Overlapped NACKs: Improving Multicast Performance in Multi-access Wireless Networks

A wide variety of network applications require the use of reliable multicast protocols to disseminate data from one source to a potentially large number of receivers simultaneously. We focus on multicast in single channel multi-access wireless networks and consider Automatic Repeat reQuest (ARQ) based error control algorithms. We propose a simple NACK based method, called overlapped NACKs, that exploits the physical nature of the transmitted NACK signals in order to achieve a high Signal to Noise Ratio (SNR) even in the presence of NACK collisions. As an example, we apply the proposed method to Bluetooth, quantify its reliability and compare the achievable throughput with respect to the multi-unicast case and to an ACK based protocol. Results show that the overlapped NACK method has the potential to substantially increase the throughput over the ACK based protocol and provides good reliability.