Differential Kalman Filter-based Variable Mobile Underwater Multiuser Communication Technologies

With marine development,demand for variable mobile underwater acoustic multiuser communication technology becomes more and more urgent.Unlike radio channel,underwater acoustic channel is atrocious,complex and changeable,therefore,we need to carry out research on variable mobile multiuser communication technology for underwater acoustic channel.Variable mobile multiuser communications mean that underwater multiple nodes with relative variable mobile velocities transmit data to the receiver simultaneously,but their data don't reach the receiver at the same time.Intersymbol interference,multiple access interference,near far effect and variable Doppler shift problems are incurred by variable mobile underwater multiuser communications,therefore,the received signal is complex.How to extract the data of the expected user1 from the distorted received signal is the main research content of the dissertation.Spread spectrum communication technology is characterized by strong performance of resisting interference and good multiple access capability;channel equalization link and multiple access interference suppression link can be integrated into one link by virtual user technology,simplifying system structure;blind adaptive multiuser detection algorithm is characterized by avoiding channel estimation,saving spectrum resources and resisting multiple access interference;differential modulation and demodulation technology is characterized by resisting Doppler shift.In the dissertation,these technologies are combined to build effective underwater multiuser communication technologies for variable mobile underwater multiuser communications.The main contents of the dissertation are as follows:(1)Research on underwater multiuser communications when transducers and hydrophones are relative static is carried out.Intersymbol interference,multiple access interference and near far effect are incurred by static underwater multiuser communications,which lowers the performance of the communication system.Intersymbol interference is treated as multiple access interference by taking advantage of virtual user technology,and blind adaptive multiuser detection algorithm and virtual user technology are combined.Least mean square blind adaptive multiuser detection algorithm,recurrence least squares blindadaptive multiuser detection algorithm and Kalman filter blind adaptive multiuser detection algorithm are proposed to realize static underwater multiuser communications.Based on the expected user1 with relative static transducer and hydrophone,research on underwater multiuser communications with mobile interfering users is carried out.By theoretical analysis and experimental verification,it is proved that virtual blind adaptive multiuser detection algorithms can be applied to underwater multiuser communications with mobile interfering users.Finally,some groups of field experiments are carried out in a pool,a river and the sea and under ice and good experimental results verify that underwater acoustic virtual blind adaptive multiuser detection algorithms are effective for static underwater multiuser communications and even underwater multiuser communications with mobile interfering users.(2)Research on underwater Doppler shift estimation is carried out.According to maximum likelihood estimation criteria,underwater Doppler shift estimation algorithm based on interpolation and iteration is proposed and the carrier frequency of the received signal can be estimated.Research on the performance limit of the proposed algorithm is carried out,and the best performance limit of the proposed algorithm can be acquired by comparing the estimated quantized frequency deviation variance with Cramer-Rao line.When there is no quantized frequency deviation,the minimum difference between the estimated quantized frequency deviation variance and Cramer-Rao line is got and the estimated quantized frequency deviation variance is 1.0147 times as much as Cramer-Rao line.Iteration number is researched by comparing order of magnitudes,that is,research that how many iterations make the estimated quantized frequency deviation variances basically close to the Cramer-Rao line at full band.After two iterations,the performance gain caused by the algorithm cannot be got and the variance of the quantized frequency deviation is close to Cramer-Rao line at full band.(3)Research on underwater multiuser communications when transducers and hydrophones are relative variable mobile is carried out.Intersymbol interference,multiple access interference,near far effect and variable Doppler shift problems are incurred by variable mobile underwater multiuser communications,which lowers the performance of the communication system.Underwater differential Kalman filter blind adaptive multiuser detection algorithm is proposed by combining blind adaptive multiuser detection algorithm,virtual user technology and differential modulation and demodulation algorithm with chiplevel.Different Doppler shifts problem of adjacent symbols are solved by taking advantage of characteristics of very similar Doppler shifts of adjacent chips.Seven users' communication experiment in Songhua River was carried out,the maximum velocity difference of different original codes in one package of data is up to 2m/s and good experimental results verify that the proposed algorithm is effective.Underwater acoustic virtual blind adaptive multiuser detection algorithms,underwater acoustic iterative frequency estimation by interpolation on Fourier coefficients algorithm and underwater acoustic differential Kalman filter blind adaptive multiuser detection algorithm are proposed in the dissertation.Intersymbol interference,multiple access interference,near far effect and variable Doppler shift problems incurred by variable mobile underwater multiuser communications are solved,and simulation and experimental verification are carried out and good results verify the effectiveness of the proposed algorithms.New ideas and theoretical basis for solving problems incurred by mobile underwater multiuser communications will be provided by the contents of the dissertation,which will lay good foundation for the development of mobile underwater communication networks.