A trellis-enhanced secure spread spectrum watermarking scheme and its performance analysis

The privacy and integrity protection of digital documents specially the case of biomedical images is a vital subject in the current world of telecommunication and digital multimedia exchanges. In this paper, a modified semi robust digital image watermarking method with tamper detection and recovery ability is proposed. For this purpose, the proposed method comprises two stages. In the first stage, a specific order of the integer wavelet coefficient of the original image forms the watermark which prepares both tamper detection and recovery ability. These abilities are created by a specific parsing of watermark bits named as dual watermarking. In the second stage of the proposed method, watermark embedding and extraction procedures are done. To be more robust, a Convolutional Error Correction Code is employed in the watermark establishment process. In the extraction process, the probable tamper will be detected and the original image shall be recovered. This method is also improved to be adopted for reversible ROI recovery of medical images even in the presence of some kind of intentional and unintentional attacks. The experimental results show that the proposed method has a high performance in the case of tamper detection and is able to recover original images from noisy ones.

A non-blind two-channel time-frequency digital bits audio watermarking scheme with error-correcting code is described in this paper. The proposed method operates by encoding the watermark bits with cyclic code before embedding them into the audio signal. Time-frequency compression-expansion technique is used to embed the watermark bits. The coefficients to be deleted or added for the time-frequency compression-expansion technique are determined using psychoacoustic model. Both channels of the stereo audio signal are used for watermark embedding. This combination of cyclic-code and two-channel approach using the robust time-frequency technique of coding watermark bits has resulted in perfect recovery of watermark under attacks.

Low Density Parity Check (LDPC) codes are Shannon-Limit approaching codes. Shannon stated the theoretical bounds for digital data transmission in a given channel capacity with error correction coding. Spread Spectrum also called as CDMA (Code Division Multiple Access) is an efficient way of radio wave communication deployed in commercial broadcasts, ham radios, military communications, police radios, etc. CDMA is a means of signal transmission in which the signal frequency is spread over a very wide bandwidth. Spreading of data is achieved prior to transmission with the help of an independent code called ‘Pseudo Noise Code’ (PN sequences), which is subsequently used in the receiver end to de-spread the signal received in order to recover the signal data. PN sequences based on prime numbers like Legendre & Weil sequences are used in the present work. An impressive part of LDPC lies in its decoding algorithm. Sum-Product Algorithm (SPA) decoding offers the best error performance amongst all the types of decoding techniques of LDPC codes and thus applied here. This paper demonstrates an idea of introducing LDPC codes along with DS-Spread Spectrum technique using Legendre & Weil sequences. In the present work, the encoding and decoding algorithms are applied after spreading of the signal. SPA decoding technique is successfully employed and simulated results are plotted taking an example design to illustrate the concepts discussed above.

This paper demonstrates how channel coding can improve the robustness of spatial image watermarks against signal distortion caused by lossy data compression such as the JPEG scheme by taking advantage of the properties of Gray code. Two error-correction coding (ECC) schemes are used here: One scheme, referred to as the vertical ECC (VECC), is to encode information bits in a pixel by error-correction coding where the Gray code is used to improve the performance. The other scheme, referred to as the horizontal ECC (HECC), is to encode information bits in an image plane. In watermarking, HECC generates a codeword representing watermark bits, and each bit of the codeword is encoded by VECC. Simple single-error-correcting block codes are used in VECC and HECC. Several experiments of these schemes were conducted on test images. The result demonstrates that the error-correcting performance of HECC just depends on that of VECC, and accordingly, HECC enhances the capability of VECC. Consequently, HECC with appropriate codes can achieve stronger robustness to JPEG—caused distortions than non-channel-coding watermarking schemes.

The watermark embedding strategy is one of factors that affect the robustness of the watermark. In this paper, a new embedding strategy based on the discrete wavelet transform (DWT) is proposed. Different from the existing schemes based on the DWT which have explicitly excluded LL subband coefficients from watermark embedding, we claim that watermarks should be embedded in the LL subband first, and then in high frequency subbands according to the visual significance of the subbands. We have compared the performance of our new embedding strategy with that of the commonly used ones, confirming the superiority of the proposed embedding strategy. Based on this strategy, a robust oblivious watermarking algorithm in the DWT domain is presented. It takes advantage of error correcting coding (ECC) and 2D interleaving techniques to lower the detection error probability. By taking a carefully designed measure in watermark bit embedding, watermarked images achieve a 2dB improvement in PSNR. The experimental results show that the watermark embedded with the proposed algorithm is robust and invisible.

This paper proposes an high embedding capacity symbol based audio watermarking process. The traditional watermark embedding processes require longer duration audio sequence in order to accommodate all the input watermark bits. Shorter duration audio sequences which are like advertisements in Television a Radio should allow the embedding of a complete watermark at least once to be able to correctly identify the owner or content. A symbol based approach for spread spectrum based audio watermark methods has been proposed in order to reduce the required size of the audio sequences for watermarking. Each group of watermark bits called as a symbol are mapped to a unique pseudo-random sequence. These PN sequence are used for actual embedding in Spread Spectrum based watermarking technique. This process while reducing the size of the audio sequence required, it also helps in reducing the errors in longer duration audio as it can allow redundant addition of watermark. An error correction method is also added to further reduce the symbol errors that are caused due to the intentional and unintentional watermark removal attacks.

Error correction coding and modulation are integral components in digital communication systems, with modulators encoding information onto carrier signals for efficient transmission, while demodulators decipher received signals amidst noise and distortions. This encoding and decoding interplay forms the foundation of reliable communication, with channel encoding crucial for fortifying data against transmission errors, and decoding ensuring data integrity by rectifying errors. However, a trade-off exists between code rate reduction for error robustness and increased redundancy necessitating wider bandwidth. Trellis Coded Modulation (TCM) emerges as innovative, seamlessly combining encoding and modulation to achieve significant coding gain while maintaining bandwidth efficiency, exemplifying the delicate balance in pursuit of communication efficiency.

The bandwidth ratio increasing of spread spectrum (SS) communication limits the performance of wideband adaptive interference cancellation (WAIC) for strong wideband interference signal. To improve the interference cancellation radio (ICR), wideband interference signal is divided into subbands to reduce the computational bandwidth of the WAIC algorithm. In this paper, a method that fits the wideband interference signal by multi-tone signals is proposed to explicitly analyze the effect of the signal bandwidth on the cancellation system and quantitatively calculate the analytical solution of the ICR. Basing on the method proposed, the performance can be evaluated by the amplitude and phase difference between the received signals from the main antenna and the auxiliary antenna. Simulations and experiments are conducted to verify the theoretical analysis, and the results are consistent. Therefore, the analytical method proposed in this paper provides the design guidelines between the ICR requirement and subband bandwidth, which can reduce the complexity in the implementation of the WAIC system.

Recently, the demand for reliable and high-speed wireless communication has rapidly increased. Orthogonal frequency division multiplexing (OFDM) is a modulation scheme that is the newest competitor against other modulation schemes used for this purpose. OFDM is mostly used for wireless data transfer, although it may also be used for cable and fiber optic connections. However, in many applications, OFDM suffers from burst errors and high bit error rates. This paper presents the utilization of a helical interleaver with OFDM systems to efficiently handle burst channel errors and allow for Bit Error Rate (BER) reduction. The paper also presents a new interleaver, FRF, the initial letters of the authors’ names, for the same purpose. This newly proposed interleaver summarizes our previous experience with many recent interleavers. Fast Fourier transform OFDM (FFT-OFDM) and Discrete Wavelet Transform OFDM (DWT-OFDM) systems are used to test the efficiency of the suggested scheme in terms of burst channel error removal and BER reduction. Finally, the general complexity of the FRF interleaver is different from that of the helical interleaver in terms of hardware requirements. The performance of the proposed scheme was studied over different channel models. The obtained simulation results show a noticeable performance improvement over the conventional FFT-OFDM and the FFT-OFDM systems with the helical interleaver. Finally, the disadvantage of the proposed FRF interleaver is that it is more complex than the helical interleaver.

In this paper, we have purposed a DWT-PCA based non-blind digital colour image watermarking scheme. We have developed two algorithms for embedding and extraction process. The original image is first DWT-decomposed, and then the colour watermark is implanted. Before embedding the watermark, the original image is segmented and principle component analysis is applied. Watermark embedding is applied in different frequency bands of the image and PSNR and NC plots are drawn for all the frequency bands. PSNR and NC are two parameters which define the correlation between the original image and watermarked image. A comparative study of plots of PSNR and NC shows that embedding in HL and LH bands is more robust and imperceptive than LL and HH band. Plots show the robustness of the scheme against various attacks. The main aim of this paper is to present a scheme for the purpose of copy right protection and authentification of the colour image data.

In this paper, an image watermarking scheme is presented, in which Least Significant Bit and discrete cosine transform are used. The discrete cosine transform is performed on the original host image, and the secret watermark image is embedded into the coefficient of discrete cosine transform, which will replace the least significant bit. The embedded secret watermark bit will cause minimal distortion of the original host image, but we cannot find the difference of the original host image and the watermarked image. The experiment based on this algorithm demonstrates that the watermarking is robust to the common signal processing techniques, including noise attack, JPEG Compression attack and so on.

The performance of a communication system having almost the same spectral efficiency as a trellis coded modulation (TCM) system with r = 2/3 convolutional encoding and 8-ary phase-shift keying (8-PSK) modulation is investigated. TCM is a common solution to the problem of adding forward error correction (FEC) coding without an attendant increase in channel bandwidth. The primary drawback to TCM is that the achievable coding gain is limited by the maximum practical number of states in the convolutional encoder. The alternative system considered uses (63, 37) Reed-Solomon (RS) encoding. The six-bit symbols at the output of the Reed-Solomon encoder undergo serial-to-parallel conversion to two three-bit symbols, which are then independently transmitted on the in-phase and quadrature components of the carrier using 8-ary biorthogonal keying. This system has a null-to-null bandwidth of 0.993R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> , which is 0.7% smaller than TCM with r = 2/3 convolutional encoding and 8-PSK modulation. The two waveforms are compared for the relatively benign case where additive white Gaussian noise is the only noise present as well as when pulse-noise interference is present.

In this paper we propose robust watermarking schema for video files based on spread spectrum theory. The main concept relies on utilization of time as temporal dimension for spreading of watermark bits that are assigned to video frames. The second level spreading that is impartial to first level, uses different set of PN sequences within the video frames what allows to utilize multiple watermarking methods designed for still images simultaneously. Two dimensional spread spectrum watermarking framework allows acquiring a high level of robustness with desired imperceptibility of hidden watermark. Two independent embedding methods LSB and DCT were tested during embedding as representative techniques of different embedding domain. The presented results show that proposed watermarking schema is able to withstand intentional attacks. The proposed system is robust and adaptive to recent and newly developed embedding technique, which could provide a requisite of robustness and protection against copyright infringement.

During the last two decades, wireless communication has been revolutionized by near-capacity error-correcting codes (ECCs), such as turbo codes (TCs), which offer a lower bit error ratio (BER) than their predecessors, without requiring an increased transmission energy consumption (EC). Hence, TCs have found widespread employment in spectrum-constrained wireless communication applications, such as cellular telephony, wireless local area network, and broadcast systems. Recently, however, TCs have also been considered for energy-constrained wireless communication applications, such as wireless sensor networks and the ‘Internet of Things.’ In these applications, TCs may also be employed for reducing the required transmission EC, instead of improving the BER. However, TCs have relatively high computational complexities, and hence, the associated signal-processing-related ECs are not insignificant. Therefore, when parameterizing TCs for employment in energy-constrained applications, both the processing EC and the transmission EC must be jointly considered. In this tutorial, we investigate holistic design methodologies conceived for this purpose. We commence by introducing turbo coding in detail, highlighting the various parameters of TCs and characterizing their impact on the encoded bit rate, on the radio frequency bandwidth requirement, on the transmission EC and on the BER. Following this, energy-efficient TC decoder application-specific integrated circuit (ASIC) architecture designs are exemplified, and the processing EC is characterized as a function of the TC parameters. Finally, the TC parameters are selected in order to minimize the sum of the processing EC and the transmission EC.

Trellis-coded modulation (TCM) is a technique that introduces forward error correction coding without increasing the bandwidth of the channel signal. TCM combines binary convolutional codes with M-ary modulation in one operation. The waveform is assumed to be transmitted over a channel with both additive white Gaussian noise (AWGN) and pulse-noise interference (PNI). In addition to a TCM waveform consisting of a rate r = 2/3 convolutional code with 8-phase-shift keying (8-PSK) modulation (analogous to the IEEE 802.11g TCM mode) and a TCM system consisting of two rate r = 1/2 convolutional codes encoding data that is modulated on the inphase and quadrature channels, respectively, with 4-pulse amplitude modulation (4-PAM) is examined. As compared to an r = 2/3, 8-PSK TCM system, the decoding complexity of the r = 1/2, 4-PAM TCM system is significantly less when the number of encoder memory elements is large. For both TCM systems, the effect of varying the number of encoder memory elements when PNI is present is examined. It is found that as the number of encoder memory elements increases the negative effect of PNI decreases. When the total number of memory elements in the r = 1/2, 4-PAM TCM system is twice that of the r = 2/3, 8-PSK TCM system (each r = 1/2 encoder has the same number of memory elements as the r = 2/3 encoder), the r = 1/2, 4-PAM TCM system has better immunity to PNI than the r = 2/3, 8-PSK TCM system.