Optimal rate allocation for wireless multicast systems employing hybrid-ARQ with Chase combining

The throughput of conventional wireless multicast systems is limited by the multicast user with the lowest channel quality, which leads to a very low throughput especially if the number of users is large. In this paper, we show that hybrid-automatic repeat request with Chase combining (HARQ-CC) is a promising technique to overcome this problem and optimize the transmission rate of wireless multicast systems with HARQ-CC. We analyze the throughput of wireless multicast systems with HARQ-CC and derive a closed-form approximation for the optimal rate. To further improve performance, we propose a dynamic rate allocation scheme which combines the advantages of conventional multicast and HARQ-aided multicast.