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UTRAN Radio Resource Management u Introduction u Handover Control u Soft/Softer Handover u Inter Frequency Handover u Power Control u Closed Loop Power Control u Open Loop Power Control u Interference Management u Load Control u Call Admission Control u Congestion Control u Packet Data Transmission u Packet Data Control u Dynamic Scheduling BTS 1 BTS 3 BTS 2 UE

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Page 1: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UTRAN Radio Resource Management

u Introductionu Handover Control

u Soft/Softer Handoveru Inter Frequency Handover

u Power Controlu Closed Loop Power Controlu Open Loop Power Control

u Interference Management

u Load Control

u Call Admission Controlu Congestion Control

u Packet Data Transmission

u Packet Data Controlu Dynamic Scheduling

BTS 1

BTS 3

BTS 2UE

Page 2: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 2Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

References

H. Holma, A. Toskala (Ed.), “WCDMA for UMTS”, Wiley, 5th edition, Wiley, 2010H. Kaaranen, et.al., “UMTS Networks: Architecture, Mobility and Services”,

Wiley, 2001. (see chapter 4)

A. Viterbi: “CDMA: Principles of Spread Spectrum Communications,” AddisonWesley, 1995.

J. Laiho, A. Wacker, T. Novosad (ed.): “Radio Network Planning andOptimisation for UMTS,“ Wiley, 2001

T. Ojanperä, R. Prasad, “Wideband CDMA for Third Generation MobileCommunication”, Artech House, 1998.

R. Prasad, W. Mohr, W. Konhäuser, “Third Generation Mobile CommunicationsSystems”, Artech House, March 2000.

3GPP standards:

u TS 25.214: “Physical Layer Procedures“ (esp. power control)u TR 25.922: “Radio Resource Management Strategies“u TR 25.942: “RF System Scenarios“

Page 3: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 3Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

u Efficient use of limited radio resources (spectrum, power, code space)u Minimizing interferenceu Flexibility regarding services (Quality of Service, user behaviour)u Simple algorithms requiring small signalling overhead onlyu Stability and overload protectionu Self adaptive in varying environmentsu Allow interoperability in multi-vendor environments

Radio Resource Managementalgorithms control theefficient use of resourceswith respect tointerdependent objectives:– cell coverage– cell capacity– quality of service

RRM – High-Level Requirements

Page 4: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 4Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

RRM – Components

Radio Resource Management

MediumAccessControl

Packet DataControl

LoadControl

HandoverControl

PowerControl

Core Network/ other RNCs

Physical layer

typically inRNC

typically inNodeB

Page 5: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 5Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Handover Control: Basics

General: mechanism of changing a cell or base station during a call or session

Handover in UMTS:u UE may have active radio links to more than one Node Bu Mobile-assisted & network-based handover in UMTS:

u UE reports measurements to UTRAN if reporting criteria (which are set bythe UTRAN) are met

u UTRAN then decides to dynamically add or delete radio links dependingon the measurement results

Types of Handover:u Soft/Softer Handover (dedicated channels)u Hard Handover (shared channels)u Inter Frequency (Hard) Handoveru Inter System Handover (e.g. UMTS-GSM)u Cell selection/re-selection (inactive or idle)

All handover types require heavy support from the UMTS network infrastructure!

Page 6: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 6Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Macro Diversity & Soft Handover (Wrap-Up)

Downlink: combining in the mobile stationUplink: combining in the base station and/or radio network controller

NodeB 1NodeB 2

UE

Page 7: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 7Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Soft/ Softer Handover

u In soft/softer handover the UE maintains active radio links to more than oneNode B

u Combination of the signals from multiple active radio links is necessary

Soft Handoveru The mobile is connected to (at least) two cells belonging to different NodeBsu In uplink, the signals are combined in the RNC,

e.g. by means of selection combining using CRCSofter Handover

u The mobile is connected to two sectors within one NodeBu More efficient combining in the uplink is possible like

maximum ratio combining (MRC) in the NodeB instead of RNC

Note:u In uplink no additional signal is transmitted, while in downlink each new link

causes interference to other users, therefore:u Uplink: HO general increase performanceu Downlink: Trade-off

Page 8: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 8Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Soft and Softer Handover in Practice

Page 9: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 9Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Soft Handover Control

• Measurement quantity, e.g.EC/I0 on CPICH

• Relative thresholds dadd &ddrop for adding & dropping

• Preservation time Tlink toavoid “ping-pong” effects

• Event triggered measurementreporting to decreasesignalling load

MeasurementQuantity

Link to 1 Link to 1 & 2 Link to 2 time

CPICH 1

CPICH 2

ddrop

NodeB 1 NodeB 2

dadd Tlink

UE

soft handoverarea

Page 10: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 10Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Soft Handover – Simulation Results

Soft handover significantly improves the performance, but …

0%

5%

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5 15 25 35 45 55

Offered Traffic [Erlang per site]

Out

age

Pro

babi

lity

(Blo

ckin

gan

dD

ropp

ing)

1 linkmax 2 SHO linksmax 4 SHO linksmax 6 SHO links

Page 11: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 11Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Soft Handover – Simulation Results II

… the overhead due to simultaneous connections becomes higher!

0

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1 2 4 6

Max. Active Set Size

Mea

nN

umbe

rofA

ctiv

eLi

nks

Page 12: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 12Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Handover f1 Û f2 always neededbetween layers

Hierarchical cell structure (HCS)

Macro Micro Macro

f1

f2

f1

Handover f1 Û f2 neededsometimes at hot spot

Hot-spot

f1

f2f1 f1

Hot spot

Inter-Frequency Handover

u Hard handoveru Inter-frequency measurements of target cell needed in both scenariosu Mobile-assisted handover (MAHO)

u slotted (compressed) mode for inter-frequency measurements to find suitabletarget cell

u also supports GSM system measurementsu Database assisted handover (DAHO)

u no measurements performed on other frequencies or systemsu use cell mapping information stored in data base to identify the target cell

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UMTS Networks 13Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Cell Selection/Re-selection

u “Handover” when UE is idle or there is noactive connection between UE andUTRAN

u Goal: find a suitable cell to camp on

u The cell to camp on is chosen by the UEon measured link quality Q, e.g. EC/I0 onCPICH (after cell-search)

u Cell re-selection with hysteresis H toavoid “ping-pong” effects

u Additional offsets for Q on differentfrequencies, e.g. to support hierarchicalcells

u Mapping functions for Q between UMTSand GSM to support priorities

u Cell selection and re-selection mainlyperformed internally in UE, but controlledby UTRAN with broadcast of neighbourcell frequencies and control parameters(hysteresis, mapping, etc.)

NodeB 1NodeB 2

UE

Q1 > QminQ1 > Q2

Cell selection border

Q1Q2

Page 14: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 14Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Power Control: Basics

Controls the setting of the transmit power in order to:u Keep the QoS within the required limits, e.g. data rate, delay and BERu Minimise interference, i.e. the overall power consumption

Power control handles:u Path Loss (Near-Far-Problem), Shadowing (Log-Normal-Fading) and

Fast Fading (Rayleigh-, Ricean-Fading)u Environment (delay spread, UE speed, …) which implies different

performance of the de-interleaver and decoder

Uplink: per mobileDownlink: per physical channel

Three types of power control:u Inner loop power controlu Outer loop power control (SIR-target adjustment)u Open loop power control (power allocation)

Downlink power overload control to protect amplifieru Gain Clipping (GC)u Aggregated Overload Control (AOC)

Page 15: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 15Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Near-Far Problem:• Spreading sequences are not orthogonal

(multi-user interference)• Near mobile dominate• Signal to interference ratio is lower for far

mobiles and performance degrades

The problem can be resolved throughdynamic power control to equalize allreceived power levels

AND/OR

By means of joint multi-user detection

Near-Far Problem – Power Control (Wrap-Up)

NodeB

UE 1

UE 2

Page 16: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 16Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Closed Loop Power Control

u Closed loop power control is used on channels, which are established in bothdirections, such as DCH

u There are two partsu Inner Loop Power Control (ILPC): receiver generates up/ down

commands to incrementally adjust the senders transmit poweru Outer Loop Power Control (OLPC): readjusts the target settings of the

ILPC to cope with different fading performance

NodeB

UE

control command: Up/DownExample: Uplink Closed Loop Power Control

Inner Loop(1500 Hz)

SIR > SIRtarget ?

Outer Loop(£ 100Hz)

target adjustmentBLERtarget

RNC

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UMTS Networks 17Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Impact of Power Control

-8

-6

-4

-2

0

2

4

6

0 0.2 0.4 0.6 0.8 1

pow

er/

fadi

ng[d

B]

time [sec]

2

3

4

5

6

7

8

0 0.2 0.4 0.6 0.8 1

E b/N

0[d

B]

speed = 3 km/h

Example: UMTS Closed Loop Power Control in the slow fading channel

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UMTS Networks 18Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Power Control Performance

5

5.5

6

6.5

7

7.5

0 20 40 60 80 100 120Velocity [km/h]

Requ

ired

UL

SIR

[dB]

PedAVehA

SIR requirement strongly depends on the environment (due to differentfast fading conditions – Jakes models)Þ outer loop power control needed to adapt SIR

Page 19: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 19Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Open Loop Power Control

u Open loop power control is used on channels that cannot apply closedloop power control, e.g. RACH, FACH

u The transmitter power is determined on the basis of a path loss estimatefrom the received power measure of the opposite direction

u To avoid excessive interference, probes with incremental power stepsuntil a response is obtained: “power ramping”

NodeB

UE

Open Loop Power Control on RACH

Page 20: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 20Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

CDMA Overload

• CDMA systems tend tobecome unstable– More traffic increases the

interference– More interference requires

higher power– More power increases the

interference …

• Methods are required to limitthe system load– Restrict the access to the

system– Overcome overload

situations

Page 21: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 21Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Interference in CDMA Networks

u Frequency reuse factor is oneu CDMA is subject to high multiple access interferenceu Soft capacity: CDMA capacity (e.g. number of users) determined by the

interference is softu Handling of interference is the main challenge in designing CDMA networks

Interference Problem

Inter-Symbol Interference (ISI) Delayed components from thesame user signal interfere due tomultipath propagation

Multiple Acces Interference – MAI Different user signals interferedependent on the access scheme

Intra-Cell Interference Interference caused by the usersbelonging to same cell

Inter-Cell Interference Interference caused by the usersbelonging to neighbor cells.

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UMTS Networks 22Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Cell Breathing

u CDMA systems: cell size depends on the actual loadingu Additional traffic will cause more interferenceu If the interference becomes too strong, users at the cell edge can no

more communicate with the basestationu CDMA interference management

u Restriction of the users access necessaryu Cell breathing makes network planning difficult

Example: cell brething with increasing traffic

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UMTS Networks 23Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Cell Breathing (contd.)

coveragelow load

coveragemedium load

coveragehigh load

Coverage depending on load: load causes interference, which reduces thearea where a SIR sufficient for communication can be provided

shadowed area: connection maybe lost

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UMTS Networks 24Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Coverage vs. Capacity

u Capacity depends on:u QoS of the users (data rate, error performance (bit-error-rate))u User behaviour (activity)u Interference (out of cell)u Number of carriers/ sectors

u Coverage (service area) depends on:u Interference (intra- & inter-cell) + noiseu Pathloss (propagation conditions)u QoS of the users (data rate, error performance (bit-error-rate))

u Thus, trade-off between capacity and coverage

Page 25: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 25Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Coverage vs. Capacity

u Downlink limits capacity while uplink limits coverageu Downlink depends more on the load (users share total transmit BS power)

0 20 40 60 80 100 120 140 160 180 2000

0.5

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¬Downlink

Uplink®

Erlangs (2% GOS)

Max

imum

cell

radi

us(k

m)

13kbps circuit switched service capacity versus maximum cell radius

Page 26: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 26Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Example of Coverage and Best Server Map

Application: RF engineering (cell layout)Legend: violet indicates high signal level, yellowindicates low level

cove

rage

map

Application: HO decisionLegend: color indicates cell with bestCPICH in area

best

serv

erm

ap

Page 27: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 27Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Load Control: Basics

u Main objective:u Avoid overload situations by controlling system loadu Monitor and controls radio resources of users

u Call Admission Control (CAC)u Admit or deny new users, new radio access bearers or new radio

linksu Avoid overload situations, e.g. by means of blocking the requestu Decisions are based on interference and resource measurements

u Congestion Control (ConC)u Monitor, detect and handle overload situations with the already

connected usersu Bring the system back to a stable state, e.g. by means of

dropping an existing call

Page 28: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 28Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Resource Consumption

• Service/BLER-dependentresource consumption

• Uplink example:– Service I: Voice

Rb = 12.2kbps, Eb/Nt = 5dBaI = 0.99%

– Service II: DataRb = 144kbps, Eb/Nt = 3.1dBaII = 7.11%

• In downlink there is additionaldependency on the locationof the user– Cell center ® low

consumption– Cell edge ® high

consumption

a

Page 29: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 29Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Admission/ Congestion Control

Basic algorithm• Admission control is triggered

when load ³ thr_CAC– New users are blocked– Existing users are not

affected as long as load <thr_ConC

• Congestion Control istriggered when load ³thr_ConC– Reduce consumption of one

or several users– Simple action: drop the user– Repeat until load <

thr_ConC

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UMTS Networks 30Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

0%

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50%

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ckin

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obab

ility

thr_CAC = 50%thr_CAC = 75%thr_CAC = 90%

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Offered Traffic [Erlang per s ite]

Dro

ppin

gPr

obab

ility

thr_CAC = 50%thr_CAC = 75%thr_CAC = 90%

Tradeoff between blocking and droppingExample: 64k per user, urban

Call Admission Control: Simulation Results I

Page 31: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 31Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

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90%

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Offered Traffic [Erlang per site]

Cell

Load

ing

thr_CAC = 50%thr_CAC = 75%thr_CAC = 90%

Cell load depending on CAC thresholdExample: 64k per user, urban

Call Admission Control: Simulation Results II

Page 32: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 32Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Packet Data Control: Channel Switching

u Flexibility of packet servicesu Asymmetrical data ratesu Very low to very high data ratesu Control information/user information

u Efficient transmission making good use of CDMA characteristicsu Dedicated channel (DCH)

u Minimise transmission power by closed-loop power controlu Independence between uplink and downlink capacity

u Common channelu Random access in the uplink (RACH)u Dynamic scheduling in the downlink (FACH)

u Adaptive channel usage depending on traffic characteristicsu Infrequent or short packets Þ Common channel (Cell_FACH)u Frequent or large packets Þ Dedicated channel (Cell_DCH)u No packet transmission Þ UE “stand by” modus (URA_PCH)

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UMTS Networks 33Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

CELL_DCH CELL_FACH CELL_DCH

Page Download Time Reading Time

DCH Active Time“Chatty Applications”

Channel Switching – Example

u Example: Web serviceu Chatty apps.: keep alive message, stock tickers, etc.

(e.g. 100 bytes every 15 sec)u Second stage: when no activity in CELL_FACH then switch to URA_PCH

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UMTS Networks 34Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

· Power Control:– Balances user received quality (BLER, SIR)– Users at cell center get less share of BTS

transmit power assigned than at cell edge– Occurrence of power overload

· Rate Adaptation:– Transmit power ~ data rate– Users at cell edge get lower data rate assigned

than at cell center– Reduces also power overload

· On DCH combination of power control andrate adaptation

– Rate assignment at begin of a transmissionbased on load and user location

– Rate adaptation when ongoing transmissionaccording to power consumption and overload

– Based on RRC-signaling (time horizon:100msec … 10sec)

NodeB

UE 1

UE 2low data rate

area

high data ratearea

Power Control vs. Rate Adaptation

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UMTS Networks 35Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Rate Adaptation Performance

Rate adaptation significantly improves the RRM performance on DCH.

UMTS_urban, 50 kByte

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abili

ty

384k64kadaptive

UMTS_urban, 50 kByte

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8

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Cell Throughput [kBit/sec]M

ean

Del

ay[s

ec]

384k64kadaptive

Page 36: UTRAN Radio Resource Management - Startseite TU … · UTRAN Radio Resource Management uIntroduction ... (Ed.), “WCDMA for UMTS”, Wiley, 5th edition ... by UTRAN with broadcast

UMTS Networks 36Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

Dynamic Scheduling

• “Statistical multiplexing” of datapackets from different dataflows on one shared medium,e.g. on DSCH or HSDPA

• Scheduling with time-horizon of2msec … 1sec

• Optimised usage of radioresources

• Exploitation of the short-termvariations on the radiochannels (opportunisticscheduling)

• Can provide certain degree ofQoS

NodeB

Sample Flow

Flow #1

Flow #3

UE 3

UE 2

UE 1

Flow #2