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Impact of GPRS on existing GSM services

Juan Ventura

Supervisor: Professor Raimo KantolaInstructor: Ph. D. Peng Zhang

Helsinki University of TechnologyNetworking Laboratory

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Table of contents

Background

GPRS service

Impact on existing GSM services

Simulation model

Simulation results

Conclusions

Future work

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Background (I)

Impressive growth of Internet Success of mobile networks

wireless Internet

Current cellular networks

circuit switching

Highly inefficent utilization of radio resources

Service expensive time-oriented charging

Slow data rates

Inefficiencies of circuit-switched mobile networks for transporting bursty data traffic

Forburstydata

traffic

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Packet switching techniques in wireless networks

Statistical multiplexing optimized usage of resources

Multi-slot operation higher data rates

Shorter access times

Cheap service volume based charging

General Packet Radio Service (GPRS) for GSM

Background (II)

CDPD, GPRS, etc

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New network nodes

Changes in NSS and BSS

Impact on network planning

SGSN, GGSN, backbone network, firewalls, border gateways

GPRS register in HLR

New interfaces between “old” and “new” nodes

Protocol control unit (PCU) and channel control unit (CCU)

New resources for GPRS

GPRS - Impact on GSM network

Impact on existing GSM services Impact on existing GSM servicesSubject of the Thesis

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Two alternatives when GPRS introduction:

1. Allocating new spectrum for GPRS

High investments in new cell sites or new TRXs

Waste of unused GSM capacity

Frequency re-plan

2. Sharing current spectrum between GPRS and GSM

Dedicating GSM traffic channels to GPRS only

Dynamic sharing between GPRS and GSM, with GSM priority

GPRS - Resource management

(I)

2. Sharing current spectrum between GPRS and GSM

three techniques

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1. Complete Partitioning

2. Complete Sharing

3. Partial Sharing

• Always gives the best GPRS performance• Allows more flexibility in catering to the QoS requirements• Best able to adapt to a changing network load profile

PARTIAL

SHARING

Channel allocation techniques in a GPRS/GSM network:

1. Complete Partitioning

2. Complete Sharing

3. Partial Sharing

Reduction of Capacity&Quality of existing GSM services

GPRS - Resource management

(II)

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Impact on existing GSM services (I)

Effects of GPRS partial sharing implementation on existing GSM services:

1. Interference effects - reduction of quality (QoS)

The interference probability of GSM services increases

2. Blocking effects - reduction of capacity (GoS)

Less traffic channels available for GSM services Difference between new calls and handovers

Handover performance major criterion in a GSM network

Guarantee the QoS and GoS of existing GSM services at the same time that having an effective GPRS service

Network planning problem

2. Blocking effects - reduction of capacity (GoS)

otherstudies

Thesisgoal

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Impact on existing GSM services

(II)

Several ways of counteracting the reduction of capacity:

New frequency assignment strategies

New bandwidth for the operators

New TRXs without allocating new bandwidth

For future UMTS networks, handover between GPRS and UMTS

Queueing new call attempts

(.....)

Handover prioritization schemes

high cost, scarce spectrum

high cost, frequency re-plan

easy, unacceptable handover failure

easy, cheap, increase in call blocking

Improving GoS of existing GSM services at the same time that prioritize handovers over new calls

Handover prioritization schemes

high complexity

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Impact on existing GSM services

(III)

Handover prioritization schemes:

1. Non-prioritize scheme (NPS)

Both new calls and handovers are handled without preference Most typically employed by cellular technologies

2. Reserved channel scheme (RCS)

Reserving a number of channels exclusively for handovers 2.1. Pre-reservation 2.2. Post-reservation

3. Queueing priority scheme (QPS)

Existence of handover area

3.1. FIFO priority queueing 3.2. Measurement-based priority queueing (MBP)

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Impact on existing GSM services

(IV)

Handover prioritization schemes:

4. Sub-rating scheme (SRS)

Sub-rating an existing call to accommodate a handover Penalty: reduction of voice quality

5. Hybrid schemes

Combination of the aboved schemes

•Evaluate the performance degradation of GSM traffic when GPRS partial sharing implementation•Evaluate the effectiveness of these handover schemes for improving handover performance

Researchproblem

Practicalapproach

Simplified case study of a GPRS/GSM network

SIMULATION

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Simulation (I)

Simulation methodology event-driven simulator

Simulation library developed in C++

System model:

Single cell microcell with 4 TRXs• 3 signalling channels• 29 traffic channels

Uplink procedure resource contention/reservation

Fixed channel allocation

Traffic models

Mobility models

(...)

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Evaluation criteria:

Probability of new call blocking

Probability of handover failure

Carried traffic (network capacity)

Channel utilization

Simulation (II)

Two different scenarios for the microcell:

Basic microcell scenario

Overlaid macrocell/microcell scenario

•Fast handovers carried by the umbrella macrocell•Macrocell overlaying 7 microcells

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Simulation results (I)

1. Basic microcell scenario:

Non-prioritized scheme (NPS):•Effects of increasing Ngprs (growth of subscriber numbers)

almost negligible unacceptable

considerable regarding Phf-handover schemes-

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Simulation results (II)

Reserved channel scheme (RCS) Ngprs = 4

•Effects of increasing Nho

RC

S-p

reR

CS

-pos

t

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Simulation results (III)

Queueing priority scheme (QPS) Ngprs = 4

•Two different queueing policies: FIFO and MBP•Two degradation intervals for comparison purposes

Performance of both queueing schemes is roughly the same Better performance than RCS but more implementation complexity

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Simulation results (IV)

Sub-rating scheme (SRS) Ngprs = 4

•Effects of increasing Nsub

Best handover performance without degrading Pnb Highest implementation complexity

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Simulation results (V)

2. Overlaid macrocell/microcell scenario:

•Ngprs = 4 •Aoff = 21Erlangs Phf = Pnb = 2% (rush hour - worst case situation)

Overall teletraffic performance is enhanced Multiple layers of cells in current GSM networks

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Conclusions (I)

Particular results for a microcell with 4 TRXs:

For Ngprs =1, 2 (“low” GPRS penetration factor):•Capacity reduction of GSM traffic is almost negligible•Benefit of reserving additional channels to GPRS users

For Ngprs=4 (“medium” GPRS penetration factor):•Capacity reduction of GSM traffic is considerable, but can be overcome to a certain extent by using handover schemes

•An umbrella macrocell improves the overall performance

For Ngprs=6, 8 (“high” GPRS penetration factor):•Capacity reduction of GSM traffic is excessive and an umbrella macrocell is not enough to ensure sufficient capacity

•Capacity expansion is necessary (new TRXs or new cell sites)

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Conclusions (II)

General conclusions:

Ngprs GSM capacity degradation

Depending on the type of cell and the value of Ngprs different handover schemes to be used

Selection of a particular handover prioritization scheme tradeoff between its implementation complexity and performance

•NPS, RCS When implementation cost is a major concern

•SRS Best handover performance and highest network capacity

•QPS Best choice in terms of hand. performance and implem. complexity

Significant growth of GPRS users capacity expansion compulsory

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Future work

Performance study of both services (GSM and GPRS) using different handover prioritization schemes

Performance tradeoff between both services

Different scenarios

Changes required in the simulator:

Accurate GPRS traffic model (e.g. ETSI WWW traffic model)

More complex simulation environment

Less restrictive assumptions

more validation for the results

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Questions?