Rain Fade Mitigation: UPC, ACM, Site Diversity, and Antenna Sizing
Practical techniques for mitigating rain fade on satellite links—uplink power control, adaptive coding and modulation, site diversity, and antenna sizing tradeoffs.
This article is part of our Satellite Spectrum Interference & Congestion: Operator Field Guide
Uplink Power Control (UPC)
The simplest approach to rain fade compensation. The system monitors transmission quality and boosts uplink power when it detects rain-induced attenuation, then reduces power back to nominal when conditions improve. UPC requires sufficient power headroom at the transmitter and must respect regulatory and satellite operator limits on EIRP. Over-boosting risks equipment stress or increased interference to other services.
Site Diversity
A satellite connects to two or more ground stations instead of relying on a single site. If heavy precipitation hits one station, the link can still be maintained via another location outside the storm cell. This reduces the likelihood that any single storm cuts off critical service, but comes with higher infrastructure and coordination complexity—usually reserved for high-value or mission-critical traffic.
Larger or Better-Placed Antennas
Using larger receiving antennas than clear-sky minimums improves link margin and makes the system less sensitive to moderate fades. Strategic siting—avoiding microclimates prone to frequent heavy rain—also reduces risk. This is a design-time mitigation: build more margin into Ka and Ku links where rain is a known factor.
Adaptive Coding and Modulation (ACM)
ACM automatically drops to a more robust modulation and coding scheme when conditions worsen, sacrificing throughput to keep the link alive. When conditions improve, it returns to more aggressive modulations and higher rates. This lets you maximize throughput in clear weather while maintaining viable service during rain events. ACM is especially useful in high-frequency systems where fade depth and duration can vary dramatically.
How Fading Interacts With Interference
Rain fade does not exist in a vacuum. A link operating with comfortable margin in clear weather might survive mild interference, but under heavy rain, the same interference can push it over the edge. As lower bands fill and more traffic moves to rain-sensitive frequencies, operators rely more on dynamic tools and risk misattributing outages to the wrong cause. Getting the classification right is critical—not just technically, but for SLAs, regulatory reporting, and commercial decisions.