There are many high-precision indoor positioning solutions, especially the mainstream UWB positioning and Bluetooth positioning.
Bluetooth&UWB
Bluetooth technology has a history of more than 20 years since its inception in 1999. It has experienced technical changes in several important stages of Bluetooth 2.0, 2.1, 3.0, 4.0, 4.2, 5.0, 5.1, and 5.2. At present, Bluetooth low energy is familiar to everyone. 4.0, Bluetooth 5.1, among which Bluetooth 5.1 introduces a new “direction finding” function, which can use AOA/AOD positioning algorithm to achieve high-precision positioning.
UWB technology originated from the pulse communication technology that emerged in the 1960s. It uses ultra-wide baseband pulses with extremely wide spectrum to communicate, so it is also called baseband communication technology, wireless carrier communication technology, etc. UWB is different from traditional communication technology. It realizes wireless transmission by sending and receiving extremely narrow pulses at nanosecond or microsecond level, so it occupies a wide spectrum range and has high time resolution.
Location Algorithm
The positioning algorithm is the core of positioning accuracy. Whether it is UWB or Bluetooth, there are currently three main positioning algorithms: TDOA, TOF, and AOA.
- TOF is the time of arrival, and TOF locates by measuring the propagation time of the signal between the mobile terminal and three or more base stations, respectively, and it uses circular positioning.
- TDOA is based on the time difference of arrival positioning, and the system needs to have a precise time synchronization function. There are two kinds of time synchronization, one is to do time synchronization through wired, and wired time synchronization can be controlled within 0.1ns. The other is to do time synchronization wirelessly. The wireless synchronization can generally reach 0.25ns, and the accuracy is slightly lower than that of wired time synchronization.After the base station time is synchronized, the tag will send a broadcast message. After the base station receives it, it will mark the time stamp of the received message and send the content to the server, The server calculates the target location according to the time stamps of the positioning messages of other base stations.
- AOA positioning generally calculates the angle of arrival based on the phase difference, and is generally not used alone. Since AOA involves the problem of angular resolution, if it is simply AoA positioning, the farther it is from the base station, the worse the positioning accuracy.
| Location Algorithm | Locate feature | Power consumption | complexity | distance | Concurrent capacity | Environmental adaptability | sync | delay | precision |
| TOF | two-way, active | high | mid | 25m | mid | strong | No | low | high |
| TDoA | Up/Down, Active/Passive | low | mid | 25m | mid | weak | Yes | low | mid |
| AoA | Up，active | low | high | 25m | high | weak | Yes | low | mid |
Through the above content, the definition of Bluetooth AOA is not difficult to understand, so what are the advantages and disadvantages between UWB positioning using TOF/TDOA algorithm and Bluetooth AOA?
- positioning accuracy
Ideally, UWB positioning and Bluetooth AOA positioning can reach centimeter accuracy. In the actual scene, UWB has a stronger ability to penetrate obstacles than Bluetooth; And the effective transmission distance of UWB is more than 10m, which is about twice that of Bluetooth positioning.
- Power consumption
Take the base station in the same scenario as an example. At present, UWB base stations need active power supply and solar power supply, while Bluetooth can work for a long time with a single battery, which has obvious advantages in operation and maintenance.
- cost
Subject to the signal propagation distance, the distance between the two adjacent points of the Bluetooth base station is about 6 meters, and the distance between the two adjacent points of the UWB base station is about 20-50 meters. Depending on the occlusion, Bluetooth positioning needs more equipment in order to achieve the desired accuracy in terms of the number of devices.
conclusion
Bluetooth positioning is more applicable in civilian scenes, such as hospitals, supermarkets, parking lots, etc. such scenes focus on users and pay more attention to users’ experience in the scene, such as car search, location search, etc. UWB positioning is more suitable in enterprise scenarios, such as factories, chemical industries, power plants, etc. Such scenarios take enterprises as the core, pay more attention to personnel safety and management, and have higher requirements for positioning accuracy. The combination of Bluetooth&UWB is a good solution, such as Apple Tag
