Performance assessment of cross polarization models at millimetre wavelengths along EarthSpace path in Nigeria

Abstract

Rain-induced depolarization impairments have been a constraint on the effective use of satellite communication systems at millimetre wave band especially in the tropical regions like Nigeria. This region often experiences high and varying degree of rainfall intensity accompanied with large raindrops due to distortion of raindrops when dual orthogonal polarization is employed to double the channel capacity without increasing the bandwidth. This paper examines the performance of five cross polarization discrimination (XPD) models at millimetre wavelengths over ten (10) different locations in Nigeria using five years climatological data acquired from Tropospheric Observatory Data Acquisition Network (TRODAN) of the Centre for Atmospheric Research (CAR). The performance of five different XPD models namely: recent ITU-R 618-15, old ITU-R-722, SIM, CHU and DHW were tested based on the level of estimated interference due to tropospheric effects. The results revealed that at Ku-band uplink/downlink frequencies (10/14 GHz), the unwanted signals will completely overshadow the co-polarized signal between 0.001 and 0.018% of time for the new ITU-R model at Jos, Yola, Sokoto and Nsukka. However, at fade level between 8.93 and 11.08 dB, the crosstalk is prevalent at the receiving station. Though, the recent ITU-R model received wider acceptance, the performance in this study is ranked the lowest while SIM model displayed the best performance. The study therefore recommends, SIM model as the most preferred model to be adopted in estimating depolarization in this region. However, further experimental data for validation is suggested to substantiate this assertion. Key words: Millimeter waves, cross polarization discrimination (XPD) models, co-polar attenuation, earth-space paths, tropical region.