Research On Key Technologies Of Non-orthogonal Multiple Access

In recent decades,the development of wireless communication has changed from traditional voice services to current broadband data services,which has a profound impact on people's lifestyle and information technology evolution.In order to support the rapid development of the mobile Internet and the Internet of Things,the fifth generation of mobile communication systems for 2020 and the future is already in full swing.The evolution of multiple access technology has become the sign of every generation of communication systems.The existing multiple access technology is limited by orthogonal resources,and can not meet the requirements of high spectrum and large connection of 5G system.Non-orthogonal multiple access technology can multiplex the transmission information of multiple users in the same time-frequency resource,thereby improving the spectrum efficiency of the system and satisfying the simultaneous access of a large number of users,which will undoubtedly become one of the core technologies of 5G.Theoretical analysis shows that NOMA has greater performance advantages than traditional OMA technology under the same spectrum resources.Firstly,the current non-orthogonal multiple access technology is analyzed comprehensively by this paper,including its transmitter structure and receiver principle.Based on the difference of system principles,the corresponding NOMA classification schemes are proposed,namely,scrambling-based NOMA,interleaving-based NOMA,spreading-based NOMA,coding-based NOMA.Also,the preliminary simulation results are given.At the same time,it is pointed out that although the transmitter of various NOMA schemes are different,they can be described by a unified structure.Secondly,in order to accurately analyze the cross-correlation properties of the spreading sequences,this paper introduces the related theory of Welch bound,and quantitatively analyzes the characteristics of the spreading matrix from multiple dimensions such as root mean square cross correlation and maximum cross correlation.It is proposed that the maximum cross-correlation approximation Welch bound is used as the evaluation index to optimize the new spreading sequence,so that the root mean square cross-correlation of the constructed spreading sequence can reach the Welch theoretical boundary,while minimizing the maximum cross-correlation approaching Welch bound.Finally,this paper proposes a security-based non-orthogonal multiple access scheme based on the characteristics of bandwidth-like noise,initial value sensitivity and good correlation characteristics of chaotic sequences.At the same time,since the proposed system does not use the spreading technology,the channel coding is performed at a low code rate under the same spectral efficiency,and the coding gain of the system is fully exploited by time diversity.