Research On OFDM Modulation And Demodulation Technology Based On Software Defined Radio

With the development of society and the explosive growth of information accompanied by tenser spectrum resources,People are stricter about communication performance.Owing to its advantages,such as the configurability of multi-channel orthogonal subcarriers,high frequency spectrum utilization rate,the strong anti-jamming ability and the simple channel equalization,OFDM modulation technology has become a research hotspot in recent years.At the same time,OFDM technology is sensitive to synchronization errors.It may lead to large BER with small synchronization errors.Moreover,OFDM experimental platform based on hardware has the characteristics of long design cycle,high cost and difficult implementation.Therefore,this paper designed a complete framework of OFDM system by learning the principle of OFDM technology and the key technologies involved.Based on the LABVIEW and USRP device,an OFDM experimental platform was built.After deeply studying the synchronization problem,I analyzed and compared the advantages and disadvantages of three synchronization timing algorithms.At last,an improved weighted synchronization timing algorithm based on CAZAC sequence was proposed.The main content and achievements of this paper are as follows:1.The basic principle of OFDM modulation technology and the key technologies involved were studied,including cyclic prefix,synchronization technology,and the basic framework of OFDM system.At the same time,several high-order modulation technologies widely used at present are compared,and their advantages and disadvantages are analyzed.Several high-order modulation technologies widely used were compared.2.The synchronization problem was emphatically studied which includes synchronization timing error and frequency offset error.The influence of synchronization error to system was analyzed theoretically.Three synchronization timing algorithms based on training sequence,including S&C algorithm,Minn algorithm,Park algorithm,were studied,as well as the Moose algorithm for frequency offset correction.Finally,an improved weighted synchronization timing algorithm based on CAZAC sequence was proposed.3.Based on software defined radio platform,this paper designed and built a complete OFDM communication system,including transmitter VI and receiver VI.The main modules included text to bit conversion module,16QAM modulation and demodulation module,OFDM modulation and demodulation module,training sequence module,pulse shaping filter module,time delay and frequency offset module and synchronization module.4.Implementing the synchronization algor:ithm on OFDM system.The M(d)curves and MSE curves were compared and analyzed,which can explain the performance of the four algorithms,S&C algorithm,Minn algorithm,Park algorithm and improved synchronization timing algorithm.Finally,the experimental results shown that the normalized energy of the sub-peaks caused by AWGN noise was less than 0.1 except for a single shar:p main peak.Besides,When SNR was 20,the value of MSE approximated to 10-3 and the system error rate was less than 10-4.Therefore,the proposed synchronization timing algorithm has the advantages of higher timing accuracy and lower system bit error rate.