Due to poor indoor signal, GPS cannot be used for indoor positioning.
However, the demand for indoor positioning is wide, and many
applications need to locate the position of people or objects in the
indoor space, especially warehouse management.
TOF ranging is a
algorithm of Radio frequency (rf) positioning, which belongs to the
two-way ranging technology, it uses the data signals on the flight time
between tramsmitter and receiver to measure the distance between two
points.
Measurement steps:
1. Measure the time interval between the master sending the data signal and receiving the slave response signal, note as Tt.
2.
Measure the time interval between the slave receiving the data signal
from the master and sending the response signal,note as Tr.
3. The
one-way flight time for the signal between the master and
slave:Tf=(Tt-Tr)/2.the distance between the two points: d=c*Tf,
c represents the electromagnetic wave propagation speed.
SX1280
is a 2.4G range-finding chip based on LoRa modulation newly launched by
semtech. In addition to the commonly used wireless communication
functions, SX1280 also integrates TOF (time-of-flight) ranging function.
Advantage:
The
algorithm has been integrated in the chip, and the ranging results can
be obtained with simple operations, which can be used for users to
quickly realize indoor positioning.
Implementation plan:
This algorithm needs at least 5 wireless modules with SX1280 chip，it require one center, three base stations and at least one positioning module.
◆ The
center is responsible for receiving and counting the distance
information of the positioning module and uploading it to the server.
◆ The
three base stations used as slaves in the ranging, they need to be
installed evenly in the warehouse for the positioning module to
calculate the distance.
◆ The positioning module is installed on
the goods that to be located, center measure the distances between the
three base stations separately (ranging status), and upload these three
distances to the center (communication status).
Specific steps are as follows:
1. The positioning module is in the receiving state.
2. The center sends the instruction that obtain positioning information to the positioning module.
3. The positioning module switches to the ranging state.
4. The positioning module measures the distance with base station 1, and obtains the distance d1.
5. The positioning module measures the distance with base station 2, and obtains the distance d2.
6. The positioning module measures the distance with the base station 3, and obtains the distance d3.
7. The positioning module switches to the communication state.
8. The positioning module uploads d1, d2, d3 to the center.
9. The center uploads d1, d2, and d3 to the server.
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