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NSMA Annual Meeting May 22-23, 2001 - Arlington, VA Propagation Panel

NSMA Annual Meeting May 22-23, 2001 - Arlington, VA Propagation Panel Rain Cell Modeling and Correlation of Radio Path Fading Application To Prediction Of Interference Degradation A Review Robert Ferguson WorldCom (972)729-5129 Robert.Ferguson@wcom.com. Overview of This Presentation

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NSMA Annual Meeting May 22-23, 2001 - Arlington, VA Propagation Panel

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  1. NSMA Annual Meeting May 22-23, 2001 - Arlington, VA Propagation Panel Rain Cell Modeling and Correlation of Radio Path Fading Application To Prediction Of Interference Degradation A Review Robert Ferguson WorldCom (972)729-5129 Robert.Ferguson@wcom.com

  2. Overview of This Presentation The Problem Summary of the Rain Cell Model Computer Simulation Technique Fade Correlation Results - Format and Usage Discussion and Conclusion Addendum This report is a condensed version of three previous presentations given at NSMA (WG-23) meetings. Contact Robert Ferguson at Robert.Ferguson@wcom.com or (972)729-5129 for more details.

  3. The Problem: In the mm-wave bands, rain fade is the dominant outage mechanism on the typical path. During significant rain events, when the full fade margin of the desired path is needed, interfering paths are also often faded due to rain -- at least to some extent. Traditional methods of setting interference criteria, which assume a constant level of interference, are conservative. (Simultaneous fading on the desired and interfering paths is not considered.) Can the correlation of fading on desired/interfering paths be quantified and more appropriate interference criteria be developed ?

  4. Example Interference Path Geometries - Rain Fade Correlation(Correlation Depends on Angles and Distances) Q Site B R P Receive Site A A deep rain fade at Site A (from B) will coincide with: A deep fade on Path Q, less likely a fade on Path R, still less likely a fade on Path P But, a complete analysis depends on path lengths and rain cell geometry (shape / /extent), intensity and likelihood

  5. Example: Interference Path Geometry - Rain Fade CorrelationDoes Fade Correlation Reduce Apparent Harmful Interference ? (Angles and distances, rain cell characteristics must be considered) Q R Cell 2 P Cell 1 Receive Site A • Degree of correlation depends on path and critical rain cell dimensions • If Cell 1 is typical, high correlation of fading at A with paths P, Q, R • If Cell 2 is typical, correlation of fading at A with paths P, R will be less

  6. The Need to Integrate System Geometry and Rain Cell Modeling Without consideration of the long term patterns of rain cell shape, intensity, and likelihood in a locale, interference effects may be evaluated inaccurately. If details of the primary fading mechanism (rain attenuation) of millimeter wave systems are ignored, the tendency is to over estimate the degradation of intrasystem/intersystem interference. Integration of rain cell modeling (for a given locale) with proposed system layouts may provide a worthwhile improvement in traditional design evaluation techniques. How is rain cell modeling implemented ? First you need a model ...

  7. Rain Cell Modeling OverviewBased on Capsoni Model, Radio Science Volume 22, Number 3, Pages 387-404, May-June 1987 • A “Rain Cell” is defined as connected region where the rain intensity (mm/hr) exceeds a given threshold • Rain cells have intensity and spatial characteristics which have been statistically modeled based on experimental data collected using meteorological radar • In the Capsoni Model, an elliptical rain cell is specified by: • Peak rain rate (mm/hr) - Rm - at cell center • Elliptical cell axial ratio = Minor Axis/Major Axis • Orientation of ellipse (“tilt”) w.r.t. coordinate system • Characteristic radius at which intensity falls by 1/e of Rm • The Capsoni Model specifies a cell “1/e radius” statistical distribution for an assumed cell peak rain rate; on average, higher peak rate rain cells have smaller “1/e radii”

  8. Rain Cell Modeling Overview - continuedBased on Capsoni Model, Radio Science Volume 22, Number 3, Pages 387-404, May-June 1987 • Intuitively, rain cell statistical characteristics are related to the point rain rate cumulative time distributions specified by the Crane and ITU rain zone classification systems • Capsoni, et al, describe a methodology to convert the point rainfall rate rate time distribution data to the statistical factors necessary to complete a rain cell model which can reproduce the assumed point rainfall rate statistics • This model can be used to evaluate the rain fade correlation effects on example desired/interfering path geometries

  9. Elliptical Rain Cell Model GeometryCell Defined by Rm (Peak Rain Rate mm/hr) and rho_x, rho_y Minor Axis (0.0, rho_y) (1/e * Rm) Rain Rate Isopleth (rho_x, 0.0) Major Axis Intensity falls off to infinity R = Rm * exp (-sqrt( xf*xf + yf*yf)) where: xf = x/rho_x and yf = y/rho_y By definition, at (rho_x,0.0), R = 1/e * Rm at (0.0,rho_y), R = 1/e * Rm Cell Axial Ratio = Minor Axis/Major Axis (on any rain rate isopleth) = rho_y/rho_x< 1.0 9

  10. Rain Cell Ellipse Major Axis “Split Geometry” Illustration(Proposed Modification To Model For Interference Analysis)Model Ellipse Extends to Infinity on One Side of Major Axis (“1/e” Radius Shown) y2 100 mm/hr Isopleth y1 x2 Major Axis x1 Assume only one portion of the split rain cell is “active” If rain at origin, also at x1 and y1 If NO rain at origin, rain at x2 and y2 As drawn, Minor/Major Axis Ratio = ~ 0.5

  11. Rain Rate Simulation - Random Factors Follow Model StatisticsFade Correlation Statistics Are Accumulated As Simulation Runs Simulation Radius Generate random rain cells, following rain zone statistics, within Simulation Radius Desired Path Random Cells Factors: Peak Rain Rate - Rm Cell Radius - rho Location of cell center Axial Ratio Major Axis Tilt Angle Cell Split Criteria Interfering Path Simulation should reproduce the point rain rate statistics assumed 11

  12. Desired / Interfering Path Fading Time MatrixDescribes Joint Fade Probability, Thus “Fade Correlation” Interfering Path Fade Increments - In dB 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 >15.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 … >40.0 Note: The Sum of All Times In The Matrix Represents All Joint Fading Conditions Desired Path Fade Increments - In dB Note: One matrix would apply to a specific desired and interfering path geometry and rain zone Entry Indicates Percentage of Time That: D-Path Is In Fade Between 9.0 dB and 10.0 dB AND I-Path Is In Fade Between 5.0 dB and 6.0 dB

  13. Example Desired / Interfering Path Fading Time MatrixEntire Matrix Describes Likelihood of All Joint Fade Conditions(Incremental “Buckets” Are 1 dB) Desired Path _ Cumulative Fade Time Below ___________ 4.05049 % 0.70138 0.45177 0.34129 0.27644 0.23020 0.19616 0.16879 0.14638 0.12799 0.11219 0.09916 0.08807 0.07864 0.07014 0.06262 0.03670 Incremental D-Path Fade Time Fade Below ______ __________ 0 dB 3.34911 % 1 0.24961 2 0.11048 3 0.06484 4 0.04625 5 0.03404 6 0.02737 7 0.02241 8 0.01839 9 0.01581 10 0.01302 11 0.01109 12 0.00943 13 0.00850 14 0.00752 15 0.00646 20 0.00349 ... Interfering Path Fade - 1 dB Increment _ 0 dB1 dB2 dB3 dB4 dB5 dB6 dB7 dB8 dB9 dB … Time D-Path Fade > 6 dB 0.0044 0.0113 0.0072 0.0025 0.0009 0.0003 … Time Contribution (%) D-Path Fade 6 to 7 dB, I-Path Fade 3 to 4 dB = 0.0025% Sum of All I-Path Fade Times With D-Path Fade of 6 to 7 dB = 0.02737% Robert Ferguson - WorldCom Robert.Ferguson@wcom.com (972)729-5129

  14. Desired / Interfering Path Fading Time Matrix- UsageIllustration of Interference Adjusted Outage Calculation Interfering Path Fade Increments - In dB 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 >15.0 0.0 1.0 2.0 3.0 4.0 5.0 ... 21.0 22.0 23.0 24.0 25.0 26.0… >40.0 Solid Line Represents (Schematically) Altered Fade Margin Threshold Due To Interference; With No Fade On I-Path, Degradation is 26.0 - 24.0 dB = 2.0 dB As I-Path Fades, Degradation Decreases Desired Path Fade Increments - In dB Sum of Incremental Times Below Solid Line Gives Time Below I-Adjusted Threshold, Or Outage Time Sum of All Incremental Time Entries Below 26 dB Represent “Time Faded Below” 26 dB Percentage - Assumed No-I Threshold of Desired Path Robert Ferguson - WorldCom Robert.Ferguson@wcom.com (972)729-5129

  15. Possible Data Exchange Flow - Breakpoints (For Discussion Only) Verify Accuracy Simulation Program Fading Matrices Database Data Reduction Program Simulation Parameters Processed Data Design Programs Common Access Functions Robert Ferguson - WorldCom Robert.Ferguson@wcom.com (972)729-5129

  16. Discussion and Conclusion Discussion Does The Problem Need To Be Solved ? Is “Standardization” of A Process Realistic ? Intra-Company Vs. Inter-Company Usage Interference Criteria - Time or dB or ? IEEE 802.16 / NSMA ? Next Steps Conclusion Robert Ferguson - WorldCom Robert.Ferguson@wcom.com (972)729-5129

  17. Addendum

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