Adaptive Relaying in Noncoherent Cooperative Networks

This correspondence considers a cooperative network in which binary frequency-shift-keying (BFSK) modulation is employed to facilitate noncoherent communications between a source and a destination with the help of relays. Proposed is an adaptive cooperative scheme that employs two thresholds as follows. One threshold is used to select retransmitting relays: a relay retransmits to the destination if its decision variable is larger than the threshold, otherwise it remains silent. The other threshold is used at the destination for detection: the destination marks a relay as a retransmitting relay if the decision variable corresponding to the relay is larger than the threshold, otherwise, the destination marks it as a silent relay. Then the destination combines the signals from the retransmitting relays and from the source to make the final decision. The average end-to-end (e2e) bit-error rate (BER) is derived in a closed-form expression for a two-relay network. The problems of selecting optimal thresholds or jointly optimal thresholds and power allocation to minimize the average BER are investigated. Simulation results are provided to validate our analysis. Compared to the previously proposed piecewise-linear (PL) detection scheme, our proposed scheme yields a superior performance under a wide range of channel conditions when optimal thresholds or jointly optimal thresholds and power allocation are employed.