1. Capacity and Load Sharing in Dual-Mode Mobile Networks
Author: Juha Peura
Supervisor: Prof. Patric Östergård
Instructor: M.Sc. Jarkko Laari, DNA Finland Oy

2. Agenda Background Objectives of the thesis Capacity Load sharing
Conclusions

3. Background The amount packet data in mobile networks
have increased dramatically
Operators have to guarantee quality of service
New solutions needed for traffic handling

4. Objectives of the thesis
What are the main performance bottlenecks in
todays mobile networks?
Is it possible to ease the situation with load sharing
algorithms?

5. Capacity – channel elements
Channel element is a measure of node B hardware resources
Separate CE pools for UL/DL, common to all sectors
One 12.2 kbps speech service uses one channel element
HSUPA takes up to 32 CEs, non-serving cells
reserves also CEs
CEs are a capacity bottleneck in uplink direction
Many RAX-boards have 64 CEs
Suggested minimum is 128 CEs

6. Capacity – Iub transmission
Symmetric bit pipe between base station and RNC
3GPP have specified two transport methods: ATM and IP
Implemented using so called E1s
Maximum throughput of one E1 is 2 Mbps
For speech traffic one E1 has been sufficient
Fast packet connections need multiple E1s
Transmission is a capacity bottleneck in downlink
Base station buffers data from Iub
Future choice – Ethernet/IP transmission

7. Capacity – HSDPA
HSDPA uses the power margin left over from R99 services
HSDPA throughput depends on achievable Signal-to-
interference and noise ratio (SINR)
Power allocated for HSDPA effects the throughput largely
Throughput[Mbps] = x SINR^ x SINR

8. Load sharing Enhances performance by pooling together resources
Inter Frequency Load Sharing
- Traffic sharing between WCDMA carriers
Directed Retry to GSM
- Speech traffic diverted from WCDMA to GSM

9. Directed Retry to GSM Why? 3G most beneficial for PS data users
3G UEs are becoming more common and
coverage improves constantly
-> free capacity to GSM
More resources for data users
Balances load between networks
No additional investments

10. Directed Retry to GSM - limitations
Only applicable to speech traffic
Coverage of UMTS and GSM cells should be same
Overloading of GSM network possible
Should not be used if GSM -> UMTS
handovers are in use (ping-pong effect)
GSM target cell quality not guaranteed (blind ISHO)
-> call drops
Increased signaling, mobiles not reachable during
LA updates
Configuration to entire network can be laborious
3G users may wonder why they are in GSM

11. Directed Retry to GSM - principles
Redirection decission based on cell load
(used downlink carrier power)
After cell load exeeds specified sharing threshold, speech calls
are diverted to GSM network
Sharing fraction parameter specifies the percentage of directed calls
while the cell load is above the sharing threshold
Released power can be allocated for PS users
Sharing parameters can be assigned independently to each cell
Cell load (downlink carrier power)
time
sharing threshold
Directed Retry active
this load directed to GSM
max carrier power
capacity reserved for HSDPA

12. Load sharing - traffic profiles
speech
packet

13. Load sharing - measurements
Functionality and different parameters were first
tested in a single cell
Larger scale test in live network for a three week period
20 most loaded cells were chosen for the measurement
Feature was tested with ”radical” parameters to really find
out how load sharing performed
A set of key performance indicators (KPI) was defined to
assess the effects of the feature
DR-success ratio, Speech setup success rate, dropped calls,
admission number, lack of CEs, speech traffic (Erl), PS traffic ….
Network counters were used to gather information
about the functionality
Raw data was filtered and manipulated for final results

14. Load sharing - results Directed Retry to GSM worked well in overall
Total of speech call redirection attempts, 86033
were succesful
DR-success rate was 92 %, with carefull cell selection
> 95 % success rate possible

15. Load sharing – results UMTS
KPI
DR - FALSE
DR - TRUE
Difference
Speech setup success rate
99,63
29,29
-71 %
Dropped calls percentage
0,36
0,53
48 %
Speech traffic (Erl)
1,12
0,39
-65 %
PS R99 traffic (Erl)
1,86
2,06
11 %
PS R99 setup success rate
94,41
98,96
5 %
PS R99 retainability
94,14
97,97
4 %
HS traffic (Erl)
0,72
0,79
10 %
HS User Thu DL (kbps)
139,24
158,21
14 %
HS User Thu UL (kbps)
33,38
42,58
28 %
HS setup success rate
97,32
97,65
0 %
HS completion success rate
79,35
76,36
-4 %
CS speech payload (kbits)
-59 %
HSDPA RAB attempts
7 %
HS drop %
17,13
20,06
17 %
Admission number
2 949
1 504
-49 %
Failed after admission
3 013
2 789
-7 %
NG user down-switches
15 733
8 057
UL hardware lack
2 351
817

16. Load sharing – results GSM
KPI
DR - FALSE
DR - TRUE
Difference
TCH attempts
32 %
TCH H_Block %
0,06
0,02
-62 %
TCH T_Block %
0,73
1,66
129 %
TCH RF_Loss %
0,14
0,23
60 %
TCH traffic (Erl)
2,67
3,26
22 %

17. Conclusions Transmission, CEs and HSDPA power allocation
can form a capacity bottleneck
Load sharing between UMTS and GSM works reliably,
if configured well
Performance of PS users can be enhanced with
Directed Retry to GSM, at least a little
3G traffic still relatively low, it is questionable if
load sharing is needed at this point.

18. Future research Load sharing between UMTS carriers
more sophisticated feature than Directed Retry to GSM
between UMTS2100 and UMTS900
two way directions taking into account cell load
applicable to all services
Service based handover

19. THANK YOU !