Space-Time Mesh Codes for the Multiple-Access Relay Network: Space vs. Time Diversity Benefits

We consider a wireless multiple access network where the sender nodes are aided by a number of relay nodes. A transmission of bit-messages is completed in two phases: in the first phase each sender node originates its message which is overheard at the relay node, and in the second phase each relay node transmits the parity bit calculated from the overheard bit-messages. The low-density parity-check codes are used at the sender nodes in the time-domain, and the low-density generator-matrix code is formed across the spatial domain. At the access node, the received bits from multiple sender nodes and relay nodes are thus encoded in both the time and the spatial domain. We call this combination a space-time mesh code here. In this paper, an iterative decoding scheme is designed for the mesh code and its BER performance in AWGN, fast Rayleigh fading, and quasi-static Rayleigh fading channels are investigated. We note that there is an important trade-off relation between the time-domain and the spatial domain coding. Namely, the time-domain coding is desired when the channel exhibits fast fading; while the spatial domain coding is preferred when the channel is in quasi-static fading state.