Abstract—In this paper we investigate the optimal relay location in the sense of maximizing suitably defined coverage region for MIMO relay channel. We consider the general Rayleigh fading case and assume that the channel state information is only available at the receivers (CSIR), which is an important practical case in applications such as cooperative vehicular communications. In order to overcome the mathe- matical difficulty regarding determination of the optimal relay location, we provide two analytical solutions, and show that it is possible to determine the optimal relay location (for a desired transmission rate) at which the coverage region is maximum. Monte Carlo simulations confirm the validity of the analytical results. Numerical results indicate that using multiple antennas increases coverage region for a fixed transmission rate, and also increases the transmission rate linearly for a fixed coverage.

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