An Adaptive, High Performance Mac For Long-Distance Multihop Wireless Networks

We consider the problem of efficient MAC design for long-distance WiFi-based mesh networks. In such networks it is common to see long propagation delays, the use of directional antennas, and the presence of inter-link interference. Prior work has shown that these characteristics make traditional CSMA-based MACs a poor choice for long-distance mesh networks, prompting several recent research efforts exploring the use of TDMA-based approaches to media access.In this paper we first identify, and then address, several shortcomings of current TDMA-based proposals, which exhibit inefficienct throughput and delay charactersistics as they use fixed-length transmission slots that cannot adapt to dynamic variations in traffic load. We show that throughput achieved by existing solutions falls far short of the optimal achievable network throughput. Current TDMA-based solutions also only apply to bipartitie network topologies due to interference scheduling contraints. In this paper, we present JazzyMac, a simple, practical and efficient MAC protocol that addresses the above limitations. JazzyMac achieves efficiency by enabling variable-length link transmissions slots; each node can adapt the length of their transmission slots in accordance with changing traffic demands. JazzyMac is practical as it can be applied to arbitrary network topologies, and each node can use purely local information for slot adaptation. Finally, the use of dynamic slot lengths allows JazzyMac to achieve better tradeoffs between throughput and delay.We evaluate JazzyMac using detailed simulation over a range of traffic patterns and realistic topologies. Our results show that JazzyMac improves throughput in all considered scenarios. This improvement is often substantial (e.g.,in 50% of our scenarios, throughput improves by over 40%) and is particularly pronounced for the common case of asymmetric traffic (e.g.,leading to almost 100% improvements). Furthermore, JazzyMac can achieve much better average delay for the same throughput.