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 < 1s), low packet delay (< 240ms) and negligible data path jitter (median 0ms), essential for real-time applications.