The Research On The Mitigation Of Phase Noise In SCMA-OFDM System

SCMA(Sparse Code Multiple Access) is a novel multiple access technique in the 5th generation mobile communication system(5G).Based on LDS-MA(Low Density Signature Multiple Access), SCMA can utilize sparse coding to realize multiplexing for more than one user. Through co-designing of digital modulation and spreading code, the SCMA maps bits to an SCMA code directly. Compared with the traditional LDS, the shaping gain of an multidimensional constellation is the main contribution of the performance in SCMA. In addition, benefit from the sparse code, SCMA has lower detection complexity. However, phase noise may have more terrible influence on SCMA because of the utilization of multidimensional constellations and symbol mapping. Therefore, the study of phase noise suppression algorithm in SCMA system has an important guiding significance.In this paper, we conduct a research on SCMA system architecture and the key technology of the physical layer. The multi-dimensional codes design and MPA detection are studied separately. In addition, we present the principle of desingning the different multi-dimensional constellation and the principle of reducing the complexity of MPA.The phase noise is caused by the jitter and instability of oscillator circuit? so it is inevitable in the actual communication system. In this paper, we study the effect of phase noise in communication system, especially the effect on OFDM system. Analysis about the effect of phase noise in time domain and frequency domain has been presented and it is verified by simulation result. Furthermore, we study the main phase noise suppression algorithm, such as ML(Maximum Likelihood) algorithm, CPE(Commom Phase Error) elimination algorithm, and we also do a full research and analysis on the structure and procedure of the algorithms. Based on the understanding of the advantages and disadvantages of the algorithms, we analyzed their applicability in SCMA system.Based on the study of the algorithms in references and property of SCMA system, we propose a mitigation scheme which can compensate phase noise both in time and frequency domains in this paper. The method roughly compensates the phase noise in time domain by CP and compensates for phase noise with pilots in frequency domain. The difference between the method in and the proposed method in this paper is that our proposed method doesn’t need to transit from frequency domain to time domain, and it doesn’t involve complicated matrix operation either, whose complexity is greatly reduced. Simulation results show that, the proposed method can effectively cancel the impact of phase noise.