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 Optimisation work & results Summary & future work 09/04/2019

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 09/04/2019

UMTS network architecture Iu Uu CS domain Iub Node B RNC Iu CS MSC / VLR GMSC Circuit switched USIM ME Cs HLR Iur Iu PS SGSN GGSN Packet switched PS domain External Networks UE UTRAN CN UE = User Equipment ME = Mobile Equipment USIM = UMTS SIM UTRAN = UMTS Terrestial Radio Access Network RNC = Radio Network Controller Painottuu UE & UTRAN, Node B vastaa GSM tukiasemaa ja RNC tukiasemaohjainta. Joitakin eroja 09/04/2019

Handover types Soft Handovers (SHO): Hard Handovers: Soft and softer handover Hard Handovers: Inter-frequency handover Inter-system handover SHO: Uuden tyyppinen händäri yhteys on useampaan kuin yhteen tukiasemaan samaan aikaan. tarkemmin seuraavalla kalvolla. HHO: inter-freq on (basic GSM) = 2 taajuuksien välinen, esim hot spot. Inter system UMTS-GSM. 09/04/2019

Soft and Softer Handover (1/2) Soft handover Softer handover RNC RNC Node B 1 Node B 2 Maninta aktiivisetistä, Yhditelystä Selection vs MRC Sector 1 Sector 2 09/04/2019

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) 09/04/2019

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 09/04/2019

Soft Handover Algorithm Maximum active set size = 2 09/04/2019

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 09/04/2019

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 09/04/2019

Measurement Results (1/3) Measurement results for CPICH Ec/N0 filter coefficient Measurement results for active set weighting coefficient 09/04/2019

Measurement Results (2/3) Measurement results for addition window Measurement results for drop window 09/04/2019

Measurement Results (3/3) Performance comparison between initial and optimised values 09/04/2019

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 09/04/2019

The End Thank you! Questions 09/04/2019