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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 services Subject 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, withGSM 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 handovers2.1. Pre-reservation2.2. Post-reservation

3. Queueing priority scheme (QPS)

� Existence of handover area3.1. FIFO priority queueing3.2. 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 trafficwhen 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 unacceptableconsiderable regarding Phf

-handover schemes-

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Simulation results (II)

� Reserved channel scheme (RCS) Ngprs = 4•Effects of increasing Nho

RC

S-pr

eR

CS-

post

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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 umbrellamacrocell 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 Ngprsdifferent handover schemes to be used

� Selection of a particular handover prioritization schemetradeoff 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 assumptionsmore validation

for the results

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