Buffer-Aided BICM-OFDM Relaying

In this paper, we study a cooperative diversity scheme for wireless systems where the relay is equipped with a buffer. We consider practical frequency-selective channels and adopt the combination of bit interleaved coded modulation and orthogonal frequency division multiplexing (BICM-OFDM). We propose a novel link selection protocol for BICM-OFDM systems where the relay either transmits or receives in a given time slot depending on the quality of the links. We derive closed-form upper bounds for the asymptotic worst-case pairwise error probability and the diversity gain of the considered buffer-aided relaying scheme for infinite buffer size. We show that impressive diversity gains can be achieved with buffer-aided relaying compared to conventional relaying at the expense of packet delay. In fact, for buffers of infinite (or very large) size, the diversity gain is doubled for links with identical frequency diversity, and even a higher diversity gain advantage is possible for non-identical diversity links. The derived analytical results and performance gains are corroborated by simulation results, where we also show that for buffers of moderate size, a significant coding gain can be achieved, if not any diversity gain.