Opportunistic relaying in wireless networks

We analyze fading Interference relay networks with n ad hoc nodes and m half-duplex relays , all operating in the same frequency band. This setup has attracted significant atten-tion and several schemes have been reported in the literature. However , most of the proposed solutions require either centrally coordinated scheduling or detailed channel state information (CSI) at the source nodes. We propose an opportunistic relaying scheme that alleviates these limitations , without sacriicing the system throughput scaling in the regime of large n. The scheme entails a two-hop communication protocol , where sources com-municate with destinations only through half-duplex relays. The key idea is to schedule at each hop only the subset of nodes that can benefit from multiuser diversity. To select the source and destination nodes for each hop , only integer-value CSI feedback is required from the receivers (relays for the first hop , and destina-tion nodes for the second hop). Moreover , the relays operate in a completely distributed fashion , with no cooperation. For the case when n is large and m is fixed , we show that the proposed scheme achieves a system throughput of m/2 bits/sec/Hz. In contrast , the upper bound of (m/2) log log n bits/sec/Hz is achievable with only more demanding CSI assumptions and full cooperation between the relays. Furthermore , we show that (by allowing m to grow as a function of n , and then finding the optimal order of m that maximizes throughput) the system throughput of the proposed scheme scales as m = θ (logn).