Hean-Teik Chuah

Multiuser detection for DS-CDMA systems using evolutionary programming

This article introduces a new multiuser detection scheme which uses evolutionary programming (EP) to detect the user bits based on the maximum-likelihood decision rule. The major advantage of the proposed detector is that it has a lower computational complexity compared to other popular evolutionary-algorithm-based detectors. The simulation results show that the EP has always converged to the optimum solution with a small number of generations. The simulated average computational time performance demonstrates that this approach achieves practical ML performance with polynomial complexity in the number of users.

CLASSIFICATION OF MULTI-TEMPORAL SAR IMAGES FOR RICE CROPS USING COMBINED ENTROPY DECOMPOSITION AND SUPPORT VECTOR MACHINE TECHNIQUE

This paper presents a combined Entropy Decomposition and Support Vector Machine (EDSVM) technique for Synthetic Aperture Radar (SAR) image classification with the application on rice monitoring. The objective of this paper is to assess the use of multi-temporal data for the supervised classification of rice planting area based on different schedules. Since adequate priori information is needed for this supervised classification, ground truth measurements of rice fields were conducted at Sungai Burung, Selangor, Malaysia for an entire season from the early vegetative stage of the plants to the ripening stage. The theoretical results of Radiative Transfer Theory based on the ground truth parameters are used to de. ne training sets of the different rice planting schedules in the feature space of Entropy Decomposition. The Support Vector Machine is then applied to the feature space to perform the image classification. The effectiveness of this algorithm is demonstrated using multi-temporal RADARSAT-1 data. The results are also used for comparison with the results based on information of training sets from the image using Maximum Likelihood technique, Entropy Decomposition technique and Support Vector Machine technique. The proposed method of EDSVM has shown to be useful in retrieving polarimetric information for each class and it gives a good separation between classes. It not only gives significant results on the classification, but also extends the application of Entropy Decomposition to cover multi-temporal data. Furthermore, the proposed method offers the ability to analyze single-polarized, multi-temporal data with the advantage of the unique features from the combined method of Entropy Decomposition and Support Vector Machine which previously only applicable to multi-polarized data. Classification based on theoretical modeling is also one of the key components in this proposed method where the results from the theoretical models can be applied as the input of the proposed method in order to de. ne the training sets.

Paddy Fields as Electrically Dense Media: Theoretical Modeling and Measurement Comparisons

Early models for paddy fields consist of a single-layered medium in which coherent effects within clusters of leaves are considered but multiple volume scattering is not. In this paper, the paddy canopy is modeled as a multilayered dense discrete random medium consisting of cylindrical and needle-shaped scatterers. Consideration is given to the coherent and near-field effects of the closely spaced scatterers through the Dense Medium Phase and Amplitude Correction Theory and Fresnel corrections, respectively, in the phase matrix. Then, this dense medium phase matrix is applied in the radiative transfer equations and solved up to the second order to consider double-volume scattering. Ground truth measurements of paddy fields were acquired at Sungai Burung, Selangor, Malaysia, for an entire season from the early vegetative stage of the plants to their reproductive stage. Measured parameters are used in the theoretical model to calculate the backscattering coefficients of paddy fields. Theoretical analysis of the simulation results shows in particular that second-order effects are important for cross-polarized backscatter data and that coherent effects need to be considered at lower frequencies. However, the use of needles to represent paddy leaves tends to underestimate the HH-polarized backscattering coefficients especially at the latter stages of plant growth, i.e., when the leaves are broader. The results are also used for comparisons with the backscattering coefficients obtained from RADARSAT images as well as that of earlier models to test the validity of the dense medium model with promising results.

A FINITE-DIFFERENCE TIME-DOMAIN (FDTD) SOFTWARE FOR SIMULATION OF PRINTED CIRCUIT BOARD (PCB) ASSEMBLY

This paper describes the design of a three-dimensional (3D) finite-difference time-domain (FDTD) simulation software for printed circuit board (PCB) modeling. The flow, the dynamics and important algorithms of the FDTD simulation engine will be shown. The software is developed using object-oriented programming (OOP) approach, to enable code reuse and ease of upgrade in future. The paper begins by looking at how a 3D PCB structure is created using cubes, and proceed to show the inclusion of various lumped components such as resistors, capacitor, inductor and active semiconductor components into the model. The architecture of the FDTD simulation program is then carefully explained. Finally a few sample simulation examples using the software will be illustrated at the end of the paper.

BER estimation of optical WDM RZ-DPSK systems through the differential phase Q

The optical return-to-zero differential phase-shift keying system is analyzed to determine the accuracy of the differential phase Q method in estimating the bit-error rate (BER). It is found that it consistently underestimates the BER though it successfully predicts the qualitative behavior of single-channel and wavelength-division-multiplexed systems for back-to-back and point-to-point configurations. A simple modification reduced the underestimation and produced accurate results.

TRANSMITTER AND RECEIVER DESIGN OF AN EXPERIMENTAL AIRBORNE SYNTHETIC APERTURE RADAR SENSOR

An Experimental Airborne Synthetic Aperture Radar (SAR) Sensor has been designed and,developed at Multimedia University, Malaysia. The airborne system is an inexpensive C-band, single polarization, linear-FM airborne radar sensor. An innovative cancellation network is implemented to overcome the poor isolation of the circulator thus allow a single antenna to be used for transmitting and receiving the radar signal. The system will be used for monitoring and management of earth resources such as paddy fields, oil palm plantation and soil surface. This paper highlights the design and development of the SAR transmitter and receiver, as well as the evaluation result of the sensor. Calibration has been performed in the laboratory to verify the performance of the radar sensor. External calibration is accomplished by using three artificial point targets, i.e., 12” conducting sphere, 4”×8” dihedral corner reflector and 8” trihedral corner reflector. The field measurements are conducted in an empty car park, which is a low reflection outdoor environment. Both range detection and radar cross section (RCS) measurement capability are verified in the field experiments.

A SAR Autofocus Algorithm Based on Particle Swarm Optimization

In synthetic aperture radar (SAR) processing, autofocus techniques are commonly used to improve SAR image quality by removing its residual phase errors after conventional motion compensation. This paper highlights a SAR autofocus algorithm based on particle swarm optimization (PSO). PSO is a population-based stochastic optimization technique based on the movement of swarms and inspired by social behavior of bird flocking or fish schooling. PSO has been successfully applied in many different application areas due to its robustness and simplicity (1-3). This paper presents a novel approach to solve the low-frequency high-order polynomial and high- frequency sinusoidal phase errors. The power-to-spreading noise ratio (PSR) and image entropy (IE) are used as the focal quality indicator to search for optimum solution. The algorithm is tested on both simulated two-dimensional point target and real SAR raw data from RADARSAT-1. The results show significant improvement in SAR image focus quality after the distorted SAR signal was compensated by the proposed algorithm.

Design of a Microstrip Patch Antenna Array for Airborne SAR Applications

A microstrip patch antenna array has been developed for a C-band airborne Synthetic Aperture Radar. The antenna operates at 6 GHz with a bandwidth of 168 MHz (SWR<1.5). It is a rectangular patch fed by a probe from a feed network placed behind the ground plane. A cost effective substrate with low dielectric constant and moderate loss is used for the patch and feed network. The antenna has an optimally shaped beam pattern (with a beamwidth of 24°) in the E-plane with the sidelobe suppressed by 15 dB. In the H-plane, a narrow beamwidth of 3° is designed with the sidelobes suppressed by 30 dB. The antenna achieved a gain of 21.2 dBi. A practical method to compensate for the losses in the feed distribution network is introduced.

A Comparison of Autofocus Algorithms for SAR Imagery

A challenge in SAR system development involves compensation for nonlinear motion errors of the sensor platform. The uncompensated along-track motions can cause a severe loss of geometry accuracy and degrade SAR image quality. Autofocus techniques improve image focus by removing a large part of phase errors present after conventional motion compensation. It refers to the computer-automated error estimation and subsequent removal of the phase errors. Many autofocus algorithms have been proposed over the years, ranging from quantitative measurement of residual errors to qualitative visual comparison. However, due to the fact that different data sets and motion errors were employed, it is difficult to perform comparative studies on various algorithms. This paper compares and discusses some practical autofocus algorithms by using a common data set. Standard focal quality metrics are defined to measure how well an image is focused. Their implementation schemes and performance are evaluated in the presence of various phase errors, which include polynomial-like, high frequency sinusoidal, and random phase noise.

Electromagnetic scattering from an electrically dense vegetation medium

A vegetation medium can generally be modeled as a discrete random medium where scatterers such as disks, needles, and cylinders are used to represent the leaves, branches, and trunks. At low frequency, it is possible that the spacing between the scatterers is comparable or smaller than the wavelength. This medium is considered electrically dense, and the coherence effect from the scatterers indicates that the assumption of independent scattering of the scatterers is no longer valid. In addition, in a dense vegetation medium where the scatterers are close to each other, near field interactions should also be considered. In this paper, the coherence effect from the various correlated scatterers is taken into account by introducing the array phase correction to the phase matrices of the scatterers. For the near field interaction effect, both the Fresnel phase correction and the amplitude correction are considered. The Fresnel phase correction is incorporated by including the higher order terms in the phase of the scattered field from a scatterer, whereas the amplitude correction is obtained from the near field amplitude term of the scattered field. These corrected phase matrices for the disks, needles, and branches are applied in the single layer random discrete medium where the second order iterative radiative transfer solutions are obtained. Theoretical analyses of the effects of these corrections to the backscattering returns for various volume fractions, frequencies, incident angles, orientations, and sizes are carried out. It is found that the array phase correction is important for an electrically dense medium, whereas the amplitude and the Fresnel phase corrections are required when the frequency increases and enters into the Fresnel region. Good agreements are obtained from the comparisons of the theoretical predictions with the multifrequency and multipolarization measurement results of the Japanese cypress and boreal forest.