The likelihood of line-of-sight (LoS) is an essential component in any radio channel model. It is particularly useful for radio network planning and urban coverage prediction. Empirical LoS models are hard to derive due to a strong dependency on local topology and the need for large measurement datasets. Since buildings are the major obstructions in a dense urban environment, we propose a new theoretical model to determine the LoS probability for air-toground channels based on local building geometry and knife-edge diffraction theory. The model takes into account key statistical parameters such as building height, building size, building coverage, street width and street angle distribution. The theoretical model is shown to agree well with ray tracing simulation results. The statistical parameters, such as mean building height, percentage of area covered by buildings (building coverage) and building density, can all be easily obtained for a specific location. We also derive equations for the likelihood of LoS for a direct slant path. These equations can be used in the analysis of air-to-ground channels.
This paper describes a fully three-dimensional deterministic propagation model based on a radar crosssection analysis of terrain pixels and building walls. The model utilises a variable resolution terrain database as well as a buildings database to predict signal strength, time dispersion and fading information[, in addition to providing spatial information (e.g. arrival angles) for the propagation channel. It considers scattering from illuminated terrain pixels and building walls as well as considering off-axis terrain and rooftop diffraction contributions.The model can be particularly useful for integrating macrocells and microcells e.g. predicting interference in a microcell due to a nearby macrocell or vice versa. Signal strength predictions from the model show good agreement with narrowband measurements for a rural macrocell. The effects of buildings and foliage in the prolpagation channel are investigated, and reveal that large errors can result if these effects are ignored. The accuracy improvement of the 3-D analysis over the simpler 2-D approach is also demonstrated. 0-7803-3659-3/97 $1 0.00 0 1 997 IEEE 1957
Abstract-In this paper, an advanced site-specific image-based ray-tracing model is developed that enables multielement outdoor propagation analysis to be performed in dense urban environments. Sophisticated optimization techniques, such as preprocessing the environment database using object partitioning, visibility determination, diffraction image tree precalculation, and parallel processing are used to improve run-time efficiency. Wideband and multiple-input-multiple-output (MIMO) site-specific predictions (including derived parameters such as theoretic capacity and eigenstructure) are compared with outdoor site-specific measurements at 1.92 GHz. Results show strong levels of agreement, with a mean path-loss error of 2 dB and a mean normalized-capacity error of 1.5 b/s/Hz. Physical-layer packet-error rate (PER) results are generated and compared for a range of MIMO-orthogonal frequency-division-multiplexing (OFDM) schemes using measured and predicted multielement channel data. A mean E b /N 0 error (compared to PER results from measured channel data) of 4 and 1 dB is observed for spatial-multiplexing and spacetime block-code schemes, respectively. Results indicate that the ray-tracing model successfully predicts key channel parameters (including MIMO channel structure) and thus enable the accurate prediction of PER and service coverage for emerging MIMO-OFDM networks such as 802.11n and 802.16e.
This paper describes a 3-D integrated propagation model, which considers propagation effects in both urban and rural environments. It uses a variable resolution Digital Terrain Map (DTM) as well as building and foliage databases. Scattering off terrain pixels and building walls is modelled, as are off-axis terrain and rooftop diffraction contributions. The scattered power is estimated from radar cross-section analysis of the illuminated pixels and walls. The effects of foliage attenuation are also fully considered. The model predicts signal strength and time dispersion and provides fading and arrival angle information for the propagation channel.Narrowband measurements in both urban and rural areas show very good agreement with the predicted results. The accuracy of different foliage-loss and diffraction-loss models has been assessed, with the ITU-R foliage-loss model and the UTD model giving the best results. It is shown that large errors can result if the effects of foliage are ignored in the modelling process. 0-78034320-4/98/$5.00 0 1998 IEEE
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