RSSI introduction
Received signal strength indicator(RSSI): The received wideband power, including thermal noise and noise generated in the receiver, within the bandwidth defined by the receiver pulse shaping filter, for TDD within a specified timeslot. The reference point for the measurement shall be the antenna. This is a value reported for the strength of a frame that has been received; it acts much like a "volume" indicator for the transmission. The RSSI may be reported in many different ways, but a common method is in dBm.
RSSI technology
A positioning technique in which the distance between the signal point and the receiving point is determined by the strength of the received signal, and then the positioning calculation is performed according to the corresponding data.
For example, the positioning engine of the ZigBee network CC2431 chip of wireless sensor uses this technology and algorithm.
An indication of the average signal strength of the receiver input obtained by the receiver measurement circuit. This measurement generally does not include antenna gain or loss of the transmission system.
The received signal strength indicator (RSSI) indicates the strength of the received signal. The RSSI is implemented after the reverse channel baseband receives the filter.
To obtain the characteristics of the reverse signal, the following processing is performed in the specific implementation of the RSSI: The baseband IQ power is integrated within 104 us to obtain the instantaneous value of the RSSI, that is, the instantaneous value of the RSSI (instantaneous) = sum (I^2 + Q^2). Then, the instantaneous values of the 8192 RSSIs are averaged within about 1 second to obtain an average RSSI, that is, RSSI (average) = sum(RSSI (instantaneous))/8192. At the same time, the maximum value of the instantaneous RSSI value within one second and the ratio of the instantaneous RSSI value greater than a certain threshold are given. (Number of times the instantaneous RSSI value is greater than a threshold/8192). The RSSI is obtained by performing power integration in the digital domain and then inferring the RSSI to the antenna port. Inconsistent transmission characteristics of reverse channel signals affect the RSSI accuracy.
When no load is used, the average RSSI value is the main method for determining interference. In a newly deployed site, only a few UEs are used, and the RSSI level in the no-load scenario is less than –105 dBm. When multiple services exist, the average RSSI value does not exceed –95 dBm. You can also determine whether interference exists based on the receive quality FER. By checking whether interference is caused by overshoot coverage, you can also determine whether interference exists based on the Ec/Io and the received power of the MS. For external interference, use a spectrum analyzer to further check whether interference sources exist.
RSSI level and signal strength
The RSSI test represents the relative quality of the signal received by the device. The RSSI indicates the strength level of the signal received at the antenna and cable levels after any possible loss. The higher the RSSI value, the stronger the signal. When tested in negative numbers, reading close to zero indicates a stronger signal. For example, -50 is a very good signal, -75 is relatively reasonable, and -100 is no signal at all.
Even though RSSI and dBm are different units tested, they all indicate signal strength. dBm is the power factor for measuring strength. The recommended value is 1 mW. dBm is a pure indicator, and RSSI is a relative indicator.
For a good signal test, subtract the noise from the signal power. A bigger difference in signal and noise means better signal strength.
What is the relationship between RSSI and signal strength?
Although there is no universal solution, we will try to decompose the approximate correlation between RSSI and quality ratio.
Values for signal quality range from 0% to 100%. The higher the value, the higher the connection quality. These are theoretical figures related to local noise under ideal conditions. Depending on the system and equipment you are using, it is determined differently and is based on the signal strength and noise tolerance. If this value is above 25 - 30%, then the signal is usually available.
Noise tolerance = Signal (dBm) - Noise (dBm)
For example, if Signal (RSSI) = -55db, Noise = -85db, then:
(-55db signal) - (-85db noise) = 30 noise tolerance
Higher noise margins mean clearer signals. For example, using the full 54 Mbps data rate would require a noise margin of at least 25 dB.
Normal
db >= -50 db = 100% quality
db <= -100 db = 0% quality
For the RSSI signal between -50db and -100db
Quality ~= 2 * (db + 100)
RSSI ~= (Quality/2) - 100
For example:
High quality: 90% ~ = -55 dB
Medium quality: 50% ~ = -75 dB
Low quality: 30% ~ = -85 dB
Unavailable quality: 8% ~= -96db
