Publications

The Microwave Landing System (MLS) will be deployed throughout the world in the 1990s to provide precision guidance to aircraft for approach and landing at airports. At Lincoln Laboratory, we have developed a computer-based simulation that models the performance of MLS and takes into account the multipath effects of buildings, the surrounding terrain, and other aircraft in the vicinity. The simulation has provided useful information about the effects of multipath on MLS performance.

A set of mathematical models and computer programs have been developed to characterize multipath propagation in an airport environment. When combined with system mathematical models, these models are intended to provide a firm technical basis for assessing the performance of candidate Microwave Landing Systems (MLS) in realistic airport environments. The two paramount issues in developing these models have been 1) validation based on actual field test data and 2) computer running time. The obstacles modeled include buildings and aircraft, as well as the ground which can cause both specular reflections and diffuse scattering. In addition, the shadowing effects due to runway humps, and aircraft, buildings approaching the line of sight between transmitter and receiver are included. Computational procedures are presented for obtaining the salient multipath parameters, i.e., relative magnitude, phase, directional angles, Doppler frequency, and time delay. Computer programs have been written for these algorithms using the Fortran programming language, with structured programming methods, such as Iftran, employed whenever possible. A presentation is given of computer validation data for the computational procedures. A comparison of these computer validation results with experimental field data demonstrates good agreement in all cases of interest. The computer running time for these computer programs is quite reasonable, e.g., it takes about five times longer than actual flight time to run a model of typical airport environment on an IBM 370 model 168.

This report summarizes MLS multipath work carried out at Lincoln Laboratory from March 1974 to Sept. 30, 1975. The focus of the program is the development of realistic models for 1) the multipath in representative real world environments and 2) the multipath characteristic of candidate MLS techniques. These multipath and system models are used in a comprehensive computer simulation to predict the strengths and weaknesses of major MLS systems when subjected to representative real world environments. The report is organized into two volumes. Volume I describes the algorithms and validation of various portions of the program. In Volume II, the simulation (or selected portions thereof) is applied to key multipath related MLS issues. Mathematical models are given for the major MLS multipath sources (ground reflections, building and aircraft reflections, and shadowing by objects and humped runways), and it is shown that they agree (Doppler and scanning beam) considered in phase II of the U.S. MLS program are presented together with validation by comparison with theory and bench tests. Also presented are the results of a general study in motion averaging. The (validated) computer simulation (and portions thereof) is then applied to studying 1) the critical areas required by the TRSB system to avoid excessive reflection effects, 2) the expected TRSB performance of a specific TRSB system at Friendship International Airport (MD).

This report summarizes MLS multipath work carried out at Lincoln Laboratory from March 1974 to Sept. 30, 1975. The focus of the program is the development of realistic models for 1) the multipath in representative real world environments and 2) the multipath characteristic of candidate MLS techniques. These multipath and system models are used in a comprehensive computer simulation to predict the strengths and weaknesses of major MLS systems when subjected to representative real world environments. The report is organized into two volumes. Volume I describes the algorithms and validation of various portions of the program. In Volume II, the simulation (or selected portions thereof) is applied to key multipath related MLS issues. Mathematical models are given for the major MLS multipath sources (ground reflections, building and aircraft reflections, and shadowing by objects and humped runways), and it is shown that they agree (Doppler and scanning beam) considered in phase II of the U.S. MLS program are presented together with validation by comparison with theory and bench tests. Also presented are the results of a general study in motion averaging. The (validated) computer simulation (and portions thereof) is then applied to studying 1) the critical areas required by the TRSB system to avoid excessive reflection effects, 2) the expected TRSB performance of a specific TRSB system at Friendship International Airport (MD).