Awad Kh. Al-Asmari

Spectral broadening effects of high-power amplifiers in MIMO–OFDM relaying channels

The combination of MIMO–OFDM is a very attractive solution for broadband wireless services. Thus, the two prominent fourth-generation (4G) cellular systems, WiMAX and LTE-advanced, have both adopted MIMO–OFDM transmission at the physical layer. OFDM signal however suffers from nonlinear distortions when passed through high-power amplifier (HPA) at the RF stage. This nonlinear distortion introduces out-of-band spectral broadening and in-band distortions on the transmitted signals. 4G cellular standards have placed strict limits on the allowable spectral broadening in their spectrum mask specifications, to insure that data transmission on a given channel is not interfering significantly with an adjacent channel user. In this article, we characterize the out-of-band spectral broadening introduced by HPA when MIMO–OFDM signals are transmitted over multiple relaying channels. Expressions for the power spectral density of MIMO–OFDM signals are derived over multiple relay channels, and the cumulative effects of HPA on the spectrum of the transmitted signals are estimated. It is shown that depending on the number of relays and the relaying configuration employed, it may happen that a transmitted MIMO–OFDM signal with the transmit spectrum mask initially within the allowable set limit at the source node arrives at the destination violating this limit due to the cumulative effects of the multiple HPA’s in a multihop relaying channel.

Optimum bit rate pyramid coding with low computational and memory requirements

This paper presents the optimum bit allocation for fixed rate pyramid coding structures which use a lowpass filter with nominal bandwidth of /spl pi//4 for predecimation filtering. This technique results in about 32% less in the computational complexity and 20% less in the memory requirements than the conventional filters used for pyramid coding. Three different algorithms are introduced. In the first algorithm the decimated image is transmitted at 8 bpp and the difference image is DCT-encoded. In the second algorithm the decimated image is encoded using BTC and the difference image is DCT-encoded, while in the third algorithm the decimated image is BTC-encoded with further quantization of the DCT coefficients of the difference image. These algorithms achieve high compression rate and allow at the same time a low complexity encoder. >

On the effect of amplifier non-linearity on the capacity of MIMO systems

This paper investigates the effect of nonlinearity on the capacity of MIMO systems and develops a capacity-enhancing MIMO transmission technique suitable for deployments over nonlinear channels. Nonlinearity arises in communication systems in several ways. In this work, we focus on the nonlinearity introduced at the transmitter side by the High Power Amplifier (HPA), the last stage in the communication chain at the transmitter. Water-filling and Eigen beamforming solutions, which are well-known capacity-enhancing techniques in linear MIMO channel are re-examined for the case of nonlinear channels. We show that these algorithms degrade significantly when used over MIMO channels exhibiting nonlinearities, except when the amplifier nonlinear distortions effects are factored into the algorithms. Factoring the HPA effects into the algorithms, the capacity of the resulting nonlinear channel approaches the linear channel case.

A new video compression algorithm for different videoconferencing standards

In this paper, a new and simple predictive coding algorithm for video compression and multimedia communication for different network applications is investigated. This algorithm is called semi-hexagonal absolute moment block truncation coding (SH-AMBTC). It enjoys better objective and subjective qualities over the standard square shaped AMBTC. This technique based on the prediction of the bit-map of the middle frames in a sequence from the bit-map of the end frames (the first and the last frames in the group). It is of very low complexity comparing to the standard algorithm MPEG. The new algorithm adds no complexity to the existing AMBTC algorithm.

A DWT Ordering Scheme for Hiding Data in Images Using Pixel Value Difference

A scheme is proposed to hide data in images based on a prioritised ordering of the content of the host image. The embedding process uses the watermark strength to determine the ordering of the 16 regions resulting from the second level wavelet transform DWT decomposed content of the host image. The DWT decomposed sub-bands of the cover image were analysed, transformed using the Pixel Value Difference (PVD), and then ranked in terms of their ability to withstand changes that do not imperil the visual quality (PSNR) of the watermarked image depending on which an N×N-sized watermark stream is hidden in the 8 highest ranked sub-bands. Using the proposal, a 256×256 Lena image had the capacity to accommodate up to 96800 bits of a watermark logo while still maintaining an appreciable visual quality manifested by a PSNR value of 33.66 dB.

Progressive edge detection compression for fingerprint images

In this article, a progressive fingerprint image compression (for storage or transmission) that uses an edge detection scheme is developed. First, the image is decomposed into two components: the primary component, which contains the edges, and the secondary component, which contains the textures and the features. Then, a general grasp for the image is reconstructed in the first stage at bit rates of 0.0223 and 0.0245 bpp for the tested fingerprints images (samples 1 and 2), respectively. The quality of the reconstructed images is competitive with the 0.75‐bpp target bit set by the FBI standard. Also, the compression ratio and the image quality of this algorithm are competitive with other methods reported in the literature. The compression ratio for our algorithm is about 45:1 (0.180 bpp).

A Hybrid Fusion Technique for Watermarking Digital Images

A hybrid fusion technique (HFT) that offers improved imperceptibility, better robustness to attacks and superior quality in terms of watermark image recovery than is realisable using the traditional Discrete Wavelet Transform (DWT), Discrete Cosine Transform (DCT) digital watermarking techniques or methods that utilise their direct combination is presented in this work. The separate DWT and DCT methods embed the watermark image directly on the wavelet or cosine coefficients of the cover image, while methods that combine both the DWT and DCT are certain to directly embed the watermark on some parts of the cover image twice. Unlike all these methods, our proposed HFT technique spreads the watermark in the transform (wavelet and cosine) domains separately and then the watermarked images from the two images emanating from the two domains are fused together to generate the final watermarked image - producing a hybrid. Such hybridisation allows us to exploit the individual benefits derivable from the separate use of the DWT and DCT methods. Experimental evaluations show that combining the two transforms in this manner offers improved performance in terms of imperceptibility, robustness to jpeg and other kinds of attack on the published (watermarked) image and quality of recovered watermark image than is obtainable using the methods that are based solely on the DWT or DCT techniques or their direct combination. The proposed HFT technique guarantees additional protection for digital images from illicit copying and unauthorised tampering.

A Pyramid-Based Watermarking Technique for Digital Color Images Copyright Protection

This paper proposes a pyramid-wavelet watermarking scheme for ownership verification of digital color images. The discrete wavelet transform (DWT) has been used extensively in recent years in watermarking systems. It provides the necessary perceptual invisibility and robustness. In this paper, a pre-DWT process is implemented using optimal pyramid transform (OPT), where one of the error images that are resulted from the pyramid transform is decomposed using DWT, and a watermark is inserted in one of its colors; red, green, or blue. Then, the watermarked color image is reconstructed. The filters used for OPT and DWT decomposition are randomly generated to increase the security of this algorithm. The simulation results show that the proposed algorithm achieves high average correlation against Gaussian and Salt-and-Paper noise

Ergodic Capacity of Nonlinear MIMO---OFDM Relaying Channels

This paper derives the ergodic capacity of nonlinear MIMO–OFDM relaying communication channels. We consider MIMO–OFDM relaying system where the transmitter, relays, and the receiver are all equipped with