RSSI(Received SignalStrength Indication) ranging is the strength indication of the received signal.A positioning technique that can be calculated by measuring the distance between the signal point and the receiver point by the signal strength and weakness received.

Distance-measurement

RSSI requires higher parameters for communication channels. The distance measurement theory is based on the principle that the signal power is attenuated by the distance transmitted by radio or sound waves.The distance between the nodes can be calculated by the attenuation model between the signal and distance based on the transmitting power of the beacon node and the signal power received by the node.However, due to distance and obstruction, the power intensity of the signal is attenuated, which indirectly affects the accuracy. It is important to understand that each distance measurement has its advantages and disadvantages.

1. Advantages of RSSI Distance Measurement Mode

• The power consumption of RSSI distance measurement was lower.
• The cost of RSSI distance measurement is low compared with TOF distance measurement. It is not affected by transmitting delay and antenna delay. The hardware cost, software cost and time cost are relatively low.

Easy to use.In general, it is a function of commercial wireless transceiver chips to calculate receiving wireless signal strength.

2. Restrictions on RSSI Distance Measurement

• Environmental factors. The accuracy of distance measurement is influenced by obstacles, weather and non-range signals.For example, the energy of electromagnetic waves is attenuated if there are obstacles on both sides, especially metal ones.
• Signal energy instability due to radio channel multidiameter decline
• The measurement accuracy is influenced by antenna orientation and antenna gain.

3. Completion 

In general, RSSI distance measurement is suitable for situations where the environment is empty and the environment is less disturbing. It is the only way to improve communication quality and reduce background noise.In practical environment, RSSI is mainly used in short distance measurement and indoor positioning.

TOF range measurement

TEF is called Time of Flight. TEF distance measurement is a method of flight time measurement. Traditional techniques include Two Way Ranging and one Way Ranging. The TOF distance measurement method is Two Way Rangin technology, which uses signal time between two transceivers to measure the distance between nodes.

Advantages of TOF Range

• The method of TOF distance measurement is two-way ranging, which reduces the error of distance measurement compared with one-way rang measurement.
• TOF distance measurement is dependent on flight time. Time measurement accuracy does not vary significantly with increasing test distance. The performance is more stable and the distance can be accurately measured is greater.

Error analysis of TOF distance measurement

1. The interval between wireless transceiver and wireless transmission is very short.In the TOF range measurement scheme, distance measurement depends on time measurement, but a small time error of up to 300,000 km/s can result in a larger distance error, so the exact distance required for the timing system of the transceiver and transceiver is also very high.

2. Time delay. Time delay includes sending delay, receiving delay, and antenna delay."When distance-measuring signals are processed and modulated by digital and analog signals, transmission and reception over the radio can result in some delay errors."Antenna transmitting/receiving signals may not be uniform because the delay in one radiation direction may be different from the other, and the delay time of different antennas may vary due to the quality of the antenna.

3. Multichannel refers to the phenomenon in which the transmitter is reflected and diffracted from the transmitter to the receiver.This effect becomes serious when there is an obstacle between the transmitter and the receiver.

Summary

In practical applications, wireless signals are subject to a number of instability factors, and different disturbances in different application environments. These interference factors can affect the transmission of wireless signals, and consequently affect the stability and accuracy of communication systems, distance measuring systems, or positioning systems.

Take the ranging system as an example, in order to make the distance measuring system more accurate, it is necessary to verify each interference factor, determine the law of its existence, and eliminate or minimize the influence of interference factor on the measurement result by compensation.