Aggregate Interference
Understanding Aggregate Interference
In isolated systems, interference analysis is straightforward: one transmitter, one victim, one path loss calculation. Modern spectrum environments are far more complex. A satellite earth station receiver may face interference from dozens of terrestrial 5G base stations, each individually compliant with emission limits but collectively raising the earth station's noise floor by several dB. This cumulative effect is aggregate interference.
The challenge is statistical. Each interferer has its own EIRP, activity factor (the fraction of time it transmits), location (which determines path loss), and antenna orientation (which determines how much energy points toward the victim). Since these parameters vary across the population, the aggregate is a random variable best characterized by its probability distribution. Regulatory bodies like the ITU-R and FCC require that aggregate interference stay below defined thresholds at the 95th or 99th percentile of this distribution.
Prx,i = EIRPi − PL(di) − Lpol + Grx(θi)
Aggregate (linear sum):
Iagg = Σ Prx,i (in milliwatts, then convert to dBm)
I/N Criterion:
Iagg/N ≤ −6 dB (1 dB noise rise) for most ITU-R recommendations
SINR Degradation:
ΔSINR = −10 × log10(1 + Iagg/N)
Example: 10 interferers at −100 dBm each → Iagg = −90 dBm. If the noise floor is −95 dBm, I/N = +5 dB (noise floor raised by ~6 dB).
Interference Sources in Shared Spectrum
| Source Type | Mechanism | Typical Level | Mitigation |
|---|---|---|---|
| Co-channel | Same frequency, same band | Dominant | Geographic separation, power control |
| Adjacent channel | Spectral leakage from neighbor | −30 to −50 dBc | Guard bands, better filtering |
| Intermodulation | Nonlinear mixing of multiple signals | −40 to −60 dBc | Linear components, PIM control |
| Out-of-band spurious | Harmonics, clock leakage | −60 to −80 dBc | Filtering, shielding |
| Front-end overload | Strong nearby signal desensitizes Rx | Variable | Bandpass filtering, LNA bypass |
Frequently Asked Questions
How do you calculate aggregate interference?
Sum the received power from every interfering source at the victim location. For each source, compute received power using EIRP, path loss, polarization loss, and victim antenna gain toward that source. Sum in linear (milliwatts), then convert back to dBm. Monte Carlo simulation is standard because interferer positions, powers, and activity factors are random variables. Evaluate at the 95th or 99th percentile per ITU-R recommendations.
Why is aggregate interference harder to manage than single-source interference?
A single interferer can be located and mitigated. Aggregate interference comes from many individually weak sources that are collectively significant. Ten sources at −100 dBm each produce −90 dBm aggregate. No single source dominates, so mitigation requires system-level approaches: frequency plan adjustments, population-wide power reduction, or accepting a higher noise floor.
What regulatory standards address aggregate interference?
ITU-R uses I/N criteria (typically −6 dB, meaning no more than 1 dB noise rise). FCC's CBRS framework (3.5 GHz) uses −80 dBm/10 MHz threshold at Navy radar receivers. ETSI EN 301 893 for 5 GHz DFS limits aggregate RLAN interference to below radar detection thresholds.