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
09/04/2019

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
09/04/2019

4. UMTS network architectureIu 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

5. 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

6. 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

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)
09/04/2019

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

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
09/04/2019

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

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

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

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
09/04/2019

16. The End
Thank you!
Questions
09/04/2019