Design And Application Of Precoding Based On Multi-carrier System

In order to meet the requirements of more diverse services of future wireless communication system,waveform,as one of the key technologies,will face more stringent optimization goals.The fifth generation mobile communication named optimized multi-carrier waveforms that based on orthogonal frequency division multiplexing(OFDM)as OFDM-based systems.OFDM-based systems improve spectrum utilization and flexibility of OFDM without losing its advantages by frequencydomain filtering or time-domain windowing.However,as one type of the multi-carrier systems,OFDM-based have problems of high peak-to-average power ratio(PAPR)and inter-carrier interference(ICI)due to the instability of the actual communication channel,which limit the development of the OFDM-based schemes in practical applications.Precoding is a simple but effective multi-carrier optimization technique,it generally does not affect the spectral efficiency of the system and has the advantage of linear operation.In this paper,two precoding optimization scheme are proposed to improve the performance of OFDM-based systems.The main research contents are summarized as follows:1.A precoding scheme for ICI suppression of OFDM-based systems.Firstly,a general precoding model of OFDM-based systems is proposed.Based on this model,an analysis method is proposed for the anti-frequency offset performance,and the quantified analysis for signal and ICI are introduced based on the cross ambiguity function of transmitting pulses and receiving pulses.In addition,a precoding scheme with bidirectional ICI cancellation is proposed for the problem of ICI,which weighted multiple subcarriers in the two directions of the target carrier for ICI elimination.The proposed scheme can obtain better anti-frequency offset capability due to better ICI removing performance without extra computation burden.The simulation results show that the scheme can obtain higher carrier-to-interference power ratio than the traditional precoding scheme and reduce the bit error rate of the system either in the OFDM or in some examples of OFDM-based system.2.A precoding scheme for PAPR reduction of OFDM-based systems.Aiming at the problem of high PAPR in OFDM-based systems,the basic principle and the general design rules of precoding matrix to suppress PAPR are given in this thesis.Then the problem of reducing the peak value of the signal is transformed into an optimization problem that minimizes the instantaneous power variance of signal subject to the constraint of unchanged average instantaneous power.There are two considerations for precoding matrix,i.e.,improving the phase of the carrier and the aperiodic autocorrelation of transmitted data,to be used to improve the performance of PAPR suppression.An algorithm based on the gradient search algorithm is proposed to solve the above minimization problem when jointly optimization of the aperiodic autocorrelation and phase of transmitted data are considered.Furthermore a simplified scheme for the number of iterations is proposed for reducing the complexity of the algorithm.Simulation results show that the algorithm can achieve better PAPR suppression without affecting or even slightly increasing the bit error rate performance of the system.