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

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

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?

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

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

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

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

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

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

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

Load sharing - traffic profiles speech packet

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

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

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 UL hardware lack 2 351 817

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 %

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.

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

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