Impact of gprs on existing gsm services
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Helsinki University of Technology Networking Laboratory. Impact of GPRS on existing GSM services. Juan Ventura. Supervisor: Professor Raimo Kantola Instructor: Ph. D. Peng Zhang. Table of contents.  Background  GPRS service

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Impact of GPRS on existing GSM services

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Helsinki University of Technology

Networking Laboratory

Impact of GPRS on existing GSM services

Juan Ventura

Supervisor: Professor Raimo Kantola

Instructor: Ph. D. Peng Zhang

Table of contents

 Background

 GPRS service

 Impact on existing GSM services

 Simulation model

 Simulation results

 Conclusions

 Future work

Background (I)

 Impressive growth of Internet

 Success of mobile networks



 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

Background (II)

 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

 CDPD, GPRS, etc

General Packet Radio Service (GPRS) for GSM

GPRS - Impact on GSM network

 New network nodes

 SGSN, GGSN, backbone network, firewalls, border gateways

 Changes in NSS and BSS

 GPRS register in HLR

 New interfaces between “old” and “new” nodes

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

 Impact on network planning

 New resources for GPRS

 Impact on existing GSM services

Subject of

the Thesis

Impact on existing GSM services

GPRS-Resource management(I)

 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

2. Sharing current spectrum between GPRS and GSM



GPRS-Resource management(II)

 Channel allocation techniques in a GPRS/GSM network:

1. Complete Partitioning

2. Complete Sharing

3. Partial Sharing

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

Reduction of Capacity&Quality of existing GSM services

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





2. Blocking effects - reduction of capacity (GoS)

Network planning problem

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

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 complexity

high cost, scarce spectrum

high cost, frequency re-plan

easy, unacceptable handover failure

easy, cheap, increase in call blocking

Handover prioritization schemes

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

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)

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



Simplified case study of

a GPRS/GSM network


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

  • (...)

Simulation (II)

 Evaluation criteria:

 Probability of new call blocking

 Probability of handover failure

 Carried traffic (network capacity)

 Channel utilization

 Two different scenarios for the microcell:

  •  Basic microcell scenario

  •  Overlaid macrocell/microcell scenario

    • Fast handovers carried by the umbrella macrocell

    • Macrocell overlaying 7 microcells

Simulation results (I)

  • 1. Basic microcell scenario:

  •  Non-prioritized scheme (NPS):

    • Effects of increasing Ngprs (growth of subscriber numbers)

almost negligible


considerable regarding Phf

-handover schemes-

Simulation results (II)

  •  Reserved channel scheme (RCS) Ngprs = 4

    • Effects of increasing Nho



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

Simulation results (IV)

  •  Sub-rating scheme (SRS) Ngprs = 4

    • Effects of increasing Nsub

 Best handover performance without degrading Pnb

 Highest implementation complexity

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

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)

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

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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