We undertake a systematic experimental study of the effects of concurrent packet transmissions in low-power wireless networks. Our measurements, conducted with Mica2 motes equipped with CC1000 radios, confirm that guaranteeing successful packet reception with high probability in the presence of concurrent transmissions requires that the signal-to-interference-plus-noise-ratio (SINR) exceed a critical threshold. However, we find a significant variation of about 6 dB in the threshold for groups of radios operating at different transmission powers. We find that it is harder to estimate the level of interference in the presence of multiple interferers. We also find that the measured SINR threshold generally increases with the number of interferers. Our study offers a better understanding of concurrent transmissions and suggests richer interference models and useful guidelines to improve the design and analysis of higher layer protocols.

We experimentally investigate the impact of variable transmission power on link quality, and propose variable power link quality control techniques to enhance the performance of data delivery in wireless sensor networks. This study extends the state of the art in two key respects: first, while there are a number of previous results on power control techniques for wireless ad hoc and sensor networks, to our knowledge, nearly all of them have been simulated and analytically studied that assumes the idealized link conditions; second, while there are several recent experimental studies that have shown the prevalence of non-ideal unreliable communication links in sensor networks, the paper has not thoroughly investigated the impact of variable transmission power. We perform a systematic set of experiments to analyze how the transmission power changes affect the quality of low power RF wireless links between nodes. These experiments show how significant variation in link qualities occur in real-world deployments and how these effects strongly influence the effectiveness of transmission power control. We then present a packet-based transmission power control mechanism that incorporates blacklisting to enhance link reliability while minimizing interference. The effectiveness of the proposed scheme is demonstrated via test bed experiments.

Geographic routing in mobile ad hoc networks has proved to provide drastic performance improvement over strictly address-centric routing schemes. While geographic routing has been shown to be correct and efficient when location information is accurate, its performance in the face of location errors is not well understood. In this paper, we study the effect of inaccurate location information caused by node mobility under a rich set of scenarios and mobility models. We identify two main problems, named LINK and LOOP, that are caused by mobility-induced location errors. Based on the analysis via ns-2 simulations, we propose two mobility prediction schemes - neighbor location prediction (NLP) and destination location prediction (DLP) to mitigate these problems. Simulation results have shown noticeable improvement under all mobility models used in our study. Our schemes achieve up to 27% improvement in packet delivery and 37% reduction in network resource wastage on average without incurring any additional communication or intense computation.

Geographic routing has been introduced in mobile ad hoc networks and sensor networks. Under ideal settings, it has been proven to provide drastic performance improvement over strictly address centric routing schemes. While geographic routing has been shown to be correct and efficient when location information is accurate, its performance in the face of location errors is not well understood. We study the effect of inaccurate location information caused by node mobility under a rich set of scenarios and mobility models. We identify two main problems, named LLNK and LOOP, that are caused by mobility-induced location errors. Based on analysis via ns-2 simulations, we propose two mobility prediction schemes - neighbor location prediction (NLP) and destination location prediction (DLP) to mitigate these problems. Simulation results show noticeable improvement under all mobility models used in our study. Under the settings we examine, our schemes achieve up to 27 percent improvement in packet delivery and 37 percent reduction in network resource wastage, on average without incurring any additional communication or intense computation.