| The transmission of underwater sonar images is important for conducting ocean exploration,undersea rescue and other underwater activities.However,the limited bandwidth of the underwater acoustic channel conflicts with the large data size of sonar images,and there are factors affecting the image transmission quality such as noise interference,so it is challenging to achieve efficient and reliable underwater sonar image transmission.This paper focuses on satisfying the requirements of sonar image transmission for efficiency and reliability.We propose an underwater acoustic multicarrier modulation technology with high spectral efficiency based on the frequency characteristics of sonar image compressed data,and design an underwater sonar image transmission scheme with certain error-resistant capability based on sonar image characteristics.The specific research is as follows:(1)The non-uniform non-orthogonal subcarrier structure based on the frequency characteristics of the sonar image compressed data is designed to carry more effective information.The compressed data of sonar images are considered as a type of compressed bitstream images with unique frequency characteristics,which are analyzed spectrally by two-dimensional Fourier transform and Butterworth filter.A novel subcarrier structure is proposed by combining the design of subcarrier matrix with the frequency characteristics of sonar image compressed data.(2)The non-uniform non-orthogonal multicarrier modulation technology is proposed to improve the spectral efficiency.Because the non-orthogonal subcarriers are generated by frequency domain extending and time domain aliasing from the orthogonal basis,the frequency components contained are a subset of the initial orthogonal subcarriers,thus the spectral efficiency of the modulation is improved.The simulation and lake experiments show that the proposed non-uniform non-orthogonal multi-carrier modulation technology occupies less spectral resources while reducing the BER,the transmitted image has higher peak signal-to-noise ratio(PSNR)and structural similarity(SSIM)compared with the existing three typical multi-carrier modulation technologies of orthogonal frequency division multiplexing(OFDM),orthogonal wavelet division multiplexing(OWDM)and sparse nonorthogonal wavelet division multiplexing(SN-OWDM).(3)An underwater sonar image progressive transmission scheme with certain error-resistant capability is designed.The progressive compression coding based on region of interest transmits the most valuable region of interest images in priority,which saves spectral resources by getting the critical information of images in advance.The source-channel joint coding with unequal error protection adds different lengths of error correction information to compressed streams with different degrees of importance to resist transmission error and avoid distortion of the decompressed image.The simulation and lake experiments show that the underwater sonar image transmission scheme designed in this paper can achieve progressive image transmission with high compression ratio,resist transmission error effectively,and obtain decoded images with identifiable targets in the region of interest. |
