Ultra Wide-Band (UWB) is a new type of wireless communication technology. According to the specifications of the Federal Communications Commission, the working frequency band of UWB is 3.1~10.6GHz, and the ratio of the system -10dB bandwidth to the system center frequency is greater than 20% Or the system bandwidth is at least 500MHz. UWB signal generation can be achieved by modulating a narrow pulse (such as a second Gaussian pulse) with a very short transmission time (such as 2ns) to the UWB working frequency band through an up-conversion method such as differentiation or mixing.
How UWB performs positioning, then you need to use a thing called TOF (Time Of Flight) to translate that is the time of light flight.
UWB Ranging Principle
First define what is needed in relocation. Everyone knows that GPS requires three satellites to locate mobile devices. The same is true in UWB positioning. We need to fix three UWB boards. We call these three fixed UWB boards. It is Anchor, and then the UWB board in the moving state that needs to be located is called Tag.
The distance between the Anchor and the Tag can be measured by the flight time of light. For the simplest example, the distance between an Anchor and a Tag can be directly used to send a data packet with a timestamp, and the Anchor receives After the data packet, if the Anchor and the Tag have been time synchronized, the Anchor will calculate the difference between the local time and the time stamp of the tag sending the time packet to know how long the light has been flying, so that the distance can be calculated. Of course , This will cause a lot of interference, resulting in inaccurate measurement, so Decawave engineers used another method:
Decawave measures TOF to measure TOF time through two handshake, the measurement principle is as follows:
TOF two-way handshake principle
The TOF ranging method is a two-way ranging technology, which mainly uses the flight time of the signal between two asynchronous transceivers (Transceiver) to measure the distance between nodes. Because in the line-of-sight environment, the TOF-based ranging method has a linear relationship with the distance, so the result will be more accurate. We record the time between the sending end of the data packet and receiving the response as TTOT, and the time interval between the receiving end receiving the data packet and sending the response as TTAT, then the one-way flight time TTOF of the data packet in the air can be calculated as: TTOF =(TTOT-TTAT)/2.
Then according to the results of TTOF and electromagnetic wave propagation speed, the distance between the two points can be calculated D=CxTTOF
TOF ranging method and two key side constraints:
1. The sending device and the receiving device must always be synchronized
2. The length of the transmission time of the signal provided by the receiving device
In order to achieve always synchronization, the TOF ranging method uses the always offset to solve the always synchronization problem. Because of the time of the TOF ranging method and the local remote points, the side range accuracy is easily affected by the always offset in the nodes at both ends. The impact of the amount. In order to reduce the impact of such errors, a reverse measurement method is adopted here, that is, the remote node sends a data packet, the local node receives the data packet, and automatically responds. By averaging the average value of multiple measurements in the forward and reverse directions, the impact on any offset is reduced, thereby reducing the ranging error.
Positioning principle
Knowing the principle of UWB ranging, it is easy to understand the principle of UWB indoor positioning. The indoor positioning function of UWB is very similar to the principle of satellites, that is, by arranging 4 base stations with known coordinates indoors, the personnel who need to be positioned, Mr. Hu, carries a positioning tag when the device deteriorates. The tag sends silly pulses at a certain frequency, and keeps checking with 4 The base station that knows the location performs ranging, and determines the location of the tag through a certain precise algorithm!
The main technical characteristics of UWB positioning areLow power consumption, insensitive to channel fading (such as multipath, non-line-of-sight channels, etc.), strong anti-interference ability, will not interfere with other equipment in the same environment, and strong penetrating (can penetrate a block Positioning in a brick wall environment), with high positioning accuracy and positioning accuracy. SKYLAB UWB indoor positioning solution uses advanced software and hardware to locate, track and manage high-value, equipment and personnel to maximize utilization.
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