Research on adaptive digital watermarking based on spread spectrum

With the rapidly incremental demand in electronic devices, there is something in exploring multifunctional RF systems for reducing cost, minimizing the radar cross and probability of intercept, etc. This paper presents an integration system of radar and communication based on DSSS (direct sequence spread spectrum) technique, an attractive technique which is highly secure and robust. It utilizes different PN code to spread the spectrum of radar and communication data to avoid jamming mutually. Additionally, it uses BPM to gain better performance. The simulation over an ideal AWGN channel shows that the system can work perfectly

Abstract
 
 Zigbee is considered to be one of the wireless sensor networks (WSNs) designed for short-range communications applications. It follows IEEE 802.15.4 specifications that aim to design networks with lowest cost and power consuming in addition to the minimum possible data rate. In this paper, a transmitter Zigbee system is designed based on PHY layer specifications of this standard. The modulation technique applied in this design is the offset quadrature phase shift keying (OQPSK) with half sine pulse-shaping for achieving a minimum possible amount of phase transitions. In addition, the applied spreading technique is direct sequence spread spectrum (DSSS) technique, which has the effect in getting better performance for the transmitter system in multipath environments. The system is developed through the use of MATLAB/Simulink to show the performance of the proposed system in response to the appliy modulation technique.
 
 Keywords: DSSS technique, IEEE 802.15.4, MSK, OQPSK, Zigbee.

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.

Today, both the military and commercial sectors are placing an increased emphasis on global communications. This has prompted the development of several Low Earth Orbit satellite systems that promise a worldwide connectivity and real-time voice, data and video communications. Constellations that avoid repeated uplink and downlink work by exploiting Inter Satellite Links have proved to be very economical in space routing. However, traditionally Inter Satellite Links were considered to be out of reach for any malicious activity and thus little, or no security was employed. This paper proposes a secured Inter Satellite Links based network, built upon the adoption of the Direct Sequence Spread Spectrum technique, with binary de Bruijn sequences used as spreading codes. Selected sequences from the de Bruijn family may be used over directional spot beams. The main intent of the paper is to propose a secure and robust communication link for the next generation of satellite communications, relying on a classical spread spectrum approach employing innovative sequences.

The present article portrays a design and implementation of microcontroller based system for mass measuring system with good accuracy. For maintaining accuracy of the system a novel method is used which is multi channel direct sequence spread spectrum (DSSS with chaotic spreading codes) technique which is used as a filter for eliminating low frequency noise hence maintaining accuracy. It also meet the demand of development of a microcontroller based embedded system for physical parameter measurement. Such a system should monitor and provide data for examine with high accuracy.

Protection of copyright is a crucial issue in the data transmission and distribution. Considering the fact that there are different types of information available for misuse and manipulation by all the internet users it is necessary to establish the rules for copyright protection of a certain content. In this paper, special attention is given to the technical aspects of copyright protection. We took a digital image and a digital watermark into consideration. The original image has undergone a discrete wavelet transformation. Then, spread spectrum techniques were applied to the watermark. Digital watermark is then embedded into the original image. The aim of the paper is to present the comparison of results obtained using two different spread spectrum techniques in image watermarking.

This paper presents an algorithm by embedding a digital watermark into an original color image. Considering the characteristics of HVS, YUV color space is employed, this algorithm presents a new adaptive digital audio watermarking based on discrete cosine transform. The result of the experiment shows that the proposed algorithm has good robustness against various image processing and attacks, good invisibility and stability.

Vehicle-to-vehicle communication for intelligent transport systems is investigated. The performance comparison between a direct sequence spread spectrum technique and a time division technique is made assuming a random time slot assignment. This reveals that a time division scheme is superior to a spread spectrum technique under the condition that no power control is incorporated. Also, a co-channel interference cancellation technique is introduced in time division transmission, and its impact on the transmission performance is investigated by computer simulations.

In an effort to transmit information over communication channels that contain both Gaussian and non-Gaussian noise components, military and commercial applications frequently rely upon the use of direct sequence spread spectrum (DSSS) techniques. Whilst DSSS is an interference tolerant modulation scheme, situations may be encountered when the processing gain offered by the pseudonoise (PN) spreading code is inadequate. Enhancements to the interference immunity of a DSSS system can be accomplished through the use of signal processing techniques that suppress unwanted interference prior to despreading. To date, the majority of interference suppression techniques developed for DSSS applications, have concentrated on improving detector performance exclusively, and perfect synchronisation between transmitter and receiver is assumed. However, the process of PN code acquisition and tracking within a DSSS receiver is arguably one of the most critical functions within the receiver structure since, if it fails to operate correctly, the wanted signal will not be successfully recovered. An evaluation of the benefits of any interference suppression technique within a DSSS receiver would not be complete without considering at least one level within the synchronisation hierarchy. We examine the improvements in receiver performance, when the process of PN code tracking and detection employs a novel wavelet packet denoising (WPD) procedure for a variety of non-Gaussian channel scenarios.

Due to a world wide surge in the intelligent vehicle highway system (IVHS), the field of automatic vehicle identification (AVI) has been rapidly growing. The use of spread spectrum communications has not yet pervaded the AVI market. However, in the already cramped electromagnetic environment, spread spectrum techniques have gained significant popularity in many growing areas of wireless communication. AVI is perfectly suited to benefit. The fundamental advantage of spread spectrum technology in AVI applications is its invulnerability to interference and its ability to operate alongside narrow band communication systems already in place. The second advantage is the ease of licensing for spread spectrum AVI, since it does not require a dedicated frequency spectrum. It is also possible for several spread spectrum AVI systems to operate simultaneously in the vicinity of each other, using different spreading codes. This article concentrates on architecture as well as applied key signal processing techniques for a proposed direct sequence spread spectrum (DSSS) AVI system. A functional block diagram that outlines the major components of the system is presented. The system consists of three major functional parts: interrogator, transponder, and trigger. Free flow of traffic can be maintained only if the interrogator can isolate each vehicle in a common interrogation zone. DSSS allows this through code division multiple access (CDMA). The triggering system is based on the principles of speed enforcement radar. The proposed digital modulation scheme is BPSK. The DSSS modulator applies a Gold pseudo-random (PN) code to spread the spectrum of the binary signal. Despreading is carried out through the use of a PN matched filter. The antenna is assumed to have a 60/spl deg/ half-power radiation field and is placed on an existing overpass approximately 6 meters above the roadway. With 50 mW antenna transmit power, link budget analysis indicates that sufficient bit energy-to-noise power spectral density ratio is available at the receiver to generate an excellent bit error rate without requiring error control coding.

This paper investigates the scope of wavelets for performance improvement in spread spectrum image watermarking. Performance of a digital image watermarking algorithm, in general, is determined by the visual invisibility of the hidden data (imperceptibility), reliability in the detection of the hidden information after various common and deliberate signal processing operations (robustness) applied on the watermarked signals and the amount of data to be hidden (payload) without affecting the imperceptibility and robustness properties. In this paper, we propose a few spread spectrum (SS) image watermarking schemes using discrete wavelet transform (DWT), biorthogonal DWT and M-band wavelets coupled with various modulation, multiplexing and signaling techniques. The performance of the watermarking methods are also reported along with the relative merits and demerits.

In a watermarking system, robustness evaluation should be made if invisibility criteria are satisfied. For this purpose, we propose to measure the perceptual impact of a watermark on the image using the well known peak signal-to-noise ratio (PSNR) and additionally a spatial masking model that indicates "bad" pixels between the original and watermarked images. Two perceptual watermarks using pixel-wise masking in the wavelet domain are being tested, limiting the watermark strength such that the PSNR is 35 dB and in average the percentage of affected pixels is less than 25%. Extensive tests were made on several watermarked images and for different types of attacks (JPEG compression, median filtering, resizing, cropping and gamma correction) in order to see the effect of these attacks on the detector results. Simulations show some limitations of these techniques under the invisibility constraint.

Digital watermarking and data hiding are important tools for digital rights protection of media data. Spread spectrum (SS)-based watermarking and data-hiding approaches are popular due to their outstanding robustness, but their security might not be sufficient. To improve the security of SS, a SS-based image data-hiding approach is proposed by encrypting the discrete cosine transform coefficients of the host image with the piecewise linear chaotic map, before the operation of watermark embedding. To evaluate the performance of the proposed approach, simulations and analyses of its robustness and security are carried out. The average bit-error-rate values on 100 real images from the Berkeley segmentation dataset under the JPEG compression, additive Gaussian noise, salt and pepper noise, and cropping attacks are reported. Experimental results show that the proposed approach can maintain the high robustness of traditional SS schemes and, meanwhile, also improve the security. The proposed approach can extend the key space of traditional SS schemes from 10 19 to 10 47 and thus can resist brute-force attack and unauthorized detection watermark attack.

Direct sequence spread spectrum (DSSS) techniques are commonly used for characterizing RF communications channels. These techniques have relative immunity to interference and do not require a direct reference connection between the transmitter and receiver. Current DSSS propagation measurement systems use a pseudo noise (PN) sequence to probe the impulse response of the channel. However, the use of PN sequences can introduce noise into the measurements. This noise is caused by a bias term that is inversely proportional to the length of the PN-Sequence, and limits the dynamic range of the measurement system. In this paper it is shown that this bias term will not be present when zero correlation zone (ZCZ) sequences are used. Consequently the dynamic range of the measurement system is limited by the SNR instead of the sequence itself. This paper also provides test data to show the effects of the bias term and to compare and contrast the use of PN and ZCZ sequences.

A sensor system enabling real-time monitoring of organ perfusion following transplantation is presented. This system uses a three wavelength oximetry-based approach. The instrument is intended for implantation at the organ site during transplantation to provide real-time reporting of the perfusion status of the tissue for 7-10 days following the procedure. Data is transmitted from the sensor to a localized receiver using direct sequence spread spectrum techniques at 916 MHz. In this paper, the sensing method and associated electronics implementation are presented. The present status of system miniaturization is summarized along with plans for future miniaturization efforts. Preliminary sensor data is presented demonstrating the efficacy of the technique.