Joint Cooperative Diversity and Scheduling in OFDMA Relay Systems

Motivated by joint cooperative diversity and scheduling (JCDS) in frequency-flat fading relay systems, this paper proposes JCDS for frequency-selective fading relay systems with an OFDMA technique. While JCDS for frequency-flat fading relay systems uses time-varying phase rotation at the relays, JCDS in this paper uses fixed cyclic delay times instead. This technique can be considered as an extension of cyclic delay diversity in a conventional MIMO-OFDM system to a multiuser relay system in order to gain both multipath diversity and multiuser diversity. It is shown that JCDS using fixed cyclic delay has significant gains in aggregate throughput while per-link throughput can be maintained when there are enough relays. The effect of delay spread to the required number of relays and to the throughput performance are shown by simulation.