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Performance Analysis of Transport Format Combination Selection in WCDMA Enhanced Uplink

Performance Analysis of Transport Format Combination Selection in WCDMA Enhanced Uplink. Author: Teemu Björninen Supervisor: Professor Sven-Gustav Häggman Instructor: D.Sc. (Tech.) Shyam Chakraborty. Contents. Basics of WCDMA Enhanced Uplink What is E-TFC Research question and methods

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Performance Analysis of Transport Format Combination Selection in WCDMA Enhanced Uplink

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  1. Performance Analysis of Transport Format Combination Selection in WCDMA Enhanced Uplink Author: Teemu Björninen Supervisor: Professor Sven-Gustav Häggman Instructor: D.Sc. (Tech.) Shyam Chakraborty

  2. Contents • Basics of WCDMA Enhanced Uplink • What is E-TFC • Research question and methods • Results and conclusions

  3. Basics of WCDMA Enhanced Uplink • Enhanced Uplink aka HSUPA • Enhanced Uplink is standardized in 3GPP Release 6 • Enhancement to packet access domain • Reduces round trip time • Provides higher data rates, up to 5.76 Mbps • Enhanced Uplink is invisible for Rel 99 network components, separate channelisation code sets • Enabler for new services and success of 3G, together with HSDPA?

  4. Basics of WCDMA Enhanced Uplink • Changes to Rel 99 uplink • Shorter transmission time interval, 2 or 10 ms • Packet scheduling is moved from RNC to Node B enabling faster response to varying radio conditions and user bit rate requests. • Hybrid Automatic Repeat Request (HARQ) retransmission is used before RLC retransmissions. Up to eight parallel processes with soft combining. • New dedicated transport channel called Enhanced Dedicated Channel (E-DCH), TX power is an offset to DPCCH • New control channel, TX power is an offset to DPCCH

  5. Basics of WCDMA Enhanced Uplink • New protocols to MAC-layer • MAC-es • Terminated in RNC • For insequency delivery and duplicate detection • MAC-e • Terminated in Node B • Controls HARQ and scheduling

  6. What is E-TFC • E-TFC, Enhanced Uplink Transport Format Combination • E-TFC determines how much data can be send during one transmission time interval • TFC selection for Rel 99 dedicated channels is done prior to E-TFC selection • UE builds up an E-TFC restriction list • Based on bit rate limitation, which comes from Node B scheduler in the form of absolute or relative grant • Based on transmission power resources. • Selects ”the best” E-TFC from the restriction list, which maximises data throughput

  7. What is E-TFC • E-TFC contains only one transport block • Mac-level headers are 6 bits long Tsn = Transmission sequence number DDI = Data discription indicator

  8. Research Question • Study the performance of Enhanced Uplink E-TFC selection in a single cell network, without mobility • Study the impact of power reduction algortihm in E-TFC selection on selected performance indicators when Ue exceeds maximum transmission power

  9. Research Methods • Computer simulations with Ericsson’s Rasmus WCDMA simulator • Simulation results of the implemented power reduction algorithm in E-TFC selection is compared to a simpler non standardized algorithm and to the theoretical calculations • New implementation: calculates the needed reduction, reduces TX power back to allowed level (Algorithm 2) • Simple implementation: when max TX power is exceeded, TX power is multiplied by 0,5 (Algorithm 1) • Three measured indicators: system throughput, user throughput and maximum allowed E-TFC per transmission time interval

  10. 1800 1600 1400 1200 1000 System throughput [kbps] 800 600 400 200 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Users in the cell Results, Theoretic Approach • What is possible to achieve? • Parameter values and used scheduler determines the limits, max rate is set to 1800 kbps

  11. Results, System Throughput • New implementation (Algorithm 2) has better performance than the simpler one (Algorithm 1)

  12. Results, User Throughput • Individual user throughputs are close to theoretical calculation • With small grant Ue is able to fully exploit the grant • With four and six users the scheduling functionality allows ”too good” throughputs

  13. Results, Allowed E-TFC • In a single user case the distribution of the biggest allowed E-TFCs of algorithm one is more spread than algortihm two

  14. Results, Allowed E-TFC • When the user amount in the cell increases, the distribution figure of allowed E-TFCs has only one or two spikes. Placement of spikes moves to left on X-axis when user amount increases

  15. Conclusions • All three measured indicators show that implemented Algorithm 2 performs better in power and interference limited situations • Enhanced Uplink requires quite high transmission power. Ue has to operate close to max tx power • Parameter selection is very important! • Pdu size • Max bit rate • Used scheduler type

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