LiT MAC: addressing the challenges of effective voice communication in a low cost, low power wireless mesh network

In this work, we consider the goal of enabling a local voice communication system, within a village, using a low cost and low power wireless mesh network. The design of an appropriate MAC is a major challenge in this context. Towards this goal, we present LiT: a full-fledged TDMA-based MAC protocol for real-time applications over such networks. We showcase the practicality of such a system through implementation-based evaluation of LiT on an inexpensive, low power 802.15.4 platform. While there is plentiful literature on the use of TDMA for wireless mesh networks, a practical multi-hop TDMA system remains elusive. In this regard, LiT addresses several practical concerns. It has built-in support for time-synchronization, has a flexible interface with routing, and has a dynamic TDMA schedule dissemination mechanism. LiT is multi-channel capable and is centrally controlled. It achieves robustness in the face of wireless packet errors by making extensive use of soft-state mechanisms. With appropriate duty cycling, LiT can make nodes run for several weeks without power off the grid. Evaluation of LiT on outdoor testbed shows quick flow setup (latency s), low packet delay (ms) and negligible data path jitter (median 0ms), essential for real-time applications.