Research On Multi-carrier Underwater Acoustic Spread Spectrum Communication Technology

The in-depth exploration and utilization of the vast ocean has promoted the vigorous development of underwater acoustic communication spread spectrum technology.As an effective means of mining the marine world,underwater acoustic spread spectrum communication technology has become one of the hot spots in marine scientific research.High concealment and strong anti-jamming ability are the advantages of spread spectrum communication technology.It can overcome the bad channel conditions and achieve reliable information transmission under low SNR.Although it has high reliability,the number of users that the traditional spread spectrum communication system can accommodate is limited and the communication rate is low.Multicarrier modulation technology has high spectrum efficiency,and it has strong resistance to cross-talk and multi-path interference caused by frequency selective fading.Combining multicarrier technology with spread spectrum technology can play their respective advantages and make up for each other's shortcomings.Firstly,this paper introduces the basic principle and key technology of multicarrier spread spectrum communication,and introduces and discusses the generator principle,sequence characteristics and related characteristics of spread spectrum sequence in detail.Then,an underwater acoustic spread spectrum communication system based on equalization technology is built.Due to the complexity of underwater acoustic channel,it is necessary to select the appropriate algorithm for channel estimation to determine the structure of equalizer.In this paper,the least mean square(LMS)adaptive equalization,zero forcing(ZF)equalization and least mean square error(MMSE)equalization are studied for the single carrier underwater acoustic spread spectrum system,and the simulation results and pool experiment results are given.Next,the multicarrier CDMA technology is studied,and the system performance of MC-CDMA,MC-DS-CDMA and MT-CDMA is simulated and analyzed.Then the performance of time domain multicarrier spread spectrum communication system is analyzed.The actual underwater acoustic channel is analyzed and modeled,and then the time-domain multicarrier spread spectrum communication system is analyzed from spectrum overlapping,multipath effect and Doppler effect in turn.Finally,the adaptive equalization technology of underwater acoustic time domain multicarrier frequency domain is studied.LMS algorithm,RLS algorithm and NLMS algorithm are studied and simulated.Finally,the pool experiment is carried out to verify the performance of the three algorithms.Through simulation and experimental verification,LMS algorithm is simple to implement,but its convergence is poor,and its convergence is affected by the convergence step(u).With the increase of u,the convergence speed increases,but the error after convergence also increases,while RLS algorithm has good convergence,but its implementation is too complex,and the performance of NLMS is between the two,which has better convergence and is also better than L MS is simpler,and the BER performance of three algorithms is compared with MMSE algorithm.It can be seen that the BER performance of RLS is the best,NLMS algorithm is the second,LMS algorithm is the second,MMSE algorithm is the worst.When choosing equalizer,we should consider the hardware cost and performance improvement brought by equalization algorithm.