© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY1 XII. Site Specific Predictions Using Ray Methods General considerations Ray tracing using.

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY1 XII. Site Specific Predictions Using Ray Methods General considerations Ray tracing using 2D building database Ray tracing from a 3D building database Slant plane / vertical plane method Full 3D method Vertical lane Launch (VPL) method Ray tracing for indoor predictions Using ray methods to predict statistics of delay and angle spread

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY2 Goals and Motivation Goal –Make propagation predictions based on the actual shape of the buildings in some region Motivation –Achieve a desired quality of service in high traffic density areas –Install systems without adjustment –System simulations and studies –Predict higher order channel statistics

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY3 Ray Techniques for Site Specific Predictions Numerical solvers (finite difference, finite element and moment methods) not practical for urban dimension Ray techniques are the only viable approach Predictions using 2D building data base Pin/cushion vs. image method Prediction using 3D building data base Vertical plane/slant plane - enhanced 2D methods Full 3D method Vertical plane launch - approximates full 3D method

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY4 Physical Phenomena and Database Requirements Physical phenomena that can be accounted for –Ground reflection and blockage –Specular reflection at building walls –Diffraction at building corners, roofs –Diffuse scattering from building walls (for last path segment) Database requirements for predictions –Terrain –Buildings decomposed into groups of polyhedrons that are : Stacked (wedding cake buildings) or side-by-side Polygonal base with vertical sides Some codes assume flat roofs Vector vs pixel (area element) data base –Reflection coefficients at walls, diffuse scattering coefficient

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY5 Specular vs Diffuse Reflection from Walls Complex construction leads to scattering –Mixture of construction materials –Architectural details –Windows - glass, frame Simplifying approximations for large distances  r1r1 s1s1 s2s2 r2r2 Specular reflection ~ 1/ (r 1 + r 2 ) 2 Diffuse reflection ~ A/ (s 1  s 2 ) For all construction, |  (  )|  1 for   90°

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY6 Modeling Limitations Cannot accurately predict phase of ray fields –Position accuracy of building data base ~ 0.5 m –Do not know wall construction - uncertainty in magnitude and phase of reflection coefficient Local scattering contributions not computed –Do not consider vehicles, street lights, signs, people, etc. –Most codes do not include diffuse scattering Cannot predict fast fading pattern in space –Predict small area average by summing ray powers Can be used to predict statistical parameters

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY7 Ray Tracing Using a 2D Building Database Building are assumed to be infinitely high –Almost all models neglect transmission through the building –2D ray tracing around building in the horizontal plane Rays that are considered –Multiple specular reflections from the building walls –Single or double diffraction at the vertical edge of a building –Ground reflection –Diffuse scattering from the building walls Advantages: –Account for low base station antennas among high rise buildings –Computationally efficient Limitations: –Less accurate in an area of mixed building heights –Fails for rooftop base stations

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY8 Two Dimensional Ray Tracing Technique Rx Tx No Diffraction Single Diffraction Double Diffraction Rays are traced to corners, which act as a secondary sources for subsequent trace.

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY9 Reflected ray paths found from multiple Rays traced outward from the source imaging of the source in the building walls at angular separation,  << w/R, must determine if the ray from an image must use capture circle to find rays passes through the actual wall, or through that illuminate the receiver (or the analytic extension of the wall. equivalent procedure). Dia = L  Image vs Pin Cushion Method for 2D Rays Rx Tx Rx Image Method Pin Cushion Method Tx Rx

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY12 Predictions for a Generic High Rise Environment Rectangular Street Grid Propagation Down Streets, Around Corners - Specular Reflection at Building Walls Diffraction at Building Corners

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY16 Ray Path for High Rise Model All Path Include Direct Path + Path from Image Source to Account for Ground Reflections Main Street –R m : m reflections at building on main street Perpendicular Streets - one turn paths –R mn : m reflections at building on main street, n reflections on perpendicular street + ground –R m DR n : building reflections separated by corner diffractions Parallel Streets - two turn paths –R mnp : m, n, p, building reflections on main, perpendicular, parallel street –R m DR np, R mn DR p, : building reflections + diffraction at a single corner –R m DR n DR p : building reflections + diffraction at two corners

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY20 Vertical Plane/Slant Plane Method Building Height Range Tx Rx c b d c b d 0 Tx Left propagation channel Right propagation channel Rays are traced in the vertical plane containing TX and RX to account for propagation over buildings. Rays are traced in the slant plane containing TX and RX to account for propagation around buildings.

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY21 Slant/Vertical Plane Prediction for Aalborg, Denmark at 955MHz T. Kurner, D.J. Cichon and W. Wiesbeck, “Concepts and Results for 3D Digital Terrain-basedWave Propagation Models: An Overview,” IEEE Jnl. JASC 11, Sept. 1993

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY22 Missing Rays in Slant Approximation Unless the building faces are perpendicular to the vertical plane, reflected rays lie outside of the vertical plane Multiply reflected rays will not lie in the slant plane Neglects rays that go over and around building Missing rays cause significant errors for high base station antenna

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY25 Ray Tracing Using a 3D Building Database Rays that are considered: –Can account for all rays in 3D space –Some programs consider diffuse scattering –Some simplification is made, i.e. flat roofs and/or vertical walls Rays that are not considered: –Often unable to include rays that undergo more than one diffraction –Usually does not include transmission into the buildings Advantages: –Very robust model, works for many building environments Limitations: –Limited to a maximum of 2 diffractions (unable to account for multiple rooftop diffraction) –Computationally very inefficient

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY28 Vertical Plane Launch (VPL) Method Finds rays in 3D that are multiply reflected and diffracted by buildings Assumes building walls are vertical to separate the trace into horizontal and vertical components Pin cushion method gives the ray paths in the horizontal plane Analytic methods give the ray paths in the vertical direction Makes approximation: rays diffracted at a horizontal edge lie in the vertical plane of the incident ray, or the vertical plane of the reflected rays

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY29 Physical Approximation of the VPL Method Treats rays diffracted at horizontal edges as being in the vertical planes defined by the incident or reflected rays (replaces diffraction cone by tangent planes) Cone of diffracted rays Vertical plane containing forward diffracted rays Vertical plane containing back diffracted rays Vertical plane containing reflected and back diffracted rays

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY33 Measurements and VPL Predictions for Rooftop Antenna (TX6 and f=908MHz) Without diffuse:  = -0.75 dB  = 5.43 dB With diffuse:  = -0.74 dB  = 5.44 dB

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY34 Measurements and VPL Predictions for Street Level Antenna (TX1a and f=908MHz) Without diffuse:  = -0.42 dB  = 8.92 dB With diffuse:  = 0.49 dB  = 8.34 dB

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY37 Diffraction at Building Corners Important to correctly model shape of building corners Luebbers diffraction coefficient used by many to model diffraction at building corners –Heuristic coefficient for lossy dielectric wedges –Developed for forward diffraction over hills –Exhibits nulls in the back diffraction direction that are not physical Building corners are not dielectric wedges, e.g., fitted with windows, metal framing Need a single diffraction coefficient to use for all corners

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY38 Reflection Away From Glancing Is Influenced by Wall Properties For low base station (BS) antenna, reflection from glass doors at Corner A influences received signal on street L-M.

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY45 Conclusions Site specific predictions are possible with accuracy Average error ~ 1 dB RMS error ~ 6 - 10 dB Requires multiple interactions for accurate predictions Six or more reflections required for best accuracy Double diffraction at vertical edges is sometimes needed Lubbers diffraction coefficient needs modification

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY46 Ray Tracing Inside Buildings Ray tracing over one floor Propagation through the clear space between furnishings and ceiling structure Propagation between floors

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY48 Effects of Floors & Ceilings Drop ceilings taken up with beams, ducts, light fixtures, etc. Floors covered by furniture Propagation takes place in clear space between irregularities

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY49 Modeling Effect of Fixtures d 2d 3d nd (n+1)d Nd x y w/2 Line Source -w/2 Assume the excess path loss for a point source is the same as that of a line source perpendicular to the direction of propagation. Represent the effects of the furnishings and fixtures by apertures of width w in a series of absorbing screens separated by the distance d. Use Kirchhoff-Hyugens method to find the field in the aperture of the n + 1 screen do to the field in the aperture of the n screen. The field in the aperture of the first screen is the line source field.

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY54 Predictions at 900 MHz in a University Building Diffraction at far corners of hallway is responsible for the received signal when the direct rays go through many walls.

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY55 Propagation Between Floors Can Involve Paths That Go Outside of the Building RX TX 9.20 m 2.62 m 2.1 m7.50 m 1.3 m Propagation can take place via paths that go outside the building via diffraction or reflection from adjacent buildings. Stair wells, pipe shafts, etc. are also paths for propagation between floors. Direct propagation between floors has losses: ~ 5 - 8 dB for wooden floors ~ 10 dB for reinforce concrete > 20 dB for concrete over metal pans

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY57 Summary of Propagation in Buildings Ray codes for coverage over on floor –Need to account for 2 or 3 reflections and 1 diffraction event –Can achieve low errors (  < 6 dB) Propagation through clear space can give excess loss at lower frequencies Propagation between floors can involve paths that lie outside of buildings

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY58 Predicting Statistics of Channel Parameters Need high order channel statistics (e.g. delay spread DS and angle spread AS) for advanced system design Measurements are expensive and time consuming Not sure if measurements for one link geometry, city, apply elsewhere Monte Carlo simulation using site specific predictions allow different link geometry, cities to be examined Simulations allow modifications of building database Relate statistics of channel parameters to the statistical properties of the building distribution

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY60 Delay Spread (DS) and Angular Spread (AS) Obtained from the Ray Simulation Delay Spread Angle Spread (approximate expression for small spread) From mth ray from the jth mobile

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY63 Greenstein Model of Measured DS in Urban and Suburban Areas Greenstein, et al., “A New Path Gain/Delay Spread Propagation Model for Digital Cellular Channels,” IEEE Trans. VT 46, May 1997.

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY75 Conclusions Site specific predictions are possible with accuracy Average error ~ 1 dB, RMS error ~ 6 - 10 dB Requires multiple interactions for accurate predictions6 or more reflections, double diffraction at vertical edges Site specific prediction can be used for Monte Carlo simulation of statistical channel characteristics Delay Spread is not strongly dependent on path geometry or building statistic Angular Spread at base station depends strongly on antenna height and building height distribution Weak correlation between Delay Spread and Angular Spread Further work needed on reflection and diffuse scattering at the building walls

© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY1 XII. Site Specific Predictions Using Ray Methods General considerations Ray tracing using.

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© 2000 by H. L. BertoniPolytechnic University, Brooklyn, NY1 XII. Site Specific Predictions Using Ray Methods General considerations Ray tracing using.

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