What Causes Adjacent-Satellite Interference in GEO and How to Prevent It
Learn what causes adjacent-satellite interference in GEO orbits, why it's getting worse, and the practical steps operators can take today to detect, prevent, and mitigate ASI events.
This article is part of our Satellite Spectrum Interference & Congestion: Operator Field Guide
Adjacent-satellite interference (ASI) happens when your receive antenna picks up not only the wanted GEO satellite, but also one or more neighboring satellites that share coverage, frequency, and polarization. Their signals show up as extra interference in your C/(N+I) ratio, eating directly into link margin. With hundreds of active geostationary satellites sharing the equatorial belt and average spacing well under two degrees in congested regions, small user terminals with wide beamwidths naturally collect energy from adjacent slots.
Why GEO Is More Vulnerable Now
Several trends push GEO closer to its interference limits. The belt is more crowded than a decade ago, with tighter spacing and more services per slot. Ka-band and HTS spot-beam systems rely on smaller user dishes with wider beams, increasing susceptibility to ASI and cross-polarization. A noisier RF environment from cellular systems and growing constellations compounds the problem. And higher dependence on interference-free space services—broadcasting, broadband, GNSS, scientific missions—means the consequences of interference are more severe.
What Causes ASI at an Operator Level
Most ASI traces back to ground-side issues. Small dishes (45-65 cm) have only a few dB of gain difference between on-axis and the nearest neighbor at sub-degree spacing—meaning adjacent satellite signals arrive only slightly weaker than the wanted signal. Mis-pointing during installation is one of the most common root causes; tiny movements in azimuth or elevation cause large changes in received power. Polarization errors leak orthogonal co-frequency signals into the wanted channel. Excessive uplink power drives amplifiers into compression, generating intermodulation products that spill across carriers. And external RF sources—5G near C-band, aircraft altimeters, radar—can overload satellite receivers with symptoms that look similar to ASI.
How ASI Shows Up in Your Service
Operators typically see gradual C/(N+I) degradation and shrinking link margins, increased error rates with modulation stepping down more often, and customer-visible issues like pixelation, intermittent disconnects, or throughput drops. Interference costs the sector both money and reputation: pay-TV outages trigger churn and rebates, and mission-critical links experience delays with far higher stakes.
How to Prevent and Mitigate ASI
Treat ASI as a design input, not an afterthought. Before deployment, obtain coordination status and EIRP maps from neighboring satellites. Quantify likely ASI levels for your dish sizes and orbital separations, and reserve sufficient C/(N+I) margin. Enforce disciplined pointing and polarization procedures using professional tools rather than signal bars alone. Control power and stay in the linear region—start carriers at low power and verify amplifier linearity. Deploy continuous spectrum monitoring, enable Carrier ID where supported, and ensure geolocation capability is available for serious events. Harden ground stations against terrestrial emitters with bandpass filters. And work with neighbors and regulators—participation in coordination processes and data sharing are now table stakes for GEO operators.