An incremental relaying protocol based on the adaptive decode-and-forward relaying scheme is presented for a cooperative wireless network with binary frequency-shift keying modulation. To reduce error propagation and satisfy biterror-rate (BER) requirement, the proposed protocol employs two thresholds. One threshold is used to select reliable relays: if a relay is requested to re-trnsmit, it will do so if its decision variable is larger than the threshold; otherwise, it remains silent. The

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... threshold is used at the destination as follows: the destination sends a request to re-transmit if the decision variable corresponding to a received signal is smaller than the threshold, otherwise, the destination sends a request to stop retransmissions. 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 maximise the throughput while the BER meets a given constraint is investigated. Simulation results show that our proposed protocol leads to a considerable improvement in the performence of cooperative diversity systems.