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| Table 1 |
Air University Review, May-June 1969
Since before World War II there has been a continuous operational pressure for increasing the number and improving the performance of functions which electronic equipment provides for the operation of aircraft. The response to this pressure has been a series of individually tailored avionic systems, which have provided a variety of new capabilities as well as improved performance of older ones. In consequence, avionic components now account for a large and steadily increasing portion of the total cost of owning and operating military aircraft.
From 6 to 24 separate radio terminals are installed in current aircraft, and together with their ground counterparts they provide communications to and from the aircraft, identification of the aircraft, and information for use in navigating the aircraft. The numerous black boxes” have separate power supplies, antennas, control, and indicators. They use many portions of the radio frequency spectrum: VLF, LF, HF, UHF, SHF. (Table 1) In some instances use of these spectrum allocations has been highly inefficient. The channels are characterized by a variety of modulation techniques even in the same frequency band, with resulting incompatibilities.
Table 1
The separate systems for communication, navigation, and identification (C, N, & I) all have the general function of transferring information. Their functional commonality has led logically to the concept of consolidating or integrating CNI by the use of common radio signal techniques sharing common radio channels. But earlier investigations of the feasibility of this concept disclosed that operational considerations were too diverse to allow effective integration with then current technologies.
The growing recognition that the redundant avionic systems could be used in a mutually supporting way to improve the total capability has given impetus to a number of programs for integrating them in some systematic way that would reduce costs and improve performance.
An examination of planning documentation indicates that there are many new and improved C, N, & I systems projected for implementation during the next five years. It is reasonable to presume that this proliferation will continue unless steps are taken to achieve integration. (Table 2) One such step was the concept study which I was designated to report upon and which formed the basis for this article. The study included a review of existing C, N, & I systems, a derivation of operational needs for communication, navigation, and identification functions; a synthesis of a feasible CNI system, and its capabilities; and comparison of it with separate systems as they might exist in the future.
Table 2
Almost all of the many different missions performed by military aircraft have a common portion, which may be called the terminal and enroute phases, consisting of taxi, takeoff, departure, enroute segments, and the corresponding return and recovery segments. (Figure 1) For a transport aircraft, these segments constitute the entire mission; for other aircraft, such as strike, reconnaissance, or close air support aircraft, requirements beyond those for the terminal and enroute phases differ according to the mission. An integrated CNI system should satisfy the needs for the terminal and enroute phases of the flight profile because these are common to all missions. The needs peculiar to the mission objective area for some missions may not be accommodated in other aircraft; for example, radar bombing sets, fire-control systems, etc. The needs common to all military aircraft are in the areas of communication, navigation, and identification.
Figure 1. terminal and enroute phases, consisting of taxi, takeoff, departure,
enroute segments, and the corresponding return and recovery segments
Communication needs. Each individual aircraft communicates with a number of control stations during the course of its mission and may also communicate with other aircraft. Aircraft, then, may be regarded as highly mobile subscribers needing communication at any time, regardless of their location, with ground command and control stations and other aircraft. The location of these other subscribers generates a need for long-distance and short-distance coverage on a worldwide basis. Under certain circumstances it is desirable that the communications be secure, antijam, and authentic.
Navigation needs. Navigation accuracies are of two types, absolute and relative. Absolute implies a knowledge of position with respect to a worldwide grid; relative implies a knowledge with respect to a particular point in a more or less localized area. The requirement to provide absolute and relative navigation accuracies applies to a worldwide coverage for long-range and short-range navigation in the same sense that there is need for similar coverages for communication purposes. There is a need for a common grid navigation function to facilitate air-ground combatant operations in the objective area. Under certain circumstances, it is desirable that navigation data also be secure, antijam, and authentic.
Identification needs. Identification, friend or foe (IFF), is required ground-to-air and air-to-air. It is presently accomplished for both air-to-air and ground-to-air by cooperative means.
the integrated system
System integration per se has no intrinsic value. An integrated CNI system to be of value should meet in some real measure the following objectives: It should provide an enhanced capability to communicate, navigate, and provide identification; it should effect substantial economies in weight, volume, power consumption, and cost of the avionics aboard the aircraft and should provide similar economies in the supporting ground configurations; it should result in economies in maintenance, supply, training, and other logistic considerations; it should conserve the radio frequency spectrum, and its radio links should have reduced vulnerability to enemy actions. Any proposed integrated system should have all this potential.
Although the thrust of this investigation has been toward elimination of unnecessary redundancy, the fact that redundancy may be necessary for reliability and survivability has not been overlooked.
The CNI environment. The overall concept presented here has been derived from consideration of the information needs of the aircraft in performance of its mission. Much of this information is derived from a cooperative environment by means of radio links. Systems such as TACAN (tactical air navigation), LORAN (long-range navigation), and UHF (ultra high frequency) radio provide signals from which the aircraft can extract information for the conduct of its mission. In addition, information must be returned to this cooperative environment of command centers, friendly radars, traffic control, etc., for coordination of one aircraft mission with another. When examined from the viewpoint of information transfer, the separate functions of communication, navigation, and identification appear to have sufficient features in common to postulate that they can all be performed through a single radio terminal in the aircraft. This hypothesis, a single terminal on board the aircraft with a coordinated environment external to the aircraft to interact with this terminal, is the key concept in the study. The cooperating terminals, ground, air, or space, will be identical or will at least use many identical modules from the viewpoint of an information system performing many functions for the aircraft and its environment. The integrated system must be considered as a whole.
Consideration of the whole involves three major areas: the aircraft terminal, the space portion, and the ground or surface-based portions of the electronic environment. These three segments of the CNI environment operate together to provide the direct and relay CNI services.
The aircraft terminal consists of a wideband transceiver, antenna, user set, signal processor, and computer. The terminal has a large degree of flexibility in that different functions can be performed with the same hardware by appropriately programming the computer and processor. The space portion of the environment consists of groups of satellite repeaters, which are employed for relaying signals to or from aircraft and other terminals. The ground portion of the environment consists of terminals that are programmed to provide for direct transmission of signals to and from aircraft, or for access to the satellites for relaying signals over long distances. It also includes the equipment necessary for the real-time monitoring and control of the system.
Figure 2 is a block diagram of the CNI terminal in the aircraft. The terminal is a wideband radio link operating at a frequency in the UHF or higher bands. The signal is digital. The generation, formatting, and detection of signals are controlled by a signal data processor. Both the transmitted and received information in the signal is routed, addressed, or manipulated by the data processor, which is a basic part of the terminal.
Figure 2. A block diagram of the CNI terminal in the aircraft
The digital signal format and the signal processor afford resolution of signal timing to within fractions of a microsecond, permitting accurate ranging on CNI sources external to the CNI-equipped aircraft. Synchronization with an absolute time standard, which is part of the ground environment, provides one of the elements of data from which position can be computed and in addition will provide signals having the characteristics necessary for the IFF or collision-avoidance functions. The wideband digital signals also provide the basis for jam resistance, for multiplexing several functions onto one transmitter, and for permitting signals transmitted from many sources to occupy simultaneously the same portion of the radio spectrum (multiple access).
The multiplexing/multiple-access capability permits an aircraft to transmit or receive 2400 bits per second digital voice simultaneously with the reception and processing of navigation signals and the transmission of required identification signals. The processor could also permit automatic readout of status information such as position, heading, speed, should the control system require these data. The spacecraft functions as a communications relay. Direct coverage from a terminal in an aircraft to a ground terminal or another aircraft terminal is line-of-sight, but the repeaters in the satellite extend this coverage to any other ground terminal or aircraft in sight of a satellite visible to a CNI-equipped aircraft. The spacecraft also performs a second function of relaying navigation signals from a ground station to aircraft or other user, where they are processed to obtain precise position. The satellite deployment configuration employed in this analysis consisted of four satellites and three ground-control stations. The satellites form a constellation at synchronous altitude, one satellite being stationary and the other three in inclined elliptical orbits that cause them to follow a racetrack pattern about the fixed satellite when viewed from the ground. Four such satellites placed 90 degrees apart at the equator provide global coverage, with the exception of a small part of the South Polar Region.
The ground or surface portion of the electronic environment will provide the same services as are provided by the existing C, N, or I equipments. The way in which the service is provided will differ markedly from the way current equipment operates. There are various ways in which a CNI terminal or combination of terminals can perform such functions as instrument landing, local area navigation, and air traffic control. The determination of the best or most efficient way was beyond the scope of the analysis that has been performed. The analysis has been limited to considering how each of the C, N, & I ground systems might be replaced by a CNI-compatible ground environment terminal that provides the same services. The selection of the configuration of the integrated ground system(s) awaits further detailed engineering. Some possible configurations merit brief description.
A single CNI terminal on the ground can provide a high-resolution ranging signal in the direct mode, as well as an authenticated, jam resistant communication channel in the direct or relay mode. Such a terminal could functionally replace G/A UHF stations and HF stations, the distance-measurement transponder portion of TACAN, and the IFF beacon interrogator used at radar sites.
Two or more separate CNI terminals at known ground locations, working in conjunction with a CNI-equipped aircraft, could provide a capability for position fixing, as well a redundant communication accesses. Combinations of terminals appropriately sited may provide the information and functions now performed by TACAN or LORAN or provide a signal environment for precision guidance or instrument landing. Terminals configured this way could have application to precision bombing guidance for close air support.
A single terminal with a directional antenna and suitably programmed signals, in conjunction with the aircraft CNI terminal could provide increased accuracy in the GCA function, with lower power requirements while still maintaining the voice capability.
Operations and the users. An aircraft equipped with a CNI capability would operate in much the same manner as it would if the communication, navigation, and identification functions were separately automated. This will be radically different from current techniques that require the pilot to use voice transmission, manual position charting, and manual activation of identity codes for IFF. Much of the routine reporting and position determination now performed manually could be perform automatically. Furthermore, the additional capabilities offered by a CNI system are expected to point the way to fruitful changes in operational procedures and doctrine.
technology
Four advances in technology, in combination, make a major impact on the possibility of achieving a practical and fully integrated CNI system. These advances are satellites, sophisticated modulation multiplexing signal structures, digital techniques for signal processing and computation, and microminiature component technology.
Satellites as communication relay stations. One of the principal barriers to earlier attempts to achieve integrated CNI systems has been the dissimilarity of radio techniques for long-range and short-range purposes. A single technique suitable for both long and short ranges is a fundamental requirement for a fully integrated system. Recently proven satellite technology makes this possible. Radio techniques formerly suitable only for short distance (line-of-sight) are now also suitable for long distances because relaying by satellites can now provide worldwide coverage at relatively low costs. In the past, line-of-sight relay stations on the ground or in aircraft have been technically feasible, but the cost of obtaining needed worldwide coverage has been prohibitive. In other words, long-distance coverage of sufficient quality and satisfactory reliability can now be provided by the same signaling techniques suitable for short distances and at costs competitive with other long-distance techniques for both communications and navigation.
Sophisticated signal structures. Two new basic types of wideband signal formats, namely, spread spectrum and frequency hopping, and many hybrid combinations of these, have been studied extensively in the last decade. Various applications have been considered, and some have been brought to prototype design and others to operational inventory.
There is developing in this country a good understanding of these signal structures and their capabilities. The importance of this type of signal structure to an integrated CNI system cannot be overemphasized. The use of one of these sophisticated signal structures will provide all of the following desirable characteristics: the capability to multiplex or share the radio channel for CNI signals, the capability for all air and ground terminals to have access to each other as needed, the capability to utilize efficiently the satellite relay station as a multiple-access channel, the capability to have antijam protection, the capability to provide authentic signals, the capability to provide accurate navigation at long distances, and the capability of encoding for security purposes. Many of these features can be provided individually or in some combination by less sophisticated signaling structures, but the fact that they can all be provided by one structure is an essential element of the technical feasibility of a fully integrated CNI system.
Digital techniques for signal processing and computation. The advances in digital computation are well known. It should suffice to say that airborne digital computers are available which can be time-shared to perform a large number of computational, control, and processing functions.
There have been similar advances in the processing of discrete (digital) signals. The state of the art encompasses an understanding of the solid state devices, components, and circuits for equipment needed for signal processing (the generation, modulation, transmission, reception, demodulation, and detection) for the new sophisticated digital signal structures.
Microminiature component technology. The advances already made in miniaturization of solid state devices and components allow for fabrication of low-cost equipment capable of providing a limited form of integrated CNI equipment sufficiently reliable and inexpensive to compete favorably with separate, redundant equipment. It is anticipated that in the near future, through the further development of “large-scale integration,” new device and component technology will become available to support the sophisticated signal structures that might be used for the fully integrated CNI system.
transition
This analysis was not constrained to trying to make the system evolve from present equipments. The emphasis has been on achieving a fully integrated system. An approach to achieving the fully integrated system, one which takes account of today’s investment in separate systems and the evolution from these systems to the integrated system, is the objective of a study which is currently in progress.
However, there has been a sufficient examination of the alternatives of separate, partially integrated, and fully integrated systems and their costs to indicate that improved performance and increased savings are proportionate to the amount of integration obtained. If integrated and separated CNI systems could be compared in the abstract, marked reductions in cost as well as advantages would accrue to the integrated system. When one adds the practical considerations of amortizing the heavy current investment in separate systems and of continuing the costs of operating and maintaining the separate systems during an eight- to ten-year period of evolution, then little if any savings result until the transition is complete. After that, the savings in capital costs and in operating and maintenance expenses will be substantial, the amounts being proportional to the degree of integration that is obtained. This appears to be true regardless of the time at which an integrated program is initiated. This suggests that early efforts be undertaken to control and constrain the development of new separate systems so that they will be compatible with evolution to an integrated system, and/or to reduce the planned development of these new separate systems in some orderly way to achieve early cost benefits.
This report summarizes an investigation of the merits of an integrated communications, navigation, and identification system for military aircraft. The investigation sought to determine whether current technology can provide an integrated CNI system that will meet the worldwide military needs in the 1970 time period more effectively than the present separate communications, navigation, and identification systems, and at reduced cost. The analysis disclosed that the concept of an integrated CNI system utilizing new technology is promising and that the promise is such as to warrant further development.
Hq Electronic Systems Division, AFSC
Acknowledgment
The author, having been designated to report the results of the group study, wishes to acknowledge the contributions made by the technical staff members of ASD (SEG), SAMSO, RADC, AF AL, and the MITRE and Aerospace Corporations during their participation in the study.
William J. Sen is Technical Adviser of the Directorate of Planning and Technology, Electronic Systems Division, Air Force Systems Command, Laurence G. Hanscom Field, Massachusetts. He was employed by the Signal Corps Aircraft Radio Laboratories, Wright Field, Ohio, 194-46, transferring to the Air Force in 1947. He left the laboratories in 1952 for a planning position which led to his being designated senior technical planner for Wright Air Development Center in 1956. He became Technical Director for Electronic Systems, Hq Air Research and Development Command, in 1957. Mr. Sen was Special Assistant (Technical) to the Commanding General, Air Force Command and Control Development Division, from 1960 until he assumed his present position in 1962.
Disclaimer
The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.
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