In this paper, we extend the analysis of multipath routing presented in our previous work, so that the basic restrictions on the evaluation and optimization of that scheme can be dropped (e.g., disjoint paths and iden...
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In this paper, we extend the analysis of multipath routing presented in our previous work, so that the basic restrictions on the evaluation and optimization of that scheme can be dropped (e.g., disjoint paths and identical paths in terms of failure probability). In that work, we employed diversity coding in order to provide increased protection against frequent route failures by splitting data packets and distributing them over multiple disjoint paths. Motivated by the high increase in the packet delivery ratio, we study the increase we can achieve through the usage of multiple paths in the general case, where the paths are not necessarily independent and their failure probabilities vary. For this reason, a function that measures the probability of successful transmission is derived as a tight approximation of the evaluation function P-succ. Given the failure probabilities of the available paths and their correlation, we are able to find in polynomial time the set of paths that maximizes the probability of reconstructing the,original information at the destination.
In this paper, we develop an analytical framework for evaluating multipath routing in mobile ad hoc networks. The instability of the topology (e.g., failure of links) in this type of network due to nodal mobility and ...
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In this paper, we develop an analytical framework for evaluating multipath routing in mobile ad hoc networks. The instability of the topology (e.g., failure of links) in this type of network due to nodal mobility and changes in wireless propagation conditions makes transmission of time-sensitive information a challenging problem. To combat the inherent unreliability of these networks, we propose a routing scheme that uses multiple paths simultaneously by splitting the information between a multitude of paths, so as to increase the probability that the essential portion of the information is received at the destination without incurring excessive delay. Our scheme works by adding an overhead to each packet, which is calculated as a linear function of the original packet bits. The resulting packet (information and overhead) is fragmented into smaller blocks and distributed over the available paths. The probability of reconstructing the original information at the destination is derived in an analytical form and its behavior is studied for some special cases. It is shown that, under certain constraints, the packet dropping probability decreases as the number of used paths is increased.
Symmetrical multilevel diversity coding with independent data streams has recently been studied by Roche et al., and the admissible coding rate region was determined for the case of three levels. In particular, it was...
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Symmetrical multilevel diversity coding with independent data streams has recently been studied by Roche et al., and the admissible coding rate region was determined for the case of three levels. In particular, it was shown that coding by superposition is optimal, which means that optimality can be achieved by very simple coding. However, it is very difficult to generalize their proof to an arbitrary number of levels, In this paper, we use a new approach to study this problem, and we show that coding by superposition is optimal for symmetrical multilevel diversity coding in general, We also discuss how our result can be applied when the source consists of correlated data streams. The techniques we use are new in multiuser information theory, and our work sheds some light on the standing problem of characterizing those multilevel diversity coding systems for which coding by superposition is optimal.
We introduce a new class of problems called network information flow which is inspired by computer network applications. Consider a point-to-point communication network on which a number of information sources are to ...
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We introduce a new class of problems called network information flow which is inspired by computer network applications. Consider a point-to-point communication network on which a number of information sources are to be mulitcast to certain sets of destinations. We assume that the information sources are mutually independent. The problem is to characterize the admissible coding rate region. This model subsumes all previously studied models along the same line. In this paper, we study the problem with one information source, and we have obtained a simple characterization of the admissible coding rate region. Our result can be regarded as the Max-flow Min-cut Theorem for network information flow. Contrary to one's intuition, our work reveals that it is in general not optimal to regard the information to be multicast as a "fluid'' which can simply be routed or replicated. Rather, by employing coding at the nodes, which we refer to as network coding, bandwidth can in general be saved. This finding may have significant impact on future design of switching systems.
Multilevel diversity coding was introduced in recent work by Roche and Yeung. In a multilevel diversity coding system, an information source is encoded by a number of encoders. There is a set of decoders, partitioned ...
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Multilevel diversity coding was introduced in recent work by Roche and Yeung. In a multilevel diversity coding system, an information source is encoded by a number of encoders. There is a set of decoders, partitioned into multiple levels, with each decoder having access to a certain subset of the encoders. The reconstructions of the source by decoders within the same level are identical and are subject to the same distortion criterion. Inspired by applications in computer communication and fault-tolerant data retrieval, we study a multilevel diversity coding problem with three levels for which the connectivity between the encoders and decoders is symmetrical. We obtain a single-letter characterization of the coding rate region and show that coding by superposition is optimal for this problem. Generalizing to a symmetrical problem with an arbitrary number of levels, we derive a tight lower bound on the coding rate sum.
Inspired by mobile satellite communications systems, we consider a source coding system which consists of multiple sources, multiple encoders, and multiple decoders. Each encoder has access to a certain subset of the ...
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Inspired by mobile satellite communications systems, we consider a source coding system which consists of multiple sources, multiple encoders, and multiple decoders. Each encoder has access to a certain subset of the sources, each decoder has access to certain subset of the encoders, and each decoder reconstructs a certain subset of the sources almost perfectly. The connectivity between the sources and the encoders, the connectivity between the encoders and the decoders, and the reconstruction requirements for the decoders are all arbitrary. Our goal is to characterize the admissible coding rate region. Despite the generality of the problem, we have developed an approach which enables us to study all cases on the same footing. We obtain inner and outer bounds of the admissible coding rate region in terms of Gamma(N)* and <(Gamma)over bar>(N)*, respectively, which are fundamental regions in the entropy space recently defined by Yeung, So far, there has not been a full characterization of Gamma(N)*, so these bounds cannot be evaluated explicitly except for some special cases. Nevertheless, we obtain an alternative outer bound which can be evaluated explicitly. We show that this bound is tight for all the special cases for which the admissible coding rate region is known, The model we study in this paper is more general than all previously reported models on multilevel diversity coding, and the tools we use are new in multiuser,information theory.
This paper evaluates the performance of DS/CDMA with diversity coding and multiuser interference (MUI) cancellation in fading multipath channel. The diversity technique considered in this paper, is different from the ...
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This paper evaluates the performance of DS/CDMA with diversity coding and multiuser interference (MUI) cancellation in fading multipath channel. The diversity technique considered in this paper, is different from the conventional scheme and transmits different information over different channels. It is shown that, this diversity scheme performs better than conventional diversity scheme, and when combined with MUI cancellation provides significant performance improvement. Effects of partial band jamming on the system are also considered.
In a diversity coding System, an information source is encoded by a number of encoders. There are a number of decoders, each of which can access a certain subset of the encoders. In this paper, we study a diversity co...
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In a diversity coding System, an information source is encoded by a number of encoders. There are a number of decoders, each of which can access a certain subset of the encoders. In this paper, we study a diversity coding problem in which there are two levels of decoders. The reconstructions of the source by decoders within the same level are identical, and are subject to the same distortion criterion. Our results imply a principle of superposition when the source consists of two independent data streams. Practical codes achieving zero error can easily be constructed for this special case. A class of open problems on this topic is also suggested.
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