Design And Implementation Of SEFDM System Based On Direct Sequence Spread Spectrum

Wireless communication has now became an important part of human society.With the rapid development of communications,the number of users and terminal devices has grown explosively,resulting in a wide variety of electronmagnetic interference in wireless networks,which poses a huge challenge to the reliability and security to the information transmission.Moreover the increasing number of equipments and users puts more pressure on spectrum resources.The spectrally efficient frequency division multiplexing(SEFDM)based on direct sequence spread spectrum(DSSS),referred to as the'DS-SEFDM system',has the advantages of both schemes,e.g.,reliable transmission ability of DSSS scheme and high spectral efficiency of SEFDM,which can satisfy requirements of future communications.In this thesis,we focus on the characteristics of the DS-SEFDM system,proposed the low complexity receiver design corresponding to the DS-SEFDM system,moreover,the proposed design has been implemented on the software-defined radio platform.The main contributions of this thesis can be organized as follows.Firstly,based on the requirements of anti-interference and high spectrum efficiency,the DS-SEFDM system combining DSSS and SEFDM.Secondly,the transmitter and receiver design of the DS-SEFDM has been proposed.The spreading process is performed in frequency domain in transmitter,then the spreading symbols are allocated to the non-orthogonal subcarriers and transmitted.In receiver,due to the signal properties of DS-SEFDM system,the traditional detection algorithm in SEFDM system is inapplicable to the detection of DS-SEFDM signal due to the high complexity.Based on the principle of traditional detection algorithm and the characteristics of the DS-SEFDM system,a new detection algorithm has been proposed to suppress the intercarrier interference in SEFDM system.In SEFDM system,the inter-carrier interference is severe,however,most interference occurs in adjacent sub-carrier.The proposed algorithm considers few adjacent sub-carriers in detection process and can significantly reduce the complexity compared with conventional algorithm,in which all sub-carriers are taken into consideration.Further,the performance of the algorithm is simulated results verified the proposal.Finally,the implementation of the DS-SEFDM system is achieved using UniversalSoftware Radio Peripheral(USRP),transmitter encapsulated the IEEE 802.11 a preamble and DS-SEFDM into a data packet.In receiver,the preamble structure is utilized to perform packet detection,packet selection and fine synchronization in the time and frequency domains.Through the utilization of the proposed detection algorithm in receiver,it is shown that the DS-SEFDM system has the advantages of reliable transmission and high spectrum efficiency.