Multihopping Strategies: An Error-Exponent Comparison

Multihop channels are believed to provide benefits in performance because the reduction in transmission distance per hop directly translates to increased channel gains. However, a potential concern of multihop transmission is that the incurred delay also increases with the number of hops, and hence may pose challenges for delay-sensitive applications. This paper investigates the issue of delay from the perspective of error exponents, motivated by the fact that delay is tightly coupled with reliability. Two multihopping strategies are compared. The concatenated coding strategy, in which relay nodes perform inner coding and the source-destination pair further performs outer coding, is shown to provide near-optimal performance at low rates. In contrast, the pass-or-decode strategy, where relay nodes can either decode-and-forward or simply pass the received symbols, is shown to outperform the concatenated coding strategy as the achievable rate increases. The comparison suggests different system architectures for high and low rate applications,respectively.