Reliable multicast in multi-access wireless LANs

Multicast is an efficient paradigm for transmitting data from a sender to a group of receivers. In this paper, we focus on multicast in single channel multi-access wireless local area networks (LANs) comprising several small cells. In such a system, a receiver cannot correctly receive a packet if tw o or more packets are sent to it at the same time, because the packets "col lide". Therefore, one has to ensure that only one node sends at a time. We look at two important issues. First, we consider the problem of the sender acquiring the multi-access channel for multicast transmission. Second, for reliable multicast in each cell of the wireless LAN, we examine ARQ-based a pproaches. The second issue is important because the wireless link error ra tes can be very high. We present a new approach to overcome the problem of feedback collision in single channel multi-access wireless LANs, both for the purpose of acquirin g the channel and for reliability. Our approach involves the election of on e of the multicast group members (receivers) as a "leader" or representativ e for the purpose of sending feedback to the sender. For reliable multicast , on erroneous reception of a packet, the leader does not send an acknowled gment, prompting a retransmission. On erroneous reception of the packet at receivers other than the leader, our protocol allows negative acknowledgmen ts from these receivers to collide with the acknowledgment from the leader, thus destroying the acknowledgment and prompting the sender to retransmit the packet. Using analytical models, we demonstrate that the leader-based protocol exhi bits higher throughput in comparison to two other protocols which use tradi tional delayed feedback-based probabilistic methods. Last, we present a sim ple scheme for leader election.