Channel Element 3G [PDF]

Zitiervorschau

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

Agenda

• Background • Objectives of the thesis • Capacity • Load sharing • Conclusions

2

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

100 % UMTS Downlink Data [MB]

90 % 80 % 60 % 50 % 40 % 30 % 20 % 10 %

24.2.2008

10.2.2008

27.1.2008

13.1.2008

30.12.2007

16.12.2007

2.12.2007

18.11.2007

4.11.2007

21.10.2007

7.10.2007

23.9.2007

9.9.2007

26.8.2007

12.8.2007

0% 29.7.2007

Percentage

70 %

Date

3

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?

4

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

5

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

6

Capacity – HSDPA • HSDPA uses the power margin left over from R99 services • HSDPA throughput depends on achievable Signal-tointerference and noise ratio (SINR) • Power allocated for HSDPA effects the throughput largely Throughput[Mbps] = 0.0039 x SINR^2 + 0.0476 x SINR + 0.1421 25 20 15

SINR dB

PHS  DSCH SINR  SF16 (1   ) Pown  Pother  Pnoise

10 5 0 0,0

0,5

1,0

1,5

2,0

2,5

3,0

-5 -10 Average cell throughput [Mbps]

7

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

8

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

9

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

10

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)

max carrier power capacity reserved for HSDPA

this load directed to GSM sharing threshold

time

Directed Retry active

11

0: 00 1: 00 2: 00 3: 00 4: 00 5: 00 6: 00 7: 00 8: 00 9: 0 10 0 :0 11 0 :0 0 12 :0 13 0 :0 14 0 :0 15 0 :0 0 16 :0 17 0 :0 18 0 :0 19 0 :0 0 20 :0 21 0 :0 22 0 :0 23 0 :0 0

packet 0: 00 1: 00 2: 00 3: 00 4: 00 5: 00 6: 00 7: 00 8: 00 9: 0 10 0 :0 11 0 :0 12 0 :0 13 0 :0 14 0 :0 15 0 :0 16 0 :0 17 0 :0 18 0 :0 19 0 :0 20 0 :0 21 0 :0 22 0 :0 23 0 :0 0

percentage of peak hour traffic

speech

percentage of peak hour traffic

Load sharing - traffic profiles

120 %

100 %

80 %

60 %

40 %

20 %

0%

time

120 %

100 %

80 %

60 %

40 %

20 %

0%

time

12

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 13

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 14 12

Cells

10 8 6 4 2 0 -

5 %

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 % % % % % % % % % % % % % % % % % % % Success rate

14

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%

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 %

240 706 657

99 813 954

-59 %

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 %

15 733

8 057

-49 %

2 351

817

-65 %

HS traffic (Erl)

CS speech payload (kbits) HSDPA RAB attempts

NG user down-switches UL hardware lack

15

Load sharing – results GSM

KPI

DR - FALSE

DR - TRUE

Difference

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 %

TCH attempts

16

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.

17

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

18

THANK YOU !

19