| Summary: | Transmission over the wireless medium is a challenge compared to its wired counterpart. Scarcity of spectrum, rapid degradation of signal power over distance, interference from neighboring nodes and random behavior of the channel are some of the difficulties with which a wireless system designer has to deal. Moreover, emerging wireless networks assume mobile users with limited or no infrastructure. Since its early application, relaying offered a practical solution to some of these challenges. Recently, interest on the relay channel is revived by the work on user-cooperative communications. Latest studies aim to re-employ the channel to serve modern wireless networks. In this work, the decode-and-forward (D&F) relay channel with half-duplex constraint on the relay is studied. Focus is on producing analytical results for the half-duplex D&F relay channel with more attention given to time allocation. First, an expression for the mutual information for the channel with arbitrary time allocation is developed. Introduction of the concept of conversion point explains some of the channel behavior and help in classifying the channel into suppressed and unsuppressed types. In the case of Rayleigh fading, cumulative distribution function (cdf) and probability density function (pdf) are evaluated for the mutual information. Consequently, expressions for average mutual information and outage probability are obtained. Optimal operation of the channel is investigated. Optimal time allocation for maximum mutual information and optimal time allocation for minimum total transmission time are worked out for the case of channel state information at transmitter (CSIT). Results revealed important duality between optimization problems. Results obtained are extended from a two-hop channel to any number of hops. Only sequential transmission is considered. A cooperative scheme is also developed based on the three-node relay channel. A two-user network is used as a prototype for a multi-user cooperative system. Based on the model assumed, an algorithm for partner selection is developed. Simulation results showed advantages of cooperation for individual users as well as the overall performance of the network.
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