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Receiver Sensitivity versus Receiver Selectivity

This page on receiver Sensitivity versus receiver selectivity describes difference between sensitivity and selectivity w.r.t. receiver.

Sensitivity and selectivity are very useful parameters for a wireless receiver.
Receiver Sensitivity- It is the smallest possible signal power level at the input of a receiver which assures proper functioning of a wireless receiver i.e. it will decode data correctly. This wireless receiver can be receiver part of a mobile phone, base station or any wireless standard compliant device such as WLAN, zigbee, Bluetooth etc.

Up to this power level system delivers Bit Error Rate within the desired range. Below this level system starts (i.e. higher in value) producing more bit errors and is not advisable to operate system below this power level.

For example, IEEE standard for Zigbee 802.15.4 specifies receiver sensitivity of 2.4 GHz device to be about -85 dBm. If one increases receiver sensitivity to say -90 dBm from -85 dBm, it will extend coverage or distance (in meters) for that particular radio/wireless device. Higher receiver sensitivity reduces the need of power hungry power amplifier at the transmitter end, which reduces power consumption and increases battery life. This is the main reason behind people going for higher receiver sensitivity when selecting a radio device.

receiver sensitivity measurement test set up
Fig.1 Receiver sensitivity measurement test setup

As shown in the figure, start with Pin of 5 dB more than the receiver sensitivity and check BER in the test system. Keep reducing Pin till BER is within acceptable range, Stop when BER is out of range of acceptance and record the Pin. This Pin is the receiver sensitivity of the Device Under Test (DUT).
Refer RF Receiver Sensitivity test and measurement setup➤.

Receiver Selectivity- It refers wireless receiver's capability to detect and decode desired signal in the presence of other unwanted interfering signals. In the other way, selectivity of the receiver means how well a receiver performs in the presence of other unwanted co-channel and adjacent channel interfering signals.

Usually these unwanted signals can never be eliminated, but if the levels of these signals are down with respect to the wanted carrier frequency then the radio receiver or wireless system will function without any errors. If the levels of these interfering signals are comparable to the desired signal, than the system starts producing errors. Filters are employed in wireless/rf receiver chain to improve the selectivity of the device.

receiver selectivity measurement test set up
Fig.2 Receiver selectivity measurement test setup

The set up is slightly changed than the sensitivity setup, here one more RF signal generator is used to generate interfering signal either within the band or near the band of the desired signal. Both the desired and interfering signals are combined using power combiner and fed to the DUT. Level of the interfering signal is increased slowly in steps from specified limit and will be checked for errors. This level till errors are within range is the selectivity level of the DUT.

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