Receiver sensitivity refers to the minimum signal received power on an antenna port for receivers to accurately decode a given signal. Receiver sensitivity can be degraded by inter-system interference, affecting the quality of received signals. Therefore, receiver sensitivity is usually used as a criterion to protect the interfered system.
Receiver sensitivity is similar to hearing of human beings. In the daily environment, people with good hearing can capture voice more flexibly. Similarly, higher receiver sensitivity enables a receiver with higher capability to capture weak signals. If the signal strength is lower than receiver sensitivity, the receiver will not receive data.
Factor
Thermal noise power within the bandwidth range
Noise factor (NF)
Minimum signal-to-noise ratio (SNR) required for decoding signals
Formula
S = 10lg(kTB) + NF + SNR
S: receiver sensitivity, in dBm. A smaller value indicates better performance of the receiver. A larger value indicates lower performance of the receiver.
k: Boltzmann constant, in J/K.
T: absolute temperature, in K. As the temperature increases, receiver sensitivity becomes larger, degrading receiver performance. Therefore, lower the ambient temperature as much as possible.
B: signal bandwidth, in Hz. Higher signal bandwidth represents a larger NF, higher receiver sensitivity, and therefore lower receiver performance.
kTB: thermal noise power within the bandwidth range, in Watts.
NF: noise factor, in dB.
SNR: signal-to-noise ratio required for decoding signals, in dB. A small value of the minimum SNR can enhance receiver performance. The minimum SNR is related to the STA moving speed, wireless environment, and required communication quality. Minimum SNR requirements are different for wireless standards and services of the same wireless standard.
Receiver sensitivity of a common 802.11g product is -85 dBm. Wireless products on the market have -105 dBm receiver sensitivity. Professional receivers provide up to -120 dBm receiver sensitivity. Receiver sensitivity doubles every time the transmit power increases by 3 dB. In most cases, the receiver sensitivity value marked on Wi-Fi devices, such as -83 dBm, is a measurement of receiver sensitivity at a rate of 11 Mbit/s and a bit error rate (BER) of 10E-5 (99.999%).
STAs have lower receiver sensitivity than APs. Therefore, the outdoor coverage distance is restricted by the STA uplink. If an AP transmits signals at full power, users may find strong signal strength on STAs but Internet access experience is poor. To prevent such an issue, reduce the transmit power of the AP to slightly higher than the receiver sensitivity of the STAs, so that the uplink and downlink of the STAs have a similar modulation and coding scheme (MCS) level after the link power budget is completed.
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