Design Of Direction Finding System Based On Low Cost Software Radio

As an important part of array signal processing,Direction of Arrival estimation has important application value in radar,indoor positioning,wireless communication,biomedicine and other fields.After years of development,there have been many highprecision DOA estimation algorithms and direction-finding systems in this field.When these direction-finding systems are applied in practice,their multi-channel signal acquisition equipment are usually required to collect the signals received by the array antenna synchronously,so as to ensure the phase coherence of the collected signals.However,such equipment is usually complicated and costly.At present,there are still some shortcomings of existing commercial direction-finding systems based on interference system,such as large volume,large number of channels,high computational complexity and high cost.Therefore,it is necessary to design a low-cost,high-precision DOA estimation system that can realize multi-channel synchronous acquisition.The main research work and the achievements covered in this thesis include:(1)This paper introduces the research status and development of DOA estimation algorithm and DOA estimation system both domestic and abroad.In addition,the advantages and disadvantages of the current domestic and foreign DOA estimation systems are analyzed.Based on the current research status,this paper proposes to use Hack RF One,a low-cost software radio device,as the multi-channel signal acquisition device to build a DOA estimation system.The overall scheme of the DOA estimation system is designed and the main technical indicators are proposed.(2)In order to solve the problem of synchronous acquisition of multi-channel signals in DOA estimation system,a synchronous acquisition subsystem based on Hack RF One is designed.The subsystem uses the clock synchronization line to synchronize the clock frequencies between Hack RF Ones,which achieves frequency synchronization.By modifying the code of the CPLD in Hack RF One,multiple synchronization devices start sampling at the same time under the control of the time synchronization pulse signal,which realizes the synchronization of time.The synchronization error of the synchronous acquisition subsystem is less than one sampling period in the case of different sampling rates,which indicates that the frequency synchronization and time synchronization are good and the signal phases between channels are coherent.(3)In this paper,a one-dimensional DOA estimation system is designed,in which a four-element uniform linear array is used to receive far-field signals from a radiation source.After passing through the four-channel synchronous acquisition subsystem,the signals are transmitted to the computer through a USB interface for algorithm processing.Then,the one-dimensional direction-finding experiment of high frequency single carrier signal is carried out by this system.MUSIC algorithm and Root-Music algorithm are respectively used to process the experimental data,and their performance under experimental conditions is compared.The experimental results show that the estimation accuracy of the Root-MUSIC algorithm is higher,with an average estimation error of 1.68° and a root mean square error of 1.94°.In addition,the system can estimate the direction of arrival of the signal with only 400 snapshots,that is,the computational complexity is low.(4)In order to verify whether the system is suitable for DOA estimation of modulated signals,the one-dimensional DOA estimation system designed in this paper is used to carry out one-dimensional direction-finding experiments of single-source Lo Ra signal.The experimental results show that the system is also effective in estimating the direction of arrival of the modulated signal.In addition,a directionfinding experiment of the two Lo Ra signal was carried out,which is to verify whether the system could estimate the direction of arrival of two radiation sources in space at the same time.When the system estimates the incident angles of two sources at the same time,the root mean square error is 2.85°,and the angular resolution is 22.6°.(5)A two-dimensional DOA estimation system is designed,which uses a fiveelement cross-shaped array to receive signals,and the signals received by the antenna array are collected by a five-channel synchronous acquisition subsystem.Afterwards,the collected signals are transmitted to the computer through the USB interface for DOA estimation using the two-dimensional MUSIC algorithm.The two-dimensional direction-finding experiment of the high-frequency single-carrier signal is carried out through this system.It can be seen from the experimental results that the system can simultaneously estimate the azimuth and elevation angles of the far-field narrowband signal,and realizes the two-dimensional DOA estimation.