HSDPA/HSUPA Packet Scheduling

JARNO NIEMELÄ [email protected]

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)

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TIME SHARED ALLOCATION OF HS-DSCH

3

Sensitivity of throuhgput for channel quality

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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.

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Input parameters for packet scheduler

 Resource allocation    HS-PDSCH and HS-SCCH powers HS-PDSCH codes Number of HS-SCCHs   QoS parameters  QoS attributes   Scheduling priority indicator (SPI) Guarantee bit rate  Downlink channel quality measurements    CQI reports Power measurements on associated DPCH HARQ acknowledgements Miscellaneous   Amount of buffered data Mobile capabilities 8301253 Advanced Topics in Radio Network Planning, TUT 6

Fairness

 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. 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:

P i

 

i i

     Instantaneous supported data rate Average served throughput  where

P i (t)

denotes the user priority.

User’s with relatively good channel conditions are served. Available information of CQI and previous transmissions is utilized.

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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

P i

 

i i

        max

j i

   where and max

R i j

(

t

 

i

(

t

is a constant that indicates the maximum

i

average supportable data from all

j

users.

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Summary

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Multi-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 dynamics of fast fading (short term variations) 8301253 Advanced Topics in Radio Network Planning, TUT 13

Throughput vs. E s /N 0

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Gain of multi-user diversity Diversity order = number of scheduled users

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Performance analysis of PS in HSDPA

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User throughput distribution 2 Mbps load for slow and 3 Mbps load for fast scheduling algorithms Pedestrian A channel (3 km/h)

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Average user throughput CELL EDGE ---------------------------------- CLOSE TO BS

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Efficiency of resource utilization

 Fast scheduling is able to use more efficiently higher MCSs.

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Link utilization

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Performance of Max C/I and PF under high load Provisioning of fairness in high load starts to be problem with Max C/I

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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) PEDESTRIAN A (3 km/h)

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Summary table of cell throughputs with minimum user throughput guarantees @ 5 % OUTAGE LEVEL

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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.

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Fast packet scheduling for E-DCH/HSUPA

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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) 2) Utilization of USTS (uplink synchronous transmittion scheme) [5] 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)

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Performance analysis (macrocellular)

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Performance analysis (microcellular)

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Performance analysis (microcellular)

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Performance analysis

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Conclusions 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 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 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.

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