The Research Of Sphere Decoding Detection In Quadrature Spatial Modulation System

Multiple-input multiple-output(MIMO)technique is always troubled by Inter-channel interference(ICI)in recent years.A innovative technique which is able to avoid ICI is becoming a research hotspot——spatial modulation(SM)technique,which activates a single antenna at each time to transmit constellation symbol,with the exploitation of the spatial position(index)of the active antenna as an additional dimension for data transmission(spatial symbol)to avoid ICI for MIMO systems.In addition,it allows the use of a single radio frequency(RF)chain at the transmitter in each slot so that it can reduce the demands for physical device in the systems.Therefore,SM technique develops rapidly in these years.In 2015,quadrature spatial modulation(QSM)technique is proposed,in which the transmitted constellation symbols are divided into two independent branches(real branch and image branch),one for in-phase and another for quadrature,to transmit simultaneously which results in additional bits of base-two logarithm of the number of transmit antennas to transmit compared to SM systems.Therefore,two transmit antennas are activated in each time in QSM systems.Considering symbol of real branch and image branch are orthogonal,ICI can be completely avoided.Therefore,QSM technique is a new method to enhance the overall spectral efficiency of the SM technique while retaining almost all inherit advantages of such systems?As QSM technique was proposed in recent years,further study about QSM systems is required.The thesis focuses on detection algorithms of QSM systems.The typical detection algorithms for QSM systems are maximum likelihood(ML)detection and near-by ML detection.The thesis applies the sphere decoding(SD)detection in SM systems to QSM systems,which achieves near ML bit error rate(BER)performance with much lower computational complexity.Moreover,based on the analysis of SD algorithms(Rx-SD and Tx-SD)in QSM systems,we take some measures to reduce searching-radius redundancy of traditional SD in order to decrease computational complexity.Sequentially,the searching-radius redundancy of detected layer can be used to estimate the searching-radius redundancy of undetected layer,so that we can deduct this part of redundancy through the radius of detected layers and obtain the improved detection algorithms named RNSD and TNSD.Finally,the thesis makes a comparison of BER performance and computational complexity among ML detection,traditional SD detection and its improved detection algorithm.Simulations show that the traditional SD detection and its improved detection have a good BER performance with ML detection,but they have a much lower computational complexities to ML detection,especially the modified TNSD algorithms.