On the error exponent of the wideband relay channel

We investigated the error exponent of the wideband relay channel. By computing the random coding error exponent of three different relay strategies, i.e., amplify-and-forward (AF), decode-and-forward (DF) and block Markov code (BMC), we found that relayed transmission can enhance the wireless link reliability significantly in the wideband regime compared to direct transmission. We also studied optimal power allocation and relay placement by maximizing the reliability function. Analytical and numerical results show, for DF and BMC relays, placing the relay node in the middle of source and destination provides the best link reliability. But for the AF relay scheme, the optimal relay placement depends on the path-loss exponent; for large path-loss exponents, half-way relay placement is also optimal.