Research On Sphere Decoding For Spatial Modulation

In the fifth generation mobile communication network,the explosive growth of mobile data services and the popularity of intelligent devices have brought forward the concept of green communication.In this trend,spatial modulation(SM)is widely studied as a new communication modulation method,which transmits information by activating a single antenna in each slot,so that the subscript position of the active antenna also carries additional spatial bit information.The single RF structure of spatial modulation can reduce the complexity of transmitter and receiver,and avoid a series of problems such as inter-channel interference(ICI)and antenna synchronization.However,SM system also has the problem of limited spectrum efficiency improvement and limited number of antennas.In order to solve these problems,many spatial modulation extension technologies,including generalized spatial modulation(GSM)and quadrature spatial modulation(QSM),have been proposed in recent years,and have attracted wide attention.In this paper,the spatial modulation system and its extended generalized spatial modulation and quadrature spatial modulation systems are studied,and the low-complexity sphere detection algorithms of each system are emphatically studied.The main research contents and contributions include:1.The specific information transmission principle of spatial modulation system is studied,and the channel model of the system is built.Based on the basic idea of sphere detection algorithm,three spherel detection algorithms SM-Rx,SM-Tx and GSM-Tx are deduced and their complexity is analyzed.The simulation results show that sphere detection algorithm is a low complexity detection algorithm for spatial modulation system,which keeps the optimal BER performance.2.Generalized spatial modulation system which allows multiple antennas to activate simultaneously to eliminate the restriction on the number of antennas and improve the spectral efficiency of the system is studied.The system principle,channel model and antenna selection algorithm are analyzed.Two sphere detection algorithms of generalized space modulation system,GSM-Rx and GSM-Tx,are deduced and their complexity is analyzed.The simulation results show that the low complexity sphere detection algorithm is still the optimal BER performance in GSM system.3.In order to further improve the spectral efficiency of SM system,this paper also studies the quadrature spatial modulation system which uses the active antenna to transmit the real and imaginary part information of the complex constellation points respectively.After researching and analyzing the system principle and model,aiming at the QSM receiver,this paper firstly improves the SM-Rx sphere algorithm in SM system and applies it to QSM system.At the same time,this paper proposes a QSM-Tx spherical detection algorithm which reduces the computational complexity of the algorithm by reducing the transmitting search space.In the application of QSM-Tx algorithm,a new method for calculating the initial radius of sphere detection is proposed,because the traditional method for calculating the initial radius is difficult to provide good BER performance.The simulation results show that the proposed QSM-Tx can reduce the complexity of ML algorithm by more than 95%,while retaining a near ML optimum detector.