Throughput Maximization in Noncoherent Cooperative Networks

An incremental relaying protocol based on the adaptive decode-and-forward (DF) relaying scheme is presented for a cooperative wireless network composed of one source, K relays, and one destination and with binary frequency-shift keying (BFSK) modulation. In order to reduce error propagation and satisfy bit error rate (BER) requirement, the proposed protocol employs two thresholds. One threshold is used to select reliable relays: if a relay is requested to retransmit, it will do so if its decision variable is larger than the threshold; otherwise, it remains silent. The other threshold is used at the destination as follows: the destination sends a request to retransmit (RR) if the decision variable corresponding to a received signal is smaller than the threshold, otherwise, the destination sends a request to stop retransmissions (RS). Then the destination combines the signals from the requested relays and from the source to make the final decision. Very-tight closed-form upper bounds for both the average BER and throughput are derived for the proposed protocol. Based on the obtained BER and throughput expressions, the problem of choosing optimal thresholds to maximize the throughput while the BER meets a given constraint is investigated. Simulation results are provided to illustrate and validate analytical results. The results show that our proposed protocol leads to a considerable improvement in the performance of cooperative diversity systems.