Near earth propagation loss model in forest for low power wireless sensor network

Radio wave propagation in the forest environment of cellular systems is an important theme, and many propagation models have been proposed. In recent years, forest applications of low power wireless sensor network are also demanded from the viewpoint of environmental protection using a compact ultra-low power sensor nodes. In this paper, we measured the distance dependency of RSSI (Received Signal Strength Indicator) in the forest environment at low antenna height 105 cm using wireless sensor modules with small pattern-antenna 2.4 GHz (3mW) and 920 MHz (20mW). As a result, at 2.4 GHz, TWDP (Two-Wave Diffuse Power) fading is significant factor influenced by ground reflection at short distance, and Rayleigh fading becomes dominant as distance becomes longer. On the other hand, in the 920MHz, scattering occurred even at a close distance with a prospect, the influence of ground reflection was relatively small, and it became clear that fading occurred at any distance. In consideration of these phenomena, we propose a new radio wave propagation model near the ground surface that can be applied 920MHz-2.4 GHz.