Rain Attenuation Study over an 18 GHz Terrestrial Microwave Link in South Korea

摘要

Absorption of microwave radio frequency signal by atmospheric rain and losses is prevalent at frequencies above 5GHz. The functioning frequencies of 18GHz are taken for the point-to-point microwave link system. This paper presents studies on rain attenuation at 18GHz, which specifies minimum performance parameters for terrestrial fixed service digital radio communication equipment. It presents a 3.2km experimental link at 18GHz between Khumdang (Korea Telecom, KT station) and Icheon (National Radio Research Agency, RRA station). The received signal data for rain attenuation and the rain rate were collected at 10-second intervals over three year's periods from 2013 to 2015. During the observation period, rain rates of about 50mm/hr and attenuation values of 33.38dB and 21.88dB occurred for 0.01% of the time for horizontal and vertical polarization. This paper highlights the discussion and comparison of ITU-R P.530-16, Moupfouma, Silva Mello, and Abdulrahman models and proposed an attenuation prediction approach where it presents the relationship between theoretical specific rain attenuation as specified by ITU-R P.838-3, gamma(%p), and effective specific rain attenuation, gamma(eff). Additionally, it studies 1-minute rain rates derived from higher time integration of 5-minute, 10-minute, 20-minute, 30-minute, and 60-minute instances which are obtained from experimental 1-minute rainfall amounts that are maintained by the Korea Meteorological Administration (KMA). The effectiveness of the proposed approach is further analyzed for 38 and 75GHz links which shows better prediction capability. Particularly, in an 18GHz link under horizontal polarization, ITU-R P. 530-16 shows the relative error margin of 71%, 60%, and 38% where as 64%, 49%, and 42% were obtained under vertical polarization for 0.1%, 0.01%, and 0.001% of the time, respectively. The limitation of research lies on the experimental system that is set up in only one location; however, the preliminary results indicate the application of a suitable 1-minute rain attenuation model for a specific site. The method provides useful information for microwave engineers and researchers in making decisions over the choice of the most suitable rain attenuation prediction for terrestrial links operating in the South Korea region, particularly for lower frequency ranges.