One-Bit Feedback Selection Schemes for Power-Efficient Multiuser and Multirelay Systems

This paper proposes new selection schemes based on one-bit feedback for a system with multiple amplify-and-forward relays and users over Rayleigh fading channels. We introduce new distributed selection (DS), simplified DS (DSS), and centralized selection (CS) schemes that reduce outage and save transmit power using one-bit feedback. The CS scheme is optimal by selecting only the dual-hop link with equivalent end-to-end SNR above the outage threshold. DS and DSS schemes, on the other hand, require less feedback at the BS and employ a decentralized selection policy. The feedback bit in those schemes render the comparison result between the first- and second- hop SNR and an appropriate threshold. The chosen selection threshold in DS and DSS schemes allows the dual-hop links for which the system outage is certain to be discarded. In the three selection schemes, transmission is switched off to save power when there is no dual-hop link meeting the selection requirement. Closed-form expressions for the DS, DSS, and CS outage probabilities are derived. Numerical results reveal that, even though DSS is a simplified version of the DS scheme, they have similar outage performance. Additionally, DS and DSS are quite competitive with CS for a small number of relays relative to the number of users.