Allocation of Radio Resources to packet-switched traffic in GPRS-like networks

Group 896GPRS Radio Resource Management

Allocation of Radio Resources to packet-switched traffic in GPRS-

like networks By group 896

Supervisors:

Hans Peter SchwefelPatrick Eggers

Students:Xin ZhouJimena Llorente MartinezDevendra PrasadFrançois DelawardeGwénaël CogetHaibo Wang


Project Description:

•Analyze existing GPRS radio resource management strategies.

•Define scenarios and input parameters, for which an algorithm for the assignment of resources to packet-switch traffic will be developed.

•Evaluate/validate the algorithm in simplified simulation models.


GPRS Introduction:

• Reuse the existing GSM infrastructure

• Introduce packet-switched routing functionality• Better data transfer rates (multislot capabilities)• Low cost and connectivity-oriented

• Migration Path to 3G Networks


Comparison between GSM/GPRS


GPRS architecture


GPRS protocols stack

Um Gb GnMS

BSS

SGSN GGSN GiTE R

LLC

SNDCP GTP GTP

GSM RF

RLC

LLC Relay

BSSGP

MAC

L1

FrameRelay

L1

FrameRelay

BSSGP

L2

L1

IP

L2

L1

IP

UDP UDP

SNDCP

LLC

RLC

MAC

GSM RF

L2 L2

L1 L1

IP

PPP

PCMCIA/ IrDA

PPP

PCMCIA/ IrDA

IP

IP

TCP/UDP

TCP/UDP

Appli

Um Gb GnMS

BSS

SGSN GGSN GiTE R

LLC

SNDCP GTP GTP

GSM RF

RLC

LLC Relay

BSSGP

MAC

L1

FrameRelay

L1

FrameRelay

BSSGP

L2

L1

IP

L2

L1

IP

UDP UDP

SNDCP

LLC

RLC

MAC

GSM RF

L2 L2

L1 L1

IP

PPP

PCMCIA/ IrDA

PPP

PCMCIA/ IrDA

IP

IP

TCP/UDP

TCP/UDP

Appli


GPRS Protocols:

GSM-RF layer: Reuse of GSM multiple access methods (TDMA/FDMA)

MAC layer: Multiplexing Scheduling Contention resolution (UL)

RLC layer: Segmentation/Re-assembly ARQ


Radio Resource Management (RRM)

• Introduction-Functions

• GSM/GPRS establishment• GSM/GPRS call maintaining• GSM/GPRS release

-Dedicated/Shared channels

• Best Effort Strategy <-> Our Proposed RRM Strategy• Resource Allocation• Reassignment• Scheduling


Best Effort : Access Control


Best Effort : Resource Assignment


Best Effort : Round Robin Scheduling


Proposed Strategy : Access Control


Proposed Strategy : Resource Assignment

TS

G GTS1

gTBFincoG

gTBFincoavailable GTS

GTS

min

min


Proposed Strategy : Scheduling

Example:

TBF G=3 30%TBF G=6 60%TBF G=1 10%

GTBFnutilizatio TS

GTS /


Simulation ModelOnly downlink traffic in 1 micro-cell, Transmission time step was set to 20ms(1 RLC block)

Cell Hand-over: NoPower Control: NoReuse Pattern: 1/3Cell Radius: 500m Frequency Hopping: Ideal Random FH

Mobility User Distribution: Uniform DistributedUser Moving: TU3 Mobility Tracking: No

Mobile Phone

Always in “active” stateCapable of using 1~4 Time Slot


Radio Channel Model

(1) Path Loss --- global mean power(2) Slow Fading --- local mean power(3) Fast Fading --- instantaneous power

(1) Path loss

(2) Slow fading

(3) Fast fading


C/I --- BLER Assumption

Network-level simulator based on link-level simulator TU3 Model Reuse pattern 1/3 Ideal Frequency Hopping Fast fading is considered Mean BLER

C/I

BLER

Mapping FunctionC/I

CS_x

BLER


C/I Generation

1. Mean C/I --- Path Loss and Reuse Pattern

Path Loss PDF(r)

pdf(r)=k*r, 15m<r<500m


0: Investigated Cell

1~6: Co-channel Cell

D: Reuse Distance

R: Cell Radius

r: MS-BTS Distance1

2

3

4 5

60

D

R

r

Reuse Pattern C/I Calculation


PDF(r) Mean C/I


2. C/I per MS --- Shadowing Effect

Lognormal Distribution

( Mean C/I, σ )

C/I for Each Mobile


Coding Scheme Selection

CIR 0~5 CS1CIR 6~9 CS2CIR 10~16 CS3CIR 16~30+ CS4

Throughput vs. C/I


BLER Generation

Random( ) > BLER Block Correct

RandomSeed

Random( ) < BLER Block Erroneous

C/I

CS_x

BLER Generation

MappingTable


Frequency Correlation Function


Path Loss

Shadowing Effect

MS ID

Distance Generation

Mean C/I

C/I per MS

CS_x Selection

BLER Mapping

RandomSeed

Block CorrectOr Erroneous

pdf(r)


Traffic ModelThe definition of a GPRS session in our model:

Packet 1 Packet 2 Packet 3

Packet Call1 Packet Call 2 Packet Call 3

Session1 Session2 Session3

Time[ s]

Time[ m]

Time[ h]

Session3


Voice

Voice

Voice

Data

Data

Data

Traffics: Mixture of GSM Voice calls and GPRS Data sessions

Each session/call was randomly assigned to a Mobile Station(MS), where each MS only represent a propagation condition(C/I) corresponding to a certain distance from the BTS.


VOICE

DATA

DATA

VOICE

Session size(# bits)

Traffic Generation Method


1. 1 session assigned to 1MS corresponding to a certain radio condition

2. 1MS can have multiple sessions based on radio condition

3. All the sessions are in the BSS to be transmitted

4. No Handover

5. Based on one Cell Configuration

6. No uplink simulation

7. Higher layers(TCP/IP, LLC) is not considered

8. ARQ for uplink is not considered

Model Assumptions


Parameters Stochastic Process

ParameterValues

GSM Arrival Time Exponential

Holding Time Exponential

GPRS Arrival Time Exponential

Session Size Geometrical P=0.5Object Size = 50 KbytesMean Session Size=100Kbytes

GSM

1/ 120secGSM

GPRS

Parameters List

Traffic Load = 5 ~ 29 ErlangGSM Voice: Traffic_Load*70%;GPRS Data: Traffic_Load*30%


Mapping GPRS session to RLC blocks

Session size (bits)

GPRS SESSION

time

time

CS-x

RLC blocks

arrival time

Mapping to block

Because in simulation the transmission was working on RLC block level.


Simulator Implementation

•General Structure – Object Oriented

•Time-Driven and Event-Motivated Simulation Process – main() and traffic_Model

•Propagation Concerned Object – MS and air_Interface

•Proposed RRM features VS “Best Effort”

•Proposed RRM Object – BSS, FIFO_Priority and resource_Pool


General Structure – Object Oriented

Access ();TS assignment (); TBF assignment ();

Scheduler ();Resource Update ();

BSS

Traffic Generator ( );

Traffic Model

Transmission ( );

Air Interface

Update Propagation ( );

Mobile Station

Output ( );

Trace

Push ( );Pop ( );

FIFO Priority

Add GSM ();Add GPRS ();

Release GSM ();Release GPRS ();

Scheduled ();

Resource Pool


Time-Driven and Event-Motivated Simulation Process

Traffic ModelT, Length, MS T, Length, MS T, Length, MSGSM events Chain

T, Length, MST, Length, MST, Length, MSGPRS events Chain

Simulation Process T<T_EndT_nex t_Frame<T_next_Event?

Transmission

Scheduling

Resource Update

Access

Timer Update

Yes No

Output Trace


Propagation Concerned Object

– MS and airInterface

MS:Assign C/I, CS, BLER to each mobile station, the process was carried on during the initialization step.

Air Interface:Frame[TRX][TS];During each RLC block transmission, generate a Random “ 0” or “1” representing “correct” or “error” according to the BLER for the MS which occupy current TS/Block.


Proposed RRM vs “Best Effort”

Best Effort Proposed RRM

Access Queuing FIFO Graded FIFO

When access queue full and new request come

Block the new request

Block the last one in queue and push new one into queue

Scheduling Round-Robin Graded Round-Robin

Resource AllocationWhen coming GPRS session has to share a TS with existing ones

Depending on how many TFI already in a TS

Depending on the sum of grades in a TS

Voice Pre-emption Yes Yes


Proposed RRM Object - 1– BSS, FIFOPriority and resourcePool

Resource Pool: store a table for all the TRX-TS.

TS data structure

Session ID, GradeTS Type 1: GSM

Session ID, GradeSession ID, GradeSession ID, GradeTS Type 2: GPRS

Pool[TRX][TS]

TS0 TS1 TS2 TS3 TS4 TS5 TS6TRX0TRX1TRX2TRX3


Proposed RRM Object – 2

FIFO_Priority:The GPRS access queue based on grade. Queue length = 7

Session ID, PriorityAccess Queue Session ID, Priority Session ID, Priority

Priority: High Low

Priority = C/I of each session according to its assigned Mobile Station

BSS will always select the first one(highest priority) in queue to assign resources.

For two sessions with the same C/I, the new one will be put after the old one(FIFO).


Proposed RRM Object – 3BSS:Manage all the convoyed sessions.

Session ID, GradeGSM Sessions Session ID, Grade Session ID, Grade

Session ID, GradeGPRS Sessions Session ID, Grade Session ID, Grade

Access Control (Voice Pre-emption) TS/TBF assignment Scheduling Correctly-received RLC blocks counting Release finished GSM/GPRS or drop GPRS with max retransmissions. TS re-assignment: after every transmission time step, try to raise

the TS numbers for each GPRS session to 4.


Performance Evaluation

• Simulator validation

• Simulations parameters

• Simulations results

• Future work


Simulator Validation

• RRM strategies: use of output functions and breakpoints to check the behaviour of access queue, choice of TRX/TS, scheduler, reassignment, pre-emption…

• Propagation /Transmission: comparison between the curve used to map C/I, BLER and throughput and the one obtained

• Traffic Model: comparison between input parameters and traffic generated (number of sessions per hour, call length, session size…)


Simulations ParametersParameter Name VALUE

Simulated Duration 4 hours

Traffic Load (TL) from 5 to 29 "Erlangs"

Number of simulations (per TL) 15

TRXS 4 (32 TSs)

Number of signalling channels 4

Number of traffic channels 28

Maximum number of multiplexed sessions per TS

32

Number of Mobile Nodes 30

Multi-slot capacity of Mobile 4TSs

Mean GSM call duration 120s

Mean GPRS session size 100kB

Access queue size 7 sessions

Maximum number of block retransmission

25


Simulations Results

• Throughput per Cell Vs. Traffic Load

• Throughput per Session Vs. Traffic Load

• Access Delay Vs. Traffic Load

• Blocking Rate GPRS Vs. Traffic Load

• Throughput per Session Vs. C/I


Throughput per Cell


Throughput per Session


Throughput Per Session Vs. C/I


Mean access delay


Blocking Rate GPRS


Future Work

• Consideration of QoS requirements (traffic model with different types of service)

• Consideration of Uplink

• Investigation of higher layers


Thank You !


BackUp: for Q&A

1) In traffic generator while calculating the mean GPRS holding time:We use average data speed: 25kbps.Which comes from some simulation output on different traffic load.

2)

Allocation of Radio Resources to packet-switched traffic in GPRS-like networks

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