What is the difference between UWB and traditional communication technology? What is UWB ultra-wideband positioning

兰博

What is the difference between UWB and traditional communication technology? What is UWB ultra-wideband positioning [Copy link]

UWB is a brand-new communication technology that is very different from traditional communication technology. Unlike the use of carriers in traditional communication systems, this system transmits data by sending and receiving extremely narrow pulses below the nanosecond level, thereby obtaining a bandwidth of the order of GHz. The most basic working principle of ultra-wideband technology is to send and receive Gaussian single-cycle ultra-short pulses with strictly controlled pulse intervals. The ultra-short single-cycle pulses determine the wide bandwidth of the signal. The receiver directly uses the front-end cross-correlator to convert the pulse sequence into a baseband signal, thereby reducing the intermediate frequency in traditional communication equipment and greatly reducing the complexity of the equipment. Because UWB has a strong data transmission rate advantage, but is also limited by the transmission power, achieving short-distance high-speed wireless data transmission will become an important application field of UWB, such as various current WLAN and WPAN applications.

What is the difference between UWB ultra-wideband system and traditional narrowband system?

Compared with the traditional narrowband system, the UWB ultra-wideband system has the advantages of super strong penetration, low power consumption, good anti-multipath effect, high security, low system complexity, and can provide positioning accuracy. Therefore, ultra-wideband technology can be applied to the positioning, tracking and navigation of indoor static or moving objects and people, and can provide very high positioning accuracy.

The positioning principle of UWB is basically the same as that of satellite navigation. As shown in the figure below, the satellite coordinates are known, and the receiving device on the ground can determine its own position coordinates (plane and elevation coordinates) by receiving four satellite signals at the same time. The positioning principle of UWB is to arrange four positioning base stations with known coordinates indoors, and the personnel or equipment to be positioned carry positioning tags. The tags transmit pulses at a certain frequency, continuously measure the distance with the four base stations with known positions, and calculate the position of the positioning tag through a certain algorithm.

It has low power consumption, is insensitive to channel fading (such as multipath, non-line-of-sight channels, etc.), has strong anti-interference ability, will not interfere with other devices in the same environment, has strong penetration (can be positioned in an environment where it can penetrate a brick wall), and has high positioning accuracy and precision.

UWB-based indoor positioning solutions are gradually penetrating into applications that require accurate indoor positioning information, such as airports, exhibition halls, office buildings, warehouses, underground parking lots, prisons, and military training bases.

TOF time flight principle. The time flight principle refers to various methods of measuring flight time, more precisely, it refers to the time it takes for an object or particle or other wave types such as sound waves or radio waves to travel a distance in a certain medium. The TOF ranging method was proposed by D.McCrady, but this technology only focuses on direct sequence spread spectrum communication systems. TOF ranging technology can be understood as a time difference of flight ranging method. Traditional ranging technology is divided into two-way ranging technology and one-way ranging technology. The TOF ranging method belongs to two-way ranging technology. It mainly uses the flight time of the signal between two asynchronous transceivers to measure the distance between nodes.

The first thing TDOA needs to solve is the time synchronization problem. There are two types of time synchronization. One is to synchronize time through wires. Wired time synchronization can be controlled within 0.1ns, and the synchronization accuracy is very high. However, due to the use of wires, all devices can use a central network or a cascaded method, which increases the complexity of network maintenance and construction, and the cost is also high. In addition, there is a dedicated wired time synchronizer in the system, which is expensive.

One is to synchronize time wirelessly. Wireless synchronization can generally reach 0.25ns, which is slightly less accurate than wired time synchronization. However, the system is relatively simpler. The positioning base station only needs power supply, and data can be transmitted back via WiFi, which effectively reduces costs. After the base station is synchronized, the tag sends a broadcast message. After the base station receives it, it marks the timestamp of receiving the message and sends the content to the computing server. The computing server calculates the timestamp of the positioning messages from other base stations and calculates the location of the target.

AoA positioning is based on the calculation method of phase difference. Generally, it is not used alone. AoA involves the problem of angle resolution. If AoA positioning is used alone, the farther away from the base station, the worse the positioning accuracy. AoA can be used in conjunction with ToF ranging for positioning. In this mode, a single base station can complete positioning. Two base stations can also achieve positioning through AoA

The selection of positioning method involves many factors, and comprehensive judgment is required in the system to better meet the use of the system.

在基于测距模式，相对来说容量比较低； 在TDOA模式下，若采用6.8Mbps的传送速率，标签的报文限制在12个字节内，每个报文的持续时间为95微秒，按18%的系统占空比计算，每个标签按1Hz的频率工作，系统容量接近1500个标签。若ToF配合AoA使用，能显著提升系统融合，比如，只和其中一个基站测距，其他基站辅助做角度判断，完成定位，系统容量能显著提升。

这里主要比较一下ToF和TDoA 两种模式下的功耗，ToF模式下，标签需要逐一和基站测距，需要多次测距，一般一轮测距下来，需要5ms以上。TDoA定位，标签只需要发送一个报文即可完成定位，一般从准备到发送完成也在0.5ms内完成，其功耗显著低于ToF模式。

Since the TDoA algorithm is a method based on the time difference of arrival, the hyperbolic algorithm is generally used. Its limitations determine that the TDoA algorithm has high positioning accuracy and a wide range of applications, especially in areas around base stations where the positioning accuracy is low. However, similar to complex environmental scenarios such as power plants, the system faces great difficulties in construction, and TDoA positioning is difficult to meet its application requirements. In this mode, ToF positioning can be used, or a combination of TDoA and AoA positioning methods can be used.