Dynamic Bandwidth Allocation with Fair Scheduling For WCDMA

Systems

Liang Xu, Xumin Shen, and Jon W. MarkUniversity of Waterloo

published in IEEE Wireless Communications Magazine, vol. 9, no. 2, April 2002

2005/010/12Presented by Hojin Lee(lumiere@mmlab.snu.ac.kr)

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Contents

System Model Ideal Scheduler: GPS Related Work

SCDMA – Scheduled CDMA Proposed Scheduler

CDGPS Performance Evaluation Conclusion & Comment

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System Model CDMA – code division multiple access

Chip rate Multi-code Spread factor Power control – close loop

FDD – frequency division duplex Each Mobile user is assigned to at least one dedicated c

hannel, and shares the random access channel (uplink) Dedicated channel – date Random access channel – signaling, short message

Total uplink capacity is limited by intracell and intercell multiple access interference

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CDMA: ex)

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Ideal Scheduler: GPS GPS – Generalized Processor Sharing

Max-min fair allocation Maximizes the minimum share of a source whose demand is not

fully satisfied

Intuitively, GPS serves packets as if they are in separate logical queues, visiting each nonempty queue in turn and serving an infinitesimally small amount of data.

In any finite time interval, it can visit every logical queue at least once.

GPS can’t be implemented

Packet-by-packet GPS Finish tag, virtual time, start tag

capacity

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SCDMA – Scheduled CDMA At the beginning of each time slot, BS chooses as many MSs wit

h the smallest finish tags as permitted by the system power index budget => excessive computational complexity => signaling overhead

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CDGPS – Code Division GPS : total amount of backlogged traffic of flow i at the end

of time slot k without service : the end time of slot k-1 : the backlogged traffic at time : estimated traffic arrival rate of flow i during slot k

If == 0, = 0 If > 0, = , If < CT

The remaining resource is distributed to users who expected more than their guaranteed service

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Performance Evaluation (1/2) C = 2Mbps Perfect power control T: 10 ms

4 homogenous best effort packet data flow L: 5120 bits Poisson process, shaped by leaky bucket regulator with = 20L and =

C/4

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Performance Evaluation (2/2) 10 voice flows

on-off model - on: 40%, CBR 16 kbps, 80 bits 3 video flows

VBR 8-state MMPP model - Average duration in each state: 40 ms

4 best effort data flow Poisson process - 2560 bits, 256 kbps

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Conclusion & Comments

SCDMA => complexity, signaling o/h CDGPS => simple, use idle network resources

No comparison CDGPS with SCDMA Simulation environment is not clearly explained Power control is not trivial Soft Capacity => intercell interference