The Theoretical Limits of Watermark Spread Spectrum Sequence

Chaotic sequences have good correlation properties and they can be used as address sequences in Spread Spectrum Communication. Chaotic functions are highly sensitive to initial condition and exhibit non-linear behavior. In Chaotic spread spectrum communication systems, different user may be assigned different sequences generated with different initial conditions. Set of binary sequences with good pair wise cross- correlation property finds applications in Direct Sequence- Code Division Multiple Access (DS-CDMA) systems. Security in Direct Sequence-Code Division Multiple Access systems is relatively limited. To enhance security in Direct Sequence- Code Division Multiple Access systems, chaotic sequences are generated. In this paper we analyze the generation of chaotic binary sequences and study of auto correlation and cross correlation properties.

The relation between the digital watermarking and spread-spectrum is analyzed in this paper at the beginning. Then, a spread-spectrum adaptive digital watermarking scheme based on the wavelet transform is proposed and the system for this digital watermarking algorithm based on DSP is realized. Finally, a testing on the image digital watermarking processing system by DSP is conducted. The result from the testing approves that the system is flexible and can accomplish watermark embedding and detecting.

Chaotic spread spectrum sequence is an important element in spread spectrum communication. To m sequences and Gold sequences with finite length and number, a new method for improved Chebyshev chaotic sequence is generated by the mixed iteration of the Tent map and Chebyshev map. It has a great significance to quantitative analysis of the new sequence generated by the improved Chebyshev mapping, and it can adapt the spread spectrum communication well in MC-CDMA system. Select m sequence, Gold sequence and improved Chebyshev chaotic sequence as the spread spectrum sequence through the BPSK modulation mode in the MC-CDMA downlink to simulation experiment. It can be proved that the error performance of the improved Chebyshev sequence is better than the other two sequences, and reveal the variation of the system error rate of the signal to noise ratio based on performed and analysis.

Spread spectrum watermarking (SSW) is one of the most widespread watermarking methods. In this paper, the characterization of the SSW from the information theoretic point of view is performed. Previous works on channel capacity analysis of watermarking systems are reviewed. Since SSW method is designed so that the host signal is unknown to the embedding encoder, Costa's results for capacity analysis of watermarking systems are not directly applicable. In this paper, watermarking embedding and detection is modeled as a channel that transmits information in the presence of noise of host and channel capacity analysis of that model is derived and the most reliable transmission rate of hidden information obtained. In addition, channel capacity for the case of presence of additive noise in the watermark channel is derived and robustness of the SSW against additive noise examined

Compared with traditional Spread Spectrum (DS-SS) communication method, in terms of bandwidth efficiency and information transmission capacity, position Code Parallel Combinatory Spread Spectrum (PC/PC/SS) communication system has better performance. At the same time, total maximum PN sequences should be chosen accurately by PC/PC/SS system fromPN sequences which are correlated, or it will lead to masses of error. The current method is not capable of distinguishing and rectifying one random false sequence. In order to deal with this issue, this paper put forward a PC/PC/SS communication system which is on the basis of the iterative method and analyzed system performances. The PC/PC/SS system with iterative method can distinguish and rectify a sequence error. Under the identical circumstance, the PC/PC/SS system has less BER than traditional PC/SS system, which is proved by computer simulation.

In this paper, the spread spectrum watermarking in wavelet domain is optimised by using a number of techniques to make it more efficient when executed by a platform running on mobile devices. The proposed techniques can be executed efficiently and consume less computational and power resources as compared to the conventional spread spectrum-based watermarking. The proposed technique represents binary bits in the watermark using symbols, wherein each symbol represents at least 2 binary bits. A symbol is then mapped into a pseudo noise sequence and embedded in the digital image. Our analytical results show that our schemes reduce the number of operations required for watermarking by ∼50%, while our experimental results show that our schemes save about ∼59 and ∼67% in processing time and energy consumption, respectively.

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.

Spread spectrum communication has good performances such as anti-noise, anti-interference and fast transmission rate, so it has been widely used in military communication and civil communication fields and others. The M-ary spread spectrum system has its unique advantages and strong practical application background with respect to direct sequence spread spectrum, and effectively solves the problem of limited bandwidth of direct spread spectrum. This paper firstly expounds the principle of traditional direct sequence spread spectrum system and then focuses on the research of the principle and system model of M-ary spread spectrum system. The error performance of M-ary spread spectrum system is also simulated and analyzed. The simulation results show that M-ary spread spectrum has a greater advantage in the bandwidth-constrained field, where high-speed data transmission is required and certain anti-noise capability is required.

Spread spectrum communication technology is one of the most critical core technologies in anti‐jamming satellite communication systems. However, it has certain technical limitations in anti‐jamming applications. For instance, frequency‐hopping spread spectrum technology exhibits weak resistance against spot jamming, while direct‐sequence spread spectrum technology is less effective in mitigating wideband interference. With the continuous development of satellite countermeasure technologies, these technical limitations will significantly constrain the performance of satellite communication systems and compromise the reliable transmission of space‐based information. Aiming at the technical limitations of spread spectrum anti‐jamming satellite communication, this paper proposes a solution based on blind source separation technology to enhance the anti‐jamming capability of spread spectrum communication. This paper establishes a blind source separation‐based anti‐jamming communication prototype system, verifying the feasibility of applying blind source separation to communication anti‐jamming. It conducts an in‐depth analysis of the characteristics and existing issues in spread spectrum anti‐jamming satellite communication systems, identifies the problems and challenges of applying blind source separation to such systems, and proposes potential solutions.

Proposes a method for designing spread sequences for a spread spectrum (SS) communication and ranging system. The proposed sequence is composed by concatenated equivalently odd and even (EOE) inner-sequences and an M outer sequence. We have previously proposed EOE sequences that have equivalently good properties of both even and odd correlation, what are important features for acquisition and demodulation in SS communications. Usually, simple concatenation of pseudonoise-sequences results in sequences with bad autocorrelation properties. Unlike the latter, concatenation of EOE inner sequences result in sequences with good correlation properties, exhibiting low sidelobe peaks, what is useful for achieving stable acquisition. The proposed sequences have long period. Therefore, the single concatenated EOE sequence is suitable for a spread spectrum system with both communication and ranging functions.

Wavelets are considered as powerful signal processing tools that provide an effective alternative to conventional signal transforms. Spread spectrum plays an important role in CDMA communication system. Because of its unique characteristics, it has been first used for military applications. So spread spectrum communication via, discrete wavelet transform and thresholding becomes effective now a days. This paper describes a near optimal threshold estimation technique for signal denoising in spread spectrum communication using Double Density Discrete Wavelet filter. A new threshold calculating formula is utilized. Performance of the proposed system is found to be better than the conventional spread spectrum receiver.

In this paper, we conduct research on effective and robust time-delay estimation methodology for spread spectrum communications. The development of underwater acoustic spread spectrum communication technology derived from the demand for underwater remote, reliable communication. Due to the underwater acoustic channel belt width, background noise and high rate of Doppler frequency shift, severe multipath effect, absorption problems such as uneven, makes the communication quality serious decline. We firstly analyze the fast time-delay estimators to serve as the prior knowledge, and later, we analyze the channel estimation techniques. Finally, we test the error and efficiency. Results show that the system has better ability to resist noise and multiple access interference, and improve the chaotic spread spectrum sequence to better the performance of the system of traditional chaotic spread spectrum sequence. The experimental result proves the effectiveness of proposed methodology. In the future, we plan to conduct more literature reviews to modify the current technique.

Digital watermarking is a technique that aims at hiding a message signal in a multimedia signal for copyright claim, authentication, device control, or broadcast monitoring, etc. We focus on embedding watermarks into still images. We propose to scramble the watermark with pseudo-noise (PN) or orthogonal codes before it is embedded into an image. We also try to incorporate error correction coding (ECC) into the watermarking scheme, anticipating reduction of the watermark bit error rate (WBER). We consider to adopt trellis-based schemes (including trellis-code modulation (TCM) and turbo codes) to improve the WBER. Due to the similarity between the PN/orthogonal coded watermarking and the spread spectrum communication, it is natural that, following similar derivations regarding data BER, we derive certain explicit quantitative relationship regarding the trade-off between the WBER and the distortion suffered by the original image, which is measured in terms of the embedded image's signal-to-noise ratio (abbreviated as ISNR).

In this work, we propose a new digital watermarking scheme for extremely high-resolution printing images applicable to On-Demand Publishing (ODP) system. We designed our scheme by considering the following requirements: (i) high image quality, (ii) high security, and (iii) watermark immunity (robustness). In order to attain these requirements we employ the idea of Spread Spectrum (SS) watermarking technique in our scheme and modify it to be applicable to color (CMYK) binary printing images. Simulation results verified that we could embed a watermark spreading over the entire output image as a weak energy and still keep high image quality. Also the watermark could be robustly decoded by controlling some parameters even after some possible attacks by a third party.

When a binary fingerprinting codeword is embedded into multimedia content by using a spread-spectrum (SS) watermarking scheme, it is difficult for colluders to perform a symbol-wise attack using their codewords. As discussed in regard to SS fingerprinting schemes, averaging their copies is a cost-effective attack from the signal processing point of view. If the number of colluders is known, an optimal detector can be used against an averaging attack with added white Gaussian noise. The detector first estimates the variance of additive noise, and then calculates correlation scores using a log-likelihood-based approach. However, the number of colluders is not usually known in a real situation. In this paper, we simplify the optimal detector by making statistical approximations and using the characteristics of the parameters for generating codewords. After that, we propose an orthogonal frequency division multiplexing-based SS watermarking scheme to embed the fingerprinting codeword into multimedia content. In a realistic situation, the signal embedded as a fingerprint is in principle attenuated by lossy compression. Because the signal amplitude in a pirated codeword is attenuated, we should adaptively estimate the parameters before calculating the scores. Different from the optimal detector, the simplified detector can easily accommodate changes in signal amplitude by examining the distorted codeword extracted from a pirated copy. We evaluate the performance of the simplified detector through simulation using digital images as well as codewords.