Throughout the application of UWB technology as the core and power plants, chemical plants and other industrial enterprise personnel positioning system, on the positioning accuracy have argued that cm-level accuracy can be achieved on the practical application, however, always sent a little meaning, any products have the theoretical value and practical value, for example, some new energy vehicles so-called standard range of 300 km, but in fact may be even less than 200, some mobile phone claims to standby for 7 days, also didn't see how many people can stick to 1 day without charging, positioning system too, whether UWB technology, or WIFI, bluetooth, etc., regardless of the actual application scenarios and the deployment of precision are all play rascal,
Before we understand the positioning accuracy, we understand the distance measuring method of the UWB: first TDOA and TOF,
TOF
Flight Time (Time of flight, TOF) is a kind of two-way ranging technology, it is by measuring the UWB signal in the base station and round-trip flight Time to calculate the distance between the label, according to the mathematical relation, point to the distance of known points is constant, so it must be known points as the center of the circle, with the constant radius of the circle, there are two known points, there are two points of intersection, with three known points and distance as three circles, they made at the same point, the point is the location of the tag,
Locating method based on TOF ranging don't depend on the time synchronization of base station and label, so there is no clock synchronization deviation error, but the time depends on the clock precision of TOF ranging method, the clock offset will bring the error, in order to reduce the ranging error caused by the clock offset, usually USES the direction of the positive and negative two measurement methods, namely remote base station sends ranging information, the receiving range information label and reply, and then launched by label range information, remote base station reply, by calculating the average flight time, reduce the time migration between the two, so as to improve the ranging accuracy,
TDOA
Arrival Time (the Time Differenceof concatenated, TDOA) is a method of using the Arrival Time to locate the called hyperbolic positioning, outgoing label card UWB signal at a Time, all the base station receives the label positioning range wireless signal, if there are two known points of received signal base station, labels and distance between the base station is different, so the two received signals Time node is not the same, according to the mathematical relationship, to known for constant points, two points must be in these two points as the focus of the hyperbola, so there are four known points (four positioning base station) there will be four hyperbola, four hyperbolic to is the location of the label,
TDOA algorithm is not directly using the signal arrival time, but the use of multiple base station receives the signal of the time difference to determine the position of the moving targets, so compared with TOA does not need to add special timestamp to clock synchronization, positioning accuracy is relatively improved,
Applicable scenario
Two algorithms respectively suitable for what kind of scene? TOF suitable environment more complex scenarios, such as manufacturing factories, power plants, chemical plants, office buildings, such as TDOA is suitable for the environment is relatively simple and clear application scenarios, such as outdoor sports, warehouse, etc., TOF, TDOA choose reference can range from label, positioning accuracy, single regional support label capacity, installation environment, whether to support a reverse data control (e.g., vibration), such as
In practice, there are many factors will affect the precision and to improve the accuracy, need to control the source of interference, the position of the base station installation cannot close to large metal, stay away from glass Windows, glass walls, liquid container, fluorescent lamp, large machinery and equipment, high power radio device, such as the installation of the antenna to be vertical to the ground, and second, label way of wear, because the absorption of UWB signal has a strong force, so close to the chest label will significantly affect the accuracy and is difficult to eliminate the multipath effect, due to the electromagnetic wave propagation in the space after some reflection of metal or other medium, when the inevitable cause multipath effect, so this part of the impact on the accuracy of the late only through sample processing and algorithm to compensate for,
Most claims that can achieve the cm-level positioning on the market, but in practice, to laboratory the theoretical support of the insufficiency of the application, to achieve the ideal state, in addition to the deployment fluctuation kongfu, the most important thing is to the deep understanding of the application scenario, cloud and cool technology for many years focused on power plant, in combination with the practical situation of power plant and the technique of UWB positioning personnel positioning system, to control the cost under the condition of achieve good location accuracy, meet the needs of power plant, real, this is not just the cause of the advanced technology, more lies in the cultivation industry for many years as a result, the choice of scheme, get twice the result with half the effort, and vice pesters, never the best application solutions, the most suitable for the actual situation, is the ideal,