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In Part I of this report the optimum MTI receiver was derived and analyzed for the case in which the radar pulses were emitted from the transmitter equally spaced in time. For typical long range ATC surveillance radars , aliasing of the target and clutter spectra results in detection blind speeds at multiples of approximately 70 knots. It is well known operationally that these blind speeds can be eliminated by staggering the transmitter PRF. Heretofore, there has been no thorough theoretical analysis of the effect of staggered PRF on the spectral distribution of the target and clutter signals. It is shown in Part II that the clutter spectral density continues to fold over at the PRF, but that the signal spectrum becomes dispersed in frequency, somewhat like an anti-jam signal. The effect that this phenomenon has on the performance of the optimum processor is evaluated in terms of the signal-to-interference ratio (SIR) criterion that was derived in Part I. It is further noted that even when the target Doppler shifts are more than one PRF apart, the spectra are distinguishable, suggesting that unambiguous Doppler estimation may be possible. This concept is explored in detail using the MTI ambiguity function. It is shown that good SIR performance can be obtained by choosing the stagger parameters to minimize the height of the subsidiary Doppler side-lobes. The resulting design problem is noted to be similar to that of obtaining good antenna patterns for arrays having non-uniformly spaced elements.

An overview of the issues involved in the design of dual lane runways is presented. These issues include: centerline spacing, parallel taxiway, high speed exits, midpoint versus end point crossing, threshold stagger, and departure/arrival runway preference. An interactive graphics simulation was developed on the TX-2 computer. The simulation provides the capability for an airport designer to easily input dual lane runway configurations. ATC controllers were employed for over 100 hours to control and direct simulated traffic to various dual lane configurations. A set of preliminary criteria for dual lane runway configurations are presented along with recommendations for future work.

The performance of three candidate modulation schemes for DABS is analyzed in this report and a comparison on the basis of probability of error per bit is made. The three types of modulation are PAM, DPSK, and FSK. The results show that, at a given level of interference and signal-to-noise ratio, DPSK and FSK have a lower P(e)/bit than PAM and this difference is significant in most cases. In addition to P(e)/bit, however, the choice of modulation and message format depends on the capacity required, bandwidth occupancy, and cost of implementation. This list consideration is especially important with regard to the transponder.

A classical problem in radar theory is the detection of moving targets in a ground clutter plus receiver noise background. Improvements in clutter rejection have recently been made by replacing analog MTI processors by their digital equivalents as this eliminates many of the problems associated with the maintenance of the analog hardware. In an attempt to determine the ultimate improvements possible using this new technology, the MTI problem was formulated as a classical detection problem and solved using the generalized likelihood ratio test. By manipulating the likelihood ratio, the receiver could be interpreted as a clutter filter in cascade with a Doppler filter bank. The performance of the optimum receiver was evaluated in terms of the output signal-to-interference ratio and compared with well-known MTI processors. It was shown that near-optimum performance can be obtained using a sliding weighted Discrete Fourier Transform (DFT). All of the results in Part I assume uniformly spaced transmitted pulses, which, for high velocity aircraft, leads to aliasing of the target and clutter spectra and detection blind speeds. In Part II the maximum likelihood method is applied using a more general model for the non-uniformly sampled target returns. This leads to an optimum receiver that is a slightly more complicated version of the sliding weighted DFT. In addition to removing the detection blind speeds, it is found that unambiguous Doppler measurements

The role of surveillance radar will change as the evolving ATC system relies more heavily upon cooperative beacons, but radars will still remain as an important system element. Today's radars have major limitations for an automated ATC environment because they report unwanted targets (ground, bird, and weather clutter) and because they are expensive to operate and maintain. In addition, to minimize ground clutter, radars are usually sited relatively close to the ground and consequently their performance is not adequate to detect small, distant, low-flying aircraft. By exploiting today's digital technology and by using a completely linear signal processing system, it is now possible to obtain a major improvement in MTI performance. The Lincoln Laboratory has demonstrated a 48-db clutter improvement factor on a 15-rpm scanning S-band ASR-type radar. This clutter rejection capability is about 20 db greater than exhibited by radars now in the field. By selection of more appropriate radar parameters, still greater fixed clutter and weather rejection can be achieved.

This report covers the work done under the first phase of a continuing program of field tests on ATCRBS transponders. Characteristic transponder parameters were measured to determine their degree of compliance with the current specifications. A mobile van was outfitted with electronic test equipment which simulated the transmitter and receiver sections of a ground interrogator and allowed measurement of transponder parameters. A horn antenna located near the aircraft under test was used to couple signals to and from the transponder. The tests were performed at nine civilian airports on transponders installed in operational general aviation aircraft. The results of the measurements on the first 96 units are reported in detail and tentative conclusions drawn.

A concept formulation study of the control aspects of the fourth generation air traffic control system is presented. The results of this study are not strongly influenced by present-day equipment. They are influenced by certain aspects of present airspace utilization and procedures which appear necessary for the design of an effective system. The inputs to the control system design include the fourth generation air traffic demand, characteristics of fixed elements (types of aircraft, etc.), and disturbances such as weather effects. The control system which has been formulated includes flight plan generation, flow control, conformance monitoring, and collision avoidance as control functions. A baseline control system is given as a first iteration of the fourth generation system. The baseline system is defined by classifying types of airspace, conformance requirements, and required segregation of classes of flight paths. The airspace is divided into three categories: positive control air space containing only controlled aircraft, controlled (mixed) air space containing both controlled and cooperative aircraft, and uncontrolled airspace containing uncontrolled aircraft. Cooperative aircraft must be able to accept IPC co-ands as well as simplified flight plans when flying in high density retied air space. The surveillance, navigation, and communications systems complete the interacting parts of the control system. Candidate fourth generation system concepts ranging from the completely tactical to the highly strategic have been described both in this report and elsewhere. In order to characterize a proposed concept we have drawn up a list of decisions which we find must be made in the course of a flight. We then consider where these decisions are made and thereby characterize the system. The feasibility of generating conflict free flight plans is investigated with the aid of analytical models. A consideration of the factors which influence the flight planning process is presented. Use is made of a generally accepted traffic density model for the 1995 time period. The expected number of conflicts for selected routes and the distances required to resolve conflicts are evaluated. The use of aircraft performance characteristics in evaluating the effectiveness of conflict resolution maneuvers is discussed. The level of conformance necessary for conflict free flight plans is determined for each maneuver. For cases in which the required conformance was unrealistically high, it was determined that providing velocity structure in high density airspace permitted a decrease in conformance requirements. Factors which directly influence the capability of aircraft to conform to flight plans in a strategic system as well as the relevant technology areas peculiar to the implementation of conflict free flight plans are considered. The conclusions reached during this study are followed by recommendations for future work in specific areas.

Runway 4-R at Logan Airport cannot now be used with full effectiveness because of tall ships passing through the runway's approach clearance zone. The key to utilizing the full length of Runway 4-R at Logan Airport for longer periods of time is to establish a channel surveillance system that would allow both ships and aircraft to safely share the air space above the channel. A laser-gate alarm system across the channel, at the approaches to the clearance zone, has been proposed for alerting tower operators to the passage of tall ships. A surface detection (ASDE) radar would maintain surveillance during passage of the ship. This ship detection concept was explored and developed within Lincoln Laboratory with cooperation and encouragement from MASSPORT and members of the FAA Burlington office. This report completes the study and field measurements program, sponsored by MASSPORT, for the evaluation of an experimental laser-gate ship-detection system. The study and field Measurements program supports the conclusion that a reliable, fail-safe, laser-gate system can be designed, installed and operated to detect ships entering the clearance zone of Runway 4-R. System feasibility has been established for visual meteorological conditions both day and night. Ship masts of 1-inch diameter at speeds up to 15 knots can be reliably detected under visual meteorological conditions for laser-path-lengths up to 3000 feet. An operational system can be de signed for visibility ranges down to 1/4 mile with laser path lengths of 1800 feet and with the expectation that performance would be substantially the same. The system design is amenable to various balance s between mast-height margin, VFR runway length and displaced threshold duty factor. In the recommended system, the laser-gates may be placed at a height of about 45 feet, which will detect ships tall enough to intrude the clearance zone, while allowing small craft to pass without alarm. This configuration would permit full use of the 10,000-foot runway, while providing an 11- to 21-foot margin for narrow objects which might be less than one-inch wide at the laser-gate height. Analysis of ship traffic indicates that the use of a laser-gate system at the 40- to 50-foot height under nighttime visual meteorological conditions would permit the full-length use of Runway 4-R throughout the night except for the times of passage of 4 to 7 ships on the average. During the early nighttime hours having the heaviest nighttime air traffic, less than one ship alarm would be expected on the average. Operational system design relations are presented which permit a spectrum of design options. False alarms would be at a negligible level in a multiple-parallel-beam operational system and an infrequent false alarm could be checked with the ASDE radar. Recommendations are made for a program which would lead to an operational laser-gate ship-detection system fully integrated with airport facilities and activities. This program would initially involve the design and installation of one prototype laser-gate, which would be integrated with the airport surface detection radar to establish optimum system configuration, develop operational procedures, and to test more extensively the reliability and fail-safe features of the surveillance system. Upon satisfactory completion of the tests and studies, the prototype could be used as one element of an operational system. This report contains in Appendix B engineering guidelines for the recommended prototype laser-gate system.

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To develop plans for a viable ATC system over the next 25 years a whole spectrum of studies can be conducted, each concerned with a different time frame. The spectrum, when laid out over time, is bracketed by two extreme cases. 1. One extreme is analysis of the present ATC system to identify its shortcomings, followed by synthesis studies to identify evolutionary ways of overcoming these shortcomings. 2. At the other extreme one can study the ATC system sufficiently far into the future that decisions need not be constrained by existing equipment, airspace utilization and procedures. Between these two extremes are other studies concerned with developing plans for intermediate time frames. To be effective, study (1) must be done immediately. Study (2) should precede many of the studies for intermediate time frames since the results of study (2) should be available to influence what is done in intervening periods. In this report we view the Fourth Generation Concept Formulation Study as study (2). Thus the results are not strongly influenced by present day equipment and are influenced by present airspace utilization and procedures only where they appear to be as good or better than other ways of operating the system. The ATC system is designed to fulfill certain needs of the nation. To satisfy those needs the ATC system must achieve specific objectives. The major objective of the system is to provide safe, expeditious flow of air traffic at reasonable cost. It is generally accepted that to achieve this objective certain functions in the area of surveillance, navigation, and communication must be performed and that considerable data processing in the ATC system is required. The examination of ways of achieving various performance levels of these functions is the subject of concept formulation in -- the areas of surveillance, navigation, communication and data processing. Given that the surveillance, communication, and navigation functions are performed, there are other functions which are required in order to achieve the objectives of the ATC system. These functions, which include flow control, metering, sequencing, spacing, conformance and hazard monitoring, and conflict and hazard resolution make up the control aspects of the ATC system. In terms of the operation of the ATC system the surveillance, communication and navigation functions must be performed if the control functions are to be performed. In terms of the design of the system, however, the surveillance, communication, and navigation functions cannot be specified in detail until the required control functions are determined in detail. Thus, studies in the control area must be performed in a timely manner in order to insure that studies in the other areas will be conducted at a high level of efficiency. Control studies seek to determine the detailed characteristics of the functions which will be performed to achieve the objectives of the ATC system.