Ridha Ghayoula

Steering an adaptive antenna array by LMS algorithm

An adaptive antenna system consists of a combination of multiple antenna elements with a signal-processing capability to optimize its radiation and/or reception pattern automatically in response to the signal environment.

Pattern Synthesis Using Hybrid Fourier-Neural Networks for IEEE 802.11 MIMO Application

In this paper, the application of Articial Neural Network (ANN) with back-propagation algorithm and weighted Fourier method are used for the synthesis of antenna arrays. The neural networks facilitate the modelling of antenna arrays by estimating the phases. The most important synthesis problem is tond the weights of the linear antenna array elements that are optimum to provide the radiation pattern with maximum reduction in the sidelobe level. This technique is used to prove its effectiveness in improving the performance of the antenna array. To achieve this goal, antenna array for Wi-Fi IEEE 802.11a with frequency at 2 : 4 GHz to 2 : 5 GHz is implemented using Hybrid Fourier-Neural Networks method. To verify the validity of the technique, several illustrative examples of uniform excited array patterns with the main beam are placed in the direction of the useful signal. The neural network synthesis method not only allows to establish important analytical equations for the synthesis of antenna array, but also provides a great exibility between the system parameters in input and output which makes the synthesis possible due to the explicit relation given by them.

Phased arrays in communication system based on Taguchi-neural networks

Phased antenna array design is one of the most important electromagnetic optimization problems. This research combined the Taguchi method and artificial intelligence methods, used them as the prediction tool in designing parameters for the communication system, and then constructed a set of the optimal parameter analysis flow and steps. In this paper, we present an application of artificial neural networks in the electromagnetic domain. We particularly look at the multilayer perceptron network, which has been the most used of artificial neural networks architectures both in the electromagnetic domain and in the Taguchi optimization technique and describes the Taguchi method to optimize the excitations elements of the linear array to produce a radiation pattern with minimum side lobe level and null placement control. This paper investigates how the implementation of the signal processing in hardware affects the performance of the adaptive array antenna. The investigation is confined to uplink or receive antenna array only. Results of a prototype of antenna array with feeding values designed using the proposed techniques are also presented. Copyright

Formal reasoning on authentication in security protocols

In this paper, we are proposing a new formal framework for reasoning on authentication in security protocols based on analytic functions. We give sufficient conditions that, if satisfied, the protocol is declared correct with respect to authentication. We validate our approach on the Yahalom-Lowe protocol. First, we show that it satisfies these few conditions, thus, we conclude that it is correct for authentication.

Hybrid MUSIC Dolph-Chebyshev algorithm for a smart antenna system

This paper presents practical design of a smart antenna system based on direction-of-arrival estimation and Dolph-Chebyshev beam forming. Direction-of-arrival estimation is based on the multiple signal classification algorithm for identifying the directions of the source signals incident on the sensor array comprising the smart antenna system. The smart antenna system design involves a hardware part, which provides real data measurements of the incident signals received by the sensor array. This paper presents the Dolph-Chebyshev method for the synthesis and design of antenna arrays with periodic element spacing. A Field-Programmable Gate Array implementation is presented for an antenna array application employing digital beamforming. The array comprises 10 elements, equal in number receiving radio frequency and intermediate frequency components, as well as a Spartan-3E Field-Programmable Gate Array-based unit, which is responsible for the control of the array. Low-cost and switched-beam, and fully adaptive antenna array suitable for 2-GHz applications are proposed in this paper. Copyright

Miniaturisation of a 2-Bits Reflection Phase Shifter for Phased Array Antenna based on Experimental Realisation

In this paper, a controllable reflection type Phase Shifter (PS) is designed, simulated and implemented. The structure of the 2-bits PS consists of branch line coupler, delay lines and six GaAs FET switches controlled in pair. The phase shifting is achieved by turning ON one pair of switches. The circuit design is fabricated using FR4 substrate with dielectric constant equal to 4.7. The size of the realised circuit is 7cm×2.8cm. To reduce this size, two methods are used. First, shortened quarter-wave length transmission line in T model is employed to develop a compact branch-line coupler. Second, a loaded line with capacitor is used to reduce the dimension of delays lines. The two methods are combined to realise a PS with compact size equal to 4.5cm×1.96cm.

Sidelobe level reduction in linear array pattern synthesis using Taylor-MUSIC algorithm for reliable IEEE 802.11 MIMO applications

The concepts of array processing and smart antenna give a promising solution to the significant increase of data rates in wireless transmission systems. In this paper, we deal with the problem of designing linear antenna arrays for specific radiation properties of MIMO applications based on Direction-Of-Arrival estimation and Taylor beamforming techniques. The objectives of this paper can be summarized as to minimize the maximum sidelobe level (SLL), combined the Taylor method and MUSIC (Multiple Signal Classification) algorithm. The performance of this hybrid optimization determines how well the system is convenient for a reliable wireless communication and interference reduction. This paper will discuss the application of MUSIC algorithm for linear array antenna (4, 8 and 16 antennas) in order to estimate the Direction-Of-Arrival of various angles of elevation and azimuth.

Improving MIMO systems performances by concatenating LDPC decoder to the STBC and MRC receivers

Multiple-input multiple-output (MIMO) systems are commonly used in wireless communications to ensure high bit-rate and high capacity transmission. Space time block coding (STBC) is a technique used in MIMO to provide transmit diversity in communication over fading channels. Although STBC has full diversity gain, the coding gain need to be improved by using channel coding such as low density parity check (LDPC) codes or Turbo codes. This paper evaluates the performance of MIMO systems and the improvement obtained by concatenating LDPC codes. MIMO are based on spatially separated multiple transmitting and receiving antennas to provide diversity. This helps combatting the effect of multipath fading in wireless channels. For single-input multiple-output (SIMO) schemes, maximum ratio combining (MRC) receiver are used to handle redundantly the same information-bearing signal over two or more fading channel. The output of this receiver consist on soft decision metrics that can be fed to LDPC decoder for error correction. For MIMO and multiple-input single-output (MISO) systems, space time block codes (STBC) are used to generate orthogonal signals to avoid interference between signal streams. These signals are transmitted at slightly different times to benefit from temporal diversity. LDPC codes are used in conjunction with STBC to improve the error capability. This paper investigates diversity coding for MIMO systems combined with LDPC soft decoding. Performances of the proposed scheme in terms of bit error rates are reported.

Antenna array synthesis with Chebyshev-Genetic Algorithm method

This paper presents the application of a Multiobjective Optimisation Genetic Algorithm for the synthesis of linear antenna arrays. This method for antenna pattern synthesis can suppress multiple interferences by placing nulls at the directions of the interfering sources and placing the main beam in the direction of the desired signal by controlling the phase and the amplitude. To verify the performances of the method, several illustrative examples are provided to justify the proposed phaseamplitude perturbations approach based on genetic algorithms.

Circular array synthesis using Taguchi algorithm for reliable IEEE 802.11 MIMO applications

In this paper, we study an electromagnetic optimization technique using Taguchis method and apply it to circular antenna array (CAA) design. Taguchis method was developed on the basis of the orthogonal array (OA) concept, which offers systematic and efficient characteristics. The newly proposed idea is the implementation of Taguchi optimization method for CAA of order 10, 16 and 24 respectively. The optimization procedure is then used to provide an optimum set of weights for different CAAs. Obtained results show that the desired radiation pattern with optimum sidelobe level (SLL) reduction is successfully achieved. Compared to traditional optimization techniques and well-known algorithms (Particle Swarm Optimization (PSO), Genetic Algorithm (GA), and Firefly Algorithm (FA)), Taguchis method is easy to implement and efficient to reach the optimum solutions.