Analysis Of Limiter Influences On Baseband Sybol Signals

At present,lots of communication channels are nonlinear,the selection of modulation mode is determined by the channel characteristics of the system.The nonlinear channel has great influence on the transmitted signal.If the signal processed by the nonlinear component hasenvelopefluctuations,theamplitudeandthephaseofoutputsignal will be distorted,generating spectral spreading,and affecting the quality of signal transmission;the channel nonlinearity also has an important effect on the transmission power and transmission efficiency,so the input signal is required higher,usually with the requirements that the modulated signal has constant envelope or quasi-constant envelope.Then,limiters are usually used after the non-constant envelope or non-quasi-constant envelope signal to get constant envelope signals.However,the use of limiters will bring the baseband symbol signals distortion and spectral spreading.In this paper,we analyze the baseband symbol distortion and spectral spreading caused by the limiter in the quadrature modulation system,and try adopting distorted symbol waveform to realize constant envelope modulation without the limiter,exploring the modulation and demodulation mode that has higher band efficiency and lower PAPR.In the research,we use sin~2[(?t/2T)]as the baseband symbol waveform.To improve the band efficient further and keep the chip-rate without changing,we use sin~2[(?t/4T)]with twice symbol waveform length as the practical baseband symbol waveform.Meanwhile,we introduce symbol distortion artificially,and get 64 kinds of distortion waveforms and expressions,and also get the adjacent code cross correlation.Then,use the distortion waveform directly to quadrature modulation,to prove the method correctness or not.After that,to improve the band efficiency higher again and keep the chip-rate without changing,we use sin~4[(?t/4T)]as symbol signal and design the quadrature modulation and demodulation system.The method used in this paper also has reference meaning to the analysis of baseband symbol distortions and spectral spreading in other quadrature modulation system.