Bandwidth Efficient Clock Skew Compensation in TDMA-based Star Topology Wireless Networks

One of the prevalent method to achieve clock synchronization in star topology based wireless network, is by periodic transmission of a "Beacon" message from the controller. Using this message other nodes locate the start of the time frame established by the controller. This technique has not been energy efficient in case of low duty cycle applications, where the nodes have to receive the Beacon at the start of every frame even when they don't have any data to transmit. Few of existing works solve this problem by introducing a larger fixed size guard time between the transmission slots allocated to the devices. This allows the devices to skip multiple Beacons and still transmit in their allocated time slot without any collision. In such methods amount of bandwidth which remain unutilized due to fixed guard time becomes a considerably large fraction of the total available bandwidth. In this paper, we propose a novel technique to allow the nodes to skip the Beacon for certain number of frames by introducing the concept called Variable Guard Time (VGT). The number of frames that a node can remain synchronized with the coordinator without receiving the Beacon depends upon the number of Guard Slots allocated to it. This is decided based upon factors like the node's energy saving requirement, the actual clock drift rate between the devices and the available bandwidth. Simulation results show that, in terms of bandwidth utilization, the proposed idea of VGT outperforms the traditional approach of fixed guard time scheme.