Channel Estimation And CPM Demodulation Algorithm For Underwater Acoustic Frequency Hopping Communication

With the huge development of communication field,the technology of adaptive frequency hopping,which is based on conventional frequency hopping system,is bec oming one of the hot pots in the communication research.In underwater acoustic ad aptive frequency hopping communication system,channel-quality estimation is very i mportant because of the presence of noise,interference and the randomness of frequ ency jumping.In addition,in the communication system,modulation and demodulati on technology is a key part for the performance of the system.Therefore,the appro priate modulation and demodulation technology and channel quality estimation algorit hm is the key of the frequency hopping communication system.Based on the resear ch of domestic and foreign scholars,this paper shows the research of channel estim ationalgorithm and CPM signal decoding algorithm in underwater frequency hopping communication system.With the accuracy and complexity as a standard of the estim ation algorithm,the classic algorithm is optimized correspondingly and some new im proved algorithms are also proposed in this paper.Firstly,the classic maximum likelihood estimation algorithm is deduced in the d eep sea channel,and theoretical simulations is carried out under conditions of differe nt data lengths and modulation modes.A new channel estimation algorithm is propo sed according to the spectral characteristics of CPM signal.The SNR root mean squ are error of this method is 0.1 dB lower than that of the maximum likelihood estim ation algorithm,and the complexity of the algorithm is greatly reduced.In addition,the classical Kalman filter estimation algorithm is optimized,where the SVR model is used to modify the filter structure.Compared with the classical algorithm,the opt imized method solves the problem of poor performance at high signal-to-noise ratio,and the root mean square error is at least reduced 0.08dB.Then,in the shallow sea channel,CPM spectrum estimation algorithm is optimi zed to expand the application scope.The simulations show that the root mean squar e error is 0.08dB less than that in the deep sea channel,which is about 0.18dB.Its complexity is also low and suitable for the real-time estimation.The classical Kalma nfilter algorithm is improved to be applicable to shallow channel.The root mean sq uare error of SNR is about 0.15dB in the improved method,but the performance wi llbecome worse at high signal-to-noise ratio.Finally,an improved algorithm for low complexity demodulation and decoding of CPM signal which is based on channel estimation,is proposed.In the Gaussian white noise channel,the differential subtraction state sequence detection algorithm is introduced in detail,and the simulation experiment is carried out under different con ditions.An improved CPM demodulation algorithm is proposed.The experimental res ults show that the BER of the improved algorithm is significantly lower than that of the differential subtraction algorithm.