Joint decentralized slot allocation and time synchronization in a TDMA based MAC

Application of wireless networking technology in tactical and mission-critical environments requires wireless connectivity meets certain quality of service requirements; for example, in such environments timely and reliable delivery of data plays a critical rule in the mission success. For such applications TDMA based MAC scheduling is considered an attractive option. However, to have a functional TDMA based MAC for ad hoc multi-hop networks, we need to have efficient and scalable mechanisms for time synchronization and conflict-free slot allocation among nodes. In this paper, we outline progressive decentralized mechanism by which each node can do time synchronization and slot assignment. Any new node wishing to join the network first monitors ongoing transmission activity and ascertains its pattern. Knowing the pattern of the existing transmissions, the new node can synchronize its clock and assign slots. The proposed slot assignment and time synchronization scheme is implemented on a USRP test-bench. We show that we could achieve time-synchronization accuracy on the order of a sampling period. Besides, we can maintain accuracy at this level in a perpetual way without any explicit exchange of synchronization messages.