Outage probability tradeoff between unicast and multicast messages in wireless relay-multicasting networks using superposition coding

In this paper, we propose the unicast-multicast balancing protocol which improves the multicast outage probability performance satisfying maximum tolerable outage probability for unicast messages. The wireless relay-multicasting system comprises of a source S, a relay R, and K + 1 destinations D_i, i ϵ {0, 1, ⋯K}. Each D_i{D₀}, i ϵ {0, 1, ⋯K} wants to receive only the multicast messages. On the other hand, D₀ should receive both multicast and unicast messages. At S, using the superposition coding, unicast messages are linearly combined with the multicast messages by assigning fractions a and 1 - α of the available power to the source S. This combined messages are broadcasted by S in the first transmission phase. In the second transmission phase after decoding multicast messages, R transmits the multicast messages. We show that there exists the range of α above which the outage probability of the unicast messages will be equal to or lower than the target error probability, which is the maximum tolerable outage probability ε at which the pair, S - D₀, for unicasting can still maintain reliable communication. Simulation results confirm the efficiency of the proposed scheme and we show that multicast messages is able to achieve the better outage performance with increasing target error probability ε.