Payload Length and Rate Adaptation for Multimedia Communications in Wireless LANs

We provide a theoretical framework for cross-layer design in multimedia communications to optimize single-user throughput by selecting the transmitted bit rate and payload size as a function of channel conditions for both additive white Gaussian noise (AWGN) and Nakagami-m fading channels. Numerical results reveal that careful payload length adaptation significantly improves the throughput performance at low signal to noise ratios (SNRs), while at higher SNRs, rate adaptation with higher payload lengths provides better throughput performance. Since we are interested in multimedia applications, we do not allow retransmissions in order to minimize latency and to reduce congestion on the wireless link and we assume that packet loss concealment will be used to compensate for lost packets. We also investigate the throughput and packet error rate performance over multipath frequency selective fading channels for typical payload sizes used in voice and video applications. We explore the difference in link adaptation thresholds for these payload sizes using the Nafteli Chayat multipath fading channel model, and we present a link adaptation scheme to maximize the throughput subject to a packet error rate constraint.     

Novel wavelet-based QIM data hiding technique for tamper detection and correction of digital images

This paper proposes a tamper detection and correction technique using semi-fragile data hiding that aims to achieve high perceptual quality of images at the user-end even after malicious modifications. A binary signature and an image digest are embedded by modulating integer wavelet coefficients using dither modulation based quantization index modulation. Half-toning technique is used to obtain image digest from the low-resolution version of the host image itself. Decoder extracts the binary signature from the watermarked image for tamper detection, while the extracted image digest is used to correct the tamper region. Unlike previously proposed techniques, this novel approach distinguishes malicious changes from various common image processing operations more efficiently and also correct tapered regions effectively. Experimental results show that the proposed technique provides a superior performance in terms of probability of miss and false alarm as well as in tamper correction, compared to several existing semi-fragile watermarking techniques.     

Robust Image Transmission Over Wireless Sensor Networks

Robust image and video communications have become more imperative due to the ubiquitous proliferation of multimedia applications over wireless sensor networks. In this work, the transmission distortions on the image data induced by both channel and instant node failures for Wireless Sensor Networks (WSN) are considered. The effect of two techniques and their integration with multipath transmission are investigated to compensate the multimedia distortions at the expense of incurring additional energy consumption and/or wasting bandwidth resources. First technique is watermarking based error concealment utilizing discrete wavelet transform for embedding downsized replicas of original image into itself. The other is conventional Reed–Solomon (RS) coding utilizing additional information bits to correct bit/symbol errors. Performance results obtained from extensive simulations utilizing a communication and energy model applicable to WSN show that error concealment (EC) integrated schemes, especially EC with multipath fusion (ECMF), are more promising to compensate losses than RS-coding-integrated and pure multipath transmission techniques in WSN.     

RS-MPSK编码调制在传输压缩图像的Rayleigh衰落信道中的性能

本文研究了两种结构的ＲＳ－ＭＰＳＫ编码调制方案在传输压缩图像的Ｒａｙｌｅｉｇｈ衰落信道中的性能。采用计算机仿真的方法得到了该方案在Ｒａｙｌｅｉｇｈ衰落信道中的误比特率,并与理论上限进行了比较,将方案用于传输压缩图像时,可大大提高系统的性能,具有较高的理论意义和衫价值。     

Moment Generating Function Based Performance Analysis of Maximal-Ratio Combining Diversity Receivers in the Generalized-K Fading Channels

In this paper, we have analyzed the performance of maximal ratio combing (MRC) diversity receiver of the wireless communication systems over the composite fading environment, which is modelled by using the generalized-K distribution. However, this distribution has been considered as a versatile distribution for the precise modelling of a great variety of the short-term fading in conjunction with the long-term fading (shadow fading) channel conditions. In this proposed analysis, we have derived the mathematical expression for the moment generating function (MGF) of the generalized-K fading channel model that is used to evaluate a novel closed-form expression of the average bit error rate for (BER) the binary phase-shift keying /binary frequency-shift keying and average symbol error rate (SER) for the rectangular quadrature amplitude modulation scheme. We have also derived the mathematical expressions for the outage probability as well as the channel capacity for the generalized-K fading channel model.     

RST Invariant Image Watermarking Algorithm With Mathematical Modeling and Analysis of the Watermarking Processes

In this paper, a new rotation and scaling invariant image watermarking scheme is proposed based on rotation invariant feature and image normalization. A mathematical model is established to approximate the image based on the mixture generalized Gaussian distribution, which can facilitate the analysis of the watermarking processes. Using maximum a posteriori probability based image segmentation, the cover image is segmented into several homogeneous areas. Each region can be represented by a generalized Gaussian distribution, which is critical for the analysis of the watermarking processes mathematically. The rotation invariant features are extracted from the segmented areas and are selected as reference points. Subregions centered at the feature points are used for watermark embedding and extraction. Image normalization is applied to the subregions to achieve scaling invariance. Meanwhile, the watermark embedding and extraction schemes are analyzed mathematically based on the established mathematical model. The watermark embedding strength is adjusted adaptively using the noise visibility function and the probability of error is analyzed mathematically. The mathematical relationship between fidelity and robustness is established. The experimental results show the effectiveness and accuracy of the proposed scheme.     

Error resilient transmission of SPIHT coded images over fadingchannels

The paper introduces a method of transmitting error resilient SPIHT coded images over highly error prone Rayleigh fading channels. First, the source significance of the SPIHT coded output is obtained. Based on the significance of the bits, the channel coding is varied accordingly. Channel coding consists of a mixture of rate compatible punctured convolutional (RCPC) codes and interleaving to combat the burst errors produced by the fading channel. An additional error concealment technique is also introduced into the SPIHT decoder to improve its results in cases where errors cause the corruption of the average luminance level during decoding. Comparison with using RS block codes at a total transmission rate of 1.0 bits/pixel is carried out over fading channels with very high error rates to show the superiority of this method over methods using burst error codes     

FH-MFSK multiple-access communications systems performance in thefactory environment

A frequency-hopped (FH), M-ary frequency-shift-keyed (MFSK), spread-spectrum (SS) communication system operating over the factory radio channel is described. The performance of the system for Rayleigh, Rician, and log-normal multipath fading for factory environments is investigated. The statistics of these channels, based on recent channel modeling studies, are used to evaluate the performance of the FH-MFSK system. A quadrature rule is employed to calculate the channel error probabilities. The average bit error rate (BER) is formulated and is evaluated approximately using Stirling's formula. The numbers of simultaneous users in terms of the number of hopped frequencies, number of MFSK chips, receiver threshold, signal-to-noise ratio, and channel statistics at a fixed BER for Rayleigh, Rician, and lognormal fading channels are determined     

Two-Dimensional DPCM Image Transmission Over Fading Channels

A combined source-channel coding approach is described for the encoding, transmission, and remote reconstruction of image data. The transmission medium considered is that of a fading dispersive communications channel. Both the Rician fading and Rayleigh fading channel models are considered. The image source encoder employs two-dimensional (2-D) differential pulse code modulation (DPCM). This is a relatively efficient encoding scheme in the absence of channel errors. In the presence of fading, however, the performance degrades rapidly. By providing error control protection to those encoded bits which contribute most significantly to image reconstruction, it is possible to minimize this degradation without sacrificing transmission bandwidth. Several modulation techniques are employed in evaluation of system performance including noncoherent multiple frequency shift-keyed (MFSK) modulation. Analytical results are provided for assumed 2-D autoregressive image models, while simulation results are described for real-world images.     

基于SIFT特征点和交比值的水印图像抗攻击算法

为提高数字水印图像对常规信号和复杂几何攻击的抵抗能力,利用SIFT(scale invariant feature transform)特征点的稳健性和交比值不变特性,提出了一种数字图像顽健水印算法。首先,在原图像经过NSCT(nonsubsampled contourlet transform)变换后的低频子带系数中提取SIFT特征点并对其进行优化筛选,从中确定满足“近凸正四边形” 的系数区域作为水印嵌入的局部区域,然后利用事先设定好的一些交比值在各局部区域中确定要嵌入水印的具体系数,最后利用奇偶量化调制方法嵌入水印信息。与传统算法相比,在提取水印信息时无需对含水印图像进行几何逆变换。实验结果表明,该算法对常规信号处理及多种几何攻击具有较强的抵抗能力和顽健性。     

Decision-Feedback Receiver for Quasi-Orthogonal Space-Time Coded OFDM Using Correlative Coding Over Fast Fading Channels

Orthogonal frequency division multiplexing (OFDM) is robust against frequency selective fading, but it is very vulnerable to time selective fading. In quasi-orthogonal space-time coded OFDM (ST-OFDM) systems, channel variations cause not only inter-carrier interference among different subcarriers in one OFDM block, but also inter-transmit-antenna interference (ITAI). When applied in fast fading channels, common ST-ODFM receivers usually suffer from an irreducible error floor. In this letter, we apply frequency-domain correlative coding combined with a modified decision-feedback detection scheme to effectively suppress the error floor of quasi-orthogonal ST-OFDM over fast fading channels. The effectiveness of the proposed scheme in mitigating the effects of channel time selectivity is demonstrated through comparison with existing schemes such as zero-forcing, two-stage zero-forcing, and sequential decision feedback estimation     

A novel blind color image watermarking using upper Hessenberg matrix

It is a challenging work to design a blind color image watermarking scheme for protecting copyright, which is different from the existing schemes used binary image or grayscale image as watermark and is also different from other non-blind watermarking schemes. In this paper, we analyze the feature of the upper Hessenberg matrix, and propose a blind color image watermarking scheme using upper Hessenberg matrix of Hessenberg transform. Arnold transform is used to improve the security, and the MD5-based Hash pseudo-random algorithm is also used to improve the robustness. In the process of watermark embedding, the encrypted watermark information is embedded into the biggest energy element of the Hessenberg matrix by quantization technique. In the process of watermark extraction, the watermark is extracted from the attacked host image with blind manner. Simulation results show that the proposed scheme outperforms other related methods in the aspects of the invisibility, robustness, capacity and computational complexity.     

A robust adaptive DFE receiver for DS-CDMA systems under multipathfading channels

This paper presents a novel receiver design from signal processing viewpoint for direct-sequence code-division multiple access (DS-CDMA) systems under multipath fading channels. A robust adaptive decision-feedback equalizer (DFE) is developed by using optimal filtering technique via minimizing the mean-square error (MSE). The multipath fading channels are modeled as tapped-delay-line filters, and the tap coefficients are described as Rayleigh distributions in order to imitate the frequency-selective fading channel. Then, a robust Kalman filtering algorithm is used to estimate the channel responses for the adaptation of the proposed DFE receiver under the situation of partially known channel statistics. The feedforward and feedback filters are designed by using not only the estimated channel responses but the uncertainties and error covariance of channel estimation as well. As shown in the computer simulations, the proposed adaptive DFE receiver is robust against the estimation errors and modeling dynamics of the channels. Hence, it is very suitable for receiver design in data transmissions through multipath fading channels encountered in most wireless communication systems     

Multiuser channel estimation and tracking for long-code CDMA systems

Channel estimation techniques for code-division multiple access (CDMA) systems need to combat multiple access interference (MAI) effectively. Most existing estimation techniques are designed for CDMA systems with short repetitive spreading codes. However, current and next-generation wireless systems use long spreading codes whose periods are much larger than the symbol duration. We derive the maximum-likelihood channel estimate for long-code CDMA systems over multipath channels using training sequences and approximate it using an iterative algorithm to reduce the computational complexity in each symbol duration. The iterative channel estimate is also shown to be asymptotically unbiased. The effectiveness of the iterative channel estimator is demonstrated in terms of squared error in estimation as well as the bit error rate performance of a multistage detector based on the channel estimates. The effect of error in decision feedback from the multistage detector (used in the absence of training sequences) is also shown to be negligible for reasonable feedback error rates using simulations. The proposed iterative channel estimation technique is also extended to track slowly varying multipath fading channels using decision feedback. Thus, an MAI-resistant multiuser channel estimation and tracking scheme with reasonable computational complexity is derived for long-code CDMA systems over multipath fading channels.     

Self Embedding Watermarking Using Halftoning Technique

This paper proposes a self-embedding watermarking scheme for digital images. It exploits a digital halftoning technique to transform the host image to a halftone image, in which the content features of the host image are well preserved. This halftone image is utilized as an approximate or compressed version of the host image and further adopted as a watermark. Unlike most available self-embedding watermarking techniques, in which watermark embedding, tamper detection and image recovery are block-wise-based, our scheme is a pixel-wise and block-wise composite scheme. That is, the watermark is pixel-wise permuted and embedded in the least-significant-bit plane of the host image, while in tamper detection and image recovery, a block-wise strategy is employed. This pixel-wise and block-wise complementary mechanism can overcome a common disadvantage of previous block-wise-based self-embedding watermarking techniques. Our scheme can be used for tamper detection and alteration location. Moreover, the tampered area can be approximately recovered using the extracted watermark. Experimental results demonstrate the effectiveness of the proposed scheme.     

A novel robust logo watermarking scheme using fractional M-band wavelet transform

Digital watermarking, means of hiding/inserting a message, which can be an image, audio, video or text within the digital media. This hidden/inserting message can be later being extracted or detected for a variety of purposes. In this paper, a novel multi-resolution logo watermarking scheme using fractional M-band wavelet transform (Fr-M-band-WT) is proposed. The watermark is embedded in the multiresolution Fr-M-band-WT coefficients of low frequency bands of the host image using singular value decomposition (SVD). A multi-resolution nature of Fr-M-band-WT is exploited in the process of edge detection. Experimental results of the proposed logo watermarking scheme are compared with the previously available watermarking algorithms, fractional Fourier transform (FrFT), fractional wavelet transform (FrWT). Further, the proposed watermark extraction scheme is also tested on different attacks. The results after being investigated the proposed watermarking scheme shows a significant improvement as compared to other existing methods.     

A Robust Watermarking Scheme Using Sequency-ordered Complex Hadamard Transform

This paper presents a robust phase watermarking scheme for still digital images based on the sequency-ordered complex Hadamard transform (SCHT). The transform matrix of the SCHT exhibits sequency ordering which is analogous to frequency in the discrete Fourier transform (DFT). Hence, sequency-based image analysis can be performed for image watermarking while providing simple implementation and with less computational complexity for computation of the transform. As the SCHT coefficients are complex numbers which consist of both magnitudes and phases, they are suited to adopt phase modulation techniques to embed the watermark. In this proposed scheme, the phases of the SCHT coefficients in the sequency domain are altered to convey the watermark information using the phase shift keying (PSK) modulation. Low amplitude block selection (LABS) is used to enhance the imperceptibility of digital watermark, and amplitude boost (AB) method is employed to improve the robustness of the watermarking scheme. Spread spectrum (SS) technique is adopted to increase the security of watermark against various unintentional or intentional attacks. In order to demonstrate the effectiveness of the proposed watermarking scheme, simulations are conducted under various kinds of attacking operations. The results show that the proposed scheme is able to sustain a series of attacks including common geometric transformations such as scaling, rotating, cropping, painting, and common image-processing operations such as JPEG compression, low-pass filtering, sharpening, noising and phase perturbation, etc. Comparisons of the simulation results with the other schemes are also mentioned and the results reveal that the proposed scheme shows better robustness.     

Robust VB 2D-CELP image transmission over CDMA Rayleigh fading channels

This paper describes a new error resilient analysis-by-synthesis coding scheme and its application for robust still image transmission over CDMA Rayleigh fading channels. For the purpose of providing reliable transmission, a type-I hybrid ARQ protocol is used in a concatenated Reed–Solomon/convolutional coding scheme. However, for delay-constrained applications, the protocol is used with a limited number of retransmissions in addition to limited RS interleaving. Results of coded images are provided for the uplink of a communication system, where a slowly Rayleigh fading channel is considered.     

基于奇异值分解的半易损水印算法

随着数字图像在报刊杂志、医院、法庭中的广泛应用，越来越需要一种有效的图像认证方法，数字水印技术为上述问题提供了一个潜在的解决方案。本文提出了一种基于分组奇异值分解（SVD）的半易损水印技术，算法将经过伪随机排序的二值图像通过量化策略嵌入到分组SVD分解中最大的奇异值点，提取水印信号无需使用原始图像。仿真实验表明水印是不可察觉的，可将JPEG有损压缩同恶意攻击区分开来，能够准确地定位被篡改的图像内容。     

Chip‐interleaving direct sequence spread spectrum system over Rician multipath fading channels

Chip interleaving (CI) is a unique technique to exploit time diversity in direct sequence spread spectrum (DS/SS)‐based systems operating in fading environments. In order to facilitate design of CI systems in various fading situations, we present a performance analysis for CI DS/SS system over Rician multipath time‐varying fading channels. We derive the analytical bit error rate (BER) expression for CI DS/SS to allow fast and accurate evaluation of BER performance based on the interleaving depth selected, spreading codes employed, and the time correlation function of the channel. We then discuss some ideal cases by using the analytical results to reveal some of the insights presented in the performance analysis. For the purpose of comparison, we also obtain the BER expression for conventional DS/SS system as a special case of CI system with an interleaving depth of one. Using numerical examples, we verify the analytical results with computer simulations and illustrate the BER performance behavior of CI DS/SS system with varying interleaving depth for all possible combinations of two sets of spreading codes of different type and two different time correlation functions of the channel. Copyright © 2011 John Wiley & Sons, Ltd.