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Continue with the previous article, and then discuss RF signals.

When it comes to signals, it is inevitable to discuss noise.

The noise defined by physics is the random and disorganized sound of the frequency and intensity of sound waves. In electronics, noise is defined as the energy that can interfere with the signal (such as stray electromagnetic field) generated by the signal in the process of transmission.

Noise level (noise floor), in signalling, the quantitative measurement of noise sources and other signals transmitted by all interference signals is defined as the noise level, and its value is measured in units of dBm.

Signal to noise ratio (SNR)

Signal-to-noise ratio, that is, the ratio of signal strength to noise level. Because dBm is the log value of mW, this ratio is often thought of as a difference. SNR is an index to measure the signal quality. SNR is the ratio of received signal strength to noise level intensity. For example, if the signal strength received by the wireless device is-85dBm and the strength of the background interference signal is-100dBm, the SNR value is 15dB.

It is generally believed that the better signal quality is when the SNR value is greater than or equal to 25 dB.

RSSI

The received signal strength indicator (RSSI) is usually a collection of a series of transmission rates and signal strength. Wireless signal transmission is closely related to reception sensitivity, that is, the minimum signal quality requirements of the chip for different transmission rates.

Wi-Fi manufacturers generally specify Receive Sensitity thresholds at various rates. For a receiver, more power is needed to support higher speeds. Different signal modulation techniques and coding methods are used for different rates. The coding methods at higher rates are more likely to cause data corruption.

Link Budget (Link budget)

It is the accounting of all gain and attenuation in the sender, communication link, propagation environment and receiver in a communication system. It is usually used to estimate the furthest distance at which a signal can be successfully transmitted from the transmitter to the receiver. Its purpose is to ensure that the sender and receiver can receive and transmit signals normally according to the budget.

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