Spatial antenna diversity has been important in improving the radio link between wireless users. Historically, microscopic antenna diversity has been used to reduce the fading seen by a radio receiver, whereas macroscopic diversity provides multiple listening posts to ensure that mobile communication links remain intact over a wide geographic area. In later years, the concepts of spatial diversity have been expanded to build foundations for emerging technologies, such as smart (adaptive) antennas and position location systems. Smart antennas hold great promise for increasing the capacity of wireless communications because they radiate and receive energy only in the intended directions, thereby greatly reducing interference. To properly design, analyze, and implement smart antennas and to exploit spatial processing in emerging wireless systems, accurate radio channel models that incorporate spatial characteristics are necessary. In this tutorial, we review the key concepts in spatial channel modeling and present emerging approaches. We also review the research issues in developing and using spatial channel models for adaptive antennas.

/pdf/overview-of-spatial-channel-models-for-antenna-array-3ucqde59u0.pdf

Overview of spatial channel models for antenna array communication systems

The paper describes a geometrical optics based model to predict propagation within buildings for personal communication system (PCS) design. A ray tracing model for predicting propagation based on a building blueprint representation is presented for a transmitter and receiver located on the same floor inside a building. Measured and predicted propagation data are presented as power delay profiles that contain the amplitude and arrival time of individual multipath components. Measured and predicted power delay profiles are compared on a location-by-location basis to provide both a qualitative and a quantitative measure of the model accuracy. The concept of effective building material properties is developed, and the effective building material properties are derived for two dissimilar buildings based upon comparison of measured and predicted power delay profiles. Time delay comparison shows that the amplitudes of many significant multipath components are accurately predicted by this model. Path loss between a transmitter and receiver is predicted with a standard deviation of less than 5 dB over 45 locations in two different buildings. >

/pdf/site-specific-propagation-prediction-for-wireless-in-44jped9gi6.pdf

Site-specific propagation prediction for wireless in-building personal communication system design

Propagation characteristics of radio signals in the UHF band place fundamental limits on the design and performance of wireless personal communications systems, such as cellular mobile radio (CMR), wireless LANs, and personal communication services (PCS). Because the radio link is direct to each subscriber, the prediction of signal characteristics is most important in urban areas where subscriber density is high, and the buildings have a profound influence on the propagation. The paper starts by reviewing the characteristic signal variations observed in CMR systems employing high base station antennas to cover macrocells having radius out to 20 km. Theoretical models incorporating diffraction are shown to explain the observed range dependence and shadow loss statistics. For the low base station antennas envisioned to cover microcells of radius out to 1 km for PCS applications, signal propagation is more strongly dependent on the building environment and on the location of the antennas in relation to the buildings. Various levels of theoretical modeling of this dependence are discussed in conjunction with measurements made in various building environments. Finally, the paper discusses advances in site specific prediction for outdoor and indoor propagation. >

UHF propagation prediction for wireless personal communications

The growth of radio communication services has stimulated interest in ray propagation modeling, particularly in urban areas. The main drawback of these methods is lengthy computation time due to three-dimensional (3-D) space analysis. The model geometrical ray implementation for mobile propagation modeling (GRIMM) presented here splits the 3-D ray construction problem into two successive two-dimensional (2-D) stages without loss of generality compared with brute-force 3-D ray methods. The gain in time and simplicity enables consideration of large areas typical of a cellular environment. The reflections and diffractions (vertical or horizontal) are taken in any order, and their number can be taken large enough to meet convergence. After the description of the model, the results of simulation are compared with a set of 1465 mean power-delay profiles measured over a 30-MHz band at 900 MHz in a cellular environment for mobile positions almost uniformly spread within a 3-km radius from the base station. The model is shown to be very accurate for path-loss prediction with a mean error of about 1 dB and a standard deviation lower than 5 dB. The wide-band evaluation was performed on the delay spread (DS). This parameter was correctly predicted in about 75% of cases.

A mixed ray launching/tracing method for full 3-D UHF propagation modeling and comparison with wide-band measurements

In this paper, the effects of antenna pattern and antenna polarization on indoor obstructed (OBS) wireless channels are investigated experimentally. Our results show that linearly polarized (LP) directional antennas are more effective in combating multipath components than other types of antennas in OBS channels. The measurement results are verified with a deterministic wide-band propagation model based on image theory that takes into account the effects of building geometry, antenna pattern, and antenna polarization. Preliminary prediction results show that the propagation model holds promise for accurate and efficient in-building wireless channel prediction.

http://faculty.poly.edu/~tsr/wp-content/uploads/CV/MTJ/1994-01-Antenna%20effects%20on%20indoor%20obstructed%20wireless%20channels%20and%20a%20deterministic%20image-based%20wide-band%20propagation%20model%20for%20in-building%20personal%20communication%20systems.pdf

Antenna Effects on Indoor Obstructed Wireless Channels and a Deterministic Image-Based Wide-Band Propagation Model for In-Building Personal Communication Systems

A ray-tracing model involving multiple reflections and diffractions is proposed to predict wideband decimetric radio wave propagation in an urban area. A computer code was developed in which only buildings close to the vehicle are considered. Wall irregularities and electromagnetic properties of material are taken into account by a constant reflection factor, while diffraction attenuation is computed from geometrical theory of diffraction results. Simulated channel path losses and complex impulse responses are compared with some measurements performed in Paris at a 900-MHz central frequency.

J.-P. Rossi

Papers

A ray model for decimetric radiowave propagation in an urban area