hsdpa/hsupa packet scheduling jarno niemelÄ [email protected] 21.03.2005
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HSDPA/HSUPA Packet SchedulingHSDPA/HSUPA Packet Scheduling
JARNO NIEMELÄ[email protected]
21.03.2005
8301253 Advanced Topics in Radio Network Planning, TUT 2
OutlineOutline
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]
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Packet scheduling in WCDMA/HSDPA Rel’05Packet scheduling in WCDMA/HSDPA Rel’05
NodeB controlled packet scheduling (fast).
MULTIUSER DIVERSITY(Selection diversity)
TIME SHARED ALLOCATIONOF HS-DSCH
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Sensitivity of throuhgput for channel qualitySensitivity of throuhgput for channel quality
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Task of packet schedulerTask 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.
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Input parameters for packet schedulerInput 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
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FairnessFairness
Selection of scheduling approach is always a trade-off 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.
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Packet scheduling algorithmsPacket scheduling algorithms
Slow scheduling methods (Blind) Average C/I Round robin Fair throughput
Does not consider instantaneous radio conditions
Fast scheduling methods (Advanced/opportunistic) Maximum C/I Proportional fair Fast fair throughput
Utilizes temporary changes of radio conditions
Per TTI basis(2ms)
~100 ms scheduling period
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Slow scheduling methodsSlow 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
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Fast scheduling methods (1/2)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:
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.
Instantaneous supported data rate
Average served throughputi
ii
R tP
t
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Fast scheduling methods (2/2)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
where is the average supportable data rate of a user i and is a constant that indicates the maximum average supportable data from all j users.
max ( )
( )
j iii
i i
R tR tP
t R t
)(tRi )(max tRij
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Multi-user diversityMulti-user diversity
Fast allocation (2ms TTI) of radio resources Users with good radio conditions served Multi-user diversity (selection diversity)
Increases the system/cell throughput
The gain naturally depends on the dynamicsof fast fading (short termvariations)
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Gain of multi-user diversityGain of multi-user diversity
Diversity order = number of scheduled
users
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Performance analysis of PS in HSDPAPerformance analysis of PS in HSDPA
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User throughput distributionUser throughput distribution
2 Mbps load for slow and 3 Mbps load for
fast schedulingalgorithms
Pedestrian A channel(3 km/h)
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Average user throughputAverage user throughput
CELL EDGE ---------------------------------- CLOSE TO BS
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Efficiency of resource utilizationEfficiency of resource utilization
Fast scheduling is able to use more efficiently higher MCSs.
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Performance of Max C/I and PF under high loadPerformance of Max C/I and PF under high load
Provisioning of fairnessin high load starts to
be problem with Max C/I
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Cell throughputs (1/2)Cell throughputs (1/2)
With minimum user throughput guarantees (< 64 kbps)
PEDESTRIAN A (3 km/h) VEHICULAR A (3 km/h)
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Cell throughputs (2/2)Cell throughputs (2/2)
PEDESTRIAN A (3 km/h)
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Summary table of cell throughputs with Summary table of cell throughputs with minimum user throughput guaranteesminimum user throughput guarantees
@ 5 % OUTAGE LEVEL
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Conclusions from PS methods for HSDPAConclusions 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.
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Fast packet scheduling for E-DCH/HSUPAFast packet scheduling for E-DCH/HSUPA
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UL PS in REL’99UL PS in REL’99
RNC –based packet scheduling Upgrading based on capacity requests Downgrading based on inactivity timer
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PS approaches for Node B scheduling (1/2)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)
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PS approaches for Node B scheduling (2/2)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)
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Performance analysis (macrocellular)Performance analysis (macrocellular)
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Performance analysis (macrocellular)Performance analysis (macrocellular)
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Performance analysis (microcellular)Performance analysis (microcellular)
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Performance analysis (microcellular)Performance analysis (microcellular)
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Conclusions from PS for E-DCH/HSUPAConclusions from PS for E-DCH/HSUPA
Node B PS based on BRD is able to provide 30-40% 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.
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Main referencesMain 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.
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Accessory referencesAccessory 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.