Reliable Wireless Multicasting with Minimum Overheads in OFDM-Based WLANs

Even though multicast data transmissions in wireless communication standards doesn´t require ARQ, to achieve reliable multicast over wireless channel, using ARQ is inevitable. However, unlike unicast, a sender needs to receive multiple acknowledgements (ACKs) from group members, and transmitting ACK from each group member degrades the network performance due to the overhead including multiple ACK packet transmissions and channel access process for ACKs and so on. An acknowledgement method with a minimum overhead is proposed in this paper, called OFDMA-based Multicast ACK (OMACK). The scheme uses one OFDM symbol for acknowledgements from all member stations (STAs), and each member STA indicates their packet reception status by allocating a symbol on previously allocated its own sub-carrier within the OFDM symbol. The proposed scheme is extensively evaluated by using simulation, and the results show that the scheme significantly reduces the aforementioned overhead comparing to legacy solutions and as a consequence improves the performance of the wireless networks.