HSDPA/HSUPA Packet Scheduling JARNO NIEMELÄ jarno.niemela@tut.fi 21.03.2005 Outline Principles of packet scheduling in WCDMA / HSDPA Rel’05 Performance analysis of HSDPA PS for NRT services [1] Scheduling in E-DCH/HSUPA (NRT services) [2] 8301253 Advanced Topics in Radio Network Planning, TUT 2 Packet scheduling in WCDMA/HSDPA Rel’05 NodeB controlled packet scheduling (fast). MULTIUSER DIVERSITY (Selection diversity) TIME SHARED ALLOCATION OF HS-DSCH 8301253 Advanced Topics in Radio Network Planning, TUT 3 Sensitivity of throuhgput for channel quality 8301253 Advanced Topics in Radio Network Planning, TUT 4 Task of packet scheduler To schedule interactive and background services (NRT) for users. To allocate radio resources efficienctly for a cell such that cell capacity will be maximized while fulfilling the QoS requirements according to certain policy. To monitor allocation of NRT services and system loading. To perform load control actions. 8301253 Advanced Topics in Radio Network Planning, TUT 5 Input parameters for packet scheduler Resource allocation HS-PDSCH and HS-SCCH powers HS-PDSCH codes Number of HS-SCCHs Downlink channel quality measurements CQI reports Power measurements on associated DPCH HARQ acknowledgements QoS parameters QoS attributes Scheduling priority indicator (SPI) Guarantee bit rate Miscellaneous Amount of buffered data Mobile capabilities 8301253 Advanced Topics in Radio Network Planning, TUT 6 Fairness Selection of scheduling approach is always a tradeoff between the fairness and maximum cell throughput. C/I scheduling maximizes the system capacity with the cost of lack of fairness. Fair resources scheduling distributes equally the radio resources (codes, power and allocation time). Not completely fair. Fair throughput tries to provide the same throughput for all users. 8301253 Advanced Topics in Radio Network Planning, TUT 7 Packet scheduling algorithms Slow scheduling methods (Blind) Average C/I Round robin Fair throughput ~100 ms scheduling period Does not consider instantaneous radio conditions Fast scheduling methods (Advanced/opportunistic) Maximum C/I Proportional fair Fast fair throughput Per TTI basis (2ms) Utilizes temporary changes of radio conditions 8301253 Advanced Topics in Radio Network Planning, TUT 8 Slow scheduling methods Average C/I (Avg. C/I) Priorities users with the highest average C/I (~100 ms period) Fast fading averaged out Round Robin (RR) Cyclic order used without considering channel conditions Blind method Simple and allocates radio resources evenly between the users (=high fairness) Fair Throughput (FTH) No instantaneous channel information utilized Priorities users with lowest average throughput 8301253 Advanced Topics in Radio Network Planning, TUT 9 Fast scheduling methods (1/2) Maximum C/I (Max. C/I) Serves in every TTI (transmission time interval) the user with the best radio conditions with the largest supportable bit rate. High cell throughput, low fairness. Proportional fair (PF) Serves the user with largest relative channel quality: Ri t Instantaneous supported data rate Pi i t Average served throughput where Pi(t) denotes the user priority. User’s with relatively good channel conditions are served. Available information of CQI and previous transmissions is utilized. 8301253 Advanced Topics in Radio Network Planning, TUT 10 Fast scheduling methods (2/2) Fast fair throughput (FFTH) Aims at providing a fair throughput distribution among all the users in the cell, while still taking advantage of the fast fading variations Ri t max j Ri (t ) Pi i t Ri (t ) where Ri (t ) is the average supportable data rate of a user i and max j Ri (t ) is a constant that indicates the maximum average supportable data from all j users. 8301253 Advanced Topics in Radio Network Planning, TUT 11 Summary 8301253 Advanced Topics in Radio Network Planning, TUT 12 Multi-user diversity Fast allocation (2ms TTI) of radio resources Users with good radio conditions served Multiuser diversity (selection diversity) Increases the system/ cell throughput The gain naturally depends on the dynamics of fast fading (short term variations) 8301253 Advanced Topics in Radio Network Planning, TUT 13 Throughput vs. Es/N0 8301253 Advanced Topics in Radio Network Planning, TUT 14 Gain of multi-user diversity Diversity order = number of scheduled users 8301253 Advanced Topics in Radio Network Planning, TUT 15 Performance analysis of PS in HSDPA 8301253 Advanced Topics in Radio Network Planning, TUT 16 User throughput distribution 2 Mbps load for slow and 3 Mbps load for fast scheduling algorithms Pedestrian A channel (3 km/h) 8301253 Advanced Topics in Radio Network Planning, TUT 17 Average user throughput CELL EDGE ---------------------------------- CLOSE TO BS 8301253 Advanced Topics in Radio Network Planning, TUT 18 Efficiency of resource utilization Fast scheduling is able to use more efficiently higher MCSs. 8301253 Advanced Topics in Radio Network Planning, TUT 19 Link utilization 8301253 Advanced Topics in Radio Network Planning, TUT 20 Performance of Max C/I and PF under high load Provisioning of fairness in high load starts to be problem with Max C/I 8301253 Advanced Topics in Radio Network Planning, TUT 21 Cell throughputs (1/2) With minimum user throughput guarantees (< 64 kbps) PEDESTRIAN A (3 km/h) 8301253 Advanced Topics in Radio Network Planning, TUT VEHICULAR A (3 km/h) 22 Cell throughputs (2/2) PEDESTRIAN A (3 km/h) 8301253 Advanced Topics in Radio Network Planning, TUT 23 Summary table of cell throughputs with minimum user throughput guarantees @ 5 % OUTAGE LEVEL 8301253 Advanced Topics in Radio Network Planning, TUT 24 Conclusions from PS methods for HSDPA Selection of PS algorithm important for HSDPA capacity maximization and QoS provisioning. Multi-user diversity gain for 10-15 users 100 % in PedA and 50 % in VehA channels (over RR). Max C/I maximizes the cell throughput (with degraded QoS provisioning) Proportional fair scheduler seems to provide a trade-off between QoS and cell throughput (time dispersion of the channel still a great problem. 8301253 Advanced Topics in Radio Network Planning, TUT 25 Fast packet scheduling for E-DCH/HSUPA 8301253 Advanced Topics in Radio Network Planning, TUT 26 UL PS in REL’99 RNC –based packet scheduling Upgrading based on capacity requests Downgrading based on inactivity timer 8301253 Advanced Topics in Radio Network Planning, TUT 27 PS approaches for Node B scheduling (1/2) Blind data rate detection (BRD) Instantaneous (TTI=10ms) data rate observed by Node B and compared to maximum allowed. This information is thereafter used for resource allocation according to UE´s actual needs. PS algorithm based on resource utilization factor (RUF) 8301253 Advanced Topics in Radio Network Planning, TUT 28 PS approaches for Node B scheduling (2/2) Time Division Multiplexing (TDM) Fast allocation (TTI=2ms) based on same approach as in HSDPA. Easier to keep resource utilization closer to the planned one. Exploitation of instantaneous channel conditions. Requires uplink syncronization 1) Utilization of USTS (uplink synchronous transmittion scheme) [5] 2) Synchronization achieved through DL frames. Would require guard intervals together with using the information provided by RTT. To support SHO, only one Node B is allowed to perform scheduling decisions. Allocation strategies (RRFT, maximized transmit power efficincy (MTPE), PFT) 8301253 Advanced Topics in Radio Network Planning, TUT 29 Performance analysis (macrocellular) 8301253 Advanced Topics in Radio Network Planning, TUT 30 Performance analysis (macrocellular) 8301253 Advanced Topics in Radio Network Planning, TUT 31 Performance analysis (microcellular) 8301253 Advanced Topics in Radio Network Planning, TUT 32 Performance analysis (microcellular) 8301253 Advanced Topics in Radio Network Planning, TUT 33 Performance analysis 8301253 Advanced Topics in Radio Network Planning, TUT 34 Conclusions from PS for E-DCH/HSUPA Node B PS based on BRD is able to provide 3040% capacity gain over RNC based PS (TVM) Intuitively, channel-dependent methods are able to provide better performance Uplink synchronisation provides capacity gain of 20%. Extra signalling load might reduce the capacity gains in some extent. 8301253 Advanced Topics in Radio Network Planning, TUT 35 Main references 1. Pablo José Ameigeiras Gutiérrez, “Packet Scheduling and Quality of Service in HSDPA”, Ph. D. Thesis, Aalborg University, Denmark, October 2003. 2. José Outes Carnero, “Uplink capacity enhancements in WCDMA,” Ph. D. Thesis, Aalborg University, Denmark, March 2004. 3. H. Holma, A. Toskala (ed.), “WCDMA for UMTS,” 3rd ed., John Wiley & Sons, Ltd., 2004. 8301253 Advanced Topics in Radio Network Planning, TUT 36 Accessory references 4. J. Laiho, A. Wacker, T. Novosad, “Radio Network Planning and Optimisation for UMTS,” John Wiley & Sons, Ltd., 2002. 5. 3GPP, “Study report of Uplink Synchronous Transmission Scheme (USTS),” TR 25.854, Ver 5.00, Rel. 5., December 2001. 8301253 Advanced Topics in Radio Network Planning, TUT 37