CSI Based Wireless Indoor Positioning In 3D

Direction of arrival(DOA)estimation is a method of finding a direction of propagation of an electro-magnetic wave that impinge on an array of antennas.DOA is found by calculating the time difference of arrival of electro-magnetic wave at each element of the array.And time difference of arrival is calculated by measuring the phase shift between received electromagnetic waves at each antenna.DOA estimation has been a key task in a lot of fields,like sonar,radar,seismology etc.for almost a century.In last few decades,rapid growth of demand for data transmission rate in mobile communications led to development of more sophisticated modulation schemes and usage of multiple transmitters and receivers.Multiple receivers on a base station made it possible to use traditional array signal processing methods in mobile communications to implement DOA estimation for mobile user positioning.Also,to fulfill growing requirements for data transmission rate,Orthogonal Frequency Division Multiplexing(OFDM)modulation scheme attracted a lot of attention lately.In OFDM systems channel is divided into several sub channels with same bandwidth,then high speed serial data is converted to several low speed parallel data,modulated on these several subcarriers and finally transmitted.Complex value that describe the overall attenuation and phase shift introduced by the channel and measured at each subcarrier of each antenna is called Channel State Information(CSI).CSI is measured on a per packet basis,and it is possible to utilize this information to increase the DOA estimation.Nowadays most studied and used structure of antenna array is Uniform Linear Array(ULA).But,ULA can provide information of angle of arrival of incoming signal only relative to the array axis,i.e.one dimensional angle information.However,positioning of mobile terminal in three dimensions is expected nowadays.This means two dimensional(2D)angle information is needed to be provided.For this case planar arrays are required.In this thesis,a novel method of 2D DOA estimation technique for uniform circular array(UCA)using CSI is proposed.Firstly,using the fact that CSI among subcarriers comprises phase shift due to DOA and Time-ofFlight(ToF)number of antennas is virtually extended.Secondly,beamspace transform is applied to UCA's array manifold for CSI-UCA smoothing to virtually extend the number of observations.Finally,multiple signal classification(MUSIC)algorithm is applied on smoothed data for 2D DOA estimation.Several simulations were run to analyze the performance of proposed method,and results are provided.