The Application Research Of Spread Spectrum In Multicarrier System

In order to meet the explosive growth of data transmission rate and the number of users,the fifth generation mobile communication network(5G)requires the new transmission technology,which has higher spectrum efficiency and excellent anti-jamming ability.In the modern wireless communication technology,spread spectrum communication technology has an excellent ant-jamming performance,while multicarrier modulation technology has a high data transmission rate and can combat frequency selective fading effectively.The combination of multi-carrier and spread spectrum communication systems are more suitable for this requirement as they can further improve the system's anti-fading and anti-jamming performance.And to study their combined technologies has become a hot filed of wireless communications.In order to deal with the complicated application scene of 5G,Multicarrier time division multiple access(MC-TDMA)was put forward by our project team.The thesis mainly implements the multicarrier MC-TDMA spread spectrum scheme,studies its related technology,the specific contents are as follows:1.Implementation of CDMA-MC-TDMA program and a comprehensive simulation.MC-TDMA introduces the advantages of single carrier modulation system on the basis of traditional filter group multicarrier modulation system,and thus has very low peak average power ratio and a strong ability of anti-multipath fading and carrier non-synchronous.Multicarrier MC-TDMA spread spectrum scheme is CDMA-MC-TDMA.MC-TDMA achieves frequency diversity gain after frequency domain spread spectrum,with stronger anti-multipath fading capability.Therefore,based on the MC-TDMA frequency domain spread spectrum system,this thesis analyzes the key technologies such as interleaving mapping and MDFT filter bank adjustment,and carries on the comprehensive simulation analysis to the system performance.The simulation results and theoretical analysis show that MC-TDMA-based frequency-domain spread spectrum technology exhibits better SER performance under pedestrian channel and vehicular channel than MC-TDMA system,and the higher the number of subcarriers,the higher the SER.2.An improved set of the small set orthogonal Kasami code is proposed and used in the MC-TDMA-based frequency-domain spread spectrum system.Aiming at the problem that multiple access interference increases with the increase of the number of users in the MC-TDMA-based frequency-domain spread spectrum system,the proposed code makes a compromise between reducing peak cross correlation value and increasing the number of distinct code.The small set orthogonal Kasami code is based on the small set Kasami sequence and has lower cross-correlation properties.The number of codes generated by this algorithm is greater than Walsh code,but still far less than the number of orthogonal Gold code sequences.Therefore,an improved set of the small set orthogonal Kasami code is proposed.It has been achieved at the expense of cross correlation values.As far as cross correlation value is concerned,the proposed code is superior to the orthogonal Gold code.The simulation results show that the proposed code outperforms the orthogonal Gold code except the small set orthogonal Kasami code and Walsh code under multiuser scenario.