Adaptive Threshold Based Relay Selection for Minimum Feedback and Channel Usage

We propose adaptive threshold based relay selection scheme for type-2 (user equipment) relay that requires only minimum 1-bit feedback, for which each relay reports to the source if its R-D (relay-destination) instantaneous channel gain is above threshold (i.e., available). A source then selects the best relay among those that yields the highest S-R (source-relay) instantaneous gain, provided threshold is adjusted according to a target signal-to-noise ratio (SNR). Exact and upper bound on the symbol-error rate (SER) are derived for M-PSK signaling to show that the proposed scheme provides the SER performance close to that of an optimal scheme . Further, it is shown that the spectral efficiency can be improved without degrading the link quality in terms of the SER, via adaptive selection between relay (S-R-D) link and direct (S-D) link based on their link SNRs.