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Three-dimensional (3-D) ray-tracing and analysis is used to characterize the path angles in a rectangular building in which all interior walls are parallel or perpendicular to the exterior walls. Path angles are recorded for 500 random transmitter and receiver locations, maintaining constant range throughout a particular building model. The main contribution of this paper is the observation that when all of the path angles from all 500 trials are measured relative to one building wall and collectively analyzed in a signal strength distribution, clustering is clearly apparent. While this angle clustering in the ensemble of channels is not the same as clustering in a single channel trial, it may partially account for the clusters observed in single trials. As a practical matter, these results may impact the use and placement of directional antennas for wireless LANs in buildings of this type. Index Terms--Indoor radio communication, local area networks, multipath channels, propagation.

A study on the use of post-processing in video compression proposes a novel, postprocessing algorithm to enhance the visual quality of low bit-rate, MC-block-discrete cosine transform-based image and video compression systems. The algorithm minimizes the unwanted blocking effects and mosquito noise artifacts while maintaining image sharpness and naturalness. It is relatively simple yet performs quite well in different situations.

A postprocessing algorithm that enhances video picture quality adapts itself to pixel characteristics in a video sequence to filter out noise and preserve image detail. The system puts video signals into different classes and uses separate nonlinear filters matched to each class. The most general version of the algorithm uses motion-compensated frame averaging to improve picture quality. A suboptimal, spatial version of the adaptive postfilter enhances picture quality in a 384 kbps 3-D subband coder.

A three-dimensional spatio-temporal subband decomposition method developed for video coding functions by arranging the image sequence into various spatio-temporal frequency bands and then separating the information into spatio-temporal subbands. The method yields a 1-Mbps coder using an adaptive differential pulse code modulation scheme and adaptive bit allocation. A new vector quantization scheme is suitable for data in higher frequency bands.