Selectivity vs. Blocking in Wireless Communication

This article clarifies the difference between selectivity and blocking in wireless communication systems. It also provides links to related concepts like sensitivity.

Selectivity Defined

Selectivity refers to a receiver’s ability to filter out interference from other radio frequency (RF) devices that are operating within the same frequency band, meaning they are close in frequency to the desired signal. A transceiver with good RF selectivity maintains a solid RF coverage range.

Conversely, if a wireless system has poor selectivity, nearby interfering RF systems would need to be moved further away physically to avoid disrupting its operation.

Blocking Defined

Blocking, on the other hand, is the ability of a receiver to filter out interference from RF devices operating in different frequency bands, meaning they are farther away in frequency from the desired signal.

The “blocking” ratio is often expressed as the ratio of the level of the unwanted signal to the level of the wanted signal, and it’s typically specified in decibels (dB).

For example, a Zigbee transceiver might support 65 dB of adjacent channel rejection at a 12.5 kHz offset. This is a selectivity specification. That same transceiver might also support a 90 dB blocking specification.

Key Difference Summarized

In essence:

• Selectivity: Deals with interference from nearby frequencies within the same band.
• Blocking: Deals with interference from frequencies in different bands.