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Xiao Zhou was born in Shandong province, China, in 1982. She received the B.E. degree in automation from Nanjing University of Posts and Telecommunications, China, in 2003, the M.E. degree in information and communication engineering from Inha University, South Korea, in 2005, and the Ph.D. degree in information and communication engineering from Tsinghua University, China, in 2013. She is currently an Associate Professor and a Supervisor of master’s students with Shandong University, Weihai, China. Her current research interests include wireless communication technology, digital image processing, and computer vision. As the first author or corresponding author, she has published more than 20 journal papers, which have been indexed by SCI, and has obtained two China invention patents.
Channel estimation is a challenging problem for space time block coding (STBC) multiple-input and multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems in dynamic environments. To handle this problem and improve the system performance, this paper proposes a Kalman filter (KF) based channel estimation method applied to 2 × 2 and 4 × 4 STBC MIMO-OFDM systems. The proposed method based on the dynamic tracking property of KF is well adopted for dynamic channel estimation. First, a new orthogonal space-time codeword is adopted, and the orthogonal pilot sequences are designed to suppress the interference among transmit antennas. Then, the prediction and update characteristics of KF are researched, and the state space model is established for STBC MIMO-OFDM system. Subsequently, the channel state information (CSI) is estimated iteratively according to the KF estimation equation. At last, to further improve the accuracy of KF channel estimation, the threshold is utilized to suppress the noise in the channel impulse response (CIR) estimated by KF method. Simulation results verify that the proposed KF channel estimation method with orthogonal pilots and STBC provides better bit error ratio (BER) and normalized mean square error (NMSE) performance compared with other conventional channel estimation methods, and it can be effectively adapted to dynamic multipath propagation conditions with different low and high order modulation.
Ruiguang Tang; Xiao Zhou; Chengyou Wang. Kalman Filter Channel Estimation in 2 × 2 and 4 × 4 STBC MIMO-OFDM Systems. IEEE Access 2020, 8, 189089 -189105.
AMA StyleRuiguang Tang, Xiao Zhou, Chengyou Wang. Kalman Filter Channel Estimation in 2 × 2 and 4 × 4 STBC MIMO-OFDM Systems. IEEE Access. 2020; 8 (99):189089-189105.
Chicago/Turabian StyleRuiguang Tang; Xiao Zhou; Chengyou Wang. 2020. "Kalman Filter Channel Estimation in 2 × 2 and 4 × 4 STBC MIMO-OFDM Systems." IEEE Access 8, no. 99: 189089-189105.
Channel estimation is still a challenge for space time block coding (STBC) multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems in time-varying environments. To estimate the channel state information (CSI) precisely without increasing complexity in any significant way, this paper utilizes the sparsity and the inherent temporal correlation of the time-varying wireless channel, and proposes a novel channel estimation method applied to STBC MIMO-OFDM systems. The proposed method consists of two schemes: adaptive multi-frame averaging (AMA) and improved mean square error (MSE) optimal threshold (IMOT). First, the temporal correlation of the time-varying channel is modeled by a linear Gauss-Markov (LGM) model, and the AMA scheme is incorporated to refine the initial estimated channel impulse response (CIR) through noise reduction. Based on the LGM model, the optimal average frame number is adaptively determined by minimizing the MSE of the denoised CIR. Then, the sparsity of the wireless channel is utilized to model the CIR as a sparse vector, and the IMOT scheme is performed to further remove the noise effect by discarding most of the noise-only CIR taps. Specifically, the IMOT scheme is achieved by recovering the CIR support across the optimal “tap-to-tap” threshold derived by minimizing the MSE of each CIR tap. Moreover, the prior confidence level of the tap to be active is calculated through multi-frame statistics to further improve the performance of the IMOT scheme. Simulation results verify that the proposed AMA-IMOT channel estimation method can achieve better performance than comparison methods.
Mingtong Zhang; Xiao Zhou; Chengyou Wang. Time-Varying Sparse Channel Estimation Based on Adaptive Average and MSE Optimal Threshold in STBC MIMO-OFDM Systems. IEEE Access 2020, 8, 177874 -177895.
AMA StyleMingtong Zhang, Xiao Zhou, Chengyou Wang. Time-Varying Sparse Channel Estimation Based on Adaptive Average and MSE Optimal Threshold in STBC MIMO-OFDM Systems. IEEE Access. 2020; 8 ():177874-177895.
Chicago/Turabian StyleMingtong Zhang; Xiao Zhou; Chengyou Wang. 2020. "Time-Varying Sparse Channel Estimation Based on Adaptive Average and MSE Optimal Threshold in STBC MIMO-OFDM Systems." IEEE Access 8, no. : 177874-177895.
With the maturity of image editing software, image content has been forged frequently, posing potential threats to many critical fields. To detect forgery images effectively, this paper proposes an image copy-move forgery detection (CMFD) method based on speeded-up robust feature (SURF) and polar complex exponential transform (PCET). Firstly, image is divided into non-overlapping irregular image blocks by superpixel segmentation. Then, these image blocks are separated into two categories: smooth regions and texture regions. Secondly, after finding the keypoints by SURF, the PCET coefficients are extracted and utilized for searching similar features by feature matching algorithm. Thirdly, a strategy is used to eliminate false matched points and find the regions with dense matched points. It combines the random sample consensus (RANSAC) algorithm and a filtering scheme. Finally, mathematical morphology and an iterative strategy are adopted to refine the tampered regions. Compared with other CMFD methods, the proposed method can detect the forgery which occurs in high-brightness smooth regions or forgery images involving similar but genuine regions. Experimental results also indicate the proposed method can resist different distortions by various attacks, including rotation, scaling, blurring, joint photographic expert group (JPEG) compression, and noise addition.
Chengyou Wang; Zhi Zhang; Qianwen Li; Xiao Zhou. An Image Copy-Move Forgery Detection Method Based on SURF and PCET. IEEE Access 2019, 7, 170032 -170047.
AMA StyleChengyou Wang, Zhi Zhang, Qianwen Li, Xiao Zhou. An Image Copy-Move Forgery Detection Method Based on SURF and PCET. IEEE Access. 2019; 7 ():170032-170047.
Chicago/Turabian StyleChengyou Wang; Zhi Zhang; Qianwen Li; Xiao Zhou. 2019. "An Image Copy-Move Forgery Detection Method Based on SURF and PCET." IEEE Access 7, no. : 170032-170047.
With the wide application of color images, watermarking for the copyright protection of color images has become a research hotspot. In this paper, a robust color image watermarking algorithm based on all phase discrete cosine biorthogonal transform (APDCBT) and shuffled singular value decomposition (SSVD) is proposed. The host image is transformed by the 8 × 8 APDCBT to obtain the direct current (DC) coefficient matrix, and then, the singular value decomposition (SVD) is performed on the DC matrix to embed the watermark. The SSVD and Fibonacci transform are mainly used at the watermark preprocessing stage to improve the security and robustness of the algorithm. The watermarks are color images, and a color quick response (QR) code with error correction mechanism is introduced to be a watermark to further improve the robustness. The watermark embedding and extraction processes are symmetrical. The experimental results show that the algorithm can effectively resist common image processing attacks, such as JPEG compression, Gaussian noise, salt and pepper noise, average filter, median filter, Gaussian filter, sharpening, scaling attacks, and a certain degree of rotation attacks. Compared with the color image watermarking algorithms considered in this paper, the proposed algorithm has better performance in robustness and imperceptibility.
Xiaoyan Yu; Chengyou Wang; Xiao Zhou. A Robust Color Image Watermarking Algorithm Based on APDCBT and SSVD. Symmetry 2019, 11, 1227 .
AMA StyleXiaoyan Yu, Chengyou Wang, Xiao Zhou. A Robust Color Image Watermarking Algorithm Based on APDCBT and SSVD. Symmetry. 2019; 11 (10):1227.
Chicago/Turabian StyleXiaoyan Yu; Chengyou Wang; Xiao Zhou. 2019. "A Robust Color Image Watermarking Algorithm Based on APDCBT and SSVD." Symmetry 11, no. 10: 1227.
The existing watermarking algorithms in H.265/high efficiency video coding (HEVC) compressed domain cannot achieve intra-frame distortion drift-free and resist the recompression and signal processing attacks simultaneously. Therefore, the application of HEVC watermarking in copyright protection is limited in practice. To solve the problem, this paper proposes an intra-drift-free robust watermarking algorithm, which uses a multi-coefficients modification method to embed the watermark into intra prediction residual pixels of 4×4 luminance transform blocks in the spatial domain. Based on the spatial-domain embedding method, watermark information can be extracted from the blocks that have been attacked and merged into 8×8 size, which improves the robustness. To further improve the performance of the watermarking algorithm, the proposed algorithm uses a combination of three thresholds according to the application requirements. Experimental results on a publicly available video database (JCT-VC) have justified the effectiveness of the proposed algorithm which has better imperceptibility and robustness than existing algorithms. In addition, the proposed algorithm has high real-time performance and is suitable for application scenarios where the video is distributed on a large scale.
Yangming Zhou; Chengyou Wang; Xiao Zhou. An Intra-Drift-Free Robust Watermarking Algorithm in High Efficiency Video Coding Compressed Domain. IEEE Access 2019, 7, 132991 -133007.
AMA StyleYangming Zhou, Chengyou Wang, Xiao Zhou. An Intra-Drift-Free Robust Watermarking Algorithm in High Efficiency Video Coding Compressed Domain. IEEE Access. 2019; 7 (99):132991-133007.
Chicago/Turabian StyleYangming Zhou; Chengyou Wang; Xiao Zhou. 2019. "An Intra-Drift-Free Robust Watermarking Algorithm in High Efficiency Video Coding Compressed Domain." IEEE Access 7, no. 99: 132991-133007.
With the rampancy of pirated videos, video watermarking for copyright protection has become a widely researched topic. In this paper, zero-watermarking is applied to videos for the first time to resist high efficiency video coding compression, which can improve the robustness of the watermarking algorithm and ensure the videos’ quality. A robust video zero-watermarking algorithm based on the discrete wavelet transform, the all phase biorthogonal transform, and singular value decomposition is proposed. Utilizing the properties of hybrid transforms, robust features can be extracted from videos, and robust zero-watermarks can be constructed. Experimental results demonstrate that the proposed algorithm has strong robustness to high efficiency video coding compression attacks with different quantization parameters. In addition, the algorithm can also resist common image processing attacks, geometric attacks, frame-based attacks, and hybrid attacks. Compared with existing video watermarking algorithms, the proposed algorithm can more accurately and completely reconstruct watermark images.
Xiaoyan Yu; Chengyou Wang; Xiao Zhou. A Hybrid Transforms-Based Robust Video Zero-Watermarking Algorithm for Resisting High Efficiency Video Coding Compression. IEEE Access 2019, 7, 115708 -115724.
AMA StyleXiaoyan Yu, Chengyou Wang, Xiao Zhou. A Hybrid Transforms-Based Robust Video Zero-Watermarking Algorithm for Resisting High Efficiency Video Coding Compression. IEEE Access. 2019; 7 (99):115708-115724.
Chicago/Turabian StyleXiaoyan Yu; Chengyou Wang; Xiao Zhou. 2019. "A Hybrid Transforms-Based Robust Video Zero-Watermarking Algorithm for Resisting High Efficiency Video Coding Compression." IEEE Access 7, no. 99: 115708-115724.
Orthogonal frequency division multiplexing (OFDM) systems have inherent symmetric properties, such as coding and decoding, constellation mapping and demapping, inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) operations corresponding to multi-carrier modulation and demodulation, and channel estimation is a necessary module to resist channel fading in the OFDM system. However, the noise in the channel will significantly affect the accuracy of channel estimation, which further affects the recovery quality of the final received signals. Therefore, this paper proposes an efficient noise suppression channel estimation method for OFDM systems based on adaptive weighted averaging. The basic idea of the proposed method is averaging the last few channel coefficients obtained from coarse estimation to suppress the noise effect, while the average frame number is adaptively adjusted by combining Doppler spread and signal-to-noise ratio (SNR) information. Meanwhile, to better combat the negative effect brought by Doppler spread and inter-carrier interference (ICI), the proposed method introduces a weighting factor to correct the weighted value of each frame in the averaging process. Simulation results show that the proposed channel estimation method is effective and provides better performance compared with other conventional channel estimation methods.
Mingtong Zhang; Xiao Zhou; Chengyou Wang; Zhou; Wang. A Novel Noise Suppression Channel Estimation Method Based on Adaptive Weighted Averaging for OFDM Systems. Symmetry 2019, 11, 997 .
AMA StyleMingtong Zhang, Xiao Zhou, Chengyou Wang, Zhou, Wang. A Novel Noise Suppression Channel Estimation Method Based on Adaptive Weighted Averaging for OFDM Systems. Symmetry. 2019; 11 (8):997.
Chicago/Turabian StyleMingtong Zhang; Xiao Zhou; Chengyou Wang; Zhou; Wang. 2019. "A Novel Noise Suppression Channel Estimation Method Based on Adaptive Weighted Averaging for OFDM Systems." Symmetry 11, no. 8: 997.
The multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) technology is the combination of the OFDM and MIMO technologies, which could improve the system capacity and make efficient utilization of the frequency spectrum. This paper utilizes space-time block coding (STBC) to achieve diversity gains and combat the channel fading. However, channel estimation is an essential block for space-time block decoding (STBD). Many channel estimation methods are utilized for the single antenna OFDM system, but they cannot be directly applied to the multiple antennas system due to the interference from other antennas. In this paper, orthogonal pilot sequences are designed to suppress the interference of pilot symbols from other transmit antennas. This paper also derives a minimum mean square error (MMSE) channel estimation method in MIMO-OFDM systems. The MMSE method involves the inverse operation of the channel autocorrelation matrix, which has a large calculation complexity. To further reduce the complexity of the MMSE method, the singular value decomposition (SVD) is used to decompose the channel autocorrelation matrix, which avoids the inverse operation. Simulation results verify that the SVD channel estimation method with comb-type pilots and STBC can be effectively adapted to multipath propagation conditions.
Ruiguang Tang; Xiao Zhou; Chengyou Wang; Tang; Zhou; Wang. Singular Value Decomposition Channel Estimation in STBC MIMO-OFDM System. Applied Sciences 2019, 9, 3067 .
AMA StyleRuiguang Tang, Xiao Zhou, Chengyou Wang, Tang, Zhou, Wang. Singular Value Decomposition Channel Estimation in STBC MIMO-OFDM System. Applied Sciences. 2019; 9 (15):3067.
Chicago/Turabian StyleRuiguang Tang; Xiao Zhou; Chengyou Wang; Tang; Zhou; Wang. 2019. "Singular Value Decomposition Channel Estimation in STBC MIMO-OFDM System." Applied Sciences 9, no. 15: 3067.
In this paper, we present a study of bit error rate (BER) for orthogonal frequency division multiplexing/offset quadrature phase shift keying (OFDM/OQPSK) and OFDM/offset quadrature amplitude modulation (OQAM) systems with an isotropic orthogonal transfer algorithm (IOTA) filter. The novel noise suppression method based on an IOTA filter is proposed to reduce the error of channel estimation caused by additive white Gaussian noise (AWGN). The OFDM/OQPSK and OFDM/OQAM systems do not insert the guard interval (GI) and pilots in the signal frames, thus they possess transmission efficiency. An analysis was carried out for convolutional coded OFDM/OQPSK and OFDM/OQAM systems in Rayleigh fading channels with generator polynomials and constraint lengths. Compared with conventional OFDM/QPSK and OFDM/QAM systems with the insertion of comb-type pilots, the proposed IOTA filter-based channel estimation method can provide significant energy per bit to time-varying noise power spectral density ratio gains over time and frequency-selective propagation Rayleigh fading channels in OFDM/OQPSK and OFDM/OQAM systems.
Xiao Zhou; Chengyou Wang; Ruiguang Tang. Channel Estimation Based on IOTA Filter in OFDM/OQPSK and OFDM/OQAM Systems. Applied Sciences 2019, 9, 1454 .
AMA StyleXiao Zhou, Chengyou Wang, Ruiguang Tang. Channel Estimation Based on IOTA Filter in OFDM/OQPSK and OFDM/OQAM Systems. Applied Sciences. 2019; 9 (7):1454.
Chicago/Turabian StyleXiao Zhou; Chengyou Wang; Ruiguang Tang. 2019. "Channel Estimation Based on IOTA Filter in OFDM/OQPSK and OFDM/OQAM Systems." Applied Sciences 9, no. 7: 1454.
The popularity of image editing software has made it increasingly easy to alter the content of images. These alterations threaten the authenticity and integrity of images, causing misjudgments and possibly even affecting social stability. The copy-move technique is one of the most commonly used approaches for manipulating images. As a defense, the image forensics technique has become popular for judging whether a picture has been tampered with via copy-move, splicing, or other forgery techniques. In this paper, a scheme based on accelerated-KAZE (A-KAZE) and speeded-up robust features (SURF) is proposed for image copy-move forgery detection (CMFD). It is difficult for most keypoint-based CMFD methods to obtain sufficient points in smooth regions. To remedy this defect, the response thresholds for the A-KAZE and SURF feature detection stages are set to small values in the proposed method. In addition, a new correlation coefficient map is presented, in which the duplicated regions are demarcated, combining filtering and mathematical morphology operations. Numerous experiments are conducted to demonstrate the effectiveness of the proposed method in searching for duplicated regions and its robustness against distortions and post-processing techniques, such as noise addition, rotation, scaling, image blurring, joint photographic expert group (JPEG) compression, and hybrid image manipulation. The experimental results demonstrate that the performance of the proposed scheme is superior to that of other tested CMFD methods.
Chengyou Wang; Zhi Zhang; Xiao Zhou. An Image Copy-Move Forgery Detection Scheme Based on A-KAZE and SURF Features. Symmetry 2018, 10, 706 .
AMA StyleChengyou Wang, Zhi Zhang, Xiao Zhou. An Image Copy-Move Forgery Detection Scheme Based on A-KAZE and SURF Features. Symmetry. 2018; 10 (12):706.
Chicago/Turabian StyleChengyou Wang; Zhi Zhang; Xiao Zhou. 2018. "An Image Copy-Move Forgery Detection Scheme Based on A-KAZE and SURF Features." Symmetry 10, no. 12: 706.
With the development and popularization of the Internet and the rise of various live broadcast platforms, digital videos have penetrated into all aspects of people’s life. At the same time, all kinds of pirated videos are also flooding the Internet, which seriously infringe the rights and interests of video copyright owners and hinder the healthy development of the video industry. Therefore, robust video watermarking algorithms for copyright protection have emerged as these times require. In this paper, we review robust video watermarking algorithms for copyright protection based on original videos and compressed videos. Basic models and properties of video watermarking algorithms are described, and the evaluation indexes corresponding to each property are also introduced. To help researchers understand various existing robust watermarking algorithms quickly, some basic information and the quantitative estimation of several performances are analyzed and compared. Finally, we discuss the challenges in the research of robust video watermarking algorithms, and give possible development directions for the future.
Xiaoyan Yu; Chengyou Wang; Xiao Zhou. A Survey on Robust Video Watermarking Algorithms for Copyright Protection. Applied Sciences 2018, 8, 1891 .
AMA StyleXiaoyan Yu, Chengyou Wang, Xiao Zhou. A Survey on Robust Video Watermarking Algorithms for Copyright Protection. Applied Sciences. 2018; 8 (10):1891.
Chicago/Turabian StyleXiaoyan Yu; Chengyou Wang; Xiao Zhou. 2018. "A Survey on Robust Video Watermarking Algorithms for Copyright Protection." Applied Sciences 8, no. 10: 1891.
Channel estimation is an important module for improving the performance of the orthogonal frequency division multiplexing (OFDM) system. The pilot-based least square (LS) algorithm can improve the channel estimation accuracy and the symbol error rate (SER) performance of the communication system. In pilot-based channel estimation, a certain number of pilots are inserted at fixed intervals between OFDM symbols to estimate the initial channel information, and channel estimation results can be obtained by one-dimensional linear interpolation. The minimum mean square error (MMSE) and linear minimum mean square error (LMMSE) algorithms involve the inverse operation of the channel matrix. If the number of subcarriers increases, the dimension of the matrix becomes large. Therefore, the inverse operation is more complex. To overcome the disadvantages of the conventional channel estimation methods, this paper proposes a novel OFDM channel estimation method based on statistical frames and the confidence level. The noise variance in the estimated channel impulse response (CIR) can be largely reduced under statistical frames and the confidence level; therefore, it reduces the computational complexity and improves the accuracy of channel estimation. Simulation results verify the effectiveness of the proposed channel estimation method based on the confidence level in time-varying dynamic wireless channels.
Xiao Zhou; Chengyou Wang; Ruiguang Tang; Mingtong Zhang. Channel Estimation Based on Statistical Frames and Confidence Level in OFDM Systems. Applied Sciences 2018, 8, 1607 .
AMA StyleXiao Zhou, Chengyou Wang, Ruiguang Tang, Mingtong Zhang. Channel Estimation Based on Statistical Frames and Confidence Level in OFDM Systems. Applied Sciences. 2018; 8 (9):1607.
Chicago/Turabian StyleXiao Zhou; Chengyou Wang; Ruiguang Tang; Mingtong Zhang. 2018. "Channel Estimation Based on Statistical Frames and Confidence Level in OFDM Systems." Applied Sciences 8, no. 9: 1607.
Based on a deep understanding of all-phase digital filter (APDF) design and all-phase biorthogonal transform (APBT), this paper will further study the windowed all-phase digital filter (WAPDF) and windowed all-phase biorthogonal transform (WAPBT), discuss the principle of the WAPBT, and provide a unified construction method of the all-phase transform (APT). Based on a type of orthogonal transform, i.e., discrete sine transform (DST), an interpolation filter called an all-phase DST (APDST) filter is constructed and used for image demosaicking; it is compared with bilinear interpolation and all-phase inverse discrete cosine transform (APIDCT) interpolation filters, to test its performance in image interpolation and provide analysis and discussion. The experimental results show that APIDCT and APDST filters with a size of 7 × 7 are similar in interpolation performance, but better than the bilinear interpolation method. In addition to its use in image interpolation demosaicking, the low-pass filter designed in this paper can also be widely used in image interpolation, image denoising, image resizing, and other fields of image processing.
Xiao Zhou; Chengyou Wang; Zhi Zhang; Qiming Fu. Interpolation Filter Design Based on All-Phase DST and Its Application to Image Demosaicking. Information 2018, 9, 206 .
AMA StyleXiao Zhou, Chengyou Wang, Zhi Zhang, Qiming Fu. Interpolation Filter Design Based on All-Phase DST and Its Application to Image Demosaicking. Information. 2018; 9 (9):206.
Chicago/Turabian StyleXiao Zhou; Chengyou Wang; Zhi Zhang; Qiming Fu. 2018. "Interpolation Filter Design Based on All-Phase DST and Its Application to Image Demosaicking." Information 9, no. 9: 206.
With the rapid development of Internet of Things and multimedia technologies, people are paying more attention to the security of images and videos. To further improve the security of video content, a video watermarking algorithm based on the high efficiency video coding (HEVC) compression domain is proposed in this paper. The scheme embeds watermark information in the quantized coefficients, which can solve the cumulative error caused by watermark embedding. Moreover, the all phase biorthogonal transform (APBT), an improved transform, is used to compress the watermark data at the digital watermark preprocessing stage, optimize the watermark embedding scheme, and improve the embedding capacity of video watermarking. Due to the characteristics of HEVC video coding, most HEVC video watermarking schemes based on compression domain cannot resist recompression attack. To solve this problem, on the basis of APBT and singular value decomposition, an anti-HEVC recompression video watermarking algorithm is proposed and can effectively resist the HEVC recompression. Experimental results show that even when the quantization parameter is larger than 40, the extracted watermark still has good image quality. In addition, the algorithm also has a good performance in noise resistance.
Chengyou Wang; Rongyang Shan; Xiao Zhou. Anti-HEVC Recompression Video Watermarking Algorithm Based on the All Phase Biorthogonal Transform and SVD. IETE Technical Review 2018, 35, 42 -58.
AMA StyleChengyou Wang, Rongyang Shan, Xiao Zhou. Anti-HEVC Recompression Video Watermarking Algorithm Based on the All Phase Biorthogonal Transform and SVD. IETE Technical Review. 2018; 35 (sup1):42-58.
Chicago/Turabian StyleChengyou Wang; Rongyang Shan; Xiao Zhou. 2018. "Anti-HEVC Recompression Video Watermarking Algorithm Based on the All Phase Biorthogonal Transform and SVD." IETE Technical Review 35, no. sup1: 42-58.
Channel estimation is a key technology in improving the performance of the orthogonal frequency division multiplexing (OFDM) system. The pilot-based channel estimation method decreases the spectral efficiency and data transmission rate. Some conventional channel estimation methods cannot suppress the noise effectively, which affects the quality of the final received signals. To solve these two problems, a Haar wavelet decision feedback (DF) channel estimation method, also named the Haar wavelet method, is proposed in this paper. The proposed Haar wavelet method can suppress the noise existing at the estimated channel impulse response (CIR) effectively, based on a time-domain threshold which is a standard deviation of noise obtained by wavelet decomposition. At the same time, the proposed Haar wavelet method just requires inserting one block pilot symbol in front of the first OFDM symbol, which therefore improves the data transmission rate and spectrum efficiency greatly. Simulation results are shown to verify the effectiveness of the proposed Haar wavelet method in multipath channel propagation conditions.
Ruiguang Tang; Xiao Zhou; Chengyou Wang. A Haar Wavelet Decision Feedback Channel Estimation Method in OFDM Systems. Applied Sciences 2018, 8, 877 .
AMA StyleRuiguang Tang, Xiao Zhou, Chengyou Wang. A Haar Wavelet Decision Feedback Channel Estimation Method in OFDM Systems. Applied Sciences. 2018; 8 (6):877.
Chicago/Turabian StyleRuiguang Tang; Xiao Zhou; Chengyou Wang. 2018. "A Haar Wavelet Decision Feedback Channel Estimation Method in OFDM Systems." Applied Sciences 8, no. 6: 877.
Currently, the watermark capacity of most self-recovery fragile image watermarking schemes is fixed. That means for smooth regions and texture regions, the length of watermark information is always the same. However, it is impractical since more recovery information is needed for the recovery of texture regions. In this paper, a self-recovery fragile image watermarking with variable watermark capacity is proposed. Based on the characteristic of singular value decomposition (SVD), a new block classification method is introduced. The image blocks are classified into smooth blocks and texture blocks. For smooth blocks, the average pixel values are adopted as the recovery information to recover the tampered blocks, while for texture blocks, the quantized and coded DCT coefficients are adopted as the recovery information. After encrypted by binary pseudo-random sequence, the recovery watermark of each block is embedded into its mapping block. In the detection side, the three-level detection mechanism is applied to detect and locate the tampered regions. The experimental results prove that the proposed method achieves good tamper detection results, and the recovered image has better image quality than other self-recovery fragile watermarking methods.
Chengyou Wang; Heng Zhang; Xiao Zhou. A Self-Recovery Fragile Image Watermarking with Variable Watermark Capacity. Applied Sciences 2018, 8, 548 .
AMA StyleChengyou Wang, Heng Zhang, Xiao Zhou. A Self-Recovery Fragile Image Watermarking with Variable Watermark Capacity. Applied Sciences. 2018; 8 (4):548.
Chicago/Turabian StyleChengyou Wang; Heng Zhang; Xiao Zhou. 2018. "A Self-Recovery Fragile Image Watermarking with Variable Watermark Capacity." Applied Sciences 8, no. 4: 548.
Copyright protection for digital multimedia has become a research hotspot in recent years. As an efficient solution, the digital watermarking scheme has emerged at the right moment. In this article, a highly robust and hybrid watermarking method is proposed. The discrete wavelet transform (DWT) and all phase discrete cosine biorthogonal transform (APDCBT) presented in recent years as well as the singular value decomposition (SVD) are adopted in this method to insert and recover the watermark. To enhance the watermark imperceptibility, the direct current (DC) coefficients after block-based APDCBT in high frequency sub-bands (LH and HL) are modified by using the watermark. Compared with the conventional SVD-based watermarking method and another watermarking technique, the watermarked images obtained by the proposed method have higher image quality. In addition, the proposed method achieves high robustness in resisting various image processing attacks.
Xiao Zhou; Heng Zhang; Chengyou Wang. A Robust Image Watermarking Technique Based on DWT, APDCBT, and SVD. Symmetry 2018, 10, 77 .
AMA StyleXiao Zhou, Heng Zhang, Chengyou Wang. A Robust Image Watermarking Technique Based on DWT, APDCBT, and SVD. Symmetry. 2018; 10 (3):77.
Chicago/Turabian StyleXiao Zhou; Heng Zhang; Chengyou Wang. 2018. "A Robust Image Watermarking Technique Based on DWT, APDCBT, and SVD." Symmetry 10, no. 3: 77.
Image processing technology has been developed rapidly in recent years, and altering the content of an image is easy for everyone, but may be illegal for an attacker. Thus, it is urgent and necessary to overcome this problem to protect the integrity and authenticity of images. Watermarking is a powerful technique proposed to solve this problem. This paper introduces a robust image watermarking algorithm working in the wavelet domain, embedding the watermark information into the third level low frequency coefficients after the three-level discrete wavelet transform (DWT) and singular value decomposition (SVD). Additionally, to improve the robustness to geometric attacks, the affine-scale-invariant feature transform (ASIFT) is applied to obtain feature points which are invariant to geometric attacks. Then, features of acquired points between the watermarked image and the received image are used to realize the resynchronization to improve the robustness. Experimental results show that the proposed algorithm achieves great balance between robustness and imperceptibility, and is robust against geometric attacks, JPEG compression, noise addition, cropping, median filters, and so on.
Chengyou Wang; Yunpeng Zhang; Xiao Zhou. Robust Image Watermarking Algorithm Based on ASIFT against Geometric Attacks. Applied Sciences 2018, 8, 410 .
AMA StyleChengyou Wang, Yunpeng Zhang, Xiao Zhou. Robust Image Watermarking Algorithm Based on ASIFT against Geometric Attacks. Applied Sciences. 2018; 8 (3):410.
Chicago/Turabian StyleChengyou Wang; Yunpeng Zhang; Xiao Zhou. 2018. "Robust Image Watermarking Algorithm Based on ASIFT against Geometric Attacks." Applied Sciences 8, no. 3: 410.
Orthogonal frequency division multiplexing (OFDM) has been widely used in modern wireless communication systems. In OFDM scheme, channel estimation method is a key technology in improving the accuracy of the channel estimation and the system performance. There are many channel estimation methods in OFDM system. The least square (LS) channel estimation method is relatively simple but it is susceptible to the noise of the wireless channel. The linear minimum mean square error (LMMSE) and approximate LMMSE (ALMMSE) channel estimation methods provide good performance but are much more complex than conventional LS method. This paper proposes a novel low rank LMMSE method to simplify the filtering matrix in LMMSE method and diagonal matrix in ALMMSE method. Performance comparison is shown to verify the effectiveness of the proposed low rank channel estimation method. LMMSE and ALMMSE channel estimation methods are better than LS method, and LS method is the worst. Except the ideal channel estimation method, the low rank LMMSE channel estimation method provides the best bit error rate (BER) performance in cyclic prefix - OFDM (CP-OFDM) system. It simplifies the calculation of channel auto-correlation matrix and provides superior system performance over multipath channel conditions.
Ruiguang Tang; Xiao Zhou; Chengyou Wang. A novel low rank LMMSE channel estimation method in OFDM systems. 2017 IEEE 17th International Conference on Communication Technology (ICCT) 2017, 249 -253.
AMA StyleRuiguang Tang, Xiao Zhou, Chengyou Wang. A novel low rank LMMSE channel estimation method in OFDM systems. 2017 IEEE 17th International Conference on Communication Technology (ICCT). 2017; ():249-253.
Chicago/Turabian StyleRuiguang Tang; Xiao Zhou; Chengyou Wang. 2017. "A novel low rank LMMSE channel estimation method in OFDM systems." 2017 IEEE 17th International Conference on Communication Technology (ICCT) , no. : 249-253.
Zhi Zhang; Dongyan Wang; Chengyou Wang; Xiao Zhou. Detecting Copy-move Forgeries in Images Based on DCT and Main Transfer Vectors. KSII Transactions on Internet and Information Systems 2017, 11, 4567 -4587.
AMA StyleZhi Zhang, Dongyan Wang, Chengyou Wang, Xiao Zhou. Detecting Copy-move Forgeries in Images Based on DCT and Main Transfer Vectors. KSII Transactions on Internet and Information Systems. 2017; 11 (9):4567-4587.
Chicago/Turabian StyleZhi Zhang; Dongyan Wang; Chengyou Wang; Xiao Zhou. 2017. "Detecting Copy-move Forgeries in Images Based on DCT and Main Transfer Vectors." KSII Transactions on Internet and Information Systems 11, no. 9: 4567-4587.