Characterization of link asymmetry in wireless sensor networks

Recent experimental studies in wireless sensor networks (WSNs) have confirmed that asymmetry in the wireless links has a significant effect on the performance of WSN network protocols. Protocols which work in simulation studies often fail when link asymmetry is encountered in real deployments. Characterization of link asymmetry is thus of paramount importance for the design and operation of re-silient WSN protocols in real scenarios. This paper details an empirical study to characterize link asymmetry in WSNs. There are several factors that contribute to link asymmetry in WSNs, the major ones being environmental effects and hardware performance. In this work, we used a systematic approach to measure the effects of hardware performance, i.e. transmitter, receiver and antenna characteristics, on link asymmetry using off-the-shelf WSN devices such as Xbow Mica2 and MicaZ motes. We conducted experiments to study the variations in spectrum utilization in these WSN devices, for both wired and wireless connections, and to ascertain the effects of any frequency and amplitude mismatches on link symmetry between nodes in transmission and reception.