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
24/07/2016
2
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
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UMTS network architecture
Iu
Uu
Iub
Iu CS
Node B
MSC /
VLR
RNC
USIM
CS domain
GMSC
Circuit
switched
Node B
Cs
ME
Iur
Iu PS
HLR
Node B
RNC
SGSN
GGSN
Node B
UE
UTRAN
CN
Packet
switched
External
Networks
UE = User Equipment
UTRAN = UMTS Terrestial Radio Access Network
ME = Mobile Equipment
RNC = Radio Network Controller
USIM = UMTS SIM
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PS domain
Handover types
• Soft Handovers (SHO):
– Soft and softer handover
• Hard Handovers:
– Inter-frequency handover
– Inter-system handover
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Soft and Softer Handover (1/2)
Soft handover
Softer handover
RNC
RNC
Node B 1
Node B 2
Sector 1
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Sector 2
6
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)
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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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Soft Handover Algorithm
Measurement
P-CPICH 1
quantity
Addition
window
Drop
window
P-CPICH 2
Replace
window
P-CPICH 3
Cell 3
Event 1A =
connected add cell 1
Maximum active set size = 2
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Time
Event 1C
= replace
cell 3 with
cell 2
Event 1B
= drop
cell 2
9
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
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Optimisation of Softer Handover
• Goal for optimisation: Minimise SHO overhead and UE
transmission power without lowering quality
• Measurement method:
– Field measurements by drive tests
Nokia 6650
– Logging from the UE
• Key Performance Indocators:
– SHO overhead
Laptop
N
   nPn  1
n 1
– number of SHO events (i.e. signalling load)
– UE transmission power (SHO gain)
– Quolity indicators: BLER, Dropped calls & Failed call attempts
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Measurement Results (1/3)
• Measurement results for CPICH Ec/N0 filter coefficient
Parameter SHO
SHO
BLER
value
overhead
events
UE TX Best
power
active
average Ec/N0
Failed
Dropped
call
calls
attempts
0
2
3
4
-14,08
-15,03
-14,32
-14,95
0,00
0,00
1,33
0,33
0,33
0,19
0,18
0,19
1,37
0,11
3,45
3,58
225,00
73,67
65,33
49,00
-4,43
-4,30
-4,72
-4,23
0,00
0,00
1,00
0,33
• Measurement results for active set weighting coefficient
Parameter SHO
SHO
BLER
value
overhead
events
UE TX Best
power
active
average Ec/N0
Failed
Dropped
call
calls
attempts
0
0,06
0,85
50,00
-16,18
-4,23
0,00
0,00
1
0,60
1,24
70,33
-15,98
-4,58
0,00
4,33
2
0,58
2,61
74,33
-23,44
-4,21
0,33
5,00
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Measurement Results (2/3)
• Measurement results for addition window
Parameter SHO
SHO
BLER
value
overhead
events
UE TX Best
power
active
average Ec/N0
Failed
Dropped
call
calls
attempts
Set
Set
Set
Set
-14,95
-16,14
-15,77
-16,47
0,33
0,33
0,00
0,00
1
2
3
4
0,19
0,14
0,12
0,07
3,58
1,97
2,29
0,73
49,00
50,33
43,67
54,00
-4,23
-3,43
-4,22
-4,27
0,33
0,33
0,00
0,00
• Measurement results for drop window
Parameter SHO
SHO
BLER
value [ dB] overhead
events
UE TX Best
power
active
average Ec/N0
Failed
Dropped
call
calls
attempts
2
3
4
5
-16,18
-16,47
-16,56
-17,31
0,00
0,00
0,00
0,00
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0,06
0,07
0,10
0,12
0,85
0,73
3,64
1,71
50,00
54,00
36,67
34,00
-4,23
-4,27
-4,26
-4,10
0,00
0,00
0,00
0,00
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Measurement Results (3/3)
• Performance comparison between initial and optimised
values
Parameter SHO
set
I nitial
Optimised
24/07/2016
BLER SHO
UE
TX Best
power
overhead [ % ]
events
0,33
0,06
average
210,00 -21,81
[ dBm]
52,67
-21,99
0,55
1,13
Failed
Dropped
active
call
calls
Ec/N0
[-3,64
dB]
-3,78
attempts
0,00
0,00
0,00
0,00
14
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
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The End
•Thank you!
•Questions
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