Capacity and Load Sharing in Dual-Mode Mobile Networks

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] = 0.0039 x SINR^2 + 0.0476 x SINR + 0.1421

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. Cell load (downlink carrier power) max carrier power capacity reserved for HSDPA this load directed to GSM sharing threshold time Directed Retry active 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

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 93117 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

16. Load sharing – results GSM

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 !