Post on 18-Jan-2016
description
UMTS Key Technologies
ZTE University
Content
RAKE Receiver Handover Control Compressed Mode Admission Control Load Control Code Resource Allocation Capacity Features
Multi-path characteristics of radio channel
Electromagnetic propagation: direct radiation 、 reflection 、 diffraction and scattering
Signal attenuation: Path loss : Loss of electromagnetic waves in large scope of the
spread reflects the trend of the received signal in the spreading 。 Slow fading : Loss because of being blocked by the building and
hill in the propagation path Fast fading : Electromagnetic signals rapidly decline in a few
dozens wavelength ranges
Description of Fast fading distribution Rayleigh distribution : non line-of –sight(NLOS) transmission Rician distribution : line-of –sight(LOS) transmission
Multi-Path Effects
receiving signalreceiving signal
timetime
strengthstrength
00
sending signalsending signal
Frequency Frequency off-setoff-set caused by the movement of caused by the movement of
mobile mobile ,, that is Doppler effectthat is Doppler effect
Frequency Frequency off-setoff-set caused by the movement of caused by the movement of
mobile mobile ,, that is Doppler effectthat is Doppler effect
Sending signal Accepting signal
Interference Interference
0dB
Sending signal
-25dB
Accepting signal
fadingfading
0 + Sending signal Accepting signal
delaydelay
0 2 3 + Sending signal Accepting signal
ditheringdithering
Characteristics of Radio Propagation
RAKE Receiver can effectively overcome the multi-path RAKE Receiver can effectively overcome the multi-path
interference, consequently improve the receiving performance.interference, consequently improve the receiving performance.
RAKE Receiver can effectively overcome the multi-path RAKE Receiver can effectively overcome the multi-path
interference, consequently improve the receiving performance.interference, consequently improve the receiving performance.
RAKE Receiver
The multi-path signals contain some useful energy , therefore the UMTS receiver can combine these energy of multi-path signals to improve the received signal to noise ratio.
RAKE receiver adopts several correlation detectors to receive the multi-path signals, and then combines the received signal energy.
RAKE Receiving
d1 d2
t t t
d3
transmitti
ng
Receivin
gRake
combinationnoise
Multi-finger receiver
Traditional receiver Multi-path signals are treated as interference. The receiving performance will decline because of the
Multi-address Interference (MAI).
Precondition of Multi-finger receiver Multi-finger receiver utilizes the Multi-path Effect. Multi-finger signals can be combined through relative
process Multi-finger time delay is larger than 1 chip interval,
which is 0.26us=>78m.
Multi-finger receiver
receivertransmitter
coding decoding
Direct signal
Reflected signal
Dispersive time < 1 chip interval
Multi-finger receiver can’t supply multi-finger diversity
decodingDirect signal
Reflected signaltransmitter receiver
Dispersive time > 1 chip interval
Multi-finger receiver can supply multi-finger diversity, signal gain is improved
coding
RAKE Receiving
receiverreceiver
Single receiving
Single receiving
Single receiving
searcher calculatecalculate
combining
tt
s(t) s(t)
signal
RAKE Receiving overcomes multi-finger interference, improves receiving performance
Combination of Multi-fingers
Maximal ratio combining (MRC)
at each time delay phase shifting by adding
Finger 1
Finger 2
Finger 3
Content
RAKE Receiver Handover Control Compressed Mode Admission Control Load Control Code Resource Allocation Capacity Features
What’s ?
When UE is moving from the coverage area of one site to another, or the quality of service is declined by external interference during a service, the service must be handed over to an idle channel for sustaining the service.
Handover is used to guarantee the continuity of service.
Handover is a key technology for mobile networking.
Category of Handover
Intra-RNC, inter-Node B Inter-RNC
Soft handover (SHO)
Same Node B, Inter-sector
Softer handover
Intra-frequency Inter-frequency Inter-system (UMTS&GSM) Inter-mode (FDD&TDD)
Hard handover (HHO)
UMTS system support
multiple handover technology
Handover Demonstration
Hard
Handover
Soft
Handover
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
Soft Handover/Softer Handover
Soft Handover
Soft-Softer Handover
Softer Handover
Hard Handover
During the hard handover procedure, all the old radio links with the UE are abandoned before new ones are established, so there must be service interruption during the HHO.
Hard handover may occur in the following main cases
When the UE is handed over to another UTRAN carrier, or another technology mode.
When soft handover is not permitted (if O&M constraint)
Hard Handover
Node B
SRNCRNC or BSC
CN
Node B or BTS
Soft/Softer Handover
The soft/softer handover allows to migrate from one cell to another without service interruption or without deleting all old radio links.
UE can connecte to more than one cell simultaneously and take benefit from the macro-diversity.
Soft Handover Softer Handover
CN CN
Iur
The two Node Bs may belong to the
same RNC
The two Node Bs may belong to the Same RNC
Soft Handover Softer Handover
SRNC DRNC
CN
Node B
SRNC
CN
Soft Handover Softer Handover
Node B
CN
UMTS General Handover Trilogy
Measurement Control UTRAN demands the UE to start measurement through
issuing a measurement control message.
Handover decision UTRAN makes the decision based on the measurement
reports from UE. The implementation of handover decision is various for different vendors. It impacts on the system performance critically.
Handover execution UTRAN and UE execute different handover procedure
according to the handover command.
(A) RNC sends measurement control message to UE (Measurement Control)
(B) UE starts measurement task with the parameters included in the message, and reports measurement results ( Measurement Report)
(C) RNC stores the measurement results according to frequencies and cells
(D) RNC Estimates the quality of each carrier (including intra-frequency and inter-frequency)
(E) Quality
Decision
(G) Allocate resource in target cell, prepare to execute handover
(F) maintain the active set and monitored set
(H) Allocate resource in target cell, prepare to execute handover
Current carrier has good quality
Other system has good quality
Other carrier has good quality
( I ) If handover is required, RNC sends handover command with target cell to UE
Handover Flows
General Procedure of Handover Control (I)
Measuring The measurement objects are decided by RNC. Usually,
either Ec/Io or RSCP (Received Signal Code Power) of P-CPICH channel is used for handover decision.
ZTE RNC adopts Ec/Io measurement, because Ec/Io embodies both the received signal strength and the interference. The relation of Ec/Io and RSCP is shown as follows:
Ec/Io = RSCP/RSSI
In the above equation , RSSI ( Received Signal Strength Indicator ) is measured within the bandwidth of associated channels
Filtering The measurement results should be filtered before being
reported. Measurement filtering can be regarded as a low pass filtering procedure. The following equation is applied for filtering.
Fn=(1-a)Fn-1 + a*Mn
Variants definition : Fn : filtered measurement result ; Fn-1 : last filtered measurement result ; Mn : latest Ec/Io or RSCP measurement result received from
physical layer; a = 1/2(k/2), k means the “Filter coefficient”, which is included in the
Measurement Control message. It is decided by the UTRAN. F0 is initialized by the first measurement result M1.
General Procedure of Handover Control (II)
General Procedure of Handover Control (III)
Reporting Period report triggered handover
Base on the filtered measurement result
Event report triggered handover Base on the event
Soft Handover
Hard Handover
Period
Event
Measurement result filtered in
UE
Event decided in RNC
Handover decided in RNCMeasurement result filtered in UE Event decided in UE
Handover decided in RNC
General Procedure of Handover Control (IV)
Handover algorithm All the handover algorithms including soft handover,
hard handover and so on are implemented on the event decision made according to the measurement reports.
Events defined in 3GPP specifications Intra-frequency events : 1A~1F Inter-frequency events : 2A~2F Inter-RAT events : 3A~3D
Note: RAT is short for “Radio Access Technology”, e.g. UMTS&GSM
Concepts Related to Handover
Active Set: A set of cells that have established radio links with a
certain mobile station. User information is sent from all these cells.
Monitored Set: A set of cells that are not in the active set but are
monitored according to the list of adjacent cells assigned by the UTRAN.
Detected Set: A set of cells that are neither in the active set nor in the
monitor set.
Soft handover event
Event Description
1AQuality of target cell improves, entering a report range of relatively activating set quality
1BQuality of target cell decreases, depart from a report range of relatively activating set quality
1CThe quality of a non-activated set cell is better than that of a certain activated set cell
1D Best cell generates change
1EQuality of target cell improves, better than an absolute threshold
1FQuality of target cell decreases, worse than an absolute threshold
An Example of SHO Procedure
Pilot Ec/Io of cell 1
time
PilotEc/Io
Connect to cell1 Event 1A Event 1C Event 1B ( add cell2 )( replace cell1 with cell 3 )( remove cell3 )
Pilot Ec/Io of cell 2
Pilot Ec/Io of cell 3
⊿ t ⊿ t ⊿ t
RNS Relocation
Core NetworkCore Network
Serving RNS
Target RNS
Serviing RNS
Target RNS
Iu Iu
Iur
RNSRadio Network Sub-system
RNS relocation can : Reduce the Iur traffic significantly Enhance the system adaptability
Hard Handover
Hard handover measurement is much more complex for UE than soft handover measurement.
Inter-frequency hard handover requires UE to measure the signal of other frequencies.
UMTS employs compressed mode technology to support inter-frequency measurement.
Content
RAKE Receiver Handover Control Compressed Mode Admission Control Load Control Code Resource Allocation Capacity Features
Purpose of Compressed Mode
In order to support inter-frequency and inter-RAT handover, UE is required to perform inter-frequency and Inter-RAT measurement periodically.
The UE with one transceiver does not have the opportunity to perform inter-frequency measurement during the service period (especially the voice call) , because the transceiver is busy in transmitting and receiving the signals all the time.
Compressed mode can provide idle slot based transmission time window, which can be used for inter-frequency measurement, for the UEs in connected state, e.g. CELL_DCH.
Compressed Mode
Compressed Mode Transmission Diagram
Transmit gaps(Maximum 7 slots = 4.7ms) 1 frame(10ms)
10ms
Generation of Compressed Mode Frame
Puncturing Lower the symbol rate of physical channel when
processing the rate matching procedure
SF halving Employ half SF, e.g. employ SF64 to replace
SF128
High layer scheduling Decrease the bit rate from up layer
Content
RAKE Receiver Handover Control Compressed Mode Admission Control Load Control Code Resource Allocation Capacity Features
Admission Control
The admission control is employed to admit the access of incoming call. Its general principal is based on the availability and utilization of the system resources.
If the system has enough resources such as load margin, code, and channel element etc. the admission control will accept the call and allocate resources to it.
Purpose of Admission Control
When user initiates a call , the admission control should implement admission or rejection for this service according to the resource situation.
The admission control will sustain the system stability firstly and try the best to satisfy the new calling service’s QoS request, such as service rate, quality (SIR or BER), and delay etc. basing on the radio measurement.
Admission control is the only access entry for the incoming services, its strategy will directly effect the cell capacity and stability, e.g. call loss rate, call drop rate.
Admission Control in Uplink
Itotal_old+ΔI >Ithreshold
The current RTWP (Received Total Wide Power) value of cell, which is reported by Node B
AccessThreshold
Interference capacityService priorityReserved capacity for handover
Iown-cell
0~N
Iother-cell
The forecasted interference including the delta interference brought by the incoming service is calculated by the admission algorithm, and its result depends on the QoS and transmission propagation environment
Different ultimate user numbers Different interference threshold under different ultimate
user number conditions Different ultimate throughputs
Quantity of Subscriber
Quantity of Subscriber-- The Total Bandwidth Received by Node B
Th
e T
ota
l Ba
nd
wid
th P
ow
er
Re
ceiv
ed
by
No
de
B (
dB
m)
Ultimate Situation for different service rateThroughput
Throughput -- The Total Bandwidth Received by Node B
The
Tot
al B
andw
idth
Pow
er R
ecei
ved
by N
ode
B (
dBm
)Admission Control in Uplink
Admission Control in Downlink
Ptotal_old+△P>=Pthreshold Access Threshold
The forecasted TCP value including delta power required for the incoming service is calculated by the admission algorithm, and its result depends on the QoS and transmission propagation environment.
The current TCP value of cell, which is reported by Node B( Transmitted Carrier Power*Pmax )
Max TCP of cellService priorityReserved capacity for handover
Quantity of Subscriber
Th
e T
otal
Tra
nsm
issi
on P
ower
(dB
m)
Red : low speed serviceBlue : high speed service
The above figure illustrates the relation between ultimate user number The above figure illustrates the relation between ultimate user number
corresponds to different service rate and distance under equidistant corresponds to different service rate and distance under equidistant
distribution conditiondistribution condition
The above figure illustrates the relation between ultimate user number The above figure illustrates the relation between ultimate user number
corresponds to different service rate and distance under equidistant corresponds to different service rate and distance under equidistant
distribution conditiondistribution condition
Admission Control in Downlink
The service can be either one-direction or bi-direction type. For bi-direction service, it is admitted only after both uplink and downlink are admitted.
Admission control is the only access entry for the incoming services, its strategy will directly effect the cell capacity and stability, e.g. call loss rate, call drop rate.
Admission Control Analysis
Content
RAKE Receiver Handover Control Compressed Mode Admission Control Load Control Code Resource Allocation Capacity Features
Load control
The purpose of load control is to keep the
system load under a pre-planned threshold
through several means of decreasing it, so as to
improve the system stability.
The speed and position
changing of UE may
worsen the wireless
environment.
Increased transmitted
power will increase the
system load.
Purpose of Load Control
Overload control
Serious overload threshold
Overload recovery threshold
Admission control threshold
Common overload threshold
Cell load
Overload control
Normal state
Common overload
state
Serious overload
state
4. The load is smaller than the overload recovery threshold
3. The load exceeds the serious overload threshold
6. The load is smaller than the serious overload threshold. but greater than the common overload threshold
5. The load exceeds the serious overload threshold.
1. The load exceeds the common overload threshold
2. The load is smaller than the overload recovery threshold
Load Control Flows
Start
DecisionLight loaded Over loaded
Normal loaded
1.Handover in andaccess are forbidden2. TCP increase isforbidden3. RAB service ratedegrade4. Handover out5. Release call (call drop)
1. Handover in and access are allowed2. Transmitted code power (TCP) increase is allowed3. RAB service rate upgrade is allowed
1. Handover in and access are allowed2. TCP increase is allowed
Load Control in Uplink
Triggers RTWP (Received Total Wide-band Power) value from
measurement report exceeds the uplink overload threshold; Admission control is triggered when rejecting the access of
services with lower priority due to insufficient load capacity in uplink.
Methods for decreasing load Decrease the target Eb/No of service in uplink; Decrease the rate of none real time data service; Handover to GSM system; Decrease the rate of real time service, e.g. voice call; Release calls.
Methods for increasing load Increase the service rate.
Load Control in Downlink
Triggers TCP (Transmitted Carrier Power) value from measurement report
exceeds the downlink overload threshold; Admission control is triggered when rejecting the access of
services with lower priority due to insufficient load capacity in downlink.
Methods for decreasing load Decrease the downlink target Eb/No of service in downlink; Decrease the rate of none real time data service; Handover to coverage-shared light loaded carrier; Handover to GSM system; Decrease the rate of real time service, e.g. voice call; Release calls.
Methods for increasing load Increase the service rate.
Cell breathing is one of the means for load control
The purpose of cell breathing is to share the load of hot-The purpose of cell breathing is to share the load of hot-
spot cell with the light loaded neighbor cells, therefore to spot cell with the light loaded neighbor cells, therefore to
improve the utilization of system capacity.improve the utilization of system capacity.
The purpose of cell breathing is to share the load of hot-The purpose of cell breathing is to share the load of hot-
spot cell with the light loaded neighbor cells, therefore to spot cell with the light loaded neighbor cells, therefore to
improve the utilization of system capacity.improve the utilization of system capacity.
Cell Breathing Effect
Example for load control
Cell Breathing EffectCell Breathing Effect With the increase of activated
terminals and the increase of high
speed services, interference will
increase. The cell coverage area will shrink. Coverage blind spot occurs Drop of call will happen at the edge
of cell
Coverage and
capacity are
interrelated
Content
RAKE Receiver Handover Control Compressed Mode Admission Control Load Control Code Resource Allocation Capacity Features
UMTS Code Resource
Channelized Code (OVSF code) Uplink Channelized Code Downlink Channelized Code
Scrambling Code Uplink Scrambling Code Downlink Scrambling Code
Function of OVSF Code
OC1, OC2OC3, OC4
OC5, OC6, OC7
OC1 , OC2, OC3OC1, OC2
OC1, OC2, OC3, OC4
Uplink: distinguish different radio channels from the same UE.
Downlink: distinguish different radio channels from the same NodeB.
Function of Scrambling code
Downlink: distinguish different Cells Uplink: distinguish different UEs
PN3 PN4
PN5 PN6
PN1 PN1
Cell Site “1” transmits using PN code 1
PN2 PN2
Cell Site “2” transmits using PN code 2
Why Code Resource Planning?
The OVSF (Orthogonal Variable Spreading Factor) code tree is a scarce resource and only one code tree can be used in each cell. In order to make full use of the capacity, and support as many connections as possible, it is important to plan and control the usage of channel code resource.
Downlink scrambling code allocation should be planned to avoid the interference between neighboring cells.
The uplink scrambling codes are sufficient, but RNC should plan the codes to use for avoiding allocating same code to different users in inter-RNC handover scenario.
Code Resource Planning
The uplink and downlink scrambling code can be planned easily by computer.
The uplink channelized code does not need planning, for every UE can use the whole code tree alone.
Therefore, only the downlink channelized code is planned with certain algorithm in RNC.
Each cell has one primary scrambling code, which correlates with a channel code tree. All the users under this cell share this single code tree, so the OVSF code resource is very limited.
The downlink channelized code tree is a typical binary tree with each layer corresponds to a certain SF ranging from SF4 to SF512.
SF = 1 SF = 2 SF = 4
Cch,1,0 = (1)
Cch,2,0 = (1,1)
Cch,2,1 = (1,-1)
Cch,4,0 =(1,1,1,1)
Cch,4,1 = (1,1,-1,-1)
Cch,4,2 = (1,-1,1,-1)
Cch,4,3 = (1,-1,-1,1)
Generation of Channelized Code
OVSF Code Tree
SF=8
SF=32
SF=16
Channelized Code Characters
Code allocation restriction : The code to be allocated must fulfill the condition that its
ancestor nodes including from father node to root node and offspring nodes in the sub tree are not allocated;
Code allocation side effect : The allocated node will block its ancestor nodes and
offspring nodes, thus the blocked nodes will not be available for allocation until being unblocked .
Strategy of Channelized Code Allocation
Full utilization The fewer the blocked codes, the higher code tree
utilization rate.
Low Complexity Short code first.
Allocate codes for common channels and physical shared channels prior to dedicated channels. Guarantee the code allocation for common physical
channels.
Apply certain optimized strategy to allocate codes for downlink dedicated physical channels.
An Example of Code Allocation
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
SF = 4
SF = 8
SF = 16
SF = 32
SF = 4
SF = 8
SF = 16
SF = 32
Red spots represent the codes that have been allocated;Green spots represent the codes that are blocked by the allocated offspring codes;Blue spots represent the codes that are blocked by the allocated ancestor codes;Black spots represent the codes that to be allocated;
Choose one code from
three candidates
Planning of downlink scrambling code
PN1
PN2
PN3PN7
PN6 PN4
PN5
PN7
PN6 PN4
PN5
PN1
PN2
PN3
PN1
PN2
PN3PN7
PN6 PN4
PN5
PN1
PN2
PN3PN7
PN6 PN4
PN5
PN1
PN2
PN3PN7
PN6 PN4
PN5 PN1
PN2
PN3PN7
PN6 PN4
PN5
Content
RAKE Receiver Handover Control Compressed Mode Admission Control Load Control Code Resource Allocation Capacity Features
Capacity of UMTS
UL capacity is restrained by interference
DL capacity is restrained
by the power of NodeB
Power Rising
Power rising occurs because of the Multiple Access Interference (MAI) resulting from the non-orthogonal code channels.
UMTS network Meeting Room
Code channel transmit talk with dialects Channel power voice tone Promised channel quality listen clearly Channel power rise voice tone rise Power climb voice climb Collapse over the range can not hear each other
Power Rising
Quantity of Subscriber
Quantity of Subscriber-- The Total Bandwidth Received by Node B
Th
e T
ota
l Ba
nd
wid
th P
ow
er
Re
ceiv
ed
by
No
de
B (
dB
m)
Capacity of UMTS System
Under the circumstance of single services:
=
=
=
Capacity of UMTS System
…...
X Y Z+ +
Under the circumstance of mixed services :
UMTS Capacity Features
UMTS capacity feature UMTS capacity is Soft Capacity.
The Concept of Soft Capacity The system capacity and communication quality are
interconvertible. Different services have different capacity. Different proportion of services have different capacity
for mixed services. The capacity is also restricted to the allocation of code
resource.
Different combination of service has different capacity
Different service has
different capacity
Concept of Soft Capacity
System capacity and QoS can be interconvertedSystem capacity and QoS can be interconverted
Quality
Quality C
over
age
Cov
erag
e
CapacityCapacity
All the key technologies adopted are used to try to All the key technologies adopted are used to try to
achieve the optimal balance of the three factorsachieve the optimal balance of the three factors
All the key technologies adopted are used to try to All the key technologies adopted are used to try to
achieve the optimal balance of the three factorsachieve the optimal balance of the three factors
Crucial Factors for UMTS Network (CQC)
Coverage and Capacity
UMTS performance is determined by such factors as : Number of users Transmission rate Moving speed Wireless environment
indoors Outdoors
The radius of cell depends on such factors as: Local radio conditions (local interference) Traffic in neighbouring cells (remote interference)
Cell Radius decrease according to the Increase of user number
Coverage/capacity VS Data Rate
Higher data rate needs higher power High data rate transmission is only available nearby the
station
>12.2 kbps
>64 kbps
>384 kbps
>144 kbps
Coverage decrease
Subscriber num increase
DL/UL: Add carrier six sectors
DL/UL: Add carrier six sectors
UL Tower Mounted Amplifier (TMA) 4 Rx Div OTSR
UL Tower Mounted Amplifier (TMA) 4 Rx Div OTSR
DL transmission diversity (Tx Div) high power amplifier
DL transmission diversity (Tx Div) high power amplifier
Add basestation
“last choice”
Add basestation
“last choice”
Optimization methods
To overcome Cell Breathing Effect caused by increased traffic and meet different requirements for capacity and coverage in different environment, following solutions can be applied:
Factors Impact on UMTS capacity
RAKE Receiver
The advanced receiving and baseband processing technology is introduced to overcome the fast fading
Power Control Reducing interference, saving power and Increasing capacity
Handover Control
Impacting the capacity through applying different proportion and algorithm of soft handover
Admission Control
Admitting a connection base on the load and the admission threshold of planned capacity
Load Control Monitoring system load and adjusting the ongoing services to avoid overload
OVSF Code The Allocation of codes impacts the maximum number of simultaneous connections.
Wireless Environment
Wireless environment such as interferences, UE position and mobility etc. can influent the cell capacity
Factors affects UMTS Capacity