What is the Receiving Sensitivity and How does it affect the Transmission Distance?

The receiving sensitivity is the minimum signal receiving power that the receiver can take out the useful signal correctly. The receiving sensitivity of wireless transmission is similar to people's hearing when they are communicating. Improving the receiving sensitivity of signals can make wireless products have stronger ability to capture weak signals. 

Generally, the receiving sensitivity (such as - 83dbm) identified by WiFi wireless network equipment refers to the sensitivity level of 10 - 5 (99.999%) at the rate of 11Mbps. Many of our RF Receiver Modules can reach -114dbm sensitivity, and some professional receivers can achieve -120dbm sensitivity.

As can be seen from the figure below, the wireless signal will gradually decay during transmission. The farther the receiver is, the higher the sensitivity requirement is; with the increase of transmission distance, the received signal becomes weaker, and the high-sensitivity wireless products can continuously receive data, maintain a stable connection, and greatly increase the transmission distance

Rx is short for Receive. When the signal energy of the receiver is less than the nominal receiving sensitivity, the receiver will not receive any data, that is to say, the receiving sensitivity is the minimum threshold for the receiver to receive signals. It is related to three factors: the thermal noise in the band width, the noise figure of the system, and the minimum SNR (Signal to Noise Ratio) required for the system to take out the useful signal. The thermal noise in the bandwidth range passes through the receiver, and the noise is amplified by NF times. In order to get the useful signal out of the noise, it is necessary to require the useful signal to be SNR times larger than the noise.

Here is the formula:

Where S is the receiving sensitivity, unit is dBm; K is the Boltzmann constant, unit is J/K; T is the absolute temperature, unit is K; KT is the thermal noise power per Hz at the current temperature; B is the signal bandwidth, unit is Hz; KTB is the thermal noise power within the bandwidth range; NF is the system noise figure, unit is dB (similar to the number of environment); SNR is the Signal-to-Noise-Ratio required for demodulation, unit is dB;

The receiving sensitivity of wireless network is very important. Every 3dB increase, the receiving sensitivity will double. For example, when the transmitting energy of the transmitter is 100MW or 20dbm, if the receiving sensitivity is -83dbm at 11mb rate, the theoretical transmission distance (in an open air) is 15km; when the receiving sensitivity is -77dbm, the theoretical transmission distance (in an open air) is only half of 15km (7.5km), or equivalent to a quarter of the energy of the transmitter, which is equivalent to 25MW or 14dbm. 

In order to let the receiver "hear clearly" what the transmitter "says", the signal level strength must be greater than the receiver's receiving sensitivity (S). Of course, the smaller the receiver sensitivity (S), the better the receiver's reception performance is. Just like dogs can hear tiny sounds that humans can't hear, it means that dogs' hearing is higher than people's; the higher the sensitivity (S), the worse the receiver's reception performance is. Just like some old people who are deaf, you need to speak with a big voice before they can hear it.

As the ambient temperature increases, the sensitivity (S) will increase and the receiving performance will deteriorate. Therefore, the temperature of the environment where the system is located should be reduced as much as possible. The larger the bandwidth is, the greater the noise figure of the system is, the greater the sensitivity (S) will be, and the reception performance will deteriorate. This requires that the influence of the system bandwidth and noise figure on the sensitivity (S) should be considered when designing the receivers.

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