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DABS uplink coding

July 25, 1975
  |
Project Report
Author:
John T. Barrows
Published in:
MIT Lincoln Laboratory Report ATC-49
Topic:
surveillance
R&D area:
R&D group:

Summary

This report details the coding techniques incorporated into the DABS uplink design. Justification is given for the error control method selected in terms of the link characteristics and design constraints. Performance results, including extensive evaluation by simulation and bench test, are presented for the selected code. A binary shortened cyclic code having 24 redundant bits was selected. The overhead due to the code redundancy is minimized by a scheme in which the parity check bits are overlayed on the discrete address field in the encoded message. This code is shown to have the capability of protecting a DABS transponder from accepting an erroneous uplink message with an error probability of less than 10 to the -7 power in a severe interference environment. This same code will be used in the DABS downlink in a burst erasure correction mode. Results of the analysis of the downlink will appear in a separate report.
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Summary

This report details the coding techniques incorporated into the DABS uplink design. Justification is given for the error control method selected in terms of the link characteristics and design constraints. Performance results, including extensive evaluation by simulation and bench test, are presented for the selected code. A binary shortened cyclic...

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DABS uplink coding

Impact of obstacle shadows on monopulse azimuth estimate [project report]

July 17, 1975
  |
Project Report
Author:
Alex Spiridon
Published in:
MIT Lincoln Laboratory Report ATC-50
Topic:
surveillance
R&D area:
R&D group:

Summary

Obstacle shadows, within view of a sensor using monopulse azimuth estimate, cause an error in the azimuth estimate. This report discusses the azimuth error as a function of obstacle dimension and position, and the sensor antenna illumination.
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Summary

Obstacle shadows, within view of a sensor using monopulse azimuth estimate, cause an error in the azimuth estimate. This report discusses the azimuth error as a function of obstacle dimension and position, and the sensor antenna illumination.

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Impact of obstacle shadows on monopulse azimuth estimate [project report]

Network management

May 16, 1975
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Project Report
Author:
Herman F. Vandevenne
Published in:
MIT Lincoln Laboratory Report ATC-45
Topic:
air traffic control
R&D area:
R&D group:

Summary

This report provides a discussion of the design of the DABS network management function. Network management is responsible for the interaction between the local sensor and the adjacent connected sensors. Based on a dynamic interpretation of the coverage map and the status of the network, network management determines (a) the coverage responsibility of the local sensor, (b) which other sensors are covering the same area, and (c) which of the sensors has principal data link responsibility. Interaction is effected through message exchange over ground communication links connecting the DABS sensors.
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Summary

This report provides a discussion of the design of the DABS network management function. Network management is responsible for the interaction between the local sensor and the adjacent connected sensors. Based on a dynamic interpretation of the coverage map and the status of the network, network management determines (a) the...

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Network management

DABS link performance considerations

April 28, 1975
  |
Project Report
Author:
Gary J. Schlieckert
Published in:
MIT Lincoln Laboratory Report ATC-41
Topic:
surveillance
R&D area:
R&D group:

Summary

The DABS link performance is computed using the present values for the system operating parameters and the available models that describe environment and aircraft antenna effects. The various fade mechanisms are described, and a statistical determination of performance is proposed. The performance is computed for various sets of conditions including different ground antennas, aircraft maneuvers, antenna obstructions and the performance when aircraft are in the cone of silence. The DABS link is found to have very good overall performance with only small regions of reduced reliability that are at low angles or due to maneuvers. Those missed replies due to maneuvers are found to be sporadic from scan to scan.
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Summary

The DABS link performance is computed using the present values for the system operating parameters and the available models that describe environment and aircraft antenna effects. The various fade mechanisms are described, and a statistical determination of performance is proposed. The performance is computed for various sets of conditions including...

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DABS link performance considerations

Improved MTI radar signal processor

April 3, 1975
  |
Project Report
Author:
William H. Drury
Published in:
MIT Lincoln Laboratory Report ATC-39
Topic:
surveillance
R&D area:
R&D group:

Summary

A new type of radar digital signal processor for use with ASR radars is described. It features spectral processing accomplished by combining a 3-pulse canceller with an 8-point, weighted, discrete Fourier transform and adaptive thresholds. This combination of circuits provides a 20-dB increase in MTI improvement factor over present ASR's and is within 2 dB of optimum processing results. An auxiliary channel is provided to allow detection of any target traveling tangentially if its return exceeds the level of ground clutter return in the occupied range/azimuth cell. The spectral processing technique provides discrimination against weather clutter if the returns from weather and from the target fall into different Doppler frequency regions. The output from this equipment is digital hit reports for transmittal to the ARTS-III IOP computer.
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Summary

A new type of radar digital signal processor for use with ASR radars is described. It features spectral processing accomplished by combining a 3-pulse canceller with an 8-point, weighted, discrete Fourier transform and adaptive thresholds. This combination of circuits provides a 20-dB increase in MTI improvement factor over present ASR's...

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Improved MTI radar signal processor

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

DABS channel management

January 8, 1975
  |
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
  |
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
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