|M.Sc Student||Itzhak Dor|
|Subject||Cooperation in Communication Systems Under Uncertainty|
|Department||Department of Electrical and Computer Engineering||Supervisor||PROF. Yossef Steinberg|
|Full Thesis text|
It has long been observed that cooperation between users in a communication network can greatly improve its performance. A common assumption in previous studies is that the cooperation link is steady, and all the users in the network are aware of its existence. Moreover, the coding and decoding schemes in these work rely heavily on the specific nature of cooperation, and cannot operate without the presence of the cooperation links. Unfortunately, the assumptions that the cooperation links are reliable is not realistic in modern ad-hoc networks. Cooperation links can be unreliable, and part of the users in the system cannot be updated about their availability. In such a case we need robust coding schemes that exploit the cooperation links if they are present, but can still operate if cooperation is not possible.
In this work we study the general broadcast channel with degraded message sets and cooperation link that may be absent, and derive its capacity region under such uncertainty conditions. A generalization of this model is studied, where the cooperation link capacity is one of k possible values, and its capacity region is derived. We examine the situation where the cooperation link capacity is random and suggest a performance criterion that can be viewed as a measure of the cooperativeness of the channel: maximize the average rate of one user, subject to a constraint on the rate of the other user and the requirement that the system will operate in any realization of the (random) cooperation link. As examples to illustrate our results, the Gaussian broadcast channel is extensively examined, and its capacity is derived for the various cooperation models and assumptions suggested throughout.
We further consider two additional relay broadcast models with cooperative decoders. The first model is the non-degraded relay broadcast channel with degraded message sets. We present an inner bound and an outer bound for the capacity region, and prove that the outer bound is not tight in general, by providing a counter-example. We also study a degraded model of the dedicated relay broadcast channel and we derive its capacity region.