Capacity and Load Sharing in Dual-Mode Mobile Networks

2

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

3

Directed Retry to GSM - limitations

• Only applicable to speech traffic• Coverage of UMTS and GSM cells should be same

4

Directed Retry to GSM - principles

Cell load (downlink carrier power)

time

sharing threshold

Directed Retry active

this load directed to GSM

max carrier power

capacity reserved for HSDPA

• 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

5

Load sharing - traffic profiles

0 %

20 %

40 %

60 %

80 %

100 %

120 %

time

perc

enta

ge o

f pea

k ho

ur tr

affic

0 %

20 %

40 %

60 %

80 %

100 %

120 %

time

perc

enta

ge o

f pea

k ho

ur tr

affic

speech

packet

6

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

7

Load sharing - results

• Directed Retry to GSM worked well in overall• Total of 93117 speech call redirection attempts, 86033 were succesful• DR-success rate was 92 %, with carefull cell selection > 95 % success rate possible

Directed Retry to GSM success rate

0

2

4

6

8

10

12

14

- 5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

Success rate

Cells

8

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) 240 706 657 99 813 954 -59 %

HSDPA RAB attempts 153 603 164 147 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 -49 %

UL hardware lack 2 351 817 -65 %

9

Load sharing – results GSM

KPI DR - FALSE DR - TRUE Difference

TCH attempts 623 921 820 990 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 %

10

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.

11

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