F. Shawki

An SVD audio watermarking approach using chaotic encrypted images

This paper presents a new approach for audio watermarking using the Singular Value Decomposition (SVD) mathematical technique. The proposed approach can be used for data hiding in the audio signals transmitted over wireless networks and for multi-level security systems as will be stated in the applications section. This approach is based on embedding a chaotic encrypted watermark in the singular values of the audio signal after transforming it into a 2-D format. The selection of the chaotic encryption algorithm for watermark encryption is attributed to its permutation nature, which resists noise, filtering, and compression attacks. After watermark embedding, the audio signal is transformed again into a 1-D format. The transformation between the 1-D and 2-D formats is performed in the well-known lexicographic ordering method used in image processing. The proposed approach can be implemented on the audio signal as a whole or on a segment-by-segment basis. The segment-by-segment implementation allows embedding the same watermark several times in the audio signal, which enhances the detectability of the watermark in the presence of severe attacks. Experimental results show that the proposed audio watermarking approach maintains the high quality of the audio signal and that the watermark extraction and decryption are possible even in the presence of attacks.

Transceiver scheme for single-carrier frequency division multiple access implementing the wavelet transform and peak-to-average-power ratio reduction methods

Single-carrier frequency division multiple access (SC-FDMA) has been adopted as a possible air interface for future wireless networks. It combines most of the advantages of orthogonal frequency division multiple access (OFDMA) and the low peak-to-average-power ratio (PAPR) of single-carrier transmission. This study proposes a new transceiver scheme for SC-FDMA systems implementing the wavelet transform to decompose the transmitted signal into approximation and detail components. The approximation component can be clipped or companded whereas the detail component is left unchanged because of its sensitivity to noise. Wavelet filter banks at the transmitter and the receiver demonstrate the ability to reduce the distortion in the reconstructed signal while retaining all the significant features present in the signal. The performance of the proposed scheme is investigated with different PAPR reduction methods. Simulation results show that the proposed scheme with the hybrid clipping and companding method provides a significant performance enhancement when compared with the conventional SC-FDMA system, while the complexity of the system is slightly increased.

Joint Low-Complexity Equalization and Carrier Frequency Offsets Compensation Scheme for MIMO SC-FDMA Systems

Due to their noise amplification, conventional Zero-Forcing (ZF) equalizers are not suited for interference-limited environments such as the Single-Carrier Frequency Division Multiple Access (SC-FDMA) in the presence of Carrier-Frequency Offsets (CFOs) . Moreover, they suffer increasing complexity with the number of subcarriers and in particular with Multiple-Input Multiple-Output (MIMO) systems. In this letter, we propose a Joint Low-Complexity Regularized ZF (JLRZF) equalizer for MIMO SC-FDMA systems to cope with these problems. The main objective of this equalizer is to avoid the direct matrix inversion by performing it in two steps to reduce the complexity. We add a regularization term in the second step to avoid the noise amplification. From the obtained simulation results, the proposed scheme is able to enhance the system performance with lower complexity and sufficient robustness to estimation errors.

Uplink single-carrier frequency division multiple access system with joint equalisation and carrier frequency offsets compensation

Similar to the orthogonal frequency division multiple access (OFDMA) system, the single-carrier frequency division multiple access (SC-FDMA) system also suffers from frequency mismatches between the transmitter and the receiver. As a result, in this system, the carrier frequency offsets (CFOs) disrupt the orthogonality between subcarriers and give rise to inter-carrier interference (ICI) and multiple access interference (MAI) among users. The authors present a new minimum mean square error (MMSE) equaliser, which jointly performs equalisation and carrier frequency offsets (CFOs) compensation. The mathematical expression of this equaliser has been derived taking into account the MAI and the channel noise. A low complexity implementation of the proposed equalisation scheme using a banded matrix approximation is presented here. From the obtained simulation results, the proposed equalisation scheme is able to enhance the performance of the SC-FDMA system, even in the presence of estimation errors.

Performance enhancement of SC-FDMA systems using a companding technique

In this paper, a companding technique is proposed to effectively reduce the peak-to-average power ratio (PAPR) in single-carrier frequency division multiple access (SC-FDMA) systems. By companding the samples with large amplitudes, while enhancing those with small amplitudes, a significant reduction in the PAPR can be achieved. The performance of the proposed SC-FDMA with companding system is studied and compared with that of the standard SC-FDMA system. Simulation results show that the SC-FDMA with companding system has a lower PAPR when compared with the conventional SC-FDMA system, while the complexity of the system slightly increases. Results also reveal that the companding coefficient must be chosen carefully in order to limit the PAPR without introducing degradations into the bit error rate performance.

A new single carrier FDMA system based on the discrete cosine transform

In this paper, a new single carrier frequency division multiple access (SC-FDMA) system based on the discrete cosine transform (DCT) for uplink wireless transmissions, is introduced. The time domain expressions of the DCT SC-FDMA signals are derived. The peak to average power ratio (PAPR) of the DCT SC-FDMA signals is compared with that of the discrete Fourier transform (DFT) SC-FDMA and orthogonal frequency division multiple access (OFDMA) signals. Simulation results show that the proposed DCT SC-FDMA system provides a better bit error rate (BER) performance than the DFT SC-FDMA and the OFDMA systems. In addition, it is found that the PAPR of the DCT SC-FDMA signals is lower than that of OFDMA signals.

Equalization and Carrier Frequency Offsets Compensation for the SC-FDMA System

Recently, the Single-Carrier Frequency Division Multiple Access (SC-FDMA) system has attracted the attention as an efficient alternative to the Orthogonal Division Multiple Access (OFDMA) system in the uplink communications. In this system, the Carrier Frequency Offsets (CFOs) disrupt the orthogonality between subcarriers, and give rise to Inter-Carrier Interference (ICI), and Multiple Access Interference (MAI) among users. In this paper, the impact of the CFOs on the performance of the Discrete Fourier Transform SC-FDMA (DFT-SC-FDMA) and the Discrete Cosine Transform SC-FDMA (DCT-SC-FDMA) systems is investigated. Based on the Minimum Mean Square Error (MMSE) criterion, a new low-complexity joint equalization and CFOs compensation scheme is proposed. It is refered to as the MMSE scheme. The MMSE weights of the proposed scheme are derived taking into account the MAI and the noise. Furthermore, a hybrid scheme comprising the proposed MMSE scheme and a Parallel Interference Cancellation (PIC) stage is also suggested and investigated to further enhance the performance of interleaved subcarriers mapping systems. From the obtained simulation results, it is clear that CFOs disrupt the orthogonality between the subcarriers in SC-FDMA systems and degrade the Bit Error Rate (BER) performance. The proposed compensation schemes are able to enhance the system performance, even in the presence of the estimation errors.

Performance of the audio signals transmission over wireless networks with the channel interleaving considerations

This article studies a vital issue in wireless communications, which is the transmission of audio signals over wireless networks. It presents a novel interleaver scheme for protection against error bursts and reduction the packet loss of the audio signals. The proposed technique in the article is the chaotic interleaver; it is based on chaotic Baker map. It is used as a randomizing data tool to improve the quality of the audio over the mobile communications channels. A comparison study between the proposed chaotic interleaving scheme and the traditional block and convolutional interleaving schemes for audio transmission over uncorrelated and correlated fading channels is presented. The simulation results show the superiority of the proposed chaotic interleaving scheme over the traditional schemes. The simulation results also reveal that the proposed chaotic interleaver improves the quality of the received audio signal. It improves the amount of the throughput over the wireless link through the packet loss reduction.

Impact of the power amplifier on the performance of the single carrier frequency division multiple access system

Single-carrier frequency division multiple access (SC-FDMA) is a promising alternative to orthogonal frequency division multiple access (OFDMA) for uplink wireless communications in frequency-selective fading environments. In this paper, we investigate the impact of the power amplifier (PA) on the performance of the SC-FDMA system. The suitable saturation level thresholds of the PA that can be utilized in the SC-FDMA system are studied and determined through simulations for different modulation formats. Simulation results show that the saturation level of the PA has a significant effect on the bit error rate (BER) performance of the SC-FDMA system, especially with high order modulation formats.

Image transmission over mobile Bluetooth networks with enhanced data rate packets and chaotic interleaving

Bluetooth is a wireless personal area network. This type of networks is widely used for image communication. This paper presents a study for the transmission of images over mobile Bluetooth networks. It presents a novel chaotic interleaving scheme for this purpose. In this scheme, the chaotic Baker map is used for bit interleaving and enhanced data rate packets are used for data transmission. In the proposed scheme, the chaotic interleaver can be applied on the whole bit stream or on a packet-by-packet basis. The proposed scheme is applied with 2DH1, 2DM1, 3DH5, and 3DM5 packets. A comparison study between the proposed scheme and the traditional interleaving schemes for image transmission over correlated and uncorrelated fading channels is presented. The simulation results show the superiority of the proposed scheme over the traditional schemes. The proposed scheme also adds a degree of security to data transmission.