Assessment of dual-polarized interference due to precipitation for high-capacity satellite communication systems in Nigeria

High-capacity satellite systems are specially designed to provide several gigahertz-allotted spectra for multiple spot beams. The reliability of the communication links at high frequencies is often subjected to rain attenuation. In addition to rain attenuation, rain-induced cross-polarization is an important factor for dual-polarization microwave radio communication systems operating at such frequencies. Dual-polarized communication systems adopting frequency reuse usually encounter interference due to a change of transmission energy from one polarization state to another. Signal degradation as a result of some degree of noise causes reduction in the quality of signal between the two orthogonal channels—cross-polarization discrimination (XPD). Therefore, this study assesses the level of degradation due to interference on dual-polarized communication systems for millimeter wave’s band over some selected locations in Nigeria using 5 years (2008–2012) data collected at tropical data acquisition network of the Centre for Atmospheric Research Anyigba. Assessment of dual-polarized interference is based on cumulative distribution of XPD at different frequencies, effect of Earth station receiver frequencies on XPD, XPD–CPA (Co-polar attenuation) relationship and XPD–rain rate relations. Influence of polarization tilt angle for linear and circular polarization on XPD was also assessed. The specific result shows that XPD is extremely low at high rain rates for frequency up to 20 GHz. Depolarization effect is better at the lowest availability with higher value of XPD, and its performance contributes to system availability at the low exceedance probabilities. Port Harcourt, Nsukka, Yola and Sokoto experiences increased interference at receiver stations than other locations considered in this study, especially at Q/V band frequencies. Additional fade margin and appropriate mitigation methods for link availability and good quality of service will be required for sustainability.