Publications

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.

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.

The effects of sensor accuracy, data rate, and message delivery delay upon automated conflict detection,and resolution processing is analyzed and particular considerations for DABS/IPC operation are discussed. Various options in the design of the algorithmic logic are enumerated and a particular logic is chosen for quantitative inspection. Performance sensitivity calculations for the conflict detection and command generation functions are then presented. The influence of algorithmic logic and traffic environment upon surveillance requirements is delineated.

The Technical Development Plan for a Discrete Address Beacon System is published in two volumes. Volume I is the basic plan, while this volume (Volume II) contains a more detailed description of the 46 tasks recommended for accomplishment during Phase 1 of the development cycle. It also includes cost estimates for each task.