Overview of Adjacent Satellite Interference
The geostationary orbit arc is increasingly crowded, with average longitudinal orbit separation getting close to 2.5° or less. For Ku-band direct-to-home (DTH) TV service, a small dish of 65cm is typically preferred for ground reception, yet the beamwidth of such a small dish is wide and so unavoidably picks up unwanted signals from adjacent satellites with co-coverage, co-frequency & co-polarization, resulting in different levels of ASI.
The on-axis to 2.5° off-axis gain delta of 65cm is about 11.5dB only. If there is no EIRP delta between the satellites, this means the downlink carrier-to-adjacent satellite interference is 11.5dB. This number is small and has significant implications on the achievable performance of DTH service. For example, if the adjacent satellites do not have any carriers or are operating at back-off mode for data services at the frequency and co-coverage with the DTH service, then the DTH service can have high throughput capacity with good signal quality. However, if the carrier of an adjacent satellite is saturated, the quality of DTH service will suffer. A prudent approach would therefore be to reserve an appropriate margin for ASI.