As an emerging wireless communication technology, Ultra-Wideband (UWB) technology brings new opportunities for UAVs to achieve precise positioning in complex environments with its unique technical characteristics. UWB technology transmits information by sending and receiving nanosecond- or even picosecond-level non-sinusoidal narrow pulse signals, featuring extremely wide bandwidth, low signal power spectral density, strong anti-multipath capability, and high positioning accuracy. Applying UWB technology to UAV positioning systems and combining it with multi-base station and multi-module fusion networking can effectively improve the positioning performance of UAVs in various complex environments, expand the application scope of UAVs, and promote the further development of related fields.
II. Overview of UWB Technology
2.1 Principle of UWB Technology
UWB technology is fundamentally different from traditional communication technologies. It does not rely on sinusoidal carriers to transmit information but uses nanosecond (ns) to picosecond (ps) non-sinusoidal narrow pulses for data transmission. These extremely narrow pulses have rich spectral components, with a bandwidth typically exceeding 500MHz or even reaching several GHz, far exceeding that of traditional communication systems. The main generation methods of UWB signals include Impulse Radio (IR) and Direct Sequence Spread Spectrum (DSSS). In an IR-UWB system, only a pulse as short as less than ns needs to be generated and sent through an antenna. The information to be transmitted can be loaded by changing the amplitude, time, or phase of the pulse to achieve information transmission.
In terms of positioning, UWB technology mainly calculates the distance between targets based on the Time of Flight (TOF) principle. Common ranging methods include Two-Way Time of Flight (TW-TOF), One-Way Time of Flight (TOF), and Symmetric Single Sided Two-Way Ranging (SS-TWR). TW-TOF calculates the distance through the signal round-trip time difference between two asynchronous transceivers, which can effectively eliminate clock synchronization errors and improve ranging accuracy. TOF calculates the distance by measuring the time difference from signal transmission to reception, suitable for one-way ranging scenarios. SS-TWR combines the convenience of one-way ranging and the accuracy of two-way ranging.
2.2 Characteristics of UWB Technology
High-precision positioning**: Due to the extremely wide bandwidth of UWB signals, sub-centimeter or even millimeter-level ranging accuracy can be provided, which is crucial for UAV formation flight, precise obstacle avoidance, autonomous landing, and other tasks. For example, in UAV formation flight, high-precision positioning ensures that UAVs maintain accurate relative positions, enabling uniform formation control and dynamic adjustment.
Strong anti-interference capability**: UWB signals have low power spectral density and extremely wide bandwidth, which can effectively suppress the effects of multipath effects and other interference sources. In complex electromagnetic environments, such as urban areas with abundant electromagnetic interference, UWB technology can, like a determined行者 (walker), complete data transmission and positioning tasks stably without external interference, ensuring ranging stability.
Low power consumption**: UWB modules typically have low energy consumption, which is very important for power-sensitive devices like UAVs. Low power consumption helps extend the UAV's endurance, allowing it to perform tasks for a longer time with one charge or fuel supply.
High security**: Since UWB signal strength is low and不易 (not easy) to be detected by the outside world, it is suitable for scenarios where UAVs need to operate covertly. In special applications such as military reconnaissance and secret monitoring, UAVs using UWB technology can complete tasks without being easily discovered, improving task safety and confidentiality.
Good signal penetrability**: UWB signals have strong penetrating power, capable of passing through obstacles such as walls and trees, which solves the signal occlusion problem to a certain extent. This enables UAVs to achieve relatively reliable positioning in complex scenarios such as indoor environments and dense forest areas.
III. Architecture of UAV Multi-Base Station and Multi-Module Fusion Networking
3.1 Multi-Base Station Deployment Schemes
In UAV positioning systems, the deployment method of multi-base stations has a key impact on positioning accuracy and coverage. Common base station deployment schemes include triangular positioning, quadrilateral positioning, and cellular deployment.
Triangular positioning**: By setting up base stations at three different positions, UWB technology is used to measure the distance between the UAV and each base station, and the UAV's position is calculated based on the geometric principle of triangles. This method is suitable for scenarios with high positioning accuracy requirements and a relatively small coverage area, such as indoor UAV performance venues. Its advantages are simple calculation and fewer base stations required; the disadvantage is limited coverage, and positioning blind spots may occur if the base station layout is unreasonable.
Quadrilateral positioning**: Base stations are set at four corners to form a quadrilateral area. Compared with triangular positioning, quadrilateral positioning can expand the coverage area and improve positioning stability. In some large warehouses, factories, and other indoor environments, quadrilateral positioning can better meet the positioning needs of UAVs. However, this method requires more base stations, resulting in relatively high costs and stricter synchronization requirements for base stations.
Cellular deployment**: Drawing on the deployment method of mobile communication base stations, multiple base stations are set up in a cellular layout. This deployment method can achieve large-area seamless coverage, suitable for scenarios such as urban environmental monitoring and large logistics parks. The advantages of cellular deployment are wide coverage and uniform positioning accuracy; the disadvantages are numerous base stations, high deployment and maintenance costs, and great system complexity.
In practical applications, the appropriate base station deployment scheme should be selected by comprehensively considering factors such as cost, accuracy, and coverage according to specific scenario requirements and environmental characteristics. For example, triangular positioning may be a more suitable choice for indoor small UAV formation performance scenarios, while cellular deployment is more capable of meeting the needs of urban-scale UAV logistics distribution scenarios.
3.2 Multi-Module Fusion Methods
To further improve the positioning performance of UAVs, UWB modules usually need to be fused with other sensor modules. Common sensors fused with UWB modules include Inertial Navigation Systems (INS), Global Navigation Satellite Systems (GNSS), visual sensors, and lidar.
UWB module + INS**: This combination can provide more accurate UAV positioning information. INS can real-time measure the UAV's acceleration and angular velocity, and obtain the UAV's attitude and position information through integral calculation. However, INS has the problem of error accumulation over time. In indoor or complex environments, the UWB module assists the INS algorithm in correcting errors and suppressing error accumulation by measuring the distance between the UAV and the base station, thereby improving positioning accuracy. For example, after the UAV enters an indoor environment where GNSS signals are blocked and unavailable, the UWB-INS fusion system can continue to provide accurate positioning information for the UAV, ensuring safe flight in the indoor environment.
Visual sensor + UWB module**: This integration further enhances the UAV's positioning capability in visually challenging environments. Visual sensors can acquire image information of the UAV's surrounding environment, extract environmental feature points through image recognition and processing technologies, and calculate the UAV's position and attitude relative to these feature points. The UWB module provides accurate distance information between the UAV and the base station. After fusion, the visual sensor can use the UWB distance information to calibrate its own positioning results, while the UWB module can also rely on the environmental perception capability of the visual sensor to better cope with multipath effects and other issues. For example, in environments with dim light or indistinct texture features, using a visual sensor alone may lead to inaccurate positioning, and the addition of a UWB module can effectively improve positioning reliability.
UWB module + lidar**: This fusion also brings more powerful positioning and obstacle avoidance capabilities to UAVs. Lidar obtains three-dimensional point cloud information of the surrounding environment by emitting laser beams and measuring the time of reflected light, enabling precise perception of the position and shape of obstacles around the UAV. The UWB module provides accurate position information of the UAV. During UAV flight, the point cloud data of the lidar can be combined with the positioning information of the UWB to achieve more precise path planning and obstacle avoidance. For example, when the UAV flies through narrow passages or complex obstacle areas, the lidar can detect the position of obstacles in real-time, and the UWB module ensures that the UAV accurately knows its own position. The two work together to help the UAV safely pass through complex areas.
