Research On Key Technologies Of Broadband Constant Envelope Transmission

With the continuous development of wireless communication technology,people have increasingly higher requirements for the transmission rate of information.As a new generation of wireless communication technology in the future,6G communication will have higher goals in terms of transmission rate and network delay.While 6G is receiving more and more attention,it is also facing severe technical challenges.Millimeter wave transmission is a very promising method of 6G communication,and the multi-antenna massive MIMO system is one of the core technologies of millimeter wave transmission.Its characteristics of high transmission frequency and large number of antennas put forward higher requirements for signal power utilization.From this perspective,the importance of high power efficiency physical layer design needs to be re-understood.Constant envelope modulation can effectively reduce the peak-to-average-power-ratio of the signal and can adapt to nonlinear power amplifiers.While ensuring high power efficiency,there is no need to worry about the impact of nonlinear distortion caused by the power amplifier on system performance.Therefore,the design and research of the constant envelope modulation waveform is of great significance.This dissertation focuses on constant envelope modulation and its applications,and focuses on the physical layer waveform design based on two systems.The specific research contents are as follows:This paper first studies the basic principle,basic model and receiving detection method of the typical modulation method in constant envelope modulation ?continuous phase modulation(CPM),which lays the foundation for subsequent research.Different from traditional quadrature amplitude modulation(QAM),phase shift keying(PSK)and other modulation methods,the core idea of CPM is to include the transmitted information in the phase of the carrier,and the phase of the carrier is continuously changing.This kind of modulation method has the advantages of continuous phase,constant envelope,and high frequency spectrum utilization,and has attracted widespread attention.The paper studies the basic principles of the modulation system,then introduces the structure of the CPM transmitter and receiver,and proposes a novel preamble design,arrival detection and time-frequency synchronization methods corresponding to this preamble.In addition,the article also introduces the constant envelope orthogonal frequency division multiplexing(CE-OFDM)technology,which is a technology that combines constant envelope modulation with traditional orthogonal frequency division multiplexing(OFDM).With the help of constant envelope modulation techniques such as phase modulation or frequency modulation,the OFDM signal is secondarily modulated to the frequency or phase information of the constant envelope carrier signal,which solves the problem of OFDM peak-to-average ratio.Then this paper focus on the application of constant envelope modulation system in multi-user scenarios.The article first proposes the multi-user continuous phase modulation(MU-CPM),and introduces the basic principle,basic model and transceiver structure of MU-CPM.The core idea of MU-CPM is to preprocess the information of different users with channelization codes.After traditional CPM modulation,a CPM signal containing multi-user information is obtained.In addition,this paper also extends CE-OFDM to multi-user scenarios.The paper proposes multi-user constant envelope orthogonal frequency division multiplexing(MU-CE-OFDM),and proposes its basic model and transceiver structure.The idea of MU-CE-OFDM is to allocate multi-user information to different sub-carriers of OFDM,and then apply constant envelope constraints to the multi-user OFDM signal.The multi-user constant-envelope modulation methods proposed here,solve the problem of communication between base station station and multiple users in a scenario where a single beam signal covers multiple users,while maintaining the signal's constant-envelope characteristics.Finally,this paper studies a two-stage constant-envelope precoding scheme,which effectively utilizes large spatial degrees of freedom(Do F)gains to reduce the number of RF chains and channel state information(CSI)signaling overhead,while maintaining the constant envelope characteristics of the signal.The two-stage precoding scheme includes a high-dimensional radio frequency precoder and a high-dimensional baseband precoder.On the one hand,since different users' beams can be well divided in the spatial domain,the knowledge of global statistical information(spatial correlation matrix)can be used to design RF precoders to reduce inter-beam interference.On the other hand,the baseband precoder can be designed by using the information of the low-dimensional effective CSI to achieve spatial multiplexing gain in n beams.Therefore,the proposed two-stage precoding can reduce CSI signal overhead and the number of radio frequency chains used to send data while maintaining the constant envelope characteristics of the signal,and achieve a greater spatial multiplexing gain.