MODELING OF WIRELESS CHANNEL

Abstract

With the speedy development of wireless mobile communication, the dimensions of a cell are changing into smaller, and also the design of the mobile system needs information about transmission over certain sites. An electromagnetic wave propagation model needs to detect a wireless system. In the last few decades, several statistical and deterministic channel models have been planned in small urban areas. Compared to a statistical channel model, a deterministic channel model can solve specific, real-life situations. Considering the design of the future communication system, the Ultra wideband (UWB) system will be one of the most important application features in wireless communication, and its scenario is very complex and flexible. It is hard for general statistical channel models to differentiate these variations, making it difficult to obtain an accurate model. Currently, radio broadcasts are simulated to obtain the specific channel features of a specific situation in a determination channel model. The deterministic channel model has maintained its acceptance among scholars for a long time. In particular, uniform theory of diffraction (UTD) based approaches are still being considered even if the surrounding is complex. The subsequent subsections will acquaint the reader with the outline of contributions created during this thesis. In this study, some new time-domain (TD) solutions are proposed for non-perfectly conducting wedges. A new TD solution for single diffraction is proposed where the incident pulse illuminates one or both sides of the dielectric wedge with unlike wedge angles. Thereafter, a TD solution for double diffraction is proposed that works to all possible illumination regions of wedges. The reflection angles and reflection coefficients are modified in different wedge regions. Thereafter, a TD solution is proposed for higher-order diffraction using a single diffraction coefficient. It looks at all possible variations between the dual wedges. This technique can be applied for more than two wedges that consider all the diffraction orders. Following this, the coefficients of Uniform Theory of xvii Diffraction (UTD) coefficients in TD are proposed to be considered for transmission and diffraction phenomena from the thin dielectric wedge. Finally, novel coefficients are proposed for frequency- domain (FD) and TD. The frequency-domain Uniform Theory of Diffraction (FD-UTD) coefficient was shown to be accurate in all the regions with a thin lossy wedge. It allows the calculation of the transmitted ray by a dielectric wedge by inserting two more terms into the four-terms FD-UTD coefficient. This six-terms FD-UTD coefficient is confirmed by the available finite difference time domain (FDTD) technique. In the deep shadow region between the incident shadow boundary (ISB) and the transmitted shadow boundary (TSB), where only diffracted ray exists, the proposed FD solutions give a 14 percent improvement over the previous technique on average. Next, the doubly diffracted field by the slope diffraction coefficient behind the double wedge structure and a high lossy building is also presented. Also, the coefficient of the novel time-domain Uniform Theory of Diffraction (TD-UTD) was presented based on the inverse Laplace transform of the proposed FD solutions. Different input pulses and wedge materials have been used to test the full functionality of the proposed TD techniques. TD-UTD results are confirmed by inverse fast Fourier transform of frequency domain (IFFT-FD) results, and excellent agreements have been reported. An impulse response has also been introduced to explain the distortion of the pulse in various conditions. Finally, the TD-UTD procedure is shown to be more effective than the IFFT-FD method.