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The application of RSSI in wireless communication

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RSSI (Received Signal Strength Indication) received signalstrength indication, optional part of the wireless transmission layer, used todetermine the link quality, the RSSI value corresponding to the unit is dBm(decibel milliwatts), indicating the relative relationship between a certainpower and 1mw The specific calculation formula of the value x (dBm) and thepower P (mw) is as follows:RSSI (Received Signal Strength Indication) receivedsignal strength indication, optional part of the wireless transmission layer,used to determine the link quality, the RSSI value corresponding to the unit isdBm (decibel milliwatts), indicating the relative relationship between acertain power and 1mw The specific calculation formula of the value x (dBm) andthe power P (mw) is as follows:

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It can be seen that RSSI is not power, itis only an indication of signal strength. The monitoring of the RSSI value isgenerated after the back channel baseband reception filtering, and the basebandI/Q branch power integration is performed within 104 μsto obtain the RSSI instantaneous value, and the instantaneous value is averagedwithin 1 s to obtain the RSSI average value.

Viewing the average value of RSSI is animportant means of judging interference. The RSSI value under no load isgenerally around -110dBm. In the case of service, the RSSI average value willgenerally not exceed -95dBm. If the RSSI value is found to increasesignificantly, Then there must be reverse link interference.

In an actual wireless communicationapplication, a burst interference signal that is inevitable in the environment,for example, the A device performs a radio frequency transmission operation onthe C channel at the time T, and at the same time, the device B wants to startthe C channel radio transmission. It can be imagined that the transmissionprocess of A and B will interfere with each other, and the receiving end maynot receive the data correctly. Therefore, in the communication process, it isnecessary to avoid the phenomenon of simultaneous transmission at the samefrequency.

In order to avoid the same-frequencyinterference and improve the quality of wireless communication, the strength ofthe RSSI in the environment can be detected before the RF transmission. If theRSSI is within a certain range, the current channel is clean and will not beinterfered. Otherwise, the interference should be avoided.

In addition, in practical applications,wireless communication nodes are often battery-powered devices, which requirehigh power consumption, and most of the RF transmission processes areaccompanied by higher current consumption. How to reduce the RF transmit powerwhile ensuring the stability of communication becomes the key to low-powerdevices.

Therefore, the low-power device dynamicallyacquires the interference signal strength in the environment through the RSSIdetection before starting the transmission. If the RSSI is in the range, thecommunication quality is good, and the device can choose to use a smallertransmission power, otherwise the environmental interference is better. Usehigh power when large.

It should be noted that most RF chipmanufacturers define the RSSI value in a proprietary manner. The range of RSSIcan be selected by the vendor from 0 to the maximum (less than or equal to255). Many vendors publish RSSI execution values on product documentation andwebsites, and some vendors do not. Therefore, the RSSI obtained directly fromthe chip numerically reflects the magnitude of the ambient signal strength.

The E70-433MS wireless communication moduleintroduced by Chengdu Yihao Te Electronics has a working frequency band of433MHz and supports RSSI dynamic acquisition mode. In this mode, the modulewill automatically detect the RSSI in the environment and output the valuethrough the serial port 100 millisecond period, which is convenient for usersto dynamically obtain channel quality.

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