Link SNR

	Value
model_family	snr
Status	Served
Current release	snr-baseline-v1
Forecasts	snr_db p10, p50, p90
Horizons	1, 3, and 5 minutes
Entity	Link

Overview

Forecasts a link's signal-to-noise ratio (snr_db, in dB) at 1, 3, and 5 minutes ahead, with an 80% interval around the median. It reads the link's recent observations, pass geometry, and RF configuration from the telemetry you write with POST /telemetry, and returns forecasts through GET /predictions with model_family=snr.

Intended use and out-of-scope use

Intended use:

• A reference forecast for live links: what the link is expected to read over the next few minutes, given what it reads now.
• A baseline that more capable releases are compared against.
• Flagging links that are already weak, through the median and the lower bound of the interval.

Out of scope:

• Predicting a fade or recovery the link has not shown yet. The current release does not extrapolate a trend (see Method and version).
• Horizons beyond 5 minutes, or links not yet in view.
• Link budget design. The forecast describes the link you report, not a link you plan to build.
• Links with no recent telemetry. They are declined, never forecast as zero.

Inputs

Write one link record per link, tagged entity_id with the link ID you later pass in link_ids.

Field	Unit	Required	Description
snr_db	dB	Yes	Observed signal-to-noise ratio.
elevation_deg	deg	Yes	Satellite elevation seen from the ground station.
azimuth_deg	deg	Yes	Satellite azimuth seen from the ground station.
slant_range_km	km	Yes	Distance between the satellite and the ground station.
frequency_ghz	GHz	No	Downlink carrier frequency.
bandwidth_mhz	MHz	No	Channel bandwidth.
g_t_db_k	dB/K	No	Ground station figure of merit (G/T).
eirp_dbw	dBW	No	Satellite effective isotropic radiated power.

	Value
Measurement	link
Cadence	One record every 15 seconds while the link is in view.
Required history	The model reads the last 4 minutes. A link with no recent samples is declined with no_telemetry or insufficient_telemetry.
Frames	Elevation and azimuth are in the ground station's local horizon frame.

Omitted geometry and RF fields are filled with fixed defaults (elevation 30°, 20 GHz, 36 MHz, G/T 20 dB/K, EIRP 50 dBW), so the forecast then describes a generic link rather than yours.

{
  "measurement": "link",
  "time": "2026-10-04T12:00:00Z",
  "tags": { "entity_id": "sat-1-gs-1" },
  "fields": {
    "snr_db": 12.5,
    "elevation_deg": 45.0,
    "azimuth_deg": 180.0,
    "slant_range_km": 1200.0,
    "frequency_ghz": 20.0,
    "bandwidth_mhz": 36.0,
    "g_t_db_k": 20.0,
    "eirp_dbw": 50.0
  }
}

Explore the link budget

Geometry and RF configuration bound what any SNR forecast can be. Drag the fields below to see how elevation, frequency, power, and rain move a clear-sky free-space budget.

Elevationelevation_deg25 °Altitude550 kmFrequencyfrequency_ghz20 GHzSatellite EIRPeirp_dbw30 dBWGround G/Tg_t_db_k10 dB/KBandwidthbandwidth_mhz36 MHzRain fade0 dB

13.6dB SNR

Link closes: +10.6 dB over a 3 dB threshold

Slant range

1123 km

Free-space loss

179.5 dB

C/N₀

89.1 dB-Hz

A clear-sky free-space budget. The SNR model reads these same fields from your telemetry and learns what this formula misses.

Outputs

One item per link and horizon:

Field	Unit	Description
snr_db_p50	dB	Median forecast.
snr_db_p10	dB	Lower bound of the 80% interval.
snr_db_p90	dB	Upper bound of the 80% interval.

	Value
Horizons	1, 3, and 5 minutes. Restrict with horizon_minutes.
Cadence	Forecasts are computed on request when no fresh result exists. Check predicted_at for each item's age.
Provenance	Each item carries model_version, feature_view_id, and model_release_id. Keep them with exported results.

Request forecasts

curl --fail-with-body -sS \
  -H "x-api-key: $CONSTELLATION_API_TOKEN" \
  "https://api.constellation.space/predictions?model_family=snr&link_ids=sat-1-gs-1"

From an AI agent, call get_predictions on the MCP server with model_family set to snr and the same IDs in link_ids. Both need a key with predictions:read. GET /predictions describes the response and per-entity errors.

Tiers

A fidelity tier labels how a model is served, not what a plan includes. This model is served at Bronze, by snr-baseline-v1. Silver and Gold are not served yet.

Every plan calls the same release: plans differ in allowance, not in tier. GET /predictions takes no tier parameter.

Method and version

The current release, snr-baseline-v1, is a persistence baseline. Its median at every horizon is the link's last observed snr_db, carried forward unchanged, and the interval around it widens with the horizon. It does not extrapolate a trend, and it does not yet use the geometry and RF fields to move the median. Use it as a reference forecast.

Limitations and known failure modes

• No trend. A link that is fading or recovering is forecast flat at its last value, so the median lags real change. The lag grows with the horizon.
• Stale input. The forecast is only as recent as the last snr_db sample. Check predicted_at and your own write cadence.
• Defaults hide missing fields. A record without geometry or RF fields forecasts against fixed defaults without failing.
• Sparse samples. Fewer samples in the 4 minute window still forecast, with less evidence behind them.
• Declines are not zeros. Links without usable input appear in entity_errors; a 200 response can carry both results and errors.

Changelog

Release	Change
snr-baseline-v1	Current served release. Persistence baseline.