Variable-Rate Two-Phase Collaborative Communication Protocols for Wireless Networks

The performance of two-phase collaborative communication protocols is studied for wireless networks. All the communication nodes in the cluster are assumed to share the same channel and transmit or receive collaboratively in a quasi-static Rayleigh flat-fading environment. In addition to small-scale fading, the effect of large-scale path loss is also considered. Based on a decode-and-forward approach, we consider various variable-rate two-phase protocols that can achieve full diversity order and analyze the effect of node geometry on their performance in terms of the outage probability of mutual information. For the single-relay node case, it is shown that if the collaborator node is close to the source node, a protocol based on space-time coding (STC) can achieve good diversity gain. Otherwise, a protocol based on receiver diversity performs better. These protocols are also compared with one based on fixed-rate repetition coding and their performance tradeoffs with node geometry are studied. The second part deals with multiple relays. It is known that with N relays an asymptotic diversity order of N+1 is achievable with STC-based protocols in the two-phase framework. However, in the framework of collaborative STC, those relay nodes which fail to decode remain silent (this event is referred to as a node erasure). We show that this node erasure has the potential to considerably reduce the diversity order and point out the importance of designing the STC to be robust against such node erasure