Said E. El-Khamy

New trends in wireless multimedia communications based on chaos and fractals

The aim of this paper is to emphasize on the many possible applications of chaos and fractals in wireless multimedia communication systems and to describe the nature and properties of chaotic and fractal signals which make them suitable for solving many of the limitations of wireless channels. Among the considered applications are: (i) the use of fractals in the design of wideband and multiband antennas; (ii) the design of chaotic and fractal spreading codes for spread spectrum and CDMA systems to result in improved performance, increase the capacity and provide more security to the system; (iii) chaotic modulation techniques which provide improved performance in interference environments as well as improved security features; (iv) chaos cryptosystems; (v) fractal modulation techniques which allow multirate transmission and increased reliability; (vi) fractal based compression and watermarking techniques.

Efficient implementation of image interpolation as an inverse problem

This paper presents three computationally efficient solutions for the image interpolation problem which are developed in a general framework. This framework is based on dealing with the problem as an inverse problem. Based on the observation model, our objective is to obtain a high resolution image which is as close as possible to the original high resolution image subject to certain constraints. In the first solution, a linear minimum mean square error (LMMSE) approach is suggested. The necessary assumptions required to reduce the computational complexity of the LMMSE solution are presented. The sensitivity of the LMMSE solution to these assumptions is studied. In the second solution, the concept of entropy maximization of the required high resolution image a priori is used. The implementation of the suggested maximum entropy solution as a single sparse matrix inversion is presented. Finally, the well-known regularization technique used in iterative nature in image interpolation and image restoration is revisited. An efficient sectioned implementation of regularized image interpolation, which avoids the large number of iterations required in the interactive technique, is presented. In our suggested regularized solution, the computational time is linearly proportional to the dimensions of the image to be interpolated and a single matrix inversion of moderate dimensions is required. This property allows its implementation in interpolating images of any dimensions which is a great problem in iterative techniques. The effect of the choice of the regularization parameter on the suggested regularized image interpolation solution is studied. The performance of all the above-mentioned solutions is compared to traditional polynomial based interpolation techniques such as cubic O-MOMS and to iterative interpolation as well. The suitability of each solution to interpolating different images is also studied.

Efficient multiple-access communications using multi-user chirp modulation signals

In this paper, we present a novel technique for multi-user communication system utilizing binary chirp modulated (CM) signals. This suggested technique is motivated by the inherent interference rejection capability of such spread-spectrum type system, specially in circumstances where immunity against Doppler shift and fading due to multipath propagation are important. The used chirp signals are selected such that they all have the same power as well as the same bandwidth. Closed form expressions, as well as approximate analytical expressions, for the cross-coherence functions between the different forms of considered chirp signals are derived. The performance of a suggested coherent receiver structure is investigated and the corresponding error rates are presented. The results show that the proposed multiuser chirp signaling technique is efficient and promising as a multiple-access technique.

A modified fuzzy Sobel edge detector

A modified fuzzy Sobel method for edge detection and enhancement is proposed. This method is a modification of the fuzzy Sobel method proposed by Kuo, Lee and Liu see (IEEE Conference on Fuzzy Systems, p.1069-74, 1997). The proposed method overcomes the drawbacks of the conventional gradient methods for edge detection such as Prewitt and Sobel methods. It automatically obtains four threshold values, and apply fuzzy reasoning for edge enhancement. The edges extracted by this method are very clear and provides better representation for image edges and object contours.

Adaptive image interpolation based on local activity levels

In this paper, an adaptive warped distance method is suggested for image interpolation. This method depends on modifying the warped distance technique for image interpolation taking into consideration the level of activity in local regions of the image. This is performed by weighting the pixels used in the interpolation process with different adaptive weights. The adaptation can be extended to different traditional interpolation techniques such as bilinear, bicubic and cubic spline techniques as well as to the warped distance technique. Results show that the adaptive weighting of pixels in interpolation gives better results than that obtained using traditional interpolation methods only or by using the warped distance technique.

Performance evaluation of OFDM and single-carrier systems using frequency domain equalization and phase modulation

In this paper, we study the performance of the continuous phase modulation (CPM)-based orthogonal frequency division multiplexing (CPM-OFDM) system. Also, we propose a CPM-based single-carrier frequency domain equalization (CPM-SC-FDE) structure for broadband wireless communication systems. The proposed structure combines the advantages of the low complexity of SC-FDE, in addition to exploiting the channel frequency diversity and the power efficiency of CPM. Both the CPM-OFDM system and the proposed system are implemented with FDE to avoid the complexity of the equalization. Two types of frequency domain equalizers are considered and compared for performance evaluation of both systems; the zero forcing (ZF) equalizer and the minimum mean square error (MMSE) equalizer. Simulation experiments are performed for a variety of multipath fading channels. Simulation results show that the performance of the CPM-based systems with multipath fading is better than their performance with single path fading. The performance over a multipath channel is at least 5 and 12 dB better than the performance over a single path channel, for the CPM-OFDM system and the proposed CPM-SC-FDE system, respectively. The results also show that, when CPM is utilized in SC-FDE systems, they can outperform CPM-OFDM systems by about 5 dB. Copyright

Matched swept-frequency digital modulation for binary signaling in inhomogeneous dispersive media

A digital modulation technique which is most suitable for binary signaling through inhomogeneous dispersive media is introduced. Space-time rays are used to synthesize frequency-modulated input pulses that are either compressed in the medium with enhanced output or dispersed in the medium with widely spread output. The synthesized binary signals are shown to be in the form of swept-frequency signals which are matched to the dispersive properties of the medium. For media with quadratic phase functions, or under narrow-band conditions, the matched binary signals are linearly frequency modulated (chirp) with sweep rates that are related to the medium dispersion. The medium response to the matched chirp-modulated signals is investigated in detail. Conditions for the enhancement of the performance of the proposed modulation technique due to the available bandwidth are also discussed.

Peak-to-average power ratio reduction in space-time block coded multi-input multi-output orthogonal frequency division multiplexing systems using a small overhead selective mapping scheme

The selective mapping (SLM) scheme is one of the most popular peak-to-average power ratio (PAPR) reduction techniques proposed for multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. One of the major disadvantages of this scheme is the need for the transmission of side information (SI) bits to enable the receiver to recover the transmitted data. The authors present a small overhead SLM (s-SLM) scheme for space-time block coded (STBC) MIMO-OFDM systems. This proposed scheme improves the system bandwidth efficiency and achieves a significantly lower bit error rate (BER) than the individual SLM (i-SLM) and direct SLM (d-SLM) schemes. In addition, approximate expressions for the complementary cumulative distribution function (CCDF) of the PAPR and the average BER of the proposed s-SLM scheme are derived. The simulation results show that the proposed s-SLM scheme improves the detection probability of the SI bits and hence gives a better performance than the i-SLM and the d-SLM schemes.

Optimization of image interpolation as an inverse problem using the LMMSE algorithm

In this paper, a linear minimum mean square error (LMMSE) solution to the image interpolation problem is presented. The image interpolation problem is treated as an inverse problem considering the mathematical model by which a low resolution image is obtained from a high resolution image. In the suggested LMMSE (optimum) image interpolation algorithm, three main problems are encountered and solved. The autocorrelation matrix of the high resolution image is required prior to the interpolation process. This matrix is approximated from a polynomial based interpolated image and the sensitivity of the LMMSE solution to the estimation of the autocorrelation matrix is studied. Another problem is the noise variance estimation of the low resolution image. The sensitivity of the LMMSE solution to the noise variance estimation is also studied. The third problem is the large dimension matrix inversion process required for evaluating the high resolution image. This problem is solved by approximating the matrix to be inverted by a sparse matrix. Results show that the suggested solution is superior to polynomial based image interpolation algorithms from the mean square error (MSE) point of view. It is also efficient from the computational complexity point of view.

Fuzzy edge detection with minimum fuzzy entropy criterion

In this paper, a new fuzzy logic-based edge detection technique is proposed, in which the drawbacks of the conventional gradient-based techniques are efficiently overcome. Using the relation of the probability partition and the fuzzy 2-partition of the image gradient, the best gradient-threshold is automatically and efficiently selected. The selection algorithm is based on the condition for the entropy to reach a minimum value, since our aim is to find the best compact image representation through edges. The excellent performance of the proposed technique is exercisable through simulation results on a set of test images. It is shown how the extracted, enhanced and purified edges provide an efficient edge-representation of images.