Research On Iterative Channel Estimation For Underwater Acoustic Communication Based On MIMO-OFDM

In this paper,the iterative channel estimation technique under the underwater acoustic multiple-input–multiple-output orthogonal frequency-division multiplexing(MIMO-OFDM)communication systems is studied for time-varying double-spreading underwater acoustic channel.Due to the advantage of high frequency and superior performance against multipath interference,OFDM has become more and more important in the UWA communication community,MIMO technology is a useful method to enhance the capacity of communication systems with multiplexing and diversity.The adaptive MIMO channel estimation algorithm with low computational complexity is studied.For the underwater acoustic MIMO-OFDM communication system,an iterative receiver is proposed.The iterative channel estimation technology in the receiver is studied,which effectively improves the system performance and realizes reliable information transmission.Firstly,two key technologies of MIMO and OFDM are introduced in this paper.Exploring the advantages of combining them,the iterative receiving technology based on Turbo principle in underwater acoustic MIMO-OFDM communication is studied.The transmission characteristics of OFDM signals in underwater acoustic double-spread channel are introduced,lead out the necessity of conducting research on channel estimation techniques in underwater acoustic MIMO-OFDM communication systems is introduced.Then,the research of adaptive channel estimation algorithm under MIMO channel structure is carried out.The variable forgetting factor compromises the convergence,stability and tracking ability of the recursive least square(RLS)algorithm.The simulation results show that the improved variable forgetting factor recursive least square(IVFF-RLS)has better performance and robustness than the conventional constant forgetting factor RLS algorithm.Combining the dichotomous coordinate descent(DCD)algorithm,we study the RLS-DCD algorithm with low computational complexity,the simulation results show that the RLS-DCD algorithm can accurately estimate the channel impulse response,and its stable convergence performance is basically consistent with the RLS algorithm,and the computational complexity is much lower than the RLS algorithm under the condition of given accuracy and determined large enough number of cycles,etc.In the sparse channel,the variable forgetting factor norm RLS-DCD algorithm is studied.The simulation results show that the performance of Normalized Mean Square Deviation(NMSD)is about 15 dB lower than the conventional RLS algorithm while achieving the best convergence speed,and can cope well with the abrupt underwater acoustic channel.Finally,the research on underwater acoustic MIMO-OFDM communication iterative receiver based on Low Density Parity Check(LDPC)coding is carried out.The simulation studies the influence of LDPC coding code parameter design on decoding performance,and lays a foundation for a good performance iterative receiver.The working principle of iterative receiver consisting of MIMO signal detector,soft input soft output channel estimator and LDPC decoder is studied from the system perspective.The iterative receiver is simulated by the iterative extended soft recursive least squares channel estimation algorithm.The performance of the machine,the simulation results show the feasibility of the channel estimation algorithm and the reliability of the iterative receiver performance.