hsdpa/hsupa packet scheduling jarno niemelÄ [email protected] 21.03.2005

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]


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


Sensitivity of throuhgput for channel qualitySensitivity of throuhgput for channel quality


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.


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


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.


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


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


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


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


SummarySummary


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)


Throughput vs. EThroughput vs. Ess/N/N00


Gain of multi-user diversityGain of multi-user diversity

Diversity order = number of scheduled

users


Performance analysis of PS in HSDPAPerformance analysis of PS in HSDPA


User throughput distributionUser throughput distribution

2 Mbps load for slow and 3 Mbps load for

fast schedulingalgorithms

Pedestrian A channel(3 km/h)


Average user throughputAverage user throughput

CELL EDGE ---------------------------------- CLOSE TO BS


Efficiency of resource utilizationEfficiency of resource utilization

Fast scheduling is able to use more efficiently higher MCSs.


Link utilizationLink utilization


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


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)


Cell throughputs (2/2)Cell throughputs (2/2)

PEDESTRIAN A (3 km/h)


Summary table of cell throughputs with Summary table of cell throughputs with minimum user throughput guaranteesminimum user throughput guarantees

@ 5 % OUTAGE LEVEL


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.


Fast packet scheduling for E-DCH/HSUPAFast packet scheduling for E-DCH/HSUPA


UL PS in REL’99UL PS in REL’99

RNC –based packet scheduling Upgrading based on capacity requests Downgrading based on inactivity timer


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)


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)


Performance analysis (macrocellular)Performance analysis (macrocellular)


Performance analysis (microcellular)Performance analysis (microcellular)


Performance analysisPerformance analysis


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.


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.


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.

hsdpa/hsupa packet scheduling jarno niemelÄ [email protected] 21.03.2005

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