Abstract
Absorption of microwave radio frequency signal by atmospheric rain and losses is prevalent at frequencies above 5 GHz. The functioning frequencies of 18 GHz are taken for the point-to-point microwave link system. This paper presents studies on rain attenuation at 18 GHz, which specifies minimum performance parameters for terrestrial fixed service digital radio communication equipment. It presents a 3.2 km experimental link at 18 GHz 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 50 mm/hr and attenuation values of 33.38 dB and 21.88 dB 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, γ%p, and effective specific rain attenuation, γeff. 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 75 GHz links which shows better prediction capability. Particularly, in an 18 GHz 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.
Highlights
The 5 GHz operating frequency, liquid rain in the form of absorption and scattering becomes a serious contributor to transmission losses [1]
The method is based on the calculation of the behavior of path attenuation that exceeded for 0.01% of the time, which is the product of specific attenuation, γR, and effective path length, deff, which depends on the product of actual path length, d, and path reduction factor, r
The experimental results are observed to be underestimated by the ITU-R P.530-16 method for a path length of 3.2 km, and a similar pattern is observed from the da Silva Mello, Moupfouma, and Abdulrahman models
Summary
The 5 GHz operating frequency, liquid rain in the form of absorption and scattering becomes a serious contributor to transmission losses [1]. Rain attenuation prediction models take into account the path reduction factor, which features both path length and rainfall rate. This recommendation provides prediction methods for the propagation effects that should be taken into account in the design of digital fixed LOS links operating beyond 5 GHz, both in clear weather and in rainfall conditions. It provides link design guidance in clear step-by-step procedures including the use of mitigation techniques to minimize propagation impairments. The attenuation that exceeded for other percentages of time in the range 0.001% to 1% is deduced from the power law whose expression and estimation of the factor, r, is given in the recommendation of ITU-R P.530-16 [7]
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