Microwave Planning and Design

Slide No 1

Microwave Radio Planning and Link Design

CISCOM Training Center

Microwave Planning and Design

Slide No 2



Course Contents

• PCM and E1 TDM Overview

• Digital Multiplexing: PDH and SDH Overview

• Digital Microwave Systems Overview

• Microwave links Performance and Quality Objectives

• Topology and Capacity Planning

• Diversity

• Microwave Antennas

Slide No 3



Course Contents (con’d)

• Radio Propagation

• Microwave Link Planning and Design– Path Profile– LOS Survey– Link Budget– Performance Prediction

• Frequency Planning

• Interference

• Digital map and tools overview

Slide No 4


Planning Objectives• MW Radio Planning Objectives

– Selection of suitable radio component– Communication quality and availability – Link Design– Preliminary site location and path profile, LOS survey– Channel capacity– Topology– Radio frequency allocation (planning)

Slide No 5


PCM and E1 Overview

Slide No 6


Voice channel digitizing and TDM • Transmission:

– Voice– Data

• Voice is an analog signal and needs to be digitized before transmitted digitally

• PCM, Pulse Code Modulation is the most used technique• The European implementation of PCM includes time

division multiplexing of 30 64 kb/s voice channels and 2 64kb/s for synchronization and signaling in basic digital channel called E1

• E1 rate is 2.048 Mb/s = 32 x 64 kb/s

Slide No 7


PCM Coder Block Diagram 64 kb/s

S/HS/H QuantizerQuantizerLPFLPF EncoderEncoder 64 kb/s PCM signal

Analog signal

Slide No 8


E1 History• First use was for telephony (voice) in 1960’s with PCM

and TDM of 30 digital PCM voice channels which called E1

• E1 is known as PCM-30 also

• E1 was developed slightly after T1 (1.55 Mbps) was developed in America (hence T1 is slower)

• T1 is the North America implementation of PCM and TDM

• T1 is PCM-24 system

Slide No 9


E1 Frame• 30 time division multiplexed (TDM) voice channels, each running at

64Kbps (known as E1) • E1 rate is 2.048 Mbps containing thirty two 64 kbps time slots,

– 30 for voice, – One for Signaling (TS16)– One for Frame Synchronization (TS0)

• E1 (2M) Frame rate is the same PCM sampling rate = 8kHz, Frame duration is 1/8 kHz = 125 μs (Every 125 us a new frame is sent)

• Time slot Duration is 125 μs/32 = 3.9 μs• One time slot contains 8 bits• A timeslot can be thought of as a link running at 8000 X 8 = 64 kbps• E1 Rate: 64 X 32 = 2048000 bits/second

Slide No 10


E1 frame diagramTime Slot

0

Time Slot

1

Time Slot

2

Time Slot

31

Time Slot

30

Time Slot

29

………….

…………

Time Slot

16

…………

…………

125s

Si 0 0 1 1 0 1 1

Si 1 A Sn Sn Sn Sn Sn

Frame containing frame alignment signal (FAS)

Frame not containing frame alignment signal

1 2 3 4 5 6 7 8

Bits

Frame Alignment Signal (FAS) pattern - 0011011Si = Reserved for international use (Bit 1)Sn = Reserved for national useA = Remote (FAS Distant) Alarm- set to 1 to indicate alarm condition

Slide No 11


E1 Transmission Media

• Symmetrical pair: Balanced, 120 ohm

• Co-axial: Unbalanced, 75ohm

• Fiber optic

• Microwave

• Satellite

• Other wireless radio

• Wireless Optical

Slide No 12


GSM coding and TDM in terrestrial E1• As we know PCM channel is 64Kb/s• Bit rate for one voice GSM channel is 16Kb/s between

BTS and BSC (terrestrial)• One GSM E1 is 120 GSM voice channels• The PCM-to-GSM TRAU (transcoder) reduces no of E1’s

by 4• Each GSM radio carries 8 TCHs in the air, this equivalent

to 8x16Kb/s=2x64Kb/s between BTS and BSC.• Each GSM radio has 2 time slots in the GSM E1.• Example: 3/3/3 site require 9x2=18 E1 time slots for

traffic and time slot(s) for radio signaling links

Slide No 13


Digital Multiplexing: PDH and SDHOverview

Slide No 14


European Digital Multiplexer Hierarchy

• Plesiochronous Digital Hierarchy (PDH)

• Synchronous Digital Hierarchy (SDH )

Slide No 15


PDH Multiplexing

• Based on a 2.048Mbit/s (E1) bearer

• Increasing traffic demands that more and more of these basic E1 bearers be multiplexed together to provide increased capacity

• Once multiplexed, there is no simple way an individual E1 bearer can be identified in a PDH hierarchy

Slide No 16


European PDH Multiplexing Structure

1

30

1 E1

4 x E1

16 x E1

4 x 34

Higher order multiplexing

2048 kbps

8448 kbps

34,368 kbps

139,264 kbps

Slide No 17


European PDH Multiplexing Structure-used

MUX DEMUX

Primary PCM Multiplexing

BTSMultiplexing

DataMultiplexing

MUX DEMUX

MUX DEMUX

MUX DEMUX

MUX DEMUX

1st order 2.048 Mbps

E1

2nd order 8.228 Mbps

E23rd order

34.368 MbpsE3

VF

Data

mobile

Slide No 18


PDH Problems• Inflexible and expensive because of asynchronous

multiplexing

• Limited network management and maintenance support capabilities

• High capacity growth

• Sensitive to network failure

• Difficulty in verifying network status

• Increased cost for O&M

Slide No 19


SDH

• Synchronous and based on byte interleaving

• provides the capability to send data at multi-gigabit rates over fiber-optics links.

• SDH is based on an STM-1 (155.52Mbit/s) rate

• SDH supports the transmission of all PDH payloads, other than 8Mbit/s

Slide No 20


SDH Bit Rates

155.52 Mbit/s

622.08 Mbit/s

2.48832 Gbit/s

STM-1

STM-4

STM-16

4

4

3

STM-0 51.84 Mbit/s

STM-64

4

9.995328 Gbit/s

Slide No 21


General Transport Module STM-N

RSOH

MSOH

PayloadAU pointer

1

9

5

3

N. 270 columns

N. 9 N. 261

SOH: Section OverheadAU: Administration UnitMSOH: Multiplexer Section OverheadRSOH: Repeater Section Overhead

Slide No 22


SDH Multiplexing Structure

C-4VC-4

C-12

C-3VC-3

VC-12TU-12

TU-3TUG-3

TUG-2

AUGAU-4 STM-Nx 1

x 1x 3

x 7 x 3

x N

C: ContainerVC: Virtual ContainerTU: Tributary UnitTUG: Tributary Container GroupAU: Administrative UnitAUG: Administrative Unit Group

Mapping Aligning Multiplexing

140 Mbps

2 Mbps

34 Mbps

Slide No 23


From 2 Mbps to STM-1

STM-1VC-4

+ POH+ POH

VC-122 Mbits

(Justification)

+ SOH

SOH: Section Overhead

POH: Path Overhead

SDH MUX

Slide No 24


Containers C

=

PDH Stream

Justification bits

Container

Slide No 25


Virtual Containers VC

=

Container

Path overhead

Virtual Container

Slide No 26


SDH Advantages• Cost efficient and flexible networking

• Built in capacity for advanced network management and maintenance capabilities

• Simplified multiplexing and demultiplexing

• Low rate tributes visible within the high speed signal. Enables direct access to these signals

• Cost efficient allocation of bandwidth

• Fault isolation and Management

• Byte interleaved and multiplexed

Slide No 27


SDH Benefits over PDH• SDH transmission systems have many benefits over PDH:

– Software Control allows extensive use of intelligent network management software for high

flexibility, fast and easy re-configurability, and efficient network management.

– SurvivabilityWith SDH, ring networks become practicable and their use enables automatic

reconfiguration and traffic rerouting when a link is damaged. End-to-end monitoring will allow full management and maintenance of the whole network.

– Efficient drop and insertSDH allows simple and efficient cross-connect without full hierarchical

multiplexing or de-multiplexing. A single E1 2.048Mbit/s tail can be dropped or inserted with relative ease even on Gbit/s links.

Slide No 28


SDH Benefits over PDH- con’d

– Standardization enables the interconnection of equipment from different suppliers

through support of common digital and optical standards and interfaces.

– Robustness and resilience of installed networks is increased. – Equipment size and operating costs

reduced by removing the need for banks of multiplexers and de-multiplexers. Follow-on maintenance costs are also reduced.

– Backwards compatibly will enable SDH links to support PDH traffic.

Slide No 29


GSM Block Diagram (E1 links)

MSC1

MSC3MSC2

BSC1

BSC2

BTS

BTS

BTS

BTS

BTS

BTS

BTSBTS

SDH

PDH Abis

Slide No 30


Abis- Interface

• Connects between the BSC and the BTS• Has not been standardized• Primary functions carried over this interface are:

Traffic channel transmission, terrestrial channel management, and radio channel management

• On Abis-Interface, two types of information Traffic information Signalling information

BSC Abis-Interface

BTS

Slide No 31


Abis- Interface

• Traffic Information– The traffic on the physical layer needs ¼ TS (Time Slot)

on the E1 with bit rate = 16 Kb/s– 4 channels exist within one TS

• Signalling Information– Different rates on the physical layer: 16 Kb/s, 32 Kb/s,

and 64 Kb/s– The protocol used over the Abis-Interface is LAPD

protocol (Link Access Protocol for the ISDN D-channel)– The signalling link between the BSC and the BTS is

called RSL (Radio Signalling Link)

Slide No 32


Digital Microwave systems Overview

Slide No 33


Digital Microwave system• Equipment

– E1– MUX– IF MODEM– Transceiver

In door

Out door TRU

– FeederFor In door

Co-axial transmission line

Waveguide transmission line

For Outdoor

IF between modem ODU Transceiver (TRU)

Slide No 34


MODEM- Digital Modulation• PSK

– 2 PSK– 4 PSK– 8 PSK

• QAM– 8 QAM– 16 QAM– 32 QAM– 64 QAM– 128 QAM

Slide No 35


Protecting MW Links• Microwave links are protected against

– Hardware failure– Multipath Fading– Rain Fading

• Protection Schemes– 1 + 1 configuration– Diversity– Ring

Slide No 36


Microwave Equipment Specification• Operating Frequency

• Modulation

• Capacity

• Bandwidth

• Output power

• Receiver Thresholds @ BER’s 10-6 and 10-3

• MTBF

• FKTB

Slide No 37


RADIO EQUIPT Example: DART

Dish diameter: 30 cm

Antenna dish

Radio Equipment

Slide No 38


Slide No 39


Radio Equipment Datasheet

Slide No 40


Microwave Allocation in Radio spectrum

3 k 30 k 300 k 3 M 30 M 300 M 3 G 30 G 300 G

VLF LF MF VHF

VHF Very low frequency

LF Low frequency

MF Medium frequency

HF High Frequency

VHF Very High Frequency

UHF Ultra High Frequency

SHF Super High Frequency

EHF Extremely High Frequency

UHF SHFHF EHF

• Microwave primarily is utilized in SHF band, and some small parts of UHF & EHF bands

Slide No 41


Microwave Bands• Some Frequency bands used in microwave are

– 2 GHz– 7 GHz– 13 GHz– 18 GHz– 23 GHz– 26 GHz– 38 GHz

• The usage of frequency bands will depend mainly on the budget calculation results and the path length

Slide No 42


Microwave Capacities

• Capacities available for microwave links are – 1 x 2 Mbps with a bandwidth of 1.75 MHz – 2 x 2 Mbps with a bandwidth of 3.5 MHz – 4 x 2 Mbps with a bandwidth of 7 MHz – 8 x 2 Mbps with a bandwidth of 14 MHz – 16 x 2 Mbps with a bandwidth of 28 MHz

Slide No 43


23 GHz Band - example

21224 22456

1232

11201120

22456 23576

Low High

2 x 2 (3.5 MHz) 4 x 2 (7 MHz) 8 x 2 (14 MHz) 16 x 2 (28 MHz)Possible Number of Channels

320 160 80 40

Slide No 44


Channel Spacing

1.75 MHz 3.5 MHz

3.5 MHz 7 MHz

7 MHz 14 MHz

14 MHz 28 MHz

2 E1

4 E1

8 E1

16 E1

Slide No 45


International Regulatory Bodies• ITU-T

Is to fulfil the purposes of the Union relating to telecommunication standardization by studying technical, operating and tariff questions and adopting Recommendations on them with a view to standardizing telecommunications on a world-wide basis.

• ITU-R plays a vital role in the management of the radio-frequency spectrum

and satellite orbits, finite natural resources which are increasingly in demand from a large number of services such as fixed, mobile, broadcasting, amateur, space research, meteorology, global positioning systems, environmental monitoring and, last but not least, those communication services that ensure safety of life at sea and in the skies.

Slide No 46


Performance and availability objectives

Slide No 47


Performance Objectives and availability objectives

• Dimensioning of network connection is based on the required availability objective and performance

• Dimension a network must meet the standard requirements recommendations by ITU

• The performance objectives are separated from availability objectives

• Factors to be considered – radio wave propagation– hardware failure– Resetting time after repair– Frequency dependant interference problems

Slide No 48


ITU-T Recs for Transmission in GSM Net

• All BTS, BSC and MSC connections in GSM network are defined as multiples of the primary rate if 2 Mbps,

• ITU-T Rec G.821 applies as the overall standard for GSM network.

• ITU-T Rec G.826 applies for SDH.

Slide No 49


The ITU-T Recs (Standards)• The ITU-T target standard are based on two

recommendations: – ITU-T Recommendation G.821,intended for digital connection with

a bit rate of 64 kBit/s. Even used for digital connection with bit rates higher than 64kBit/s. G.821 will successively be replaced by G.826.

– ITU- T Recommendation G.826, used for digital connection with bit rates of or higher than 2,048 kBit/s (European standard) or 1,544 kBit/s (USA standard).

• The main difference between G.826 and G.821 is that G.826 uses Blocks instead of bits in G.821

Slide No 50


ITU-T G.821 some definitions• HRX : hypothetical Reference Connection

– This a model for long international connection, 27,500 km– Includes transmission systems, multiplexing equipment and switching

• HRDP: Hypothetical Reference Digital Path– The HRDP for high grade digital relay systems is 2500 km– Doesn’t include switching

• HRDS: Hypothetical Reference Digital Section– It represents section lengths likely to be encountered in real networks– Doesn't include digital equipments, such as multiplexers/demultiplexers.

Slide No 51


ITU-T G.821 some definitions (con’d)• SES : Severely Errored Seconds

– A bit error rate (BER) of 10-3 is measured with an integration time of 1 second.

• DM : Degraded Minutes– A bit error rate (BER) of 10-6 is measured with an integration time of 1 minute.

• ES : Errored Seconds– Is the second that contains at least one error

• RBER: Residual Bit Error Rate– The RBER on a system is found by taking BER measurements for one month

using a 15 min integration time, discarding the 50 % of 15 min intervals which contain the worst BER measurements, and taking the worst of the remaining measurements

Slide No 52


ITU-T G.821 HRX Hypothetical Reference Connection

Local Grade

Medium Grade

Medium Grade

Local Grade

High Grade

T-reference point

T-reference point

1250 km 1250 km25,000 km

27,500 km

LE LEINT INT

40 %15 % 15 % 15 %15 %

Slide No 53


ITU-T G.821 some definitions

• The system is considered unavailable when one or both of the following conditions occur for more than 10 consecutive seconds

– The digital signal is interrupted– The BER in each second is worse than 10–3

• Unavailable Time (UAT)– Begins when one or both of the above mentioned conditions occur for 10

consecutive seconds

• Available Time (AT)– A period of available time begins with the first second of a period of 10

consecutive seconds of which each second has a bit error ratio (BER) better than 10-3

Slide No 54


ITU-T G.821 performance & Availability Examples

BER 10-6

BER 10-3

DM

ES

SES

<10s >10s

SES

Available time (AT) Unavailable time (UAT)

DM

ESESESES

DM DM

Slide No 55


ITU-T G.821 Availability• Route availability equals the sum of single link

availabilities forming the route.

• Unavailability might be due to – Propagation effect– Equipment effect

Note: Commonly used division is to allocate 2/3 of the allowed total unavailability to equipment failure and 1/3 to propagation related unavailability

Slide No 56


ITU-T G.821 Performance Objectives

• SES : Severely Errored Seconds– BER should not exceed 10–3 for more than 0.2% of one second intervals in any

month – The total allocation of 0.2% is divided as: 0.1% for the three classifications– The remaining 0.1% is a block allowance to the high grade and the medium grade

portions

• DM : Degraded Minutes– BER should not exceed 10–6 for more than 10% of one minute intervals in any

month– The allocations of the 10% to the three classes

• ES : Errored Seconds– Less than 8% of one second intervals should have errors– The allocations of the 8% to the three classes

Slide No 57


G.821 Performance Objectives over HRX

Local Medium Medium LocalHigh

0.0150.015 0.0150.015

1.51.5 1.51.5

1.21.21.21.2

0.04

4

3.2

1250 km 1250 km25000 km

INT LE

SES 0.2% (0.1%+0.1% for High and Medium grade for adverse conditions0.05 0.05

DM 10 %

ES 8 %

ITU-T; G.821, F.697, F.696

Slide No 58


P & A for HRPD – High Grade

High Grade2500

0054 %(0.004+0.05)

0.4 %

0.32 %

SES (Additional 0.05% for adverse propagation

conditions)

DM

ES

0.3 % UAT

Note: between 280 to 2500 all parameters are multiplied by (L/2500)

1/10 of HRX ITU-T; G.821, Rep 1052

Slide No 59


P & A for HRDS – Medium Grade

– Used for national networks, between local exchange and international switching center

Performance and availability Objectives for HRDSPerformance parameter Percentage of any month

Class 1

280 km

Class 2

280 km

Class 3

50 km

Class 4

50 km

SES 0.006 0.0075 0.002 0.005

DM 10 % 0.045 0.2 0.2 0.5

Errored Seconds ES 8 % 0.036 0.16 0.16 0.4

RBER 5.6x10-10 Under study

Under study

Under study

UAT 0.033 0.05 0.05 0.1

IT-T; G.821, F.696, Rep 1052

Slide No 60


P & A for HRX – Local Grade– The local grade portion of the HRX represents the part between the

subscriber and the local exchange – Error performance objectives are:

BER shouldn’t exceed 10–3 for more than 0.015% of any month with an integration time of 1 s

BER shouldn’t exceed 10-6 for more than 1.5% of any month with an integration time of 1 min

The total errored seconds shouldn’t exceed 1.2% of any month

– Unavailability objectives for local grade circuits have not yet been established by ITU-T or ITU-R.

Slide No 61


Performance Predictions

• System performance is determined by the probability for the signal level to drop below the radio threshold level or the received spectrum to be severely distorted

• The larger fade margin, the smaller probability for the signal to drop below the receiver threshold level

Slide No 62


Availability• The total unavailability of a radio path is the sum of the

probability of hardware failure and unavailability due to rain

• The unavailability due to hardware failure is considered for both the go and return direction so the calculated value is doubled

• The probability that electronic equipment fails in service is not constant with time

• the high probability of hardware failure occurred during burn-in and wear-out periods

• During life time the random failures have constant probability

Slide No 63


HW Unavailability

• Unavailability of one equipment module – HW

where

MTTR is mean time to repair

MTBF is mean time between failures.

MTTR MTBF

MTTR N1

Slide No 64


Calculation of Unavailability

• Unavailability of cascaded modules

N1N1 N3N3N2N2 NnNn

i

n

i

n

ii

n

iss NNiNAN

11111111

Slide No 65


Calculation of Unavailability

• Unavailability of parallel modules

N1N1

N3N3

N2N2

NnNn

i

n

is NN

1

Slide No 66


Improvement in Availability in n+1 protection• HW protection

• Unavailability of a n+1 redundant system

212

1 1!21!2

11

n

n NNn

n

nN

Can be approximated 21 2

1N

nNn

Slide No 67


Improvement in Availability in Loop protection• HW and route protection

• Unavailability in a loop

Where,– J: Amount of hops in loop– K: Consecutive number of hop from the hub– N: Unavailability of the hop

J

kii

k

ii NNN

11

N6N5

N4

N3 N2

N1

N7

N=(N1+N2)(N3+N4+N5+N6+N7)

Slide No 68


HRDS - Example• HRDS: Medium grade class 3, 50 km. If the link is 5km

find UAT in % & s/d

• Solution:– From table of HRDS, Medium grade class 3, 50 km >>UAT =

0.05%– For 5 km >> UAT = (0.05%) * 5/50 = 0.005%– UAT = (0.005/100) * 365.25*24= 0.438h/y = 26min/y = 4s/d

N

Slide No 69


Topology Planning

Slide No 70


Capacity and Topology planning• Capacity demand per link results from transceiver capacity at those

BTS which are to be connected to the microwave link

• One transceiver reserves 2.5 time slots for traffic and signalling

• It is common to design for the higher capacity demand.

• For rapid traffic increase, the transmission network is dimensioned to reserve the capacity of 6 transceivers

• The advantage to reserve capacity– Flexibility in topology planning– New BTS s can be added to existing transmission links– New transceivers can be added without implementing new transmission links– No need for changeover to new transmission links in fully operating network

Slide No 71


Transmission Capacity Planning-Traffic Motorola-standards

• Bit rate for one voice PCM channel is 64Kb/s

• Bit rate for one voice GSM channel is 16Kb/s between BTS and BSC

• Each GSM radio carries 8 TCHs in the air, this equivalent to 8x16Kb/s=2x64Kb/s between BTS and BSC.

• Each GSM radio has 2 time slots in the GSM E1.

• Example: 3/3/3 site require 9x2=18 E1 time slots for traffic and one time slot for RSL, total is 19 time slots

Slide No 72


Transmission Capacity Planning-Example• Example: How Many Motorola micro-cells can be daisy

chained using one E1 at maximum?

• Solution:– Motorola micro cell has 2 radios (omni-2)– Each micrcell requires 2x2 time slots for traffic and 1 time slot for

rsl– So each micro cell requires 5 time slots (64 kb/s time slots)– Each E1 contains 31 time slots– [31time slots] divided by [5 time slots/microcell] gives us the the

maximum no of daisy chained microcells– So 6 microcells can be daisy chained at maximum

Slide No 73


Topology Planning• Network topology is based on

– Traffic– Outage requirements

• Most frequently used topologies– Star– Daisy Chain– Loop

Slide No 74


Star

•Each station is connected with a separate link to the MW hub.•Commonly used for leased line connections (needs low availability)

Slide No 75


Star• Advantages

– Easy to design– Independent paths which mean link failure affects only one node – Easy to configure and install – Can be expanded easily

• Disadvantages

– Limited distance from BTS or hub to the BSC– Inefficient use of frequency band– Inefficient link capacity use as each BTS uses the 2 Mbps– High concentration of equipment at nodal point – Interference problem

Slide No 76


Daisy Chain

• Advantages – Efficient use of link capacity (if BTSs are chained to the same 2Mbps)– Low concentration of equipment at nodal point

• Disadvantages– Installation planning is essential as the BTSs close – If the first link is lost, the traffic of the whole BTS chain is lost– extended bandwidth (grooming)

Application: along roads

Slide No 77


Daisy Chain

• (grooming)

Slide No 78


TreeApplication: Used for small or medium size network

• Advantages – Efficient equipment utilization by grooming– Short paths which require smaller antenna – Frequency reuse

• Disadvantages– Availability , one link failure affect many sites – Expansions might require upgrading or rearrangement

Slide No 79


LoopBTSs are connected onto two way multidrop chain

• Advantages– Provide the most reliable means of transmission protection against microwave link

fading and equipment failure– Flexibility y providing longer hops with the same antenna size, or alternatively, smaller

antenna dishes with the same hop length

• Disadvantages– Installation planning; since all BTSs of a loop must be in place for loop protection– More difficult to design and add capacity– Skilled maintenance personnel is required to make cofiguration changes in the loop

Slide No 80


Topology Planning

• Define clusters

• Select reference node

• Chose Backbone

• Decide the topology

Slide No 81


Diversity

Slide No 82


Diversity• Diversity is a method used if project path is severely

influenced by fading due to multi path propagation • The common protection of diversity techniques are:

– Space Diversity– Frequency Diversity– Combination of frequency and space Diversity– Angle Diversity

Note: frequency diversity technique takes advantage because of the frequency selectivity nature of the multi path depressive fading.

Slide No 83


DiversityDiversity Improvement

• The degree of improvement afforded by all of diversity techniques on the extents to witch the signals in the diversity branches of the system are uncorrelated.

• The improvement of diversity relative to a single channel given by:

Improvement factor where P refers to BER Diversity

nelSinglechan

P

PI

Slide No 84


Diversity Improvement

10 –3

20

10 -4

10 -5

10 -6

10 -7

4030

Diversity improvement

factor

No diversity

diversity

Fade Depth

Slide No 85


Single Diversity• Space diversity

– Employs transmit antenna and two receiver antenna– The two receivers enables the reception of signals via different

propagation paths– It requires double antenna on each side of the hop, a unit for the

selection of the best signal and partially or fully duplicated receivers

Note: whenever space diversity is used, angle diversity should also be employed by tilting the antenna at different upwards angles

Slide No 86


Space Diversity

Separate paths Tx Rx

Rx

S

1 1

1

Slide No 87


Frequency diversity• The same signal is transmitted simultaneously on two

different frequencies

• One antenna is required on either side of the hops, a unit selecting the best signal and duplicate transmitters and receivers

• A cost-effective technique

• Provides equipment protection , also gives protection from multipath fading

Slide No 88


Frequency diversityIt is not recommended for 1+1 systems, because 50% of the spectrum is utilized

For redundant N+1 systems this technique is efficient, because the spectrum efficiency is better, but the improvement factor will be reduced since there are more channel sharing the same diversity channel

1+1 systems

Slide No 89


Hot standby configuration• Tx and Rx operate at the same frequency, so there is no frequency

diversity could be expected

• This configuration gives no improvement of system performance, but reduces the system outage due to equipment failures

• Used to give equipment diversity (protection) on paths where propagation conditions are non-critical to system performance

Slide No 90


Hybrid diversity• Is an arrangement where 1+1 system has two antennas at

one of the radio sites

• This system effect act as space diversity system, and diversity improvement factor can be calculated as for space diversity

Slide No 91


Angle diversity• Angle diversity techniques are based upon differing angles of

arrival of radio signal at a receiving antenna, when the signals are a result of Multipath propagation

• The angle diversity technique involves a receiving antenna with its vertical pattern tilted purposely off the bore sight lines

• Angle diversity can be used is situations in witch adequate space diversity is not possible or to reduce tower height

Slide No 92


Combined diversity• In practical configuration a combination of space and

frequency diversity is used

• Different combination algorithms exist

• The simple method (conservative) to calculate the improvement factor for combined diversity configuration

I = Isd + Isd

Slide No 93


Combined diversity

Combined space and frequency diversity

TX

TX

RX

RX

RX

RX

f1

f1

f2

S

f2

Slide No 94


Path Diversity• Outage due to precipitation will not be reduced by use of

frequency,angle or space diversity.

• Rain attenuation is mainly a limiting factor at frequencies above ~10 GHz

• Systems operating at these high frequencies are used in urban areas where the radio relay network may from a mix of star and mesh configurations

• The area covered by an intense shower is normally much smaller than the coverage of the entire network

• Re-Routing the signal via other paths

Slide No 95


Path Diversity

• The diversity gain (I.e. the difference between the attenuation (dB) exceeded for a specific percentage of time on single link and that simultaneously on two parallel links

– Tends to decrease as the path length increases from 12 km or a given percentage of time, and for a given lateral path separation

– Is generally greater for a spacing of 8 km than for 4 km, though an increase to 12 km dose not provide further improvement

– Is not significantly dependent on frequency in the range 20 – 40 GHz, for a given geometry, and

- Ranges from about 2.8 dB at 0.1% of the time to 0.4 dB at 0.001% of the time, for a spacing of 8 km, and path lengths of about the same value for a 4 km spacing are about 1.8 to 2.0 dB.

Slide No 96


Microwave Antennas

Slide No 97


Microwave Antennas• The most commonly used type is parabolic antenna

• The performance of microwave system depends on the antenna parameters

• Antenna parameters are:– Gain – Voltage Standing Wave Ratio (VSWR)– Side and back lobe levels – Beam width– Discrimination of cross polarization – Mechanical stability

Slide No 98


Antenna Gain•The gain of parabolic antenna referred to an isotropic radiator is given by:

where: = aperture efficiency (typical values : 0.5-0.6) = wavelength in meters– A = aperture area in m2

Note : the previous formula valid only in the far field of the antenna, the gain will be decreased in the near field, near field antenna gain is obtained from manufacturer

)4

log(102 AGain

Slide No 99


Antenna Gain-cont.• This figure shows the relation between the gain of microwave dish and frequency with different dishdiameters

• Can be approximated Gain = 17.8 + 20log (d.f) dBi

where,

d : Dish diameter (m) f : Frequency in GHz

Slide No 100


VSWR• VSWR resembles Voltage Standing Wave Ratio

• It is important in the case of high capacity systems with stringent linearity objectives

• VSWR should be minimum in order to avoid intermodulation interference

• Typical values of VSWR are from 1.06 to 1.15

• High performance antennas have VSWR from 1.04 to 1.06

Slide No 101


Side and Back lobe Levels• The important parameters in frequency planning and

interference calculations are sidelobe and backlobes

• Low levels of side and backlobes make the use of frequency spectrum more efficient

• The levels of side and backlobes are specified in the radiation envelope patterns

• The front to back ratio gives an indication of backlobe levels

• The front to back ratio increases with increasing of frequency and antenna diameter

Slide No 102


Beam Width• The half power beam width of antenna is defined as the

angular width of the main beam at –3dB point

– An approximate formula used to find the beam width is:

3dB = ± 35. /D in degrees– The 10dB deflection angle is found approximately by:

10dB = 60. /D in degrees

Slide No 103


Antenna Characteristics – EIRP and ERP• Effective Isotropic Radiated Power (EIRP)

– It is equal to the product of the power supplied to a transmitting antenna and the antenna gain in a given direction relative to an isotropic radiator (expressed in watts)

– EIRP = Power - Feeder Loss + Antenna GainBoth EIRP and Power expressed in dBWAntenna gain expressed in dBi

• Effective Radiated Power (ERP)– The same as EIRP but is relative to a half-wave dipole instead of an isotropic

radiator

• EIRP = ERP + 2.14 dB• Example

Transmitter Output Power = 4 Watts = 36 dBm, Transmission Line Loss = 2 dB, and Antenna Gain = 10 dBd. Calculate the ERP– Answer: ERP = 36 - 2 + 10 = 44 dBmd

Slide No 104


Passive Repeater• Two types of passive repeaters :

– Plane reflectors– Back to Back antennas

• The plane reflector reflects MW signals as the mirror reflects light

– The laws of reflection are valid here

• The back to back antennas work just like an ordinary repeater station, but without frequency transportation or amplification of the signal

Slide No 105


Passive Repeater- cont.

• By using passive repeaters; the free space loss becomes:

AL= AFSA – GR + AFSB

where

– AFSA is the free space loss for the path site A to passive repeater

– AFSB is the free space loss for the path site B to passive repeater

– GR is the gain of the passive repeater

Slide No 106


Plane Reflectors• More popular than back to back antennas due to :

– Efficiency is around 100%– Can be produced with much larger dimensions than parabolic antennas

• The gain of plane reflectors is given by:

GR= 20 log( 139.5 . f2 .AR . cos( /2 )) in dB

where :

– AR is the physical reflector area in m2

– F is the radio frequency in GHz

is the angle in space at the passive

repeater in degrees

Slide No 107


Plane Reflectors

Slide No 108


Back to back Repeater• Use of them is practical when reflection angle is large

• The Gain of back to back antennas is given by

GR= GA1 – AC + GA2 in dB

where :– GA1: is the gain of one of the two antennas at the repeater in dB

– GA2: is the gain of the other antenna at the repeater in dB

– AC : is the coupling loss between antennas in dB

Slide No 109


Back to back antennas

Slide No 110


Antenna Characteristics - Polarization

• Co-Polarization– The transmit and receive antennas have the same polarization– Either horizontal or vertical (HH or VV)

• Cross-Polarization– The transmit and receive antennas have different polarization– Either HV or VH

Slide No 111


• Transmission of two separate traffic channels is performed on the same radio frequency but on orthogonal polarization

• The polarization planes are horizontal and vertical

• The discrimination between the two polarization is called Cross Polar Discrimination (XPD)

• Cross-Polarization Discrimination (XPD)– the ratio between the power received in the orthogonal (cross polar) port

to the power received at the co-polar port when the antenna is excited with a wave polarized as in the co-polar antenna element

• Good cross polarization allows full utilization of the frequency band

Cross Polarization

Slide No 112


Cross Polarization• To ensure interference-free operation, the nominal value

of XPD the value is usually in the rang 30 – 40 dB

• Discrimination of cross polar signals is an important parameter in frequency planning

28 MHz

Vertical

Horizontal

1 2 3 4 5 6 7 8 1’ 2’ 3’ 4’ 5’ 6’ 7’ 8’

Slide No 113


Mechanical Stability• Limitations in sway / twist for the structure of the

structure (tower or mast) correspond to a maximum 10 dB signal attenuation due to antenna misalignment

• The maximum deflection angle may be estimated for a given antenna diameter and frequency by using 10dB = 60. /D in degrees

Slide No 114


Antenna Datasheet

Slide No 115


Digital Antenna pattern

Slide No 116


Antenna Pattern

Slide No 117


Radio Propagation

Slide No 118


Electromagnetic (EM) Waves• EM wave is a wave produced by the interaction of time varying

electric and magnetic field

• Electromagnetic fields are typically generated by alternating current (AC) in electrical conductors

• The EM field composes of two fields (vectors)– Electric vector E– Magnetic vector H

• Electromagnetic waves can be– Reflected and scattered– Refracted – Diffracted – Absorbed (its energy)

Slide No 119


Electromagnetic Waves Properties• E and H vectors are orthogonal

• In free space environment, the EM-wave propagates at the speed of light (c)

• The distance between the wave crests is called the wavelength (λ)

• The frequency ( f )is the number of times the wave oscillates

• The relation that combines the EM-wave frequency and wavelength with the speed of light is:

λ = c / f

Slide No 120


Radio Wave Propagation

• The propagation of radio wave is affected by :– Frequency Effect– Terrain Effect– Atmospheric Effect– Multipath Effect

All the above mentioned effects cause a degradation in quality

Slide No 121


Frequency Effect

• Attenuation: Loss

• Propagation of radio depends on frequency band

• At frequencies above 6 GHz radio wave is more affected by gas absorption and precipitation

– At frequencies close to 10 GHz the effects of precipitation begins to dominate

– Gas absorption starts influencing at 22 GHz where the water vapour shows characteristic peak

Slide No 122


Terrain effect• Reflection and scattering

• The radio wave propagating near the surface of earth is influenced by:

– Electrical characteristics of earth– Topography of terrain including man-made structures

Slide No 123


Atmospheric effect• Loss and refraction

• The gaseous constituents and temperature of the atmosphere influence radio waves by:

– Absorbing its energy– Variations in refractive index which cause the radio wave reflect,

refract and scatter

Slide No 124


Multipath effect• Multipath effect occurs when many signals with different

amplitude and/or phase reach the receiver

• Multipath effect is caused by reflection and refraction

• Multipath propagation cause fading

Slide No 125


EM wave Reflection and scattering

• When electromagnetic waves incide on a surface it might be reflected or scattered

• Rayleigh criterion used to determine whether the wave will be scattered or reflected

• The reflected waves depend on the frequency, incidence angle and electrical property of the surface

Slide No 126


EM wave Reflections

• Reflection of the radio beam from lakes and large surfaces are more critical than reflection from terrain with vegetation

• Generally, vertical polarization gives reduced reflection especially at lower frequencies

• If there is a great risk from reflection ,space diversity should be used

Slide No 127


EM wave Reflection coefficient (ρ)

• Reflection can be characterized by its total reflection coefficient ρ

• ρ is the quotient between the reflected and incident field

• When ρ = 0 nothing will be reflected and when ρ =1 we have specular reflection

• reflection coefficient decreases with frequency

Slide No 128


EM wave Reflection coefficient-cont.

Reflection loss (ρ)

-35

-5

-15

-15-25

5

0.2 0.80.60.4Total reflection coefficient (ρ)

Amax

Amin

• The resulting electromagnetic field at a receiver antenna is composed of two components,the direct signal and the reflected signal

• Since the angle between the both components varies between 0 and 180 the signal will pass through maximum and minimum values respectively

The figure shows different

values of total reflection

coefficient, and the minimum

and maximum values

with respect to them

Slide No 129


EM wave Refraction

• Refraction occurs because radio waves travel with different velocities in different medium according to their electrical characteristics.

• Index of refraction of a medium is the ratio of the velocity of radio waves in space to the velocity of radio waves in that medium

Slide No 130


EM wave Refraction• Radio wave is refracted toward the region with higher

index of refraction (denser medium)

Incident wave

Reflected wave

Refracted wave

Medium 1

Medium 2

θi θr,n1

,n2

n2 > n1

Slide No 131


EM wave Refraction• Refractivity depends on

– Pressure– Temperature– Humidity

• Refractive Gradient (dN/dh) represents refractive variation with respect to height (h), related to the earth radius.

Slide No 132


EM wave Refraction and Ray bending• Refraction cause ray bending in the atmosphere

• In free space, the radio wave follows straight line

no atmosphere with atmosphere

Slide No 133


EM wave Refraction: K-Factor• K is a value to indicate wave bending

re :is the effective radius of the ray due to refraction

a :is the earth radius = 6350 km

– For temperate regions :dN/dh = - 40N units per Km,

K=4/3=1.33a

rK

e

Slide No 134


K-Factor and Path Profile Correction• Path profile must be corrected by K-factor

• Radius of earth must be multiplied by K-factor, less curvature of earth

Slide No 135


Formation Of Ducts- Refraction and reflectionGround Based Duct: Refraction and reflection • The atmosphere has very dense layer at the ground with a

thin layer on top of it.

Elevated Duct: Refraction only• The atmosphere has a thick layer in some height above

ground.• If both the transmitter and the receiver are within the

duct, multiple rays will reach the receiver• If one is inside and the other is outside the duct, nearly no

energy will reach the receiver

Slide No 136


Formation Of Ducts- Refraction and reflection

Earth

Elevated DUCT

Earth

Ground Based DUCT

Slide No 137


Formation Of Ducts- Explanation Refraction and reflection

Slide No 138


Ducting Probability- Refraction and reflection

• Duct probability percentage of time when dN/dh is less than –100 N units/km per specified month

• ITU-R issues DUCT Probability CONTOUR MAPS

• The ducting probability follows seasonal variations

• This difference in ducting probability can be explained by the difference in temperature and most of all by difference in humidity

• From the map the equatorial regions are most vulnerable to ducts

Slide No 139


ITU-R DUCT Probability CONTOUR MAPS

Slide No 140


Multipath Propagation - Refraction and reflection

• Multipath propagation occurs when there are more than one ray reach the receiver

• Disadvantages: – Signal strength changes rapidly over a short time and distance– Multipath delays which causes time dispersion– Random frequency modulation due to Doppler shifts– Delay spread of the received signal

• Multipath transmission is the main cause of fading

• Fading is explained in later slides

Slide No 141


Diffraction

• Diffraction occurs and causes increase in transmission loss when the size of obstacle between transmitter and receiver is large compared to wavelength

• Diffraction effects are faster and more accentuated with increased obstruction for frequencies above 1 GHz

• Transmission obstruction loss over irregular terrain is complicated function of frequency, path geometry, vegetation density and other less significant variable

• Practical methods are used to estimate the obstruction losses.

Slide No 142


Diffraction lossPractical methods are used to estimate the obstruction

losses

• Terrain Averaging: ITU-R P.530-7– Diffraction loss in this method can be approximated for losses

greater than 15 dB

Ad = -20h/F1 + 10 (dB) : ITU-R P.530-7

Where, Ad : diffraction loss.

h: height difference between most significant blockage and path trajectory.

F1: radius of first freznal zone

Slide No 143


Knife edge models • Knife edge approximation is used when the obstruction is

sharp and inside the first freznal zone– Single Knife edge– Bullington– Epostein-Peterson– Japanese Atlas

Slide No 144


Absorption• At frequency above 10

GHz the propagation of radio waves through the atmosphere of the earth is strongly effected by resonant absorption of electromagnetic energy by molecular water vapor and oxygen

Slide No 145


Rain Attenuation• When radio waves interact with raindrops the

electromagnetic wave will scatter

• The attenuation depends on frequency band, specially for frequencies above 10 GHz

• The rain attenuation calculated by introducing reduction factor and then effective path length

• The rain attenuation depends on the rain rate, which obtained from long term measurement and very short integration time

• The Earth is divided into 16 different rain zones

Slide No 146


Rain Attenuation• Rain rate is measured to estimate attenuation because it is

hard to actually count the number of raindrops and measure their individual sizes so

• Rainfall is measured in millimeters [mm], and rain intensity in millimeters pr. hour [mm/h].

• Since the radio waves are a time varying electromagnetic field, the incident field will induce a dipole moment in the raindrop will therefore act as an antenna and re-radiate the energy.

• A raindrop is an antenna with low directivity and some energy will be re-radiated in arbitrary directions giving a net loss of energy in the direction towards the receiver.

Slide No 147


Raindrop shape• As the raindrops increase in size, they depart from the

spherical shape

• Raindrops are more extended in the horizontal direction and consequently will attenuate horizontal polarized waves more than the vertical polarized.

• This means that vertical polarization

is favorable at high frequencies

where outage due to rain is dominant.

Slide No 148


Fading

• The radio waves undergo variations while traveling in the atmosphere due to atmospheric changes. The received signal fades around nominal value.

• Multipath Fading is due to metrological conditions in the space separating the transmitter and the receiver which cause detrimental effects to the received signal

Slide No 149


Fade Margins• Fade Margin is extra power

• Fade Margins will be explained in link design for the following:

• Multipath Fading– Flat Fading– Selective Fading

• Rain Fading

Slide No 150


Mutipath Fading• As the fading margin increased the probability of the

signal to drop below the receiver threshold is decreased

• Flat fading or non-selective occurs when all components of the useful signal are affected equally

• Frequency selective fading occurs if some of the spectral components are reduced causing distortion

• Total fading

Ptot =Pflat + Psel

Slide No 151


Mutipath Fading• The impacts of multipath fading can be summarized as

follows:– It reduces the signal-to-noise ratio and consequently increases the

bit-error-rate (BER)– It reduces the carrier-to-interference (C/I) ratio and consequently

increases the BER– It distorts the digital pulse waveform resulting in increased

intersymbol interference and BER– It introduces crosstalk between the two orthogonal carriers, the I-rail

and the Q-rail, and consequently increases the BER

Slide No 152


Mutipath Fading

Frequency selective fading

Normal signal

Flat fading

P

Slide No 153


Microwave Link Planning and Design

Slide No 154


Hop Calculations (Design)

Free Space LossGas Absorption

Obstacle Loss

Rain fadingMultipath fading

Link BudgetFading prediction

Performance & Availability Objectives

Predictable Statistically Predictable

Always present and predictable Predictable

if present

Not always present but statistically

predictable

Slide No 155


Path Profile

• Path profile is essentially a plot of the elevation of the earth as function of the distance along the path between the transmitter and receiver

• The purpose of path profile:– To check the free line of sight– To check the clearance of the path to avoid obstacle attenuation– When determining the fading of received signal

Slide No 156


Path Profile Example• Path profiles are necessary to determine site locations and

antenna heights

Slide No 157


Path Profile: Clearance of Path• Design objective: Full clearance of direct line-of-sight and

and an ellipsoid zone surrounding the direct line-of-sight

• The ellipsoid zone is called the Fresnel Zone

Slide No 158


Path Profile: Fresnel Zone Example

Slide No 159


Fresnel Zone• Fresnal Zone is defined as the zone shaped as ellipsoid

with its focal point at the antennas on both ends of the path

• If there is no obstacle within first Fresnel zone ,the obstacle attenuation can be ignored and the path is cleared

• Equation of path of ellipsoid

221

ddd

Slide No 160


• First Fresnel zone radius

• Fresnel zone – Exercise: Calculate the fresnel zone radius at mid path for the following cases

– 1. f= 15GHz, K=4/3, d=10km– 2. f = 15GHz, K=4/3, d=20km

• Solution:– 1. F1 (radius)

– 2. F1 (radius)

fd

ddF

211 3.17

Fresnel Zone Equation

[m]

m102015

10103.17

m71015

553.17

Slide No 161


Fresnel Zone Radii calculations“Table Tool”

4.0 10.0 15.0 20.0 30.0 40.0

7.0 9.2 12.7 13.3 15.0 17.3 18.613.0 10.3 13.6 12.1 13.6 13.8 14.215.0 10.1 14.2 11.3 13.4 12.4 13.118.0 9.2 15.2 10.6 13.8 11.6 13.023.0 7.7 17.1 9.6 14.7 10.9 13.426.0 6.7 19.6 8.6 16.0 10.1 14.138.0 5.1 23.9 7.3 18.1 9.1 15.2

Distance in kmFrequency GHz

Slide No 162


Obstacle Loss: Fresnel Zone is not Cleared

Obstacle Loss

Knife Edge obstacle loss Smooth spherical obstacle loss

Slide No 163


Knife Edge Losses

0 12 2060 dB

Slide No 164


Smooth Spherical Earth Losses

10

20

30

dB

Slide No 165


Line-Of-Sight Survey

• LOS Survey– To verify that the proposed network design is feasible considering

LOS constraints

LOS

Slide No 166


Line-Of-Sight Survey- Flowchart

LOS Survey

LOS Report

Update the design

Network Design

Slide No 167


LOS Survey EquipmentNecessary:

• Compass

• Maps : 50 k or better

• Digital Camera

• GPS Navigator

• Binoculars

• Hand-held communication equipment

• Signaling mirrors

Optional:

• Clinometer

• Altimeter

• Laptop

• Spectrum analyzer

• Antenna horn

• Low noise amplifier

• Theodolite

Slide No 168


LOS Survey Procedure - Preparation• Preparation

– Maps of 1:50k scale or better to be used and prepared– List of hops to be surveyed– Critical obstacles should be marked in order to verify LOS in the

field– Organize transport and accommodation– Organize access and authorization to the sites – Prepare LOS survey form

Slide No 169


LOS Survey Procedure - Field• Verification of sites positions and altitudes

• Confirmation of line-of-sight using– GPS– Compass– Binocular– And other methods in the next slide

• Take photographs

• Estimate required tower heights

• Path and propagation notes

Slide No 170


Other Methods of LOS Survey• Mirrors

• Flash

• Balloon

• Portable MW Equipment

• Driving along the path and taking GPS and altitude measurements for different points along it.

Slide No 171


LOS Survey Report• Site Data

– Name– Coordinates– Height– Address

• Proposed Tower Height• LOS Confirmation• Azimuth and Elevation• Path short description• Photographs

Slide No 172


Link Budget

• Includes all gains and losses as the signal passes from transmitter to the receiver.

• It is used to calculate fade margin which is used to estimate the performance of radio link system.

Slide No 173


Link Budget• Link budget is the sum of all losses and gains of the signal

between the transmitter output and the receiver input.

• Items related to the link budget– Transmitted power– Received power – Feeder loss– Antenna gain– Free space loss– Attenuations

• Used to calculate received signal level (fading is ignored)

Slide No 174


Link Budget (con’d)

Where, Pin = Received power (dBm) Pout = Transmitted power (dBm) L = Antenna feeder loss (dB) G = Antenna gain (dBi) FSL = Free space loss (dB) (between isotropic antennas) A = Attenuations (dB)

AFSLGLPP outin

Slide No 175


Link Budget

Tx

Gt Gr

Rx

Output power

Received power

Antenna gain

Branching loss Feeder

lossAntenna

gain

Feeder loss

Branching loss

Free space loss + atmospheric atten.

Fade Margin

Receiver threshold

Slide No 176


Link Budget Parameters-Free Space Loss• It is defined as the loss incurred by an electromagnetic wave as is

propagates in a straight line through the vacuum

Lp(dB) = 92.4 + 20logf(GHz) + 20logD(km)

2244

c

fDDLp

where,

Lp = free space path loss

D = distance

f = frequency

λ = wavelength

c = velocity of light in free space (3*108 m/s)

Slide No 177


Free Space Loss

Tx Rx

Lp

Link Budget Parameters

Slide No 178



• Total Antenna Gain:

Ga = 20 log (Da) + 20 log (f) + 17.8

• Atmospheric attenuation occurs at higher frequencies , above 15 GHz due to atmospheric gases, and given by:

Where d is path link in km , a is specific attenuation in dB/km

Daf

dA aa

Slide No 179



• Rx Level: Signal strength at the receiving antenna

PRx= PTx-LBRL-+GTx-LFS-Lobs+GRx - LTx feeder – LRx feeder

Where, PRx : received power level GTx :Tx gain

PTx : transmitted power level Lobs :Diffraction loss

LBRL : branching loss GRx :Rx gain

LFS : free space loss LRx feeder : Rx feeder loss

LTx feeder : Tx feeder loss

Slide No 180


Fading

• Fading types– Multipath Fading; Dominant cause of fading for f < 10 GHz

• Flat Fading• Frequency Selective Fading

– Rain Fading; Dominant cause of fading for f > 10 GHz

Slide No 181


Fade Margin and Availability

• Is the difference between the nominal input level and receiver threshold level

From Link Budget

FM = Received Power – Receiver threshold

• Fade margin is designed into the system so as to meet outage objectives during fading conditions

• Typical value of Fade Margin is around 40 dB

• Availability is calculated from the Fade Margin value as in F.1093, P.530-6, P.530-7, …

Slide No 182


Flat Fading ITU-R P.530-7

Pflat =Po . 10–F/10

where:– F equals the fade margin

– Po the fading occurrence factor

Po = k. d3.6 . f0.89 .(1+|Ep|)-1.4

Where: – k is geoclimatic factor– d is path length in Km– f is frequency in GHz– Ep: path inclination in mrad = d

hhEP

21

Slide No 183


Flat Fading- cont. ITU-R P.530-7• The geoclimatic (K) depends on type of the path

– Inland linksPlains: low altitude 0 to 400m above mean sea level

Hills: low altitude 0 to 400m above mean sea level

Plains: Medium altitude 400 to 700m above mean sea level

Hills: Medium altitude 400 to 700m above mean sea level

Plains: High altitude more than 700m above mean sea level

Hills: High altitude more than 700m above mean sea level

Mountains: High altitude more than 700m above mean sea level

– Coastal links over/near large bodies of water– Coastal links over/near medium-sized bodies of water– Indistinct path definition

• To calculate K value, refer to formulas and tables in ITU-R P.530-7

Slide No 184


Frequency Selective Fading ITU-R F.1093• Result from surface reflections or introduced by

atmospheric anomalies such as strong ducting gradients

Where,

η : Probability of of the occurrence of multipath fading

W: Signature width (GHz), equipment dependent

B : Signature depth (GHz), equipment dependent

τm: Mean value of echo delay

τr : Time delay used during measurements of the signature curves (reference delay) ns. Normally 6.3 ns

r

mB

sel WP

2

20103.4

Slide No 185


Frequency Selective Fading ITU-R F.1093

4/30

1002.

1

P

e

5.1

507.0

dm

2/

2/

2010w

w

Bc

W

Where, Po: The fading occurrence factor

Where, d : Path length (km)

Where, Bc: Signature depth

Slide No 186


Frequency Selective Fading ITU-R P.530-7

Where,Wx: Signature width

Bx: Signature depth

τx: The reference delay used to obtain signature in measurements

x: Denotes either Minimum phase (M) or Not Minimum phase (NM)

NMr

MB

NMMr

MB

Msel

NMM

WWP,

220

,

220 101015.2

Slide No 187


Space Diversity Improvement ITU-R P.453

Where,s : Vertical separation between antennas in m

f : Frequency in GHz

d : Path length

F : Fade Margin

: The difference in antenna gain between the two antenna in dB

Po : from the formula of flat fading

101001034.3

101

04.148.012.087.04 GMP

dfs o

eI

I

PP

I

PP selflatmp

mpdiv

G

Slide No 188


Rain Attenuation ITU-R P.530• Rain Intensity in mm/h

– The reference level is the rain intensity that is exceeded .01% of all the time (R0.01)

• The attenuation due to the rain in .01% of the time for a given path may be found by:

where

γR : Specific rain attenuation (dB/km)

deff : Effective path length, km

k and a are given in the table

effRR dA .

aR Rk

Slide No 189


Usable path lengths with rain intensity example: 15 GHz

Slide No 190


Rain zone contours (Americas)Rain zone contours (Far East)

Rain zone contours (Europe and Africa)

ITU-R presents the cumulative distribution of rain intensity for 15 different zone as shown below

Slide No 191


Rain Fading ITU-R P.530 • The relation between fading margin and unavailability for the path

is given by:

Where

– AR0.01 : Rain attenuation exceeded 0.01% of the time

– F: Fade margin

) / 12 . 0 log( 172 . 0 29812 . 0 546 . 0 ( 628 . 1101 . 010

F ARP

%

Slide No 192


Frequency Planning

Slide No 193


Frequency planning• Objective of frequency planning

– Efficient use of available frequency band– Keep interference level as low as possible

• Frequency plan must consider interference– C/I Objectives

• Note: the requirements depends on – Equipment– Frequency– Bandwidth

For adjacent channel interference

Slide No 194


Frequency PlanningFrequency Allocation• From operator’s point of view, it is best to get a block of

frequencies or several adjacent channels from each frequency band

– Installation and maintenance of microwave radio is less complicated– Interference analysis is only needed between operators own hops

• It is recommended to assign the available channels or frequency block to certain capacities so that 2X2, 4X2, 8X2, 16X2 will not interleave.

• Normally in 18-38 GHz, four hops using the same channel can arrive at star if they are at 90 degrees angle from each other

Slide No 195


Frequency PlanningInterference• Interference needs more concern at star points because several

microwave radios transmit and receive are close to each other• Don’t use higher transmitter output power than required• Frequency planning in star points is trivial if multiple channels are

used (inefficient use of channels)• Re use same channel (efficient use of channels)

– All stations at star transmit either high or low, while high-low alteration must be applied in chains.

– Good angle separation– Cross polarization gives extra discriminationNote: Rain has greater attenuation on horizontal polarization thus use horizontal

polarization for shorter hops

Slide No 196


Frequency Planning• The radio spectrum is allocated to various services by

ITU’s Administrative Radio Conference (WARC)

• ITU-R is responsible for providing RF channel arrangement

– Alternated channel arrangement– Co-channel arrangement– Interleaved arrangement

Slide No 197


Alternated Channel arrangement • Every channel will have opposite polarization to the

adjacent channels

• This arrangement is used(neglecting co-polar adjacent interference) if the below rule holds

XPDmin+(NFD –3)>(C/I)min

NFD=adj. Ch. Received power / adj. Ch. Power received after BB filter

• Advantage:Easily filfilled by standard antenna to radio equipment

• Disadvantage:Limited spectrum effective

Slide No 198


Co-channel arrangement• In this arrangement every radio channel is utilized twice

for independent traffic on opposite polarization for the same path

• The following demand must be fulfilled [10log(1/(1/10^((XPD + XIF)/10) +1/10^((NFD-3)/10)))] > (C/I)

Where,

NFD :Net Filter discriminator

XIF :is XPD improvement factor

Slide No 199


Channel Capacity and Separation

Capacity Channel Separation

2 X 2 Mbps 3.5 MHz

4 X 2 Mbps 7 MHz

8 X 2 Mbps 14 MHz

16 X 2 Mbps 28 MHz

Channel separation

Slide No 200


Co-channel Interference – Far

Tx/Rx Tx/Rx

Tx/Rx

Tx/Rx

Tx = f1

Rx = f2

Tx = f1

Rx = f2

Tx = f2

Rx = f1

Tx = f2

Rx = f1

Slide No 201


Co-channel Interference – Near

Tx/Rx

Tx/Rx Tx = f1

Rx = f2

Tx = f2

Rx = f1

Slide No 202


Adjacent Channel Interference

fRx fTx

Interference

Slide No 203


Receiver Threshold Degradation

• Presence of interfering signals will give a receiver threshold degradation

• The degraded receiver threshold level LTel is calculated from:

• A Rule of Thumb

Threshold Degradation < 3 dB

10/101log10 IRTe LCLTeTel LL

Slide No 204


Threshold Degradation

Receiver threshold,

dBm -82

-84

-86

-88

-80-78-76

-72

-74

-70

14 191716 1815 2120 22 23

Signal to Interference ratio, dB

3dB

Slide No 205


Channel plan

Tx=4ARx=4B

Tx=4BRx=4A

1A 7A6A5A4A2A 3A 7B6B5B4B3B2B1B

Low sub-band High sub-band

Duplex distance

Slide No 206


High / Low Tx Channel Allocation

H

LH

H

L

H

LH

H/L

L

Near interference

Slide No 207


High / Low Tx Channel Allocation

H

H/L

L

L

L

H

H H

H

L

Interference

New frequency

band

Rings with odd number of sites should be avoided

Slide No 208


Channel Plan

7 Channels

28 MHz(17x2 Mbps)

f

1A 7A6A5A4A3A2A

Slide No 209


Channel Plan

28 MHz(17x2 Mbps)

f14 MHz(8x2 Mbps)

11 Channels

Slide No 210


Channel Plan

28 MHz(17x2 Mbps)

f14 MHz(8x2 Mbps)

15 Channels

7 MHz(4x2 Mbps)

Slide No 211


Output Power

High output power

High output power

High output power

Interference

Only High output power

Slide No 212


Output Power

Low output power

High output power

Low output power

No Interference

High and low output power

Slide No 213


Interference

Slide No 214


Digital Systems and BER • Performance of digital transmission system can be

evaluated by BER, Bit Error Rate

• Telephony BER degradation versus audible degradation:– 10-6: Noise not audible– 10-5: Barely audible– 10-4: audible, understandable– 10-3: disturbing– More than 10-3: sync loss, link loss

• Data and in particular multimedia media application require a very low BER

Slide No 215


Noise in Digital SystemsNoise can originate from a variety of sources, and many of

these sources are man-made so they can be eliminated

• Thermal noise

• Noise Factor and Noise Figure

• S/N Ratio

• Receiver Thresholds

Slide No 216


White Noise in Digital Systems

• Thermal noise is generated from random motion of electrons due to thermal energy

• Pn=KTB (W) where :– k=Boltzmann’s constant – T=temperature in Kelvin– B=bandwidth of noise spectrum

• Typical values are : T=300 K , b= 6MHz , -106 dBm

Slide No 217


Noise Factor and Noise Figure• Noise Factor and Noise Figure are figures of merit used to

indicate how much the S/N deteriorates as a signal passes through a circuit or series of circuits.

• Noise factor: – Is defined in terms of signal to noise ratio

• Noise Figure NF = 10 log(F) (dB)

outputat ratiopower S/N available

inputat ratiopower S/N availableF (unitless)

Slide No 218


Noise in Digital Systems

• Signal to interference ratio defines the minimum difference between the signal and the interferer levels. It depends on bandwidth, modulation and manufacturer.

• Usually for digital system signal to interference ratio 15-25 dB

Slide No 219


Receiver Thresholds• Threshold (10-3): Received level at BER 10-3

• Threshold (10-6): Received level at BER 10-6

Threshold = White noise + Noise figure + S/N

Threshold

S/N

NF

White noise

Slide No 220


Threshold Degradation

Receiver threshold,

dBm -82-84-86-88

-80-78-76

-72-74

-70

14 1917

16 1815 2120 22 23Signal to Interference ratio, dB

3dB

• A Rule of Thumb

Threshold Degradation < 3 dB given that the required signal to interferer is not violated

Slide No 221


Cross Polar Interference XPI• Both multi path- and rain fading can result in severe

degradation of XPD level

• Cross Polar interference Cancellers (XPIC) in the receiver remove the unwanted signal that has leaked from the opposite polarization into the wanted one

The quantitative

Description of cross-

Polar interference XPI

dBE

ELogXPI

21

11.20

dBE

ELogXPD

12

11.20Where E11and E12 are

given in the next figure

Slide No 222


Cross Polar Interference

• Depolarization Causes– Scattering or reflection from land or water surfaces– Reflection from an atmospheric layer– Tropospherical turbulence

Slide No 223


Cross Polar Interference

E1

E2

E11

E22

E21

E12

Dual polarized system suffering from XPI

Slide No 224


Ways to include interference in performance calculation

• The interference calculation are performed by calculation the interference level and determining the receiver threshold degradation

• Start from allowed interference level at the input of the disturbed receiver and then comparing it with level of the interfering signal

• The degradation receiver threshold level

10/1101log10 LCLTeTel

RTeLL

Slide No 225


Interfering waves propagation mechanisms• Long-term interference mechanisms:

– Diffraction– Troposcatter– Line-of-site

• Short-term interference mechanisms:– Ducting: layer refraction/reflection– Hydrometeor scatter

Slide No 226


Selecting Interfering Stations • Before performing interference calculation the possible interfering

station must be selected in the area of interference

• Co-ordination area are the area around given station where possible co-channel interference from near site are situated

Co-ordination area for off-key hole region

Key hole region

Slide No 227


Propagation in Interference Calculations• Select interfering site by calculating coordination area

• Select minimum interference levels

• Predict interferer signal level– Decide whether an average year or worst –month prediction is required– Assemble the basic input data– Derive the annual or worst-month radio meteorological data from maps– Analyze the path profile, and classify the path according to the path geometry– Identify which individual propagation models need to be invoked– Calculate the individual propagation predictions using each of the models

identified in the previous step– Combine the individual predictions to give the overall statistics

Slide No 228


Interference Calculation • Undesirable RF coupling between radio channels

– Cross polarization: occurred in channels operating on opposite polarization

– Adjacent channel:the channel filter at the receiver and the width of

the transmitted spectrum determined the interference level– Front to back:The interference level is mainly a function of the

antenna front-to-back ratio– Over shoot:If the paths are aligned , interference due to overshoot

is critical. Use of opposite polarization or change of radio channels

is recommended.

Slide No 229


Examples of Interference RF coupling• Examples

V

H

Cross Polarization Adjacent channel

f2

f1

f1

Front-to-Back

f1f1’

Over Shoot

f1 f1’ f1

Slide No 230


Interference Calculations- cont.• Preconditions

– Network diagram: drawn to scale and angle, includes all radio-relay circuits within the frequency band concerned

– Network data : antenna types and radiation patterns, transmitter output power

– RL equipment interference data, normally given as diagrams • Digital to digital interference diagrams• Digital to analog interference diagrams• Analog to digital interference diagrams• Adjacent-channel attenuation as a function of channel spacing

– Antenna radiation patterns: for all types of antennas used in the network

Slide No 231


Interference Calculations- cont.• Interference evaluation on digital network

– It is necessary to check each antenna discrimination in the nodal stations for all disturbances

– In the beginning, only the most critical interference path has to be examined

– As a start, standard performance antennas are used, and no level adjustments are made to reduce interference problems, this case is worst case

– Co-polar operation– Cross-polar operation

Slide No 232


Digital Map and Tools Overview

Slide No 233


Digital Maps• Digitized Geographical data is needed

• Maps sampling (examples)– Urban: 20 to 50m– Suburban: 50-100m– Open: 100m

Slide No 234


Digital Maps-Geographical Databases• The choice of the geographical databases depends on the

propagation model used• A compromise has to be reached between:

– Cost– Accuracy– Calculation speed– The chosen configuration

• Geographical databases types are:– Vector data (Linear)– Altitude– Clutter (land use data)

Slide No 235


Digital Maps - Vector Data (Linear)

• Succession of points describing:– Highway– Roads– Railways– Rivers– Borders– coastlines

Slide No 236


Digital Maps - Altitude

• One altitude value per each pixel

• Each point of the pixel is assumed at the same altitude

• Two categories of altitude databases– Digital Terrain Model (DTM)– Digital Evaluation Model (DEM)

Microwave Planning and Design

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