This article presents a simple overview of the pivotal udtopics in both mobile station (MS)- and base station (BS)-udassisted cooperation in the context of cellular radio systems. udOwing to the ever-increasing amount of literature in this udparticular field, this article is by no means exhaustive, but udis intended to serve as a roadmap by assembling a repre-udsentative sample of recent results and to stimulate udfurther research. The emphasis is initially on relay-base udcooperation, relying on network coding, followed by the uddesign of cross-layer cooperative protocols conceived udfor MS cooperation and the concept of coalition network udelement (CNE)-assisted BS cooperation. Then, a range of udcomplexity and backhaul traffic reduction techniques udthat have been proposed for BS cooperation are udreviewed. A more detailed discussion is provided in the udcontext of MS cooperation concerning the pros and cons udof dispensing with high-complexity, power-hungry channel udestimation.
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