Optimization of 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 low throughput, particularly if the number of multicast 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 corresponding transmission rate. We analyze the throughput of wireless multicast systems with HARQ-CC under various channel conditions and derive a closed-form approximation for the optimal rate. The numerical evaluation of our analytical expressions reveals that HARQ-aided multicast outperforms conventional multicast in most channel environments. To further improve performance, we propose a dynamic rate-allocation scheme that combines the advantages of conventional multicast and HARQ-aided multicast. �� 2006 IEEE.Manuscript received January 12, 2010; revised March 22, 2010 and April 23, 2010; accepted May 23, 2010. Date of publication June 7, 2010; date of current version September 17, 2010. This work was supported in part by the National Research Foundation of Korea Grant funded by the Korean Government under Grant NRF-2009-352-D00121 and in part by the Ministry of Knowledge Economy under the Information Technology Research Center support program supervised by the National IT Industry Promotion Agency under Grant NIPA-2010-(C1090-1011-0011). This paper will be presented in part in the IEEE Personal, Indoor and Mobile Radio Communications Symposium, Istanbul, Turkey, September 2010. The review of this paper was coordinated by Dr. C. Yuen