Outage analysis and relay allocation for multi-stream OFDMA decode-and-forward Rayleigh fading networks

In this paper, we study a clustered two-hop decode-and-forward (DF) network consisting of a set of source-destination pairs, and a cluster of relays. We consider the case where channels are Rayleigh frequency selective, orthogonal frequency division multiple access (OFDMA) is employed, and there is no line of sight (LOS) between source and destination clusters. Approximating the capacity of a single source-relay-destination link by a Gaussian random variable (RV), the global outage probability of this network is characterized allowing for correlated OFDM subcarrier gains and arbitrary number of bits on each subcarrier. The obtained global probability of outage is used as an objective function to formulate an optimization problem to allocate relays to source-destination pairs. The outage probability minimization problem through relay allocation then is converted to a standard assignment problem, for which a low complexity algorithm based on Hungarian method is proposed. The numerical results show the precision and effectiveness of our analysis and proposed relay allocation technique.