Selection of spatially-distributed relays for two-way relaying with network coding

To help exchanging information between two sources in a two-way relaying network with multiple relays, we consider selecting one 'best' relay or a pair of 'best' relays that broadcast network-coded information to other nodes (source or relay). Further, we assume that the multiple relays are random distributed in a one-dimensional or two-dimensional space between the sources and we take the path loss between the nodes into consideration. We also select the relay(s) based on the max-min criterion in both the Single Relay Selection (SRS) scheme and the Paired-Relay Selection (PRS) scheme. In particular, we propose a Distributed VIterbi Selection Algorithm (DVISA) that selects the pair of 'best' relays in the PRS scheme and we describe how the nodes exchange information in a frame consisting of 4 time slots. Both our analytical and simulation results show that when the path-loss exponent is large and/or there is a sufficient number of relays to choose from, using two relay nodes can provide a lower outage compared with using only one relay node even under the same total transmit power.