Complexity and performance tradeoffs of near-optimal detectors for cooperative ISI channels

Cooperative communication has attracted a lot of attention for its ability to exploit increased spatial diversity available at distributed antennas on other nodes in the system. For a cooperative system employing non-orthogonal amplify-and-forward half-duplex relays, the maximum likelihood sequence estimation (MLSE) is the optimal detector in intersymbol interference (ISI) channels. The implementation complexity of the optimal detector scales exponentially with the length of effective channel impulse response (CIR), however, which becomes very long and sparse as the relay period increases. In this paper, we focus on suboptimal detector design, complexity, and performance for cooperative relays in ISI channels. We first explore use of a decision feedback sequence estimator (DFSE). Next, to exploit the structured sparsity in the effective CIR, we consider an iterative belief propagation (BP) algorithm based detector. Using simulation results, we explore the tradeoff between complexity and performance.