Optical wireless communication has the potential for extremely high data rates of up to tens of Gb/s. In this study, a hybrid modulation technique named adaptive differential amplitude pulse-position modulation (DAPPM) is proposed to improve channel immunity by utilising optimised modulation to channel. The unit transmission rate, channel capacity, peak-to-average power ratio, bandwidth requirement and power requirement of the DAPPM were determined and compared with other modulation schemes such as on-off key, pulse-amplitude modulation, pulse-position modulation (PPM), differential PPM and multilevel digital pulse interval modulation. The simulation results show that DAPPM gives better bandwidth and power efficiency depending on the number of amplitude level (A) and the maximum length (L) of a symbol. In addition, the fuzzy logic module is developed to assist the adaptation process of DAPPM. Mamdani fuzzy logic method is used in which the decisions made by the system will be approaching to what would be decided by the user in the real world.
Abstract-In this paper, B 2 -spline interpolation technique for Overset Grid Generation and FiniteDifference Time-Domain (OGG-FDTD) method was developed. B 2 -spline or biquadratic spline interpolation offers better accuracy than bilinear interpolation. Two-dimensional (2D) numerical simulations were carried out for electromagnetic (EM) field analysis to measure the scattered fields for an unknown object in free space and dielectric medium. In this work, two antennas were utilised as transmitter and receiver sequentially to transmit microwave pulses and collect the scattered fields for an unknown object in OGG-FDTD lattice. In order to analyse the stability and efficiency of the proposed method, the scattered fields for the unknown object were investigated with error analysis. The results showed that the OGG-FDTD method with B 2 -spline interpolation gave lower relative error than bilinear interpolation with 0.0009% of difference in free space, 0.0033% of difference in Case A dielectric medium, 0.236% of difference in Case B dielectric medium, and 0.003% of difference in Case C dielectric medium. Besides, the Mean Square Error (MSE) for the OGG-FDTD method with B 2 -spline interpolation was also lower than the bilinear interpolation. Hence, it proves that the OGG-FDTD method with B 2 -spline interpolation has the ability to measure the scattered fields around an unknown object accurately. For future work, the proposed method can be applied to inverse scattering to detect and reconstruct buried objects with arbitrary shapes in a complex media.
Active microwave imaging (MI) technique has been recently recommended as a new technology for early detection of malignant breast tumours. Finite-difference Time-domain (FDTD) method is an effective numerical tool for computational electrodynamics modelling. However, the main drawback of the FDTD method is difficult to model the curved boundaries and small features of arbitrary shaped fibroglandular region due to its restriction to inherent orthogonal grids. To address this issue, Chimera Overset Grid (COG) method with spline interpolation in Forward-Backward Time-Stepping (FBTS) inverse scattering technique was proposed to overcome the limitation of FDTD method. In order to analyse the accuracy of this new method to detect a malignancy tumour embedded in different classes of breast parenchymal density, the homogeneous mostly fatty breast and extremely dense breast were chosen as Case A, and Case B, respectively. The Mean Squared Error (MSE) and normalised cost error functional for reconstructed dielectric profiles utilising the proposed method achieved significantly lower values than the FDTD method in FBTS inverse scattering. The results indicated that the proposed method could accurately identify malignancy tumour location and reconstruct the breast composition in dielectric profiles.
Microwave imaging system is classified as non-invasive, simple to perform and inexpensive compared to MRI and X-Ray machine. Therefore, the novel idea of this research work is to develop a Chimera Grid Scheme (CGS) incorporate with the microwave inverse scattering technique in a low cost, non-ionising and safe short-range. The CGS with spline interpolation in Forward Backward Time-Stepping (FBTS) inversion technique can determined an accurate result especially for the biological anomalies like breast tumours at an early curable stage due to the high electrical properties contrast between malignant cells and normal cells. The findings showed that the proposed method successfully detected and reconstructed the breast structure in relative permittivity profiles. The quantitative information of reconstructed images, such as location, shape, size and internal composition also can be obtained. Furthermore, the normalised functional error for proposed method was also lower than the FDTD method in FBTS. At 150th iteration, the difference of normalised functional error between these two methods was 1.74 × 10−5. The result shows that the CGS method in FBTS inversion technique would reconstruct breast composition more precisely.
Retina and its vascular network have unique branching characteristics morphology. The abnormalities in the vascular pattern of the retina, such as vessel shape, branching pattern, width, tortuosity, or the appearance of retinal itself, may be associated with the occurrence of retinopathy or cardiovascular diseases. This paper is focus on the development of an algorithm to measure bifurcation angle of the retinal for image analysis. From survey, there is still lack of automation for bifurcation angle measurement. Thus this initial work investigates and proposes the key steps for bifurcation measurement process. The key steps of the proposed method include segmentation of the region of interest (ROI), tracing the vessels that are needed for angle determination and lastly determine the bifurcation angle by using the dot product of the traced boundaries. The results are compared with the manual measurement of the bifurcation angle using quantitative and qualitative measurement. The experimental results show promising result of the proposed method in automating the measurement of bifurcation angle of retinal. Recommendation for room of improvement is also discussed in the paper.
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