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Optimisation of Softer Handover in UMTS Network

Optimisation of Softer Handover in UMTS Network. Antti Hassinen TeliaSonera Finland, Sonera Mobile Networks Oy. Supervisor: Professor Sven-Gustav Häggman Instructor: Kari Ahtola, M.Sc. Agenda. Introduction Overview of UMTS network and handover types Soft & softer handover

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Optimisation of Softer Handover in UMTS Network

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  1. Optimisation of Softer Handover in UMTS Network Antti Hassinen TeliaSonera Finland, Sonera Mobile Networks Oy Supervisor: Professor Sven-Gustav Häggman Instructor: Kari Ahtola, M.Sc.

  2. Agenda • Introduction • Overview of UMTS network and handover types • Soft & softer handover • Optimisation work & results • Summary & future work

  3. Introduction • Thesis was made for Sonera Mobile Networks Oy in the Mobile System Planning department • Objective was to gather softer handover knowledge, get information how softer handover parameters work and optimise softer handover • Means: Literature, 3GPP specifications, IEEE publications and optimisation measurements

  4. Node B RNC USIM Node B ME Node B RNC Node B UMTS network architecture Iu Uu CS domain UE = User Equipment ME = Mobile Equipment USIM = UMTS SIM Iub Iu CS MSC / VLR Circuit switched GMSC HLR Cs Iur Iu PS SGSN GGSN Packet switched PS domain External Networks UE CN UTRAN UTRAN = UMTS Terrestial Radio Access Network RNC = Radio Network Controller

  5. Handover types • Soft Handovers (SHO): • Soft and softer handover • Hard Handovers: • Inter-frequency handover • Inter-system handover

  6. Soft and Softer Handover (1/2) Soft handover Softer handover RNC RNC Node B 2 Node B 1 Sector 1 Sector 2

  7. Soft and Softer Handover (2/2) • Soft Handover • Uplink: Selection Combining in RNC • Downlink: Maximum Ratio Combining in UE • Softer Handover • Maximum Ratio Combining both in Node B and UE • Advantages of SHO • Continuos handovers • SHO gain (reception of same signal by to Node Bs) • Avoid near-far problem • Disadvantages • SHO overhead (More resources needed than in a single link connection)

  8. Handover procedure • Measurements (e.g. CPICH Ec/N0, RSCP or downlink pathloss ) • Filtering • Reporting (Periodic or Event triggered) • Events add, drop, replace, change best, above threshold, below threshold • Soft handover algorithm • Execution CPICH = Common Pilot Channel RSCP = Received Signal Code Power

  9. Soft Handover Algorithm Maximum active set size = 2

  10. Factors effecting Softer Handover • Parameters • Addition, Drop & Replacement windows • Addition, Drop & Replacement timers • Maximum Active Set Size • CPICH Ec/N0 Filter Coefficient • Active Set Weighting Coefficient • Other factors • Network topology (macro or micro sites) • Placement of antennas • Radio environment

  11. Optimisation of Softer Handover • Goal for optimisation: Minimise SHO overhead and UE transmission power without lowering quality • Measurement method: • Field measurements by drive tests • Logging from the UE • Key Performance Indocators: • SHO overhead • number of SHO events (i.e. signalling load) • UE transmission power (SHO gain) • Quolity indicators: BLER, Dropped calls & Failed call attempts

  12. Measurement Results (1/3) • Measurement results for CPICH Ec/N0 filter coefficient • Measurement results for active set weighting coefficient

  13. Measurement Results (2/3) • Measurement results for addition window • Measurement results for drop window

  14. Measurement Results (3/3) • Performance comparison between initial and optimised values

  15. Summary and future work • Parameters CPICH Ec/N0 filter coefficient, active set weighting coefficient, addition window and drop window have the biggest effect, timers little effect • Optimisation minimised SHO overhead • No clear gain • Future work: • Testing with other services, radio enviroment (macro, micro), user speeds • Apply optimisation also to soft handover and soft - softer handover

  16. The End • Thank you! • Questions

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