Common Positioning Methods - Distance Based (ToF)

Distance based positioning, mainly by measuring the time of flight, in the mode of autonomous positioning, radar or ultrasonic

equipment can measure the distance between the body and the wall/device. In the cooperative scheme, the time of flight between

two targets is measured by sending and receiving messages.

In this ranging mode, accurate distance between two targets can be obtained without time synchronization.

Through ToF ranging positioning, there are the following characteristics:

1, long process/high power consumption

The target to be located needs to initiate and range all base stations, and even the optimized range requires at least n+2 messages

(n is the number of base stations).

Because the tag needs to interact with all the base stations, the terminal power consumption is high.

2. Low system capacity

As can be seen from the above, since the tags need to interact several times to complete the data sampling, if there are four base

stations and each packet lasts 0.5ms, at least (4+2) *0.5 = 3ms is required. In addition, the pre - and post-collision protection is

required, and the period of a tag is at least 4ms. The theoretical capacity of the area does not exceed 1000ms/ms = 250 terminals;

3, good stability

Because it is based on the bidirectional ranging scheme, it can effectively support the location outside the area. In addition, even

due to the occlusion of individual base stations, the sampling accuracy of other base stations can be obtained.

Therefore, the location based on ToF ranging mode can be applied to the scene with low power consumption, moderate capacity

and complex environment.

It shows that ToF can only be intersected at a point in a particularly ideal case, and most cases are based on the results of ranging,

which is an area surrounded by multiple circles, and the location of the label needs to be found in the area.