| With the development of wireless transmission technology and internet technology,people’s demand for mobile communication continues to grow,and new application scenarios continue to emerge.It can be predicted that the 5th Generation(5G)will soon reach its performance limit,which is difficult to meet future communication needs.Beyond 5G(B5G)mobile communication will further improve the communication rate,expand the communication range,strengthen the security of communication and enhance the intelligence of the system on the basis of 5G communication network.Therefore,B5 G communication network needs to carry out innovative research from various aspects,explore new communication frequency bands,communication scenarios,and research more efficient modulation and demodulation,coding and decoding,multiple access and other communication technologies.The traditional Multiple Input Multiple Output(MIMO)downlink transmission technology faces important challenges in system design,such as expensive radio frequency(RF)overhead and complex signal processing.Therefore,providing a more high-speed,reliable and efficient solution is an important development direction of future mobile communication represented by B5 G.In the development of MIMO technology,spatial multiplexing and spatial diversity have been widely used in real communication networks.At the same time,spatial modulation(SM),differential modulation and other new technologies,due to their high transmission rate and good system performance,can effectively reduce RF cost and receiver complexity,and become important technologies in future MIMO systems.Aiming at downlink MIMO wireless transmission in B5 G system,based on the technical characteristics of spatial modulation,combined with spatial diversity,differential modulation and other technologies,this paper studies important issues such as spectral efficiency,differential design,information security,and spatial diversity.Specific contributions are as follows:(1)A non-orthogonal space-time block code spatial modulation system is proposed to improve the spectral efficiency of the existing space-time block code spatial modulation system,aiming at the problems of low transmission rate and diversity gain when the number of antennas increases.Next,in order to further improve the transmission performance of the scheme,a new transmission matrix code at the transmitter and a low complexity detection algorithm at the receiver are designed.At the same time,the error rate expression of the system is derived theoretically.(2)Aiming at channel estimation and pilot pollution in downlink channels,a novel differential spatial modulation system is studied to realize incoherent detection and apply to massive MIMO scenarios.In order to further obtain diversity gain,a differential spatial modulation transmission scheme of space-time block coding is designed,and a low complexity signal detection algorithm at the receiver is derived,Finally,the accurate expression of the system bit error rate is obtained through theoretical analysis.(3)Three new covert transmission schemes based on space shift keying,phase shift keying and spatial modulation are proposed to solve the communication security problems in downlink MIMO wireless transmission.The proposed scheme hides secret information in ordinary space-time signals by designing space and signal constellation mapping,so that eavesdroppers cannot distinguish and intercept.At the same time,the theoretical bit error rates of the three schemes are derived theoretically,and the performance and security of the proposed schemes are verified by simulation.(4)The space-time linear coding scheme is studied to solve the problems of poor performance of incoherent detection in fast channel change and high receiver complexity.At the same time,in order to further improve the anti-jamming capability,a space-time/frequency linear coding orthogonal frequency division multiplexing transmission scheme is proposed,and the performance of the new scheme is theoretically analyzed.Finally,the effectiveness of the proposed scheme is verified through simulation and hardware implementation.This dissertation researches the new downlink MIMO wireless transmission technology for B5 G,and focuses on the design and optimization of the transmission rate,pilot cost,information security and receiver simplification of massive MIMO,making it more conducive to the application in real scenarios,can be used in future wireless communication systems,and is conducive to its industrial application and development. |
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