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.