Rate, Reliability, and Delay Tradeoffs for Decode-and-Forward Relaying

We extend the random coding error exponent to three common decode-and-forward schemes for the relay channel. The resulting bounds give achievable tradeoffs among rate, reliability, and delay, allowing comparison of decode-and-forward with direct transmission and other schemes in broader terms than asymptotic achievable rates alone. In contrast to the asymptotic case in which the achievable rates are identical, the three DF schemes each exhibit different tradeoffs. Motivated by this disparity, we explore increasing the decoder window size at the destination to improve the tradeoffs. The paper includes a brief tutorial on point-to-point error exponents for readers unfamiliar with this information-theoretic tool.