Low Antenna Ultra Wideband Propagation Measurements and Modeling in a Forest Environment

Over the past decade, research and development in wireless sensor networks has investigated novel and exciting applications for a number of different scenarios. Impulse ultra wideband (UWB) communications promises a number of benefits for use in wireless sensor networks-particularly in forest environments where it can provide robust operation along with the ability to combine communications with precision position location. In this paper, we present measurement results and empirical models for impulse ultra wideband (UWB) propagation in a forest environment. Path loss measurements were performed using a 620 picosecond duration UWB pulse, and over 14000 measurements were recorded in 93 different locations in four different forest environments: light brush, light, medium, and dense forest. Transmitters and receivers were separated by distances ranging from 4 to 50 meters. Path loss exponents were found to range from 2.2-4.3, depending on the antenna and forest density; results which are in agreement with the few existing broadband forest propagation studies presented in the literature. Small-scale fading analysis indicated that UWB signals experience Rician fading, with K-factors in the range of 8-24 dB. These measurements and models should aid in the development of future UWB outdoor sensor networks.