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Basically all wireless technologies can be located based on signal strength, signal strength mainly depends on the frequency of the
sending end, the signal strength of the sending end, the signal strength of the receiving end, because the signal transmission model
from point A to point B is related to frequency and distance, and the modulation mode has little relationship.
Therefore, Wi-Fi, BLE, ZigBee can all use positioning based on signal strength.
There are two main calculation models based on signal strength, one is to convert signal strength into distance, and the other is the
way of fingerprint.
The signal intensity is converted into distance, and the signal space free attenuation model is adopted
R=32.4+20*log (D)+20*log(M)
remark
D: wireless signal free space propagation distance, unit is km;
M: Frequency MHz, such as gsm 900MHz, DSC 1800MHz, WCDMA 2000MHz, WIFI 2.4G/5.8G, wig 60G;
R: Signal loss, expressed in dBm
The attenuation of wireless signal 1m at several common frequencies is as follows
900MHz: R=32.4+20log (1/1000) +20log900=32.4-60+59.1=31.5dB
1800MHz: R=32.4+20log (1/1000) +20log1800=32.4-60+65.1=37.5dB
2000MHz: R=32.4+20log (1/1000) +20log2000=32.4-60+66=38.4dB
2400MHz: R=32.4+20log (1/1000) +20log2400=32.4-60+67.6=40dB
5800MHz: R=32.4+20log (1/1000) +20log5800=32.4-60+75.3=47.7dB
60000MHz: R=32.4+20log (1/1000) +20log60000=32.4-60+95.6=68dB
Scenario hypothesis 1:
The transmitting power at an antenna port is 30dBm (1w), and we test at a place 100m away (without blocking), then the RSCP
received by our mobile phone should be:
Rough calculation: RSCP=30-(32.4+20*log (100/1000)+20*log (2000))
RSCP = 48.2 dBm
Scenario Hypothesis 2:
The transmitting power at an indoor distributed antenna port is 0dBm (1mW), and we test at a distance of 10m (without blocking), then
the RSCP received by our mobile phone should be:
Rough calculation: RSCP=0-(32.4+20*log (10/1000)+20*log (2000))
RSCP = 78.4 dBm
In our actual use, the R value is the signal strength of the receiving side, the output power of the transmitting side is known, and the
antenna gain is known, and the distance D can be obtained by inverse inference. Through the distance D value of multiple base stations,
the position of the terminal is obtained.
This model is only suitable for the scene with a relatively close distance, because the signal strength of every 3dBm is twice the distance,
the farther the distance, the more unreliable the accuracy;
The transmitter requires a good consistency, so when iBeacon needs to broadcast, it needs to explain the signal strength at 1 meter;
The signal strength positioning based on the fingerprint algorithm needs to do data acquisition first, record the signal data of each point,
and then locate by comparison. Therefore, in a scene, it is necessary to form a fingerprint database.
Positioning based on signal strength can be affected by a variety of environmental factors, such as the way they are worn, how many
people there are, changes in the environment, and the density of deployment at the transmitter end.
