Measurement of excess loss for fixed terrestrial links in vegetated campus environment

Abstract

In the design of fixed wireless links, having Fresnel zone clearance or in other words Line-of-Sight (LOS) link is highly recommended. Without the presence of obstacles in the first Fresnel ellipsoids, the signal attenuation of the transmission path is equivalent to free space attenuation. Nonetheless, this ideal unobstructed link cannot be attained at all times especially when the transmitting and receiving antennas are positioned near to the ground particularly below rooftop level as well as when wireless propagation channel depends on the conditions of the environment. Besides the terrain and buildings, the presence of vegetation dong the path will have an adverse effect on the receiving signal. Furthermore, trees growth over time of operation will affect the condition of the link even if the link is initially unobstructed. Hence, this research aims to determine the average value of excess path loss which is inclusive of foliage attenuation by measuring and characterizing the signal distortion attributed to vegetation that exists in the vicinity of point-to-point links based on Institute of Electrical and Electronics Engineers (IEEE) 802.11a Wireless Local Area Network (WLAN) standard at 5.8 GHz. The study on the effect of vegetation blockage is performed within the campus of Universiti Teknologi Malaysia (UTM) for both Line-of-Sight (LOS) and Near Line-Of-Sight (NLOS) links. Data acquisition is performed based on the concept of remote data logging in which data can be gathered via a remote server constantly for 24 hours and seven days a week together with the integration of daily scheduled data logged e-mailing. The behaviour of the link performance is studied and the average excess path losses are found to be 12.2 dB and 4.6 dB for NLOS links obstructed by a single tree and a row of trees respectively.