Two-Dimensional Scanning Imaging And Compressed Beamforming Based On Wi-Fi Signals

Wi-Fi(Wireless Fidelity)signals are usually in the frequency of 2.4 GHz or 5 GHz,and it's bandwidth is 20 MHz or 40 MHz.Compared with traditional optical imaging,infrared imaging,terahertz imaging and other imaging methods,Wi-Fi signals have a great advantage in imaging under bad imaging conditions such as invisible or non-line-of-sight.Especially for walls and other obstacles,Wi-Fi signal in the penetration and transmission distance are stronger than infrared,millimeter wave and terahertz wave.Therefore,Wi-Fi signal imaging technology in the indoor imaging positioning,urban anti-terrorism and indoor personnel monitoring and earthquake relief and other fields have a bright future.On the other hand,Wi-Fi signals can also be used for indoor positioning or Wi-Fi hotspots.GPS,Beidou and Glenas are able to provide real-time location navigation services,but it is difficult to cover or provide more accurate positioning information for these navigation signals in basements or large buildings.So Wi-Fi signal positioning technology can make up for their lack of positioning in the indoor environment.Wi-Fi positioning for more shopping malls,schools,stations or car parks and other public places can provide more convenient,accurate and low-cost positioning services.In addition,the Wi-Fi positioning technology can also achieve large-scale storage of goods positioning,home safety monitoring of children,criminal investigation cracked,life search and so on.In the aspect of Wi-Fi imaging,Wi-Fi SAR imaging simulation is carried out by using the distance-Doppler algorithm based on Synthetic Aperture Radar(SAR)imaging technique,using chirp signal.As the Wi-Fi signal frequency is relatively low,and the corresponding SAR imaging accuracy is not high,so it is difficult to meet the indoor sensing and positioning requirements.Therefore,we propose the method of antenna array imaging and two-dimensional scanning imaging for the characteristics of Wi-Fi signal.The directional antenna is used to obtain the reflected signal value of each pixel point of the imaging target through two-dimensional mechanical scanning imaging method,and finally reconstruct the target image.The results show that active Wi-Fi signal imaging can achieve low resolution imaging of objects.For metal objects.It is still possible to identify the metal target and its corresponding approximate profileeven the number of pixel points is low.Finally,this paper discusses the problems and the limitations of the experiment.In the aspect of Wi-Fi positioning,this paper describes several commonly used positioning methods: angle of arrival(AOA)location,time of arrival(TOA)and time difference of arrival TDOA,and a received signal strength(RSSI)location method for distance estimation.Due to their own positioning principle of the restrictions,as well as positioning performance is still inadequate.Such as CBF algorithm is robust to noise,but its resolution is low.MUSIC and MVDR algorithms rely on spectral matrix eigenvalues,so when there is few of samples,the spectrum matrix is not enough and the signal subspace is small,the positioning performance will be greatly reduced.In order to solve the problem of positioning performance and improve the positioning accuracy,this paper presents a method based on compression sensing(CS)beamforming algorithm for radio frequency wireless location research.The performance of the localization algorithm is analyzed by software simulation and experimental verification.According to the simulation results,the effect of the algorithm localization is discussed.The error rate of the positioning is calculated by changing the number of sampling times and the number of elements.The above research shows that the compressive sensing beamforming algorithm can locate the target position with high precision under the small sampling times.In addition,in the multi-target orientation,CS algorithm has a stronger directivity,positioning performance and stability.In the experimental area,through the analysis of the system parameters of the positioning system,the effects of signal frequency,uniform linear array element spacing and nonuniform linear array on the positioning results are summarized.The results show that when the antenna array is half-wave array,the frequency of the signal has little effect on the positioning result.The array pitch of the antenna array has a great influence on the stability of the experiment.In the uniform linear array of non-half-wave array and non-uniform linear array positioning effect is not ideal.The compression sensing beamforming algorithm based on the AOA localization,combined with compression sensing theory,breaking the limitations of the traditional positioning algorithm,has important guiding significance for the indoor positioning design.