Study on Analysis of Multipath Propagation for Indoor Radio Digital Communications

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The idea of implementing indoor radio communication systems is so attractive because of high mobility and no trouble in wiring. However, indoor radio multipath propagation environments limit the design of these systems. Therefore, this project of research is concerned with clarifying the characteristics of indoor radio propagation. For this pupose, it is most effective to estimate the directions of arrival and delay times of multipath waves. So far, we proposed and developed a method of estimating the directions of arrival and delay times. This method utilized the MUSIC or ESPRIT algorithms which are spectrum analysis techniques with high resolution property. During 1992 and 1993, we continued to improve the estimation method through computer simulation and indoor experiments. The results obtained are described below.1. First, we proposed a method of simultaneously estimating both the directions of arrival and delay times of multipath waves. The great advantage of this method is that w … More e can easily identify the propagation paths of incident waves based on the estimation results. In addition to computer simulation, we carried out experiments in a limited region. From the estimation results, we recongnized 5 to 10 significant waves, the directions of which are almost uniformly distributed in space and also the delay times of which are less than 50 ns. These results demonstrated the indoor radio environments are much complicated. Thus, we confirmed that diversity reception, especially the directivity diversity, is much effective for indoor radio communication systems under multipath propagation environments.2. The proposed method has great capability of classifying the multipath waves in terms of directions of arrival and propagation delay times. For the arriving waves with the low signal-to-noise ratio (SNR), however, it has some errors in the estimates of delay times and directions of arrival. Therefore, we further presented a technique of applying an adaptive(optimum) filtering to the MUSIC or ESPRIT estimator to enhance the estimation accuracy. The principle of our adaptive filtering is based on the directionally constrained adaptive array. Via computer simulation, we showed that the presented algorithm is more effective in multipath environments of the low SNR. Less