Research On The Key Technologies Of Sparse Code Multiple Access

As a new type of non-orthogonal multiple access technology,Sparse Code Multiple Access(SCMA)is one of the candidates of new multiple access technology for 5th Generation Mobile Communication Network(5G).The SCMA system has a certain overload capability and can meet the needs of massive connection of 5G wireless communication networks.Compared to orthogonal multiple access technology,non-orthogonal multiple access technology can accommodate more users when occupying the same number of physical resources.However,the complexity of message passing algorithm(MPA)adopted by the receiver side for multiple user detection(MUD)is high.In addition,since the codewords are usually mapped onto the OFDM subcarriers in the SCMA system,it has the similar characteristic of peak to average power ratio(PAPR)to that of the OFDM signal.In response to these problems,this thesis deeply studies the MPA algorithm at the receiver side,and proposes a low complexity decoding algorithm.Besides,this thesis also studies how to improve the PAPR performance of the SCMA system.The main work of the thesis is as follows:1.The structure of the SCMA system is analyzed in detail.The principle of the transmitter and the receiver is introduced.The principle of the SCMA encoder and the MPA algorithm for multi-user detection is introduced.2.Several existing MPA algorithms are deeply studied.Aimed at the MPA decoding algorithm with high complexity and slow convergence,a low-complexity detection method is proposed to reduce the user nodes to be updated in the serial updating process.The algorithm is simulated and compared with the existing algorithms.3.Aiming at the problem that the PAPR of the SCMA system is relatively high,a variety of PAPR reduction techniques are studied.Since the complexity of the repeat clipping and filtering(RCF)algorithm is high,an improved algorithm is proposed.Since the SCMA system occupying OFDM subcarriers has high PAPR,a SCMA multiple access scheme with low PAPR is proposed.This scheme uses SC-FDMA technology and further reduces the PAPR by using the PAPR reduction technique.