The higher the better? Think twice!

As research interest in the Internet of Things continue to grow, concerns are raised regarding potential limitations of the current body of knowledge on performance engineering for wireless links. Best practices in this thematic area have insofar largely been focused on human-to-human communications (e.g., wide area cellular wireless networks) and traffic patterns emerging from human actions (e.g., asymmetric bandwidth between the uplink and downlink traffic directions) in urban areas. As a result, studies of the propagation profile that would properly characterize the deployment of wireless technologies (e.g., sensor networks) in rural areas and for specific applications of machine-to-machine (M2M) communications are not sufficiently developed in the literature. To address this shortcoming, we collect and study RSSI measurements as a function of base station antenna height and at a certain distance and transmitting antenna height, under a rural setting. The measurements collected from our testbed instrumentation seem to follow closely the theoretical two-ray model. It is therefore shown here that whenever a second ray has impact on propagation characteristics there is always an optimum and minimum base station antenna height. A method for defining those heights is presented in this paper, which further allows performance optimisation of a wireless sensor network.