This paper evaluates the relative merit of amplify-and-forward (AF) and decode-and-forward (DF), the two basic modes of cooperative communications, in practical systems. Specifically, the paper considers the case where the two user channels are slow fading with similar channel qualities and the inter-user channel is some 10 dB better. Through the evaluation of the excess information rate, the analysis of the worst-case error rate, and simulations using practical turbo codes, it is consistently shown that the two modes are practically on par with each other. Furthermore, the study points to inter-user outage as the detrimental factor, and location, rather than the specific cooperative strategy, as the key element in cooperative communications.
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