Cooperative Communications in Wireless NetworksUsing Random 使用随机的无线网络中的协作通信.pptVIP

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Cooperative Communications in Wireless NetworksUsing Random 使用随机的无线网络中的协作通信.ppt

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Cooperative Communications in Wireless NetworksUsing Random 使用随机的无线网络中的协作通信

* Cooperative Communications in Networks:Random coding for wireless multicast Brooke Shrader and Anthony Ephremides University of Maryland October, 2008 Performance for fading channels and inter-session coding Joint work with Randy Cogill, University of Virginia * Introduction and Motivation Alternatives to overcome channel MAC-layer errors in multicast transmission: repeatedly send packets (ARQ) network coding Previous work: network coding outperforms ARQ for time-invariant channels coding used within (but not between) multicast sessions * For packets form where ai are generated randomly and uniformly from u-ary alphabet and Σ is sum in finite field. If ai = 0 for all i, generate new coefficients. Transmit coefficients ai in packet header Decode: solve a system of linear equations in si Form random linear combinations of K packets. Random linear coding for multicast * Previous workStable throughput in random access Setting: 2 sources, 2 destinations If user n has a packet to send, it transmits in a slot with probability pn Stable throughput: region of (λ1, λ2) for which there exists (p1, p2) such that both queues remain finite Retransmit packets Random linear coding * Increasing K Previous workStable throughput in random access Random linear coding approaches capacity as K→∞. * Previous workQueueing delay in random linear coding Time spent waiting to form a group of K Multicast: 3 destinations, q=0.9 Policy: fix K, the number of packets in coding * Previous workQueueing delay in random linear coding Policy: let k, number of packets in coding, vary according to traffic load 1 ≤ k ≤ K Unicast: 1 destination, q=0.5 As K →∞, delay performance approaches retransmission delay * Recent/Ongoing work Rateless coding naturally adapts coding rate to variations in the channel. Coding across sessions means that receivers decode additional packets that aren’t intended for them. We analyze the multicast throughput for random linear coding over a fading wirel