This chapter contains sections titled: Overview MAC convergence sublayer MAC common part sublayer MAC security sublayer MAC enhancements for 2-11 GHz operation IEEE 802.16 physical layers Coexistence BWA business and technology trends

Air Interface for Fixed Broadband Wireless Access Systems

The sections in this article are


1
Radiometers

2
Radar Scattering

3
Radar Scatterometers

4
Radar Altimeters

5
Ground-Penetrating Radars

6
Imaging Radars

7
Real-Aperture Radars

8
Synthetic-Aperture Radars

Microwave Remote Sensing

Because of its simplicity, the empirical relation A = aR^{b} between the specific attenuation A and the rainrate R is often used in the calculation of rain attenuation statistics. Values for the frequency-dependent parameters a and b are available, however, for only a limited number of frequencies. Some of these values, furthermore, were obtained experimentally, and may contain errors due to limitations in the experimental techniques employed. The aR^{b} relation is shown to be an approximation to a more general relation, except in the low-frequency and optical limits. Because the approximation is a good one, however, a comprehensive and self-consistent set of values for a and b is presented in both tabular and graphical form for the frequency range f = 1-1000 GHz. These values were computed by applying logarithmic regression to Mie scattering calculations. The dropsize distributions of Laws and Parsons, Marshall and Palmer, and Joss et al., were employed to provide calculations applicable to "widespread" and "convective" rain. Empirical equations for some of the curves of a(f) and b(f) are presented for use in systems studies requiring calculations at many frequencies. Some comparison is also made with experimental results, and suggestions are given regarding application of the various calculations.

The aR b relation in the calculation of rain attenuation

The techniques and technologies currently being investigated to detect weapons and contraband concealed on persons under clothing are reviewed. The basic phenomenology of the atmosphere and materials that must be understood in order to realize such a system are discussed. The component issues and architectural designs needed to realize systems are outlined. Some conclusions with respect to further technology developments are presented.

Standoff Detection of Weapons and Contraband in the 100 GHz to 1 THz Region

Empirical propagation models have found favour in both research and industrial communities owing to their speed of execution and their limited reliance on detailed knowledge of the terrain. Although the study of empirical propagation models for mobile channels has been exhaustive, their applicability for FWA systems is yet to be properly validated. Among the contenders, the ECC-33 model, the Stanford University Interim (SUI) models, and the COST-231 Hata model show the most promise. In this paper, a comprehensive set of propagation measurements taken at 3.5 GHz in Cambridge, UK is used to validate the applicability of the three models mentioned previously for rural, suburban and urban environments. The results show that in general the SUI and the COST-231 Hata model over-predict the path loss in all environments. The ECC-33 models shows the best results, especially in urban environments.

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Comparison of empirical propagation path loss models for fixed wireless access systems

A new model is presented for the prediction of attenuation by rain on either terrestrial or slant earth-to-space propagation paths. The model was developed using geophysical observations of the statistics of point rain rate, of the horizontal structure of rainfall, and of the vertical temperature structure of the atmosphere. The model was tested by comparison with attenuation distribution observations. The results show excellent agreement; the observations differ from model predictions by less than the rms deviations predicted by the model.

Prediction of Attenuation by Rain

Effects of Rain. Rain Structure and Rain--Rate Statistics. Rain--Rate Climate Models. Modeling Attenuation by Rain. Attenuation Mitigation via Diversity. Worst--Month Statistics. Estimating Risk. References. Appendix. Index.

Electromagnetic Wave Propagation Through Rain

PROPAGATION PHENOMENA AFFECTING WIRELESS SYSTEMS Types of Systems Design Criteria Antenna Considerations Propagation Effects Propagation Models Model Verification Statistics and Risk List of Symbols References PROPAGATION FUNDAMENTALS Maxwell's Equations Plane Waves Spherical Waves Reflection and Refraction Geometrical Optics Ray Tracing Scalar Diffraction Theory Geometrical Theory of Diffraction List of Symbols References ABSORPTION Molecular Absorption Absorption on a Slant Path ACTS Statistics List of Symbols References REFRACTION Ray Bending Path Delay Scintillation List of Symbols References ATTENUATION BY CLOUDS AND RAIN Rain Rain Attenuation Seasonal Rain Attenuation Statistics Fade Duration Fade Rate Rain Attenuation Models List of Symbols References APPENDICES INDEX Short TOC

Propagation Handbook for Wireless Communication System Design

The theories describing the effects of the troposphere on satellite communication systems operating in the microwave region are reviewed. The results of computations based upon the theories and atmospheric models are presented and compared with available experimental data. From the model computations it is seen that rain causes the major propagation problems for the frequency bands allocated to or proposed for allocation to the satellite communications service. Two effects are dominant: attenuation due to rainfall along the line-of-sight and interference between two systems operating at the same frequency and beyond each other's radio horizon due to rain scatter. The methods for calculating the magnitude of the effects of rain given the spatial distribution of rainfall intensity are available. The statistical data required for the prediction of the spatial distribution of rainfall intensity are not available.

Propagation phenomena affecting satellite communication systems operating in the centimeter and millimeter wavelength bands

The NASA advanced communications technology satellite (ACTS) propagation experiment was designed to observe the attenuation produced by rain on Earth-satellite paths operating in the Ka-band. Unwanted effects of water on the antenna reflector surface were noted. Wet-antenna attenuation could be attributed to the combined effect of a water layer on the reflector surface and water wetting the feed window surface. A model was developed to calculate the antenna reflector and feed surface water layer thickness values as a function of position on each surface. The thickness values were used to calculate the additional attenuation produced by the water layers as a function of rain rate on the antenna. The wet-antenna-attenuation prediction model was verified by sprayer tests. The goal of the ACTS propagation experiment was to obtain path attenuation statistics, statistics that represent the effects of rain on the Earth-satellite path but not on the antenna itself. The wet-antenna attenuation prediction model was used to remove the effects of water on the antenna from the combined antenna-plus-path attenuation statistics produced by the experiment. The overall efficacy of the model was demonstrated by comparing the corrected path loss statistics from two ACTS propagation experiment sites with earlier COMSTAR path loss measurements made at or near those sites. The empirical distribution functions from both the ACTS and COMSTAR experiments were identical within the expected uncertainty of an empirical annual distribution of attenuation by rain.

Robert K. Crane

Papers

Prediction of Attenuation by Rain

Electromagnetic Wave Propagation Through Rain

Propagation Handbook for Wireless Communication System Design

Propagation phenomena affecting satellite communication systems operating in the centimeter and millimeter wavelength bands

Analysis of the effects of water on the ACTS propagation terminal antenna