Optimum adaptive coding and modulation characteristics on broadband satellite communication system in tropical Nigeria

Abstract

Broadband satellite services operating at higher frequencies above 10 GHz are liable to atmospheric degradations. The effect atmospheric impairment is much higher in tropical and equatorial zones. The temporal and dynamic behaviours of precipitation has affected the optimum performance of satellite broadband applications using satellite very small aperture terminal (VSATs) for small offices and homes (SOHO). In order to improve the efficiency of satellite link operating in tropical rain zone, some propagation impairment mitigation technique (PIMT) can be employed. The objectives was to quantify the rain rate at 0.01%, quantify the rain and its effect on Ku-band frequency satellite link, examine the link attenuation level on 6 MHz and 2 MHz bandwidths and develop the optimum performance threshold for adaptive coding and modulation (ACM) in real-time operation for Nigcomsat ground station in Abuja, Nigeria. Two years measurement campaign was conducted from January 2016 to December 2018. This thesis shows that increasing the carrier power can improve the throughput, availability and reduction in the required bandwidth by 58%. This makes ACM a good candidate for bandwidth on demand applications which can greatly improve the design link for broadband satellite applications in tropical zone. This result will offer essential input to satellite operators to achieve the best spectral efficiency. The improvement in the total downtime from 2556 minutes recording the annual availability at 94.41% without ACM in 2016, to an excellent performance of 99.85%, recording annual downtime of only 42.8 minutes after the full implementation of ACM in 2018. This performance is the peak performance achievable by any satellite operator in recent time. The ITUR P. 841-4 recommended 0.01% assurance of 99.99% to achieve an annual outage of 53 minutes. However, the achieved 42.8 minutes annual outage has satisfied the standard set by Nigcomsat of 99.7% and surpassed the requirements with the implementation of ACM. This is one of the best fit attained by Nigcomsat in meeting its customer’s obligation ever in the last 7 years of Nigcomsat-1R satellite operation. This study has established the thresholds of performance for VSATs in tropical zone with seven (7) operating states of ACM in accordance with the atmospheric condition of Abuja, Nigeria.