Multipath propagation models for near line-of-sight conditions

摘要

This thesis analyzes the behaviour of a multipath channel for suburban and semi-rural areas in which line of sight (LOS) or near LOS exists between the transmitter and receiver. The objective is to characterize the broadband channel for such areas. The thesis is divided into five major parts: a background and literature survey, a theoretical analysis, experimental measurements which validate the analysis, applications to practical communication channels and a study of the effects of such a channel on typical signal waveforms.ududThe amplitudes and delay spread of a multipath model for such an environment are studied, based on a theoretical analysis of scattering from finite flat surfaces which model building walls. A broadband channel model is proposed based on the analysis. The next part of the thesis presents experimental measurements on multipath communication channels in suburban and semi-rural areas, which have LOS or near LOS propagation. The results validate the theoretical analysis. It is found that the channel is either good or very bad. The latter usually occurs close to buildings where a single dominant reflection with a relative delay of less than a microsecond produces a periodic severe fading and distortion of the signal, often making a link unusable. The area for which the channel is bad depends on the size of the building.ududThe thesis then considers applications of the broadband channel model and studies the effects of the proposed channel model on typical communication waveforms such as QPSK, direct sequence spread spectrum and OFDM. For the QPSK waveform, the effects of a single dominant reflection on the timing and carrier recovery of a coherent demodulator are studied. A methodology is also outlined for determining which locations in a defined area will show the behaviour associated with a bad channel.