OFDMA-Based Reliable Multicasting MAC Protocol for WLANs

Although many wireless communication standards include multicast as well as unicast traffic in layer 2, most parts of the specifications are limited to unicast methods. In addition, although the existing wireless standards provide reliable unicast methods using an automatic repeat request (ARQ) and a retransmission, multicast packets are not reliably transmitted using these standards. To retransmit a multicast packet, the acknowledgements (ACKs) from the receivers need to be received by the sender to determine whether a retransmission is required. However, transmitting an ACK from each group member degrades the network performance due to the overhead induced by multiple ACK packet transmissions and channel access processes for the ACKs. To solve this problem, in this paper, a medium-access control protocol called the orthogonal frequency division multiplex access (OFDMA) based multicast ACK (OMACK), with minimum ACK overhead over wireless local area networks, is proposed. The proposed scheme uses one orthogonal frequency division multiplex (OFDM) symbol for the ACKs from all member stations (STAs), and each member STA indicates its packet reception status by utilizing a subcarrier within the OFDM symbol. The proposed scheme is thoroughly examined by using simulation and theoretical methods, and the results show that it significantly reduces the aforementioned overhead and, as a consequence, improves the performance of wireless networks.