bandwidth Interference threshold (dBW)
0 Hz <Bwi 1 kHz –149
1 kHz <Bwi 10 kHz Linearly increases from –149 to –143
10 kHz <Bwi 0,5 MHz –143
0,5 MHz <Bwi 10 MHz Linearly increases from –143 to –130
10 MHz <BwI –130
Table D.9 – Pulse interference thresholds
GPS and SDCM GLONASS
Frequency band 1575,42 10 MHz 1592,9525–1609,36
MHz
Interference threshold (Pulse peak power) –10 dBW –10 dBW
Pulse duration 125 microsec, 1
millisec *
1 millisec
Off-duty factor 10 % 10 %
* For GPS receiver without SDCM.
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D.8 GNSS antenna for reception of GLONASS/GPS/SDCM signals
D.8.1 Antenna visibility field
GNSS antenna has required performance when the reception of GNSS signals
is provided within 0 - 360 in azimuth direction and 0 - 90 in elevation direction
relative to the horizontal user plane.
D.8.2 Antenna gain
Minimum antenna gain for indicated elevation angles shall not be less than one
indicated in Table D.10. Maximum antenna gain shall not exceed +7 dBi for
elevation angles more than 5 .
Table D.10 – Minimum antenna gain of GLONASS/GPS/SDCM
Elevation (о)
Minimum antenna gain
(dBi)
0 –7,5
5 –4,5
10 –3
15–90 –2
D.8.3 Antenna polarization
GNSS Antenna has circular right-hand polarization (clockwise in the direction
of propagation).
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12 Annex E. Recommendations on the troposphere model
Troposphere delay of navigation signal propagation is calculated as follows:
)()( iwethydtropo Elmddt (E.1)
where dhyd, dwet – parameters depending on a receiver altitude and five
metrological parameters: pressure P, temperature T, pressure of saturated water vapor
e, temperature – altitude response and water evaporation gradient . Here each of
these five parameters depends on receiver geographic latitude and current day of
the year D, starting from the 1-st of January:
(E.2)
where:
Dmin = 28 for northern latitudes and Dmin = 211 for southern latitudes,
mean and seasonal parameter variation,
(E.3)
(E.4)
For definition of each of these five meteorological parameters for a receiver
latitude interpolation is used for data presented in Table E.1. Meteorological
parameters for northern and southern hemispheres are identical.
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Table E.1 – Meteorological parameters for calculation of the troposphere delay.
Parameters dhyd and dwet are calculated as follows:
(E.5)
(E.6)
where
g = 9.80665 m/sec2 ,
H – receiver altitude above sea level,
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(E.7)
(E.8)
k1 = 77.604 K/mbar,
k2 = 382000 K2/mbar,
Rd = 287.054 Dj/kg/K,
gm = 9.784 m/sec2.
The function of troposphere correction m(El) is calculated as follows:
(E.9)
The correction is valid for elevations not less than 5°.
Root mean square of troposphere delay error is calculated as follows tropoi, :
)(12.0, itropoi Elm (E.10)
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13 Annex F. Transmission sequence of SDCM messages.
Table F.1 shows a sequence diagram of SDCM messages transmission order.
Messages in this sequence diagram are partitioned into 6 second fragments
(row in the Table) following each other. Total duration of the sequence – 264 sec.
Table F.1 – Transmission sequence of SDCM messages.
Time of digital
data transmission
(sec)
Digital data content
(types of transmitted messages)
1-6 C 1 C 2 C 3 C 4 C 5 C 25
7-12 C 18 C 2 C 3 C 4 C 5 C 25
13-18 C 7 C 2 C 3 C 4 C 5 C 25
19-24 C 18 C 2 C 3 C 4 C 5 C 25
25-30 C 10 C 2 C 3 C 4 C 5 C 25
31-36 C 18 C 2 C 3 C 4 C 5 C 25
37-42 C 9 C 2 C 3 C 4 C 5 C 25
43-48 C 18 C 2 C 3 C 4 C 5 C 25
49-54 C 17 C 2 C 3 C 4 C 5 C 25
55-60 C 18 C 2 C 3 C 4 C 5 C 25
61-66 C 1 C 2 C 3 C 4 C 5 C 25
67-72 C 18 C 2 C 3 C 4 C 5 C 25
73-78 C 27(28) C 2 C 3 C 4 C 5 C 25
79-84 C 26 C 2 C 3 C 4 C 5 C 25
85-90 C 7 C 2 C 3 C 4 C 5 C 25
91-96 C 26 C 2 C 3 C 4 C 5 C 25
97-102 C 10 C 2 C 3 C 4 C 5 C 25
103-108 C 26 C 2 C 3 C 4 C 5 C 25
109-114 C 9 C 2 C 3 C 4 C 5 C 25
115-120 C 26 C 2 C 3 C 4 C 5 C 25
121-126 C 1 C 2 C 3 C 4 C 5 C 25
127-132 C 26 C 2 C 3 C 4 C 5 C 25
133-138 C 6 C 2 C 3 C 4 C 5 C 25
139-144 C 26 C 2 C 3 C 4 C 5 C 25
145-150 C 7 C 2 C 3 C 4 C 5 C 25
151-156 C 26 C 2 C 3 C 4 C 5 C 25
157-162 C 10 C 2 C 3 C 4 C 5 C 25
163-168 C 26 C 2 C 3 C 4 C 5 C 25
169-174 C 12 C 2 C 3 C 4 C 5 C 25
175-180 C 26 C 2 C 3 C 4 C 5 C 25
181-186 C 1 C 2 C 3 C 4 C 5 C 25
187-192 C 26 C 2 C 3 C 4 C 5 C 25
193-198 C 27(28) C 2 C 3 C 4 C 5 C 25
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199-204 C 26 C 2 C 3 C 4 C 5 C 25
205-210 C 7 C 2 C 3 C 4 C 5 C 25
211-216 C 26 C 2 C 3 C 4 C 5 C 25
217-222 C 10 C 2 C 3 C 4 C 5 C 25
223-228 C 26 C 2 C 3 C 4 C 5 C 25
229-234 C 9 C 2 C 3 C 4 C 5 C 25
235-240 C 26 C 2 C 3 C 4 C 5 C 25
241-246 C 1 C 2 C 3 C 4 C 5 C 25
247-252 C 26 C 2 C 3 C 4 C 5 C 25
253-258 C 10 C 2 C 3 C 4 C 5 C 25
259-264 C 26 C 2 C 3 C 4 C 5 C 25
The above sequence provides meeting SBAS requirements for correction data
update time.
Table F.2 shows SBAS requirements for maximum data update time (3-rd
column) and SDCM data update time (4-th column) corresponding to the sequence
diagram presented in Table F.1.
Table F.2 – Maximum data update time.
Data type Messages
SBAS
(sec)
SDCM
(sec)
Data field of used satellites
(PRN Mask) C 1 120 60
UDREI C 2-6, 24 6 6
Fast corrections C 2-5, 24 12 6
Slow corrections C 25, 24 120 75
Ionosphere grid point C 18 300 265
Ionosphere delay data C 26 300 265
UTC time C 12 300 265
Fast corrections degradation C 7 120 80
SDCM navigation message С 9 120 120
SDCM satellite status C 17 300 265
Degradation parameters C 10 120 80
Service region C 27(28) 300 120
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14 Annex G. Transmission sequence of SDCM messages when changing
data field of used satellites (change of PRN mask)
Figure G.1 shows a sequence diagram of SDCM messages when changing data
field of used satellites, i.e. when changing PRN Mask.
Change is organized in three phases.
Phase 1 – before changing PRN Mask 4 Messages Type 1 are transmitted
sequentially which contain a new data field of used satellites (PRN Mask).
Phase 2 – preparation for using a new data field of PRN Mask. Slow
corrections are transmitted for a new data field of PRN Mask – 13 Messages Type 25
are to be transmitted. Total duration of Phase 2 is 22 sec. During this phase the user
uses an old field of PRN Mask.
Phase 3 – use of a new field of PRN Mask. At the beginning of Phase 3
Messages Type 1 is repeated, then fast corrections follow corresponding to а new
data field.
Figure G.1 shows digital data transmission process when changing PRN Mask.
Figure G.1 –Sequence diagram of SDCM messages when changing data field
of used satellites
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15 Annex I. Definitions of SDCM data application protocols
In this Section parameters definitions are given which are used in the
GLONASS/GPS navigation algorithm taking into account SDCM information. These
parameters are used to obtain a navigation solution and assess its reliability
(protection levels).
I.1 Long-term corrections
I.1.1 GPS time correction.
Time correction for i-th GPS satellite is carried out as follows:
,]δΔt)t[(tt SV,iL1SV,iSV,i
where:
t– GPS current time;
tSV,i–GPS satellite onboard time at the time of message transmission;
( tSV,i)L1 – correction to onboard time (PRN-code phase);
tSV,i – correcting of correction to onboard time.
I.1.2 Onboard clock error assessment ( tSV,i) for i-th GPS satellite for any
time kt for GPS system time and in current day:
).t(taδaδΔtδ LTi,kf1i,f0i,iSV,
I.1.3 GLONASS time correction
Time correction for i-th GLONASS satellite is carried out as follows:
SV,i n b n b SV,i b ,t t τ t γ t t t δ t ,SV i
where:
t – GLONASS current time;
tSV,i – GLONASS satellite onboard time at the time of message transmission;
tb, n(tb), n(tb) – GLONASS time parameters;
tSV,i – code phase offset correction.
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Code phase offset correction tSV,i for i-th GLONASS satellite in the
GLONASS system time is carried out as follows:
tSV,i = ai,f0 + ai,f1 (t – ti,LT),
where (t – ti,LT) is corrected at transition to a new day. If the range rate = 0,
than ai,f1 = 0.
Code phase offset correction tSV,i for i-th GLONASS satellite in the GPS
system time is defined considering GPS and GLONASS time offset:
tSV,i = ai,f0 + ai,f1 (t – ti,LT) + τ(GPS)+ ai,GLONASS ,
where:
t – GPS current time;
τ(GPS) – fractional part of a second in GPS time scale offset relatively
GLONASS time scale transmitted as a part of GLONASS satellites ephemeris
information;
ai,GLONASS – correction to GPS time scale offset relatively GLONASS time
scale transmitted by SDCM in Message 12.
I.1.4 Satellite coordinates correction
GPS uses WGS-84 coordinate system and GLONASS uses PZ-90.02.
Transition matrices from one to the other coordinate system are as follows:
90.02-PZ84WGS18,0
08,0
36,0
And back transition:
84-WGS90.02-PZ18,0
08,0
36,0
A specific feature of the transition is that the coordinate systems WGS-84 and
PZ-90.02 are parallel to each other and have only linear offset of coordinate origin. It
means that differential corrections to coordinates do not depend on the system used.
This conclusion is also valid for rate corrections.
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Vector for i-th satellite of GLONASS and GPS systems corrected in SDCM
system is defined as follows for the time t:
,tt
zδ
yδ
xδ
zδ
yδ
xδ
z
y
x
z
y
x
LTi,
i
i
i
i
i
i
i
i
i
correctedi
i
i
where:
(t – ti,LT) – is corrected at transition to a new day;
[xiyizi]T – position vector of a GLONASS or GPS satellite.
If the range rate = 0, than:
.0 ;0 ;0 i
zi
yi
x
I.1.5 Corrections to pseudoranges
Corrections to pseudoranges also do not depend on the coordinate system used.
Corrected pseudorange at the time t for i-th satellite спутника is defined as
follows:
,TCIC)t(tRRCFCPRPR iii,0fiiicorrectedi,
where:
PRi – measured pseudorange after application of corrections to the satellite
onboard time;
FCi – fast correction;
RRCi– correction to the range rate;
ICi – ionosphere correction;
TCi – troposphere correction (negative value considering troposphere delay);
ti,0f – time of applicability of the most recent fast corrections which is the
beginning of the second époque of SDCM time coinciding with the time of
transmission of the first symbol of the message block to a SDCM satellite.
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I.1.6 Corrections to pseudorange rate (RRC)
RRC for i-th satellite is defined as follows:
,tt
FCFCRRC
ousi,0f_previi,0f
previousi,currenti,
i
where:
FCi,current – the latest fast correction;
FCi,previous – the previous fast correction;
ti,0f – time of applicability of the most recent fast correction FCi,current;
ti,0f_previous – time of applicability of the FCi,previous.
I.2 Transmitted ionosphere corrections
I.2.1 Coordinates of ionosphere pierce point (IPP)
IPP coordinates are defined as the coordinates of crosspoint of the receiver-
satellite line with the ellipsoid having constant altitude of 350 km over WGS-84
ellipsoid. These coordinates are defined in latitude ( pp) and longitude ( pp) of WGS-
84.
I.2.2 Ionosphere corrections
Ionosphere correction i-th satellite is defined as follows:
i pp vppIC F τ , Fpp =
12 2
e i
e I
R cosθ1 ;
R h
where:
Fpp – deflection factor;
vpp – interpolated assessment of the vertical ionosphere delay
Re – 6 378,1363 km;
i – elevation of i- th satellite;
hI – 350 km.
Comment – For GLONASS satellites ionosphere correction (ICi) must be
multiplied by the squared ratio of GLONASS and GPS frequencies ( ГЛОНАСС/ GPS)2.
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I.2.3 Interpolated assessment of the vertical ionosphere delay
When four points are used for interpolation, interpolated assessment of the
vertical ionosphere delay at the latitude pp and longitude pp is equal to:
where:
vk – transmitted values of a vertical delay of a grid-point model for k-th IGP
angle as showed in the Figure I.1.
W1 = xpp ypp;
W2 = (1-xpp )ypp;
W3 = (1-xpp )(1-ypp);
W4 = xpp (1-ypp).
Figure I.1 –IGP numerating condition (for four IGP)
x
y
v2
1
1
2
2
pp= pp- 1
pp= pp- 1
vpp( pp, pp)USER'S IPP
v1
v3 v4
4
1k
,vkkvpp τWτ
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For IPP points between N85° and S85°:
pp 1
pp
2 1
λ λx ,
λ λ
pp 1
pp
2 1
,y
where:
1 – IGP longitude to the west of IPP;
2 – IGP longitude to the east of IPP;
1 –IGP latitude to the south of IPP;
2 – IGP latitude to the north of IPP.
Comment – If 1 and 2 cross 180о longitude when calculating xpp is considered
the difference in longitude values.
For IPP points located to the north of N85о or to the south of S85
о:
pp 1
ppy10 ,
pp 1
ppy10 ,
pp 3
pp pp pp
λ λx (1 2y ) y ,
90
where
1 – longitude of the second IGP located to the east of present IPP;
2 – longitude of the second IGP located to the west of present IPP;
3 – longitude of a nearest IGP located to the west of IPP;
4 – longitude of a nearest IGP located to the east of IPP.
When three points are used for interpolation, interpolated assessment of the
vertical ionosphere delay is as follows:
For points between 75оS and 75
оN:
vpp vk
3
kk 1
τ W τ ,
где:
W1 = ypp;
W2 = 1 – xpp – ypp;
W3 = xpp.
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xpp and ypp is calculated as for 4-points interpolation, only that 1 and 1 are
always longitude and latitude of IGP2 and 2 and 2 – others longitude and latitude.
IGP2 is always a vertex of triangle (defined by the three points) opposite to the
hypotenuse; IGP1 has the same longitude as IGP2 and IGP3 has the same latitude as
IGP2 (example is showed in the Figure I.2).
x
y
v1
1
1
2
2
pp= pp- 1
pp= pp- 1
vpp( pp, pp)USER'S IPP
v2 v3
Figure I.2 –IGP numerating condition (three IGP points)
Three-points interpolation is not provided for points located to the north of
75оN and to the south of 75
оS.
I.2.4 Selection of ionosphere grid points (IGP)
Algorithm for selection of ionosphere grid points is given below:
a) For IPP between N60° and S60°:
1) If four IGP points defining around IPP a mesh 5 x 5о are set at "1" in the IGP
Mask, they are selected; otherwise,
2) If any three IGP points defining around IPP a triangle 5 x 5о are set at "1" in
the IGP Mask, they are selected; otherwise,
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3) If four IGP points defining around IPP a mesh 10 x 10о are set at "1" in the
IGP Mask, they are selected; otherwise,
4) If any three IGP points defining around IPP a triangle 10 x 10о are set at "1"
in the IGP Mask, they are selected; otherwise,
5) Ionosphere correction is unavailable.
б) For IPP points between N60° and N75° or between S60° and S75°:
1) If four IGP points defining around IPP a mesh of size 5о latitude x 10
о
longitude are set at "1" in the IGP Mask, they are selected; otherwise,
2) If any three IGP points defining around IPP a triangle 5о of size 5
о latitude x
10о longitude are set at "1" in the IGP Mask, they are selected; otherwise,
3) If any four IGP points defining around IPP a mesh 10 x 10о are set at "1" in
the IGP Mask, they are selected; otherwise,
4) If any three IGP points defining around IPP a triangle 10 x 10о are set at "1"
in the IGP Mask, they are selected; otherwise,
5) Ionosphere correction is unavailable.
в) For IPP points between N75° and N85° or between S75° and S85°:
1) If two IGP points nearest to 75° or two IGP points nearest to 85° (partitioned
by 30о longitude if diapason 9 or 10 is used, in other cases partitioned by 90
о) are set
at "1" in the IGP Mask, a mesh 10 x 10° is formed by linear interpolation between
IGP points at 85° for generation of virtual IGP points at longitudes equal to
longitudes of IGP points at 75°; otherwise,
2) Ionosphere correction is unavailable.
г) For IPP to the north of N85°:
1) If four IGP points at N85° and longitudes W180о, W90
о, 0
о and E90
о are set
at "1" in the IGP Mask, they are selected; otherwise,
2) Ionosphere correction is unavailable.
д) For IPP южнее S85°:
1) If four IGP points at S85° and longitudes W140о, W50
о, E40
о and E130
о are
set at "1" in the IGP Mask, they are selected; otherwise,
2) Ionosphere correction is unavailable.
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Comment: This selection algorithm is based only on the data contained in the
mask not taking into account in monitoring of selected points is effected or they are
not used. In any of selected points is identified by "Do not use" feature, ionosphere
correction is unavailable. If four IGP points are selected and one of them is identified
by "No monitoring" feature, 3-points interpolation is used provided that IPP point lies
inside the triangular area for which there are three corrections.
I.3 Protection levels
Horizontal Protection Level (HPL) and Vertical Protection Level (VPL) which
are measures of reliability of navigation solution, are defined as follows:
majorHSDCM dKHPL ,
VVSDCM dKVPL ,
where:
2
v
N2 2
v,i ii 1
d s σ – dispersion of distribution model including true error
distribution along the vertical axis;
22 2 2 2
x y x y 2
major xy
d d d dd d
2 2,
where:
2
x
N2 2
x,i ii 1
d s σ – dispersion of distribution model including true error distribution
along the x axis;
2
y
N2 2
y,i ii 1
d s σ – dispersion of distribution model including true error distribution
along the y axis;
xy
N2
x,i y, i ii 1
d s s σ – covariation of distribution models along the x and y axes,
where:
sx,i – partial x derivative of the position error relative to the pseudorange error
of the i-th satellite;
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sy,i – partial y derivative of the position error relative to the pseudorange error
of the i-th satellite;
sV,i – – partial vertical derivative of the position error relative to the
pseudorange error of the i-th satellite;
2 2 2 2 2
i i,flt i,UIRE i,air i,tropoσ σ σ σ σ .
Dispersions (2
i,flt и 2
i,UIRE) are defined in Annexes I.3.2 and I.3.3. Parameters
(2
i,air and 2
i,tropo) are defined by onboard components (Section C.9).
x and y axes lie in the local horizontal plain and v axe is the local vertical.
For general case of least-squares method projection matrix S looks as follows:
x,1 x,2 x,N
y,1 y,2 y,N T 1 T
v,1 v,2 v,N
t,1 t,2 t,N
S S ... S
S S ... SS G W G G W,
S S ... S
S S ... S
where:
i-th column of the matrix G;
2
1
2
2
i i i i i i
2
1G cos El cos Az cos El sin Az sin El 1
0 0
0 0
0 0 N
W
,
where:
Eli – elevation of i-th range source (in degrees);
Azi – azimuth of i- th range source measured unticlockwise from the x axis (in
degrees);
wi – weighting factor corresponding to the i-th satellite.
Comment:
1 For easy reading the index i in the projection matrix is omitted.
2 For getting solution by the least-squares method without weighting factors
weighting matrix is set as unitary (wi = 1).
I.3.1 Definition of protection level coefficient K
Values of coefficient K are defined as follows:
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6,0K H
5,33KV .
I.3.2 Definition of error model for fast and long-term corrections
If fast corrections and long-term corrections/range parameters of SDCM and
degradation parameters are applied, then:
flt
UDRE fc rrc ltc er UDRE
UDRE fc rrc ltc er UDRE
if RSS Message Type
if RSS Message Type
2
2
2 2 2 2 2
0 10
1 10
( )
, ( )
where:
If Message Type 27 is used, UDRE – index of a specific region;
If Message Type 28 is used, UDRE – index of a specific satellite;
If no message is used, UDRE = 1.
If fast corrections and long-term corrections/range parameters of SDCM are
not applied, then degradation parameters are not used:
22
, , 8i flt i UDRE UDRE m.
If fast corrections and long-term corrections/range parameters of SDCM are
not applied relative to a satellite or if relative to the satellite Message Type 28 is not
received with ephemeris covariation but valid Message Type 28 is received for
another satellite,:
22 2
, 60i flt м.
I.3.3 Fast corrections degradation
Degradation parameter for fast corrections looks as follows:
2
u lat
fc
t t tε a
2 ,
where:
t – current time;
tu – (reference time UDREIi): if IODFj 3, then this is the time of beginning of
1-second SDCM time époch which coincides with the transmission beginning of the
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message block comprising the UDREIi data (Messages Type 2 5 or 24) which
coincide with IODFj of the used fast correction. If IODFj = 3, then this is the time of
beginning of 1-second SNT époch which coincides with the transmission beginning
of the message comprising the fast correction for the i-th satellite;
tlat – system delay (as defined in Section.054).
Comment – For UDRE parameters transmitted in Messages Type 2–5 and 24,
tu is equal to the affixment time of fast corrections as they are transmitted in the same
messages. For UDRE parameters transmitted in Message Type 6 and if IODF = 3, tu
is also equal to the affixment time of fast corrections (tof). For UDRE parameters
transmitted in Message Type 6 when IODF 3, tu is defined as the time of first bit
transmission of Message Type 6 to a SDCM satellite.
I.3.4 Corrections degradation to the range rate of change
If 0RRC , then 0rrc .
If 0RRC and 3IODF , then degradation parameter for fast corrections
looks as follows:
If 0RRC and 3IODF , then degradation parameter for the range rate of
change data looks as follows:
where:
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t – current time;
IODFcurrent – parameter IODF corresponding to the latest fast correction;
IODFprevious – parameter IODF corresponding to the previous fast correction
∆t–ti,0f – ti,0f_previous;
Ifc – fast corrections validity interval for the user.
I.3.5 Degradation of long-time corrections of GLONASS and GPS satellites
For the range rate equal to 1 degradation parameter of a long-time correction of
the i- th satellite looks as follows:
ltc ltc_lsb ltc_v1 i,LT i,LT ltc_v1ε C C max(0, t t, t t I ).
For the range rate equal to 0 degradation parameter of a long-time correction is
defined as follows:
ltcltc ltc_v0
ltc_v0
t tε C ,
I
where:
t – current time;
tltc – the time of first bit transmission of a long-term correction message to
SDCM;
[x] – largest integer less than x.
Residual error degradation:
er
er
neither fast nor long term corrections
have timed out for precision approach
Cif fast or long term corrections
have timed out for precision approach
0,
,
Degradation factor UDRE is calculated on the basis of Message Type 28 data.
T
UDRE cδ I C I ε ,
where:
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x
y
z
i
iI
i
1 ,
x
y
z
i
i
i
единичный вектор от пользователя до спутника в кадре координат ECEF WGS 84;
С = RT
R;
C = Ccovariance SF;
SF = 2scale exponent–5
;
R = E SF;
1,1 1,2 1,3 1,4
2,2 2,3 2,4
3,3 3,4
4,4
E E E E
0 E E E
0 0 E E
0 0 0 E
E
.
I.3.6 Definition of error model for ionosphere correction
Transmitted ionosphere corrections. If SDCM ionosphere corrections are
applied, looks as follows:
,
Where the same weighting factors are used for ionosphere pierce points (Wn)
and grid points selected for ionosphere correction. For each grid point the following
is valid:
ionogrid
GIVE iono iono
GIVE iono iono
if RSS Message Type
if RSS Message Type
2
2
2 2
0 10
1 10
( )
, ( )
,
ionoiono iono_step iono_ramp iono
iono
t tε C C (t t )
I ,
where:
2
UIREσ
UIRE pp UIVE
2 2 2σσ F
2
UIVE UIVE
4 32 2 2
n n,ionogridn n,ionogridn 1 n 1
σ W σ или σ W σ ,. .
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t – current time;
tiono – the time of first bit transmission of a long-term correction message to
SDCM;
[х] – largest integer less than x.
Comment – For GLONASS and GPS satellites GIVE and IONO are multiplied
by the squared ration of GLONASS and GPS frequencies ( GLONASS / GPS)2.
I.3.7 Ionosphere corrections
If SDCM ionosphere corrections are not applied, 2
UIREσ looks as follows:
2
2 2ionoUIRE pp vert
Tσ MAX , F τ
5,
where:
Tiono– ionosphere delay according to an assessment results for a selected model;
pp
vert pp
pp
9m, 0 20
τ 4, 5m, 20 55;
6 m, 55
pp – ionosphere pierce point latitude.
I.3.8 GLONASS time
Degradation parameter of a long-time correction of the i- th satellite looks as
follows:
,][ clock_clock_ockGLONASS_cl GLONASSGLONASS t-tC
where:
t – current time;
clock_GLONASSt – the transmission time of synchronization message first bit
(Message Type 12) to GEO;
[x] – largest integer less than x.
Comments:
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1. For satellites not included in GLONASS,
_ 0GLONASS clock .
2. sec/00833,0clock_ smCGLONASS .
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16 Annnex J. Additional materials and data
J.1 SDCM Coverage and Service area
J.1.1 It is necessary to distinguish the terms «SDCM Coverage» and «SDCM
Service area within SDCM Coverage».
SDCM Coverage is defined by the area in which the user receives a signal from
a SDCM GEO satellite of receives the same SDCM data via ground-based
communication channels.
SDCM Service area within SDCM Coverage is defined by the borders of one
or several, possibly not crossing, areas within which a service provider (i.e.
“organization operating SDCM”) provides access to SDCM functions for navigation
operation being realized by navigation user equipment.
For most operations global SDCM data are sufficient, i.e. correcting data and
integrity data delivered via ground links or via geostationary satellites. Service area
of such operations coincides with the SDCM coverage. Other operations will require
additional local data distributed by SDCM ground facilities only in those local areas
for which these data are valid. In general service areas for different navigation
operations may not coincide and they are defined by a service provider by deploying
SDCM ground facilities in those areas where they will be in demand. However, in
any case a system service area covers all SDCM service areas within admissible
operations effected by navigation user equipment.
The information below concerning service and coverage areas pertains to the
SDCM service area and permissible system coverage area.
Figure J.1 shows service and coverage areas for five SBAS systems:
- Wide Area Augmentation System WAAS;
- European Geostationary Navigation Overlay Service EGNOS;
- Japanese Multi-functional Satellite Augmentation System MSAS;
- Indian GPS Aided Geo Augmented Navigation GAGAN;
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- Russian Satellite Augmentation System SDCM.
Figure J.1 – Service areas of SBAS.
Currently all the systems – WAAS, EGNOS, MSAS, GAGAN transmit wide
area corrections only for GPS satellites.
J.1.2 Enhanced C/A codes of SDCM
Currently the issue of enhancing the quantity of codes to be used (by systems
of SDCM type, for example) is considered. Enhancement extent is from 19 to 39 (see
Table J.1).
Table J.1– Permissible С/А codes (enhanced table)
PRN G2 delay (chips) First 10 chips
120 145 0671
121 175 0536
122 52 1510
123 21 1545
124 237 0160
125 235 0701
126 886 0013
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127 657 1060
128 634 0245
129 762 0527
130 355 1436
131 1 012 1226
132 176 1257
133 603 0046
134 130 1071
135 359 0561
136 595 1037
137 68 0770
138 386 1327
139 797 1472
140 456 0124
141 499 0366
142 883 0133
143 307 0465
144 127 0717
145 211 0217
146 121 1742
147 118 1422
148 163 1442
149 628 0523
150 853 0736
151 484 1635
152 289 0136
153 811 0273
154 202 1026
155 1021 0003
156 463 1670
157 568 0624
158 904 0235
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17 References
1. Minimum Operational Performance Standards for Global Positioning System /
Wide Area Augmentation System Airborne Equipment - Document NO. RTCA/DO-
229D, Washington, 2006.
2. International standards and recommended practice /Annex 10 to the
Convention on the International Civil Aviation – International Civil Aviation
Organization, Edition 6, July 2006.
3. Wide Area Augmentation System (SBAS), Federal Aviation Administration
Specification, FAA-E-2892B – U.S. Department of transportation, September 1999.
4. Minimum Operational Performance Standards for Airborne Supplemental
Navigation Equipment Using Global Positioning System (GPS) - Document NO.
RTCA/DO-208, Washington, 1991.
5. Software Considerations in Airborne Systems and Equipment Certification -
Document NO. RTCA/DO-178B, Washington, 1992.
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18 Changes registration list
Version Date of change Changes Signature