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Shatin, Hong Kong

Geng Y.,Chinese University of Hong Kong | Jog V.,Chinese University of Hong Kong | Jog V.,University of California at Berkeley | Nair C.,Chinese University of Hong Kong | Wang Z.V.,Altai Technologies Ltd
IEEE Transactions on Information Theory

We establish an information inequality concerning five random variables. This inequality ismotivated by the sum-rate evaluation of Marton's inner bound for two receiver broadcast channels with a binary input alphabet. We establish that randomized time-division strategy achieves the sum rate ofMarton's inner bound for all binary input broadcast channels. We also obtain an improved cardinality bound for evaluating themaximum sum rate given by Marton's inner bound for all broadcast channels. Using these tools we explicitly evaluate the inner and outer bounds for the binary skew-symmetric broadcast channel and demonstrate a gap between the bounds. © 2013 IEEE. Source

Liew S.C.,Chinese University of Hong Kong | Kai C.H.,Chinese University of Hong Kong | Leung H.C.,Altai Technologies Ltd | Wong P.,Altai Technologies Ltd
IEEE Transactions on Mobile Computing

This work started out with our discovery of a pattern of throughput distributions among links in IEEE 802.11 networks from experimental results. This pattern gives rise to an easy computation method, which we term back-of-the-envelop (BoE) computation. For many network configurations, very accurate results can be obtained by BoE within minutes, if not seconds, by simple hand computation. This allows us to make shortcuts in performance evaluation, bypassing complicated stochastic analysis. To explain BoE, we construct a theory based on the model of an ideal CSMA network (ICN). The BoE computation method emerges from ICN when we take the limit c\to 0, where c is the ratio of the mean backoff countdown time to the mean transmission time in the CSMA protocol. Importantly, we derive a new mathematical result: the link throughputs of ICN are insensitive to the distributions of the backoff countdown time and transmission time (packet duration) given the ratio of their means c. This insensitivity result explains why BoE works so well for practical 802.11 networks, in which the backoff countdown process is one that has memory, and in which the packet size can be arbitrarily distributed. Our results indicate that BoE is a good approximation technique for modest-size networks such as those typically seen in 802.11 deployments. Beyond explaining BoE, the theoretical framework of ICN is also a foundation for fundamental understanding of very-large-scale CSMA networks. In particular, ICN is similar to the Ising model in statistical physics used to explain phenomena arising out of the interactions of a large number of entities. Many new research directions arise out of the ICN model. © 2006 IEEE. Source

Geng Y.,Chinese University of Hong Kong | Nair C.,Chinese University of Hong Kong | Shamai Shitz S.,Technion - Israel Institute of Technology | Wang Z.V.,Altai Technologies Ltd
IEEE Transactions on Information Theory

We establish capacity regions for some classes of broadcast channels with binary inputs and symmetric outputs. We investigate the more capable partial order and establish that the binary erasure channel and the binary symmetric channel form the two extremes for channels having the same capacity. Further, we apply the results to identify a class of broadcast channels for which the best-known inner and outer bounds on the capacity region differ. © 1963-2012 IEEE. Source

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