We present the design, implementation, and evaluation of a Time Division Multiplex (TDM) MAC protocol for multi-hop wireless mesh networks using a programmable wireless platform. Extensive research has been devoted to optimal scheduling algorithms for multi-hop wireless networks assuming a perfect TDM MAC protocol. However, the problem of designing and implementing such a protocol has not received due attention. We introduce a design framework that addresses the three main challenges that comprise this problem: (i) How to calibrate and optimize the TDM MAC protocol parameters given a wireless platform, (ii) how to achieve network-wide synchronization with high accuracy, minimal overhead, and most importantly, bounded delay, and (iii) how to integrate the synchronization algorithm with the TDM MAC protocol state machine using minimal hardware resources. We apply our design framework to our platform and evaluate the resulting TDM MAC protocol through controlled experiments in a wireless mesh testbed. The results demonstrate the protocol's ability to provide fairness and graceful performance degradation under packet losses and multi-hop traffic patterns that arise in mesh network deployments.

Research has shown that multi-radio multi-channel mesh networks provide significant capacity gains over single-radio mesh networks. Traditional single path routing can lead to poor utilization of the available channels in these networks. Opportunistic multipath routing can better exploit the available channel diversity in a multi-radio network. The goal of this paper is to select multiple paths that, when used concurrently, provide high end-to-end throughput. To this end, we present a metric for multipath selection in multi-radio networks. We evaluate the metric through simulations in Qualnet and show that intelligent multipath routing significantly outperforms single path routing in multi-radio mesh networks.

Multimedia transmission over wireless local area networks is challenging due to the varying nature of the wireless channel as well as the inherent difference between multimedia and data traffic. In the MAC layer, a single bit error in the packet can lead to the entire packet being discarded. This results in a higher packet error rate for larger payload sizes. Retransmission due to packet errors causes the contention window to double, and this leads to a decrease in throughput if the wireless channel does not improve for the retransmitted packets. Hence, throughput is a function of packet payload length as well as the maximum number of allowable retransmissions. In this paper, we investigate the effect of payload length adaptation and retransmissions on the throughput and capacity of multimedia users. Numerical results and simulations reveal that careful payload adaptation significantly improves the throughput performance at low signal to noise ratios (SNRs). It is also observed that excessive retransmissions reduce the effective throughput, thereby decreasing the capacity of multimedia users in the presence of data users. Since multimedia traffic is more latency constrained and less error constrained, by carefully selecting the payload length and maximum number of allowable retransmissions based on the channel conditions, a greater number of multimedia users can be supported.