Research On Channel Estimation Methods In OFDM UWAC Systems Based On Compressed Sensing

As we know,the underwater acoustic communication(UWAC)channel is too complex,resulting in channel scattering effects in the time-space-frequency domains severely.As the UWAC signals present frequency and time-doubly selective features,the receiver designer needs to consider how to come against the multipath fading as well the Doppler spread.Especially for the communication occurs in shallow sea at middle distance,it suffers from the multipath effects more seriously.In order to overcome the ISI caused by long transmission delay,orthogonal frequency division multiplexing(OFDM)has became a key technology in the UWAC fields,which can effectively solve frequency-selective fading caused by the multipath delay spread.Under the background stated above,the doubly selectively characteristics of underwater channel make UWAC face a lot of challenge.As an important part of the receiver,channel estimation technology attracts more and more attention.In this paper we will mainly focus on channel estimation me thods in OFDM UWAC system based on Compressed Sensing.Our paper describes the basic characteristics of UWAC channel,and proposes the model of OFDM UWAC systems under the influence of UWAC channel,as well as the processing steps in UWAC receiver.Moreover,we utilize BELLHOP package for the simulation and analysis of UWAC channel model.In this paper we not only describe the basic theory of compressed sensing,but also make some comparisons and simulations of several major sparse reconstruction algorithms in the UWAC model.The simulation results prove that the UWAC channel estimation methods based on the sparse reconstruction utilize the inherent sparsity of underwater acoustic channel to improve the estimation accuracy,meanwhile reducing the number of pilots used in subcarriers and improving the bandwidth utilization rate.In order to overcome the disadvantage that the traditional estimation methods mentioned above can only make effects in a single OFDM block,we propose the mixed model of channel estimation and prediction.We present a novel UWAC channel estimation algorithm called SMA-SpaRSA,the algorithm combines the channel prediction algorithm and sparse channel estimation algorithm working in a single OFDM block and carries out iterations block by block,not only ensuring the UWAC channel estimation accuracy,but also reduc ing the complexity of the traditional sparse estimation algorithm.Finally,simulation verifies the effectiveness of the proposed algorithm.