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Delay Considerations for Opportunistic Scheduling in Broadcast Fading Channels

Sharif, Masoud and Hassibi, Babak (2007) Delay Considerations for Opportunistic Scheduling in Broadcast Fading Channels. IEEE Transactions on Wireless Communications, 6 (9). pp. 3353-3363. ISSN 1536-1276. doi:10.1109/TWC.2007.06067.

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We consider a single-antenna broadcast block fading channel with n users where the transmission is packetbased. We define the (packet) delay as the minimum number of channel uses that guarantees all n users successfully receive m packets. This is a more stringent notion of delay than average delay and is the worst case (access) delay among the users. A delay optimal scheduling scheme, such as round-robin, achieves the delay of mn. For the opportunistic scheduling (which is throughput optimal) where the transmitter sends the packet to the user with the best channel conditions at each channel use, we derive the mean and variance of the delay for any m and n. For large n and in a homogeneous network, it is proved that the expected delay in receiving one packet by all the receivers scales as n log n, as opposed to n for the round-robin scheduling. We also show that when m grows faster than (log n)^r, for some r > 1, then the delay scales as mn. This roughly determines the timescale required for the system to behave fairly in a homogeneous network. We then propose a scheme to significantly reduce the delay at the expense of a small throughput hit. We further look into the advantage of multiple transmit antennas on the delay. For a system with M antennas in the transmitter where at each channel use packets are sent to M different users, we obtain the expected delay in receiving one packet by all the users.

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Additional Information:© Copyright 2007 IEEE. Reprinted with permission. Manuscript received January 30, 2006; revised July 14, 2006 and July 31, 2006; accepted August 16, 2006. [Posted online: 2007-10-22] The associate editor coordinating the review of this paper and approving it for publication was J. Zhang. This work is presented in part at IEEE Inter. Symp. on Info. Theory 2004 and IEEE INFOCOM 2005. This work is supported in part by the National Science Foundation under grant no. CCR-0133818, by the office of Naval Research under grant no. N00014-02-1-0578, and by Caltech’s Lee Center for Advanced Networking.
Subject Keywords:Broadcast channel, fading, opportunistic scheduling, packet delay, longest queue
Issue or Number:9
Record Number:CaltechAUTHORS:SHAieeetwc07
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9049
Deposited By: Archive Administrator
Deposited On:23 Oct 2007
Last Modified:08 Nov 2021 20:55

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