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DABS uplink encoder

March 4, 1975
  |
Project Report
Author:
John R. Samson
Published in:
MIT Lincoln Laboratory Report ATC-40
Topic:
surveillance
R&D area:
R&D group:

Summary

This report explains the operation of the DABS uplink encoder and provides information useful in diagnosing its performance. Several techniques which may be useful in analyzing encoder operation are presented. One technique involves only the use of address-parity tables and modulo-2 addition. The address-parity tables included are based upon the encoding polynomial prescribed in "Provisional Signal Formats for the Discrete Address Beacon System," Lincoln Laboratory Project Report ATC-30 Rev. 1, dated 25 April 1974. The error detection and correction properties of polynomial encoding schemes are not the subject of this report.
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Summary

This report explains the operation of the DABS uplink encoder and provides information useful in diagnosing its performance. Several techniques which may be useful in analyzing encoder operation are presented. One technique involves only the use of address-parity tables and modulo-2 addition. The address-parity tables included are based upon the...

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DABS uplink encoder

An analysis of aircraft L-band beacon antenna patterns

January 15, 1975
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Project Report
Author:
Gary J. Schlieckert
Published in:
MIT Lincoln Laboratory Report ATC-37
Topic:
L-band
R&D area:
R&D group:

Summary

Radiation patterns are examined for L-Band beacon antennas mounted on aircraft ranging from small, single-engine, general aviation aircraft to the Boeing 747. The data analyzed consists of antenna gain values taken in two degree steps over a spherical surface centered at the antenna location. Data from three representative scale model aircraft are studied in detail and show the effects of various airframe structural members on the radiation lobing patterns and the relative performance of antennas located at a number of positions on each scale model aircraft. Significant observations were that: -Landing gear and flaps complicate the lobing structure but do not introduce many more low gain values. -In general, antennas mounted forward of the leading edge of the wing and on fuselage bottom centerline (not too close to nosewheel) provide the best overall performance. -As an aircraft maneuvers, antenna performance degrades in direct relationship with the severity of the roll or pitch.
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Summary

Radiation patterns are examined for L-Band beacon antennas mounted on aircraft ranging from small, single-engine, general aviation aircraft to the Boeing 747. The data analyzed consists of antenna gain values taken in two degree steps over a spherical surface centered at the antenna location. Data from three representative scale model...

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An analysis of aircraft L-band beacon antenna patterns

DABS channel management

January 8, 1975
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Project Report
Author:
Edward J. Kelly
Published in:
MIT Lincoln Laboratory Report ATC-43
Topic:
surveillance
R&D area:
R&D group:

Summary

This report provides a full discussion of the design of the DABS channel management function. Channel management regulates all activity on the RF channel, scheduling ATCRBS interrogations and DABS roll-call interrogations and replies. Channel management arranges for multiple interrogations when required to satisfy both the surveillance and the communications functions of the sensor, and for reinterrogations in the event of link failure. The report consists of three major parts: Part I, Channel Control; Part II, Roll-Call Scheduling; and Part III, Transaction Preparation, Target List Update, and Transaction Update. Together they encompass the five basic subfunctions of channel management.
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Summary

This report provides a full discussion of the design of the DABS channel management function. Channel management regulates all activity on the RF channel, scheduling ATCRBS interrogations and DABS roll-call interrogations and replies. Channel management arranges for multiple interrogations when required to satisfy both the surveillance and the communications functions...

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DABS channel management

DABS timing: clocks, synchronization and restart

December 13, 1974
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Project Report
Author:
Edward J. Kelly
Published in:
MIT Lincoln Laboratory Report ATC-29
Topic:
surveillance
R&D area:
R&D group:

Summary

The DABS sensor timing subsystem, which consists of two clocks driven from a common station standard, is the subject of this paper. The subsystem configuration is described and the rationale for this design briefly given. Emphasis is on the techniques for sychronization to an external standard, coordination with other sensors and system restart after a failure or deliberate shut-down.
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Summary

The DABS sensor timing subsystem, which consists of two clocks driven from a common station standard, is the subject of this paper. The subsystem configuration is described and the rationale for this design briefly given. Emphasis is on the techniques for sychronization to an external standard, coordination with other sensors...

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DABS timing: clocks, synchronization and restart

Further studies of ATCRBS based on ARTS-III derived data

December 13, 1974
  |
Project Report
Author:
Alan G. Cameron
Published in:
MIT Lincoln Laboratory Report ATC-38
Topic:
surveillance
R&D area:
R&D group:

Summary

Lincoln Laboratory has been examining digital data extracted from operational ARTS-III radar beacon processing systems for the past eighteen months, in an attempt to determine the capabilities of today's civil Air Traffic Control Radar Beacon System. Our original report on the subject, "Empirical Assessment of ATCRBS," (Ref. [1]), covered data gathered during the first six months of the study from the Andrews AFB (ADW), Boston (BOS), and Las Vegas (LAS) ARTS-III eqUipment. This report discusses analysis of data received since the completion of that initial report, which was gathered at the Ontario, California (ONT), Albuquerque (ABQ), Minneapolis St. Paul (MSP), Milwaukee (MKE), and Boston (BOS) ARTS-III sites, and also the Suitland, Md. en route radar site. The major topics considered here are false targets caused by multipath reflections, and asynchronous interference (fruit). Four different mechanisms resulting in false targets were observed in the data and are discussed in detail in the report. In addition, levels of asynchronous interference as measured and analyzed, and two procedures are discussed by which the characteristics of the interrogators responsible for the fruit (including location) can be determined. One of these is described in detail, and shown to yield results that agree closely with known parameters. Several other topics, including improper reply decoding, are also discussed.
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Summary

Lincoln Laboratory has been examining digital data extracted from operational ARTS-III radar beacon processing systems for the past eighteen months, in an attempt to determine the capabilities of today's civil Air Traffic Control Radar Beacon System. Our original report on the subject, "Empirical Assessment of ATCRBS," (Ref. [1]), covered data...

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Further studies of ATCRBS based on ARTS-III derived data

DABS: A System Description

November 18, 1974
  |
Project Report
Author:
Paul R. Drouilhet Jr
Published in:
MIT Lincoln Laboratory Report ATC-42
Topic:
surveillance
R&D area:
R&D group:

Summary

The Discrete Address Beacon System (DABS) is a cooperative surveillance and communication system for air traffic control. It employs ground-based sensors (interrogators) and airborne transponders. Ground-to-air and air-to-ground data-link communications are accommodated integrally with the surveillance interrogations and replies. DABS has been designed as an evolutionary replacement for the current Air Traffic Control Radar Beacon System (ATCRBS) to provide the enhanced surveillance and communication capability required for air traffic control in the 1980s and 1990s. Compatibility with ATCRBS has been emphasized to permit an extended, economical transition. A principal feature of DABS is that each aircraft is assigned a unique address code. Using this unique code, interrogations can be directed to a particular aircraft, and replies unambiguously identified. Channel interference is minimized because a sensor can limit its interrogation to targets of interest. In addition, by proper timing of interrogations, replies from closely-spaced aircraft can be received without mutual interference. The unique address in each intertogation and reply also permits the inclusion of data-link messages to or from a particular aircraft. DABS uses the same frequencies for interrogations and replies as ATCRBS (1030 and 1090 MHz, respectively). The DABS interrogation is transmitted using DPSK at a 4 Mbps rate, and comprises 56 or 112 bits including the 24-bit discrete address. The reply also comprises 56 or 112 bits including address, and is transmitted at 1 Mbps using binary pulse-position modulation. Coding is used on both interrogations and replies to protect against errors. The DABS sensor provides surveillance of DABS- and ATCRBS-equipped aircraft, and data-link service to DABS aircraft. In addition, it performs radar/beacon correlation of radar target reports from a collocated radar. The DABS sensor transmits surveillance data to, and exchanges messages with, air traffic control facilities (TRACONs and ARTCCs) via low-rate digital circuits. The DABS sensor communicates directly with adjacent DABS Sensors to hand off targets and to provide surveillance and communication backup in the event of momentary link failures. Each DABS service to DABS-equipped aircraft via the ground-air data link. The DABS transponder replies to both ATCRBS and DABS interrogations, and interfaces with a variety of data-link messaged display and input devices. The rms surveillance accuracy provided by DABS is the order of 100 ft and 0.1 degree in range and azimuth, respectively. Surveillance and data-link communication capacities exceed by a substantial margin projected ATC requirements through the remainder of this century.
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Summary

The Discrete Address Beacon System (DABS) is a cooperative surveillance and communication system for air traffic control. It employs ground-based sensors (interrogators) and airborne transponders. Ground-to-air and air-to-ground data-link communications are accommodated integrally with the surveillance interrogations and replies. DABS has been designed as an evolutionary replacement for the current...

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DABS: A System Description

Maximum-likelihood detection of unresolved radar targets and multipath

November 1, 1974
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Journal Article
Author:
Robert J. McAulay
…
Published in:
IEEE Trans. Aerosp. Electron. Syst., Vol. AES-10, No. 6, November 1974, pp. 821-9.
Topic:
air traffic control
R&D area:
R&D group:

Summary

Interference in the form of multipath or uncooperative targets can seriously degrade the angle-of-arrival estimation accuracy of mutiple beam processors. In this paper, the generalized likelihood ratio test is used to derive a test to detect the presence of interference for multiple beam processors. The detector performance is then analyzed in detail with respect to its dependence on signal-to-noise ratio (SNR), signal-to-interference ration (SIR), and on the relative phase between the target and interfering signals. It is shown that good detection performance can be obtained unless the phase difference between the target and interference signals is either in or out of phase.
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Summary

Interference in the form of multipath or uncooperative targets can seriously degrade the angle-of-arrival estimation accuracy of mutiple beam processors. In this paper, the generalized likelihood ratio test is used to derive a test to detect the presence of interference for multiple beam processors. The detector performance is then analyzed...

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Maximum-likelihood detection of unresolved radar targets and multipath

Provisional message formats for the DABS/NAS interface, revision 1

October 10, 1974
  |
Project Report
Author:
David Reiner
…
Published in:
MIT Lincoln Laboratory Report ATC-33,I
Topic:
surveillance
R&D area:
R&D group:

Summary

This document defines formats for messages which are to be transmitted between DABS and NAS facilities (en route or terminal). These messages include one-way Surveillance Reports to NAS and two-way Communications Messages. The latter support data link functions between NAS and DABS equipped aircraft, as well as aiding in the monitoring and control of DABS sensors. These message formats will be used in the design and construction of interface equipment and ground data links for prototype system test and evaluation at NAFEC during Phase II of the DABS Development Program; and, with modifications resulting from this test and evaluation effort, will form the basis for the operational implementation of DABS. This document supersedes FAA-RD-74-63, dated 25 April 1974.
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Summary

This document defines formats for messages which are to be transmitted between DABS and NAS facilities (en route or terminal). These messages include one-way Surveillance Reports to NAS and two-way Communications Messages. The latter support data link functions between NAS and DABS equipped aircraft, as well as aiding in the...

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Provisional message formats for the DABS/NAS interface, revision 1

Simulation of the DABS sensor for evaluating reply processor performance

September 16, 1974
  |
Project Report
Author:
Robert J. McAulay
…
Published in:
MIT Lincoln Laboratory Report ATC-28
Topic:
surveillance
R&D area:
R&D group:

Summary

This report describes the elements of a simulations program that was designed to perform a realistic evaluation of a variety of reply processing techniques, antenna design parameters and receiver characteristics for a DABS sensor. The reply processing techniques are limited to the generation of information bit and monopulse off-boresight azimuth estimates for DABS downlink messages. The report describes the detailed characteristics of two elements of the simulation program; the data generator and reply processor, and the high degree of versatility incorporated within these elements to allow for a great many performance tradeoff studies.
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Summary

This report describes the elements of a simulations program that was designed to perform a realistic evaluation of a variety of reply processing techniques, antenna design parameters and receiver characteristics for a DABS sensor. The reply processing techniques are limited to the generation of information bit and monopulse off-boresight azimuth...

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Simulation of the DABS sensor for evaluating reply processor performance

New techniques applied to air-traffic control radars

June 1, 1974
  |
Journal Article
Author:
Charles E. Muehe
…
Published in:
Proc. IEEE, Vol. 62, No. 6, June 1974, pp. 716-723.
Topic:
air traffic control
R&D area:
R&D group:

Summary

During the past two years a program has been carried out to show how new techniques can greatly improve the performance of radars used for air-traffic control. A survey of problems associated with presently used radars was undertaken. This survey indicates that primary radar in an automated air-traffic control system can be made significantly more effective by the use of new techniques. The radar's handling of extraneous reflections (clutter) is critical to its performance. Three types of interfering clutter were found to predominate: ground clutter, weather clutter, and angels. Angels are generally accepted to be radar returns from flocks of birds. In addition, second-time-around clutter is often troublesome. For each type of clutter, all known remedies for improving the signal-to-clutter ratio were studied and radar systems were configured using appropriate sets of remedies. Some specific solutions incorporated in the resulting radar systems are: a) the use of linear large dynamic range, near-optimum digital signal processors to filter signals from clutter, b) the use of electronically step-scanned antennas to improve the correlation of aircraft and clutter returns from pulse to pulse, c) the use of multiple PRF's instead of staggered PRF's together with coherent transmitters to keep second-time-around clutter returns well correlated while still overcoming blind speeds, d) the use of a fine grained ground clutter map to give superclutter visibility on tangential targets, and e) the use of lower operating frequencies to greatly reduce weather and angel returns. Two demonstration radar systems have been implemented, an S-band radar using a mechanically rotating antenna and a UHF radar using an electronically step-scanned cylindrical antenna. Experimental results are described.
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Summary

During the past two years a program has been carried out to show how new techniques can greatly improve the performance of radars used for air-traffic control. A survey of problems associated with presently used radars was undertaken. This survey indicates that primary radar in an automated air-traffic control system...

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New techniques applied to air-traffic control radars
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