Brahim Ait Es Said

High Power Amplifier Pre-Distorter Based on Neural-Fuzzy Systems for OFDM Signals

In this paper, a novel High Power Amplifier (HPA) pre-distorter based on Adaptive Networks - Fuzzy Inference Systems (ANFIS) for Orthogonal Frequency Division Multiplexing (OFDM) signals is proposed and analyzed. Models of Traveling Wave Tube Amplifiers (TWTA) and Solid State Power Amplifiers (SSPA), both memoryless and with memory, have been used for evaluation of the proposed technique. After training, the ANFIS linearizes the HPA response and thus, the obtained signal is extremely similar to the original. An average Error Vector Magnitude (EVM) of 10-6 can be easily obtained with our proposal. As a consequence, the Bit Error Rate (BER) degradation is negligible showing a better performance than what can be achieved with other methods available in the literature. Moreover, the complexity of the proposed scheme is reduced.

Reduction of Power Envelope Fluctuations in OFDM Signals by using Neural Networks

One of the main drawbacks of Orthogonal Frequency Division Multiplexing (OFDM) are the large fluctuations of its power envelope. In this letter, a novel and efficient scheme based on Multilayer Perceptron (MLP) Neural Networks (NN) is proposed. The NN synthesizes the Active Constellation Expansion - (ACE) technique which is able to drastically reduce envelope fluctuations. This is achieved with much lower complexity, faster convergence, and better performance compared to previously available methods.

Reduction of the Envelope Fluctuations of Multi-Carrier Modulations using Adaptive Neural Fuzzy Inference Systems

In this paper, a novel scheme for reducing the envelope fluctuations in multi-carrier signals applying Adaptive Neural Fuzzy Inference Systems (ANFIS) is proposed and analyzed. Once trained with signals with very low envelope fluctuations, such as those obtained by the Active Constellation Expansion - Approximate Gradient Project (ACE-AGP) algorithm, ANFIS approximately reaches a similar reduction as with ACE-AGP for multi-carrier signals without the complexity and the large convergence time of conventional ACE-AGP. We show that our approach is less complex than other previous schemes and with better performance.

A robust and secure perceptual hashing system based on a quantization step analysis

Perceptual hashing is conventionally used for content identification and authentication. It has applications in database content search, watermarking and image retrieval. Most countermeasures proposed in the literature generally focus on the feature extraction stage to get robust features to authenticate the image, but few studies address the perceptual hashing security achieved by a cryptographic module. When a cryptographic module is employed [1], additional information must be sent to adjust the quantization step. In the perceptual hashing field, we believe that a perceptual hashing system must be robust, secure and generate a final perceptual hash of fixed length. This kind of system should send only the final perceptual hash to the receiver via a secure channel without sending any additional information that would increase the storage space cost and decrease the security. For all of these reasons, in this paper, we propose a theoretical analysis of full perceptual hashing systems that use a quantization module followed by a crypto-compression module. The proposed theoretical analysis is based on a study of the behavior of the extracted features in response to content-preserving/content-changing manipulations that are modeled by Gaussian noise. We then introduce a proposed perceptual hashing scheme based on this theoretical analysis. Finally, several experiments are conducted to validate our approach, by applying Gaussian noise, JPEG compression and low-pass filtering.

Perceptual Image Hashing

With the fast advancement of computer, multimedia and network technologies, the amount of multimedia information that is conveyed, broadcast or browsed via digital devices has grown exponentially. Simultaneously, digital forgery and unauthorized use have reached a significant level that makes multimedia authentication and security very challenging and demanding. The ability to detect changes in multimedia data has been very important for many applications, especially for journalistic photography, medical or artwork image databases. This has spurred interest in developing more robust algorithms and techniques to allow to check safety of exchanged multimedia data confidentiality, authenticity and integrity. Confidentiality means that the exchange between encrypted multimedia data entities, which without decryption key, is unintelligible. Confidentiality is achieved mainly through encryption schemes, either secret key or public key. Authentication is an another crucial issue of multimedia data protection, it makes possible to trace the author of the multimedia data and allow to determine if an original multimedia data content was altered in any way from the time of its recording. Integrity allows degradation detection of multimedia and helps make sure that the received multimedia data has not been modified by a third party for malicious reasons. Many attempts have been noted to secure multimedia data from illegal use by different techniques fields such as encryption field, watermarking field and perceptual image hashing field. The field of encryption is becoming very important in the present era in which information security is of the utmost concern to provide end-to-end security. Multimedia data encryption has applications in internet communication, multimedia systems, medical imaging, telemedicine, military communication, etc. Although we may use the traditional cryptosystems to encrypt multimedia data directly, it is not a good idea for two reasons. The first reason is that the multimedia data size is almost always much great. Therefore, the traditional cryptosystems need much more time to directly encrypt the multimedia data. The other problem is that the decrypted multimedia data must be equal to the original multimedia data. However, this requirement is not necessary for image/video data. Due to the characteristic of human perception, a decryptedmultimedia containing small distortion is usually acceptable. Deciding upon what level of security is needed is harder than it looks. To identify an optimal security level, the cost of the multimedia information to be protected and the cost of the protection itself are to be compared carefully. At present, many available image encryption algorithms have been proposed (Ozturk & Ibrahim, 2005; 2

Analysis of the robustness of wavelet-based perceptual signatures

Perceptual image hashing maps an image to a fixed length binary string based on the images appearance to the human eye, and has applications in image indexing, authentication, and watermarking. In this paper, we analyze the robustness of perceptual signatures generated by the known SHA1 hash function in the DWT domain. This is achieved by generation signatures from the coefficients of the subband LL after a DWT transformation. Experiments on large-scale database show that the proposed method is efficient, robust against common content-preserving manipulations.

Statistical analysis of the quantization stage of robust perceptual image hashing

In this paper, we consider the problem of the quantization stage of robust perceptual image hashing in authentication application. The main goal of our analysis is to study the behavior of the extracted image features to be hashed against malicious/non-malicious manipulations. In our analysis, we consider only an additive noise. Note that even if the noise is small, it can cause errors during the quantization stage of perceptual image hashing system. For this purpose, we present theoretical analysis of the extracted feature under additive noise, as well as the probability of a false quantization of these selected features. We then introduce our proposed approach based on this theoretical analysis. Finally, several experiments are conducted to validate our theoretical analysis.

Reduction of power envelope fluctuations in ECMA-368 ultra wideband communication system

ECMA-368 is a recent standard, describing the UWB physical layer (PHY-UWB) for wireless personal area network (WPAN) by using the Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) approach. However, the large power envelope fluctuations of MB-OFDM UWB signal, limits the power efficiency of the High Power Amplifier (HPA) due to nonlinear distortion. In this paper, we will use the Active Constellation Extension Approximate Gradient-Project technique (ACE-AGP) to reduce the power envelope fluctuations in real ECMA-368 system, the efficiency of ACE-AGP is compared with partial transmit sequences (PTS) algorithm. Simulation results show that the reduction of CM by ACE-AGP is better (5dB) than PTS (3dB) and with less complexity, also the BER achieved by both methods does not undergo a significant degradation.