Spatial Diversity Gains in Wireless Sensor Networks through Controlled Limited Mobility: An Experimental Approach

While Wireless Sensor Networks (WSNs) are a rapidly growing field, they still face many challenges. Some of these issues such as critical nodes, small-scale fading, and hidden nodes can be mitigated through the application of controlled limited mobile (COLMO) systems. Small movements on the scale of a fraction of the carrier wavelength can prove to dramatically change the received signal strength (RSS) and thus, link quality. With the proper sampling, it is possible to place a mobile node in a position with favorable multipath fading and greatly increase the link quality. This ability could have huge ramifications on the network, and new routing paths are enabled; therefore, new metrics and trade-offs need to be considered. By placing a Mica mote on a rotating turntable, the mote has the ability to control the location the platform so that the mote can be placed where desired. The performance of the mobile sink was analyzed in environments with various forms of fading to determine how the diversity gain of this system compares to a MIMO design. Several factors affecting the performance of the mobile sink were explored. One important issue is whether the received signal strength indicator (RSSI) or the link quality indicator (LQI) would be the most effect link quality metric. Also, the thesis determines how the sampling rate of the sampled channel affects the general performance of the mobile node.