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In many fields such as wireless communication, radar detection, and sonar positioning, it is crucial to accurately obtain the location information of the signal source. As a key positioning method, the angle of arrival direction finding technology can accurately locate the signal source by analyzing the angle at which the signal reaches the receiving device, providing strong support for the normal operation and performance optimization of related systems. The following will introduce the angle of arrival direction finding technology in detail.
Basic concepts of angle of arrival direction finding technology
Angle of Arrival (AOA) direction finding technology is a technology for positioning and direction finding based on the angle of signal arrival. Its core principle is to use a receiving device (such as an antenna array, a sensor, etc.) to receive a signal from the signal source, and to determine the direction of the signal source by analyzing the spatial angle parameters of the propagation direction when the signal reaches the receiving device. In the field of electromagnetics, the angle of arrival is a spatial angle parameter that describes the propagation direction of the wave radiation when it reaches the observation point, and is defined as the angle between the wave ray and the reference direction (such as the horizontal plane or the normal direction). In wireless communication systems, the arrival angle direction finding technology measures the incident angle of the target mobile station's transmitted signal received by the base station receiver antenna array, so that a radial line, i.e., the azimuth line, is formed between the target mobile station and the known base station, and then the position of the mobile station is determined by the intersection of the azimuth lines measured by multiple base stations.
Implementation method of arrival angle direction finding technology
Direction finding method based on array antenna
Array antenna is one of the key technologies for achieving arrival angle direction finding. It consists of multiple antenna units arranged in a certain geometric shape, and the arrival angle of the signal is calculated by analyzing the phase difference, amplitude difference and other information of the signal received by each antenna unit. For example, in a phased array radar system, by measuring the arrival angle difference of the received signal of each array element in real time, the millimeter-level resolution of the target azimuth can be achieved. In wireless communication base stations, array antennas are also often used to achieve arrival angle direction finding to improve positioning accuracy and anti-interference ability.
Classic algorithm
Least squares method: This is a common mathematical optimization method. In arrival angle direction finding, the arrival angle can be estimated by minimizing the error between the array received signal and the theoretical value. Suppose the received signal vector is x, the array response matrix is A(θ), the signal source coefficient is s, and the goal is to minimize the following error: θ̂ = arg minθ ‖x - A(θ)s‖². This method obtains the best estimated arrival angle θ̂ by minimizing the difference between the signal and the model.
MUSIC algorithm: The MUSIC (Multiple Signal Classification) algorithm is a high-resolution arrival angle estimation method. It estimates the arrival angle by eigenvalue decomposition based on the orthogonality of the signal subspace and the noise subspace. First, the covariance matrix of the received signal is calculated, and then the eigenvalue decomposition is performed to obtain the signal subspace and the noise subspace. Through the orthogonality of the noise subspace and the signal subspace, the spectral value corresponding to each angle is calculated, and the maximum value of the spectral value is found, which is the arrival angle of the signal. Its basic formula is P(θ) = 1 / [aᴴ(θ)EₙEₙᴴa(θ)], where a(θ) is the array response vector and Eₙ is the noise subspace.
ESPRIT algorithm: The ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) algorithm is a method based on array rotation invariance. Unlike the MUSIC algorithm, ESPRIT does not require eigenvalue decomposition, but estimates the angle of arrival by utilizing the rotation invariance of the array structure. First, the covariance matrix of the signal is calculated, and then the eigenvalue decomposition is performed to obtain the signal subspace and the noise subspace, and finally the angle of arrival is estimated by rotation invariance.
Application scenarios of arrival angle direction finding technology
Wireless communication field
In wireless communication systems, arrival angle direction finding technology can be used for base station positioning, mobile device positioning, etc. For example, in 5G and future communication systems, the uplink angle of arrival (UL AoA) provides basic support for key technologies such as location perception and beamforming by estimating the angle at which the user equipment (UE) signal arrives at the base station (gNB) antenna array. Combining time of arrival (ToA) and UL AoA, high-precision three-dimensional positioning of multi-base station collaboration can be achieved, providing support for indoor navigation and emergency positioning. At the same time, by accurately estimating UL AoA, the base station can perform directional beamforming for the UE, enhance the signal reception quality, reduce interference in other directions, and improve the energy efficiency of the network.
Radar detection field
Radar systems use arrival angle direction finding technology to locate targets such as aircraft, missiles, and drones. By analyzing the arrival angle of the target reflection signal received by the radar antenna array, combined with other information such as the arrival time and frequency of the signal, the position, speed, and direction of movement of the target can be accurately determined, providing important support for military defense, air traffic control, etc.
Sonar positioning field
Underwater sonar systems use arrival angle direction finding technology to locate submarines or other underwater targets. The arrival angle information of the target sound signal received by the sonar array, combined with parameters such as sound speed and propagation time, can calculate the position of the target and provide key data for ocean monitoring, underwater navigation, etc.
Challenges and solutions faced by arrival angle direction finding technology
Multipath effect
Multipath propagation will cause the arrival angle of the signal to have multiple components, which increases the complexity of estimation. The solution is to use high-resolution algorithms such as MUSIC and ESPRIT, which can distinguish the arrival angles of different paths. In addition, the use of delay information for joint estimation can improve the estimation accuracy in multipath environments.
Noise interference
In actual environments, noise interference will affect the accuracy of arrival angle direction finding. The impact of noise interference can be reduced by optimizing the antenna array design and improving the anti-interference ability of the signal processing algorithm. For example, the use of adaptive beamforming technology can dynamically adjust the weight of the antenna array according to the characteristics of the signal and noise, enhance the reception of the signal, and suppress noise interference.
As an important positioning and direction finding method, arrival angle direction finding technology plays an important role in wireless communications, radar detection, sonar positioning and other fields. By continuously optimizing the implementation method and solving the technical challenges faced, arrival angle direction finding technology will provide stronger support for the development of related fields and promote the advancement of science and technology and the expansion of applications.
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