##  [Adjacent-Band Interference](/adjacent-band-interference-0) 

 Definition

Interference produced by energy from transmissions or emissions in an immediately neighbouring frequency band that contaminates the band of interest—typically via transmitter spectral leakage, insufficient receiver selectivity or filter roll‑off—resulting in raised noise floor or spurious signal components that degrade reception within the impacted band.

 

 

 

 

 

 





## Principle

Principle

Energy present outside the target band can enter the receiver passband through imperfect filters or receiver front-ends; if that leaked energy raises the effective noise-plus-interference level above the receiver's threshold, the signal-to-noise ratio of desired signals is reduced and packet or symbol errors increase.

 

 

 

 

 





## Demonstration

Demonstration

Illustrative scenario: a transmitter in Band X emits out-of-band sidelobes close to the edge of Band Y. Recognition: the receiver for Band Y employs a filter with finite attenuation at the offending offset. Action: the leaked energy raises Band Y's noise floor. Consequence: decoding failures occur for weak signals in Band Y until the adjacent transmitter reduces power or filtering improves.

 

 

 

 

## Misapplication

Misapplication

Equating adjacent-band interference with harmonic or intermodulation products when the cause is simple spectral leakage, or assuming ABI is always eliminated by any filter without checking the required stopband attenuation and real-world filter slopes.

 

 

 

 

 





## Consequence

Consequence

ABI motivates technical requirements such as spectral masks for transmitters, minimum receiver selectivity, guard bands and certification test limits; failure to control ABI reduces usable capacity and can force increased guard bands or reduced transmit power.

 

 

 

 

## Reversal

Reversal

ABI is negligible when transmit spectral emissions meet applicable masks, receiver selectivity and front-end linearity suffice, or when digital cancellation and notch filtering remove the leakage; conversely, transient or low-level adjacent emissions may not cause measurable degradation.

 

 

 

 

 





## Boundary

Boundary

Clearly within: out-of-band energy from an adjacent allocated channel that reduces SNR inside the target channel. Boundary case: emissions at the edge that only interfere at high relative power. Clearly outside: in-band co-channel interference where transmissions occupy the same nominal frequency.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Spectral efficiency (narrow guard bands, tight packing) versus protection (filters, guard bands, stricter emission masks) against adjacent-band contamination.

 

 

 

 

 





## Synthesis

Synthesis

Adjacent-band interference highlights a physical-layer tradeoff: packing spectrum tightly increases capacity but requires stricter transmitter masks and receiver selectivity; effective system design balances spectral efficiency against practical filter and linearity limits.