Channel Estimation And Adaptive Modulation Technology Research Based On Ultrasonic Communication Channel

Due to the small loss of ultrasonic in the thick metal wall,and the signal is not affected by electromagnetic shielding,ultrasonic is well suited as signal carriers for special environments.In this thesis,ultrasonic through-metal(UTM)communication channel is the main research object.And this thesis uses the orthogonal frequency division multiplexing(OFDM)technology to overcome the severe frequency selective fading and multipath effects caused by the transmission of ultrasonic in the metal channel.This thesis also studies the channel estimation and adaptive modulation techniques in the UTM communication system.The channel estimation and interpolation algorithm based on UTM communication system are studied.A decision feedback estimation algorithm based on discrete Fourier transform(DFT)is proposed.The proposed algorithm eliminates the effect of noise on the estimation of channel response from two aspects.Firstly,the DFT is added to the channel estimation,and the impulse response of the channel containing noise is zeroed to eliminate the noise interference besides the cyclic prefix(CP).Secondly,when the interpolation algorithm is used to obtain data corresponding of the response parameters,it calculates the next OFDM symbol according to a pre sign response parameter.We compares the decision data and the modulation constellation mapping according to the minimum Euclidean distance,selecting the most appropriate modulation constellation points as the sentence data.Then according to the channel correction value,we calculate the response parameters of data symbols.Simulation results show that under the same Eb/N0,the proposed algorithm has a better performance of bit error rate and mean square error,and it improves the receiving data rate to a certain extent.The adaptive bit and power allocation algorithm based on UTM communication system is studied.In this thesis,adaptive modulation algorithm is added to the OFDM-based UTM communication system.The simulation results show that the performance of adaptive modulation system is better than that of fixed modulation system.In view of the disadvantage of high computational complexity of Hughes-Hartogs algorithm,an improved algorithm is proposed based on the existing optimization methods.In order to reduce the number of iterations and the amount of computation per iteration,the improved algorithm achieves that by changing the iteration step of bit allocation.The number of bit allocated at each iteration is greater than 1,thus reducing the number of iterations.By setting the channel gain threshold,the sub-channel with less channel gain is not involved in bit allocation,so as to reduce the comparative search in bit allocation and reduce the computational.The simulation results show that the improved algorithm reduces the computational complexity of the Hughes-Hartogs algorithm 54.3%at the coast of little performance loss.