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

A new approach to relay and user selection is proposed using threshold-based transmission to reduce outage probability and save transmit power. By exploiting properties of dual-hop transmission using amplify-and-forward (AF) relaying, new threshold-based relay and user (TRU) selection protocols that employ one-bit channel state information (CSI) feedback are proposed for multiple-relay, multiple-user systems. These new protocols have the advantages of (1) economical feedback, and (2) optional adaptive power-saving transmission. Centralized selection (CS) and distributed selection (DS) policies as well as lower-complexity suboptimal selection schemes are investigated for downlink transmission. Exact expressions for outage probability, outage diversity and feedback requirement are provided to quantify the complexity/performance trade-offs. The analysis shows that selection threshold(s) can be chosen such that transmission is interrupted when system outage is certain, which allows power saving without impairing outage performance. These protocols are compared in terms of performance, energy-efficiency and system requirement to others that trade outage performance for additional energy saving and/or reduced complexity.