Millimeter-wave propagation modeling for 5G based on rain fade data in tropical climate

Abstract

The demand for radio frequency spectrum is rapidly increasing to serve a large number of customers in business, government, and private sectors. Hence, 5G is forcibly moving forward to utilizing millimeter-waves frequency bands. Rain is the main source of impairments for the radio wave when the frequency is higher than 10 GHz. Rain attenuation can be obtained directly from measurement or predicted from a knowledge of rain intensity. The accuracy of rain attenuation prediction on short-range mm-waves terrestrial links is vital for signal strength prediction and link budget design for 5G systems and beyond. However, recent measurements at mm-wave with short path lengths (less than 1 km) show that all prediction models, including ITU-R P.530-17, cannot predict the measured rain attenuations. Two modifications are proposed on ITU-R P.530-17 rain attenuation model. Firstly, the distance factor is analyzed thoroughly. A modification on distance factor is presented as “Increment Factor” (Ifγ) for path lengths less than 1 Km and updated based on measurements at 26 and 38 GHz at 0.3km path length for one year period in Malaysia, at 25 GHz for 223 m path length in Japan and 75 GHz for 100 m path length in Korea. Secondly, an effective rain rate concept (Reff) is also proposed and modeled to eliminate the need for effective path lengths, representing rain intensities variations over a very short path. Several available measurements from various geographical locations in Malaysia and abroad with different frequencies and less than 1 km path lengths were utilized to validate both models and find good agreement. Rain attenuation impacts path loss, path loss exponent, and shadow fading are analyzed using two large-scale fading path loss models namely 3GPP and NYUSIM. The randomness behaviour of rain attenuation increases path loss exponent (PLE=2.79 at R0.01% =125 mm/h). The NYUSIM channel model provided a better estimation of the measured data of path loss compared with 3GPP. The close-in (CI) path loss model which has been implemented by NYUSIM is modified by including the Path Loss Exponent and Shadow Fading as a function of the percentage of availability (%P of time). The proposed probabilistic path loss model, which is a combination of the close-in reference LOS free space path loss, rain attenuation based on modified ITU-R P.530-17 and shadowing at different probabilities, can predict the path loss more accurately in tropical regions. The average path loss value is found at 132.36 dB at 38 GHz with a path length of 300 m for one year period and is located at 144.5 dB with considering shadowing in the urban region with σSF = 5.22 dB. This has been realized from the analysis that the 99.99% reliability with 300m link can be designed at 38GHz with an additional 12 dB fade margin in the tropical region. All of these findings will be beneficial to develop 5G channel models in an outdoor environment, especially for mm-wave and short-path lengths applications with high reliability.