Publications

The Federal Aviation Administration is currently evaluating the Discrete Address Beacon System (DABS) which will provide increased air traffic safety in current and future air traffic conditions. In addition to improved surveillance accuracy and reliability, DABS provides a two-way data link between the DABS sensor and all DABS transponder equipped...

Iterative algorithms for signal reconstruction from partial time- and frequency-domain knowledge have proven useful in a number of application areas. In this paper, a general convergence proof, applicable to a general class of such iterative reconstruction algorithms, is presented. The proof relies on the concept of a nonexpansive mapping in...

The purpose of this paper is to describe formats developed for transmitting aviation-related messages over the Discrete Address Beacon System (DABS) data link. Initial data link applications include: (1) Minimum Safe Altitude Warning (MSAW) alerts (Terminal Area) (2) Takeoff Clearance Confirmation (3) Altitude Assignment Clearance Confirmation (Enroute) (4) Weather Reports...

The angular resolution and tracking of closely spaced targets is a classical radar problem which is receiving increased attention, and terrain multipath (e.g., reflections) has long been recognized to be a principal limitation on the achievable accuracy of radar elevation trackers at low elevation angles. A variety of techniques have...

This paper presents the results of an experimental program to obtain a better quantitative understanding of low angle microwave propagation phenomena needed to assess the potential for improved elevation tracking performance. It has long been recognized that terrain multipath (e.g., reflections and/or shadowing) are a principal limitation on the achievable...

Results are developed for data traffic performance in an integrated multiplex structure which includes circuit-switching for voice and packet-switching for data. The results are obtained both through simulation and analysis, and show that excessive data queues and delays will build up under heavy loading conditions. These large data delays occur...

This report describes the MIT Lincoln Laboratory Transportable Measurements Facility (TMF), a special purpose beacon interrogator patterned after the Discrete Address Beacon Sensor. This van-mounted experimental beacon system includes all ATCRBS/DABS reply processing and monopulse processing, but not other DABS processing. It was developed to collect data at various locations...

This report examines the technical feasibility of alternate waveforms to perform the GPS functions and to result in less complex receivers than is possible with the GPS C/A waveform. The approach taken to accomplish this objective is (a) to identify, after a quick broad overview, a few promising waveforms, (b)...

This document provides a functional description of the Discrete Address Beacon System (DABS), a combined secondary surveillance radar (beacon) and ground-air-ground data link system capable of providing the aircraft surveillance and communications necessary to support ATC automation in future traffic environments. DABS is capable of common-channel interoperation with the current...

As developed by Atal and Schroeder [1], conventional Adaptive Predictive Coding (APC) of speech employs both vocal tract and pitch prediction to achieve a low energy, spectrally flattened residual. Errors in the pitch predictor can result in clipping errors which can propagate in the system for relatively long periods of...