US Spectrum Requirements: Projections and Trends - Chapter 4

Chapter 4

Radiodetermination and Radiodetermination-Satellite Services

Introduction

Radiodetermination is defined as: "[t]he determination of the position, velocity and/or other characteristics of an object, or the obtaining of information relating to these parameters, by means of the propagation properties of radio waves."[EN359] The radiodetermination service has two parts: the radionavigation service, and the radiolocation service. These services are defined herein and are treated as distinct services in subsequent sections of this report when considering their requirements for long-range spectrum planning. The radiodetermination-satellite service is the space counterpart to the terrestrial service.

The radionavigation service is defined as "[r]adiodetermination used for the purpose of navigation, including obstruction warning."[EN360] The radionavigation service is a safety service, which is defined as "[a]ny radiocommunication service used permanently or temporarily for the safeguarding of human life and property."[EN361] There are no allocations to the safety service per se, however, the radionavigation service and certain other radio services are categorized as safety services because of their use for safeguarding human life and property.

The radiolocation service is defined as "[a] radiodetermination service used for the purpose of radiolocation."[EN362] Furthermore, radiolocation is defined as "[r]adiodetermination used for purposes other than those of radionavigation."[EN363] Examples of radiolocation systems are military radar systems used for defense purposes; and a privately operated continuous wave (CW) radar system using the 1705-1800 kHz band to precisely position a ship to drill an oil well in a large body of water.

Radionavigation Service

The radionavigation service provides a number of vital functions such as aeronautical, maritime, land, and space navigation. The frequency bands allocated to the radionavigation service can be used by either the maritime or aeronautical radionavigation services, while other bands are allocated specifically to the maritime radionavigation or aeronautical radionavigation services. A total of 62 frequency bands are allocated to these three services.

The Federal Government provides radionavigation services for the safe transportation of people and goods, and to encourage the flow of commerce. DOD also develops and uses its own radionavigation services for national defense purposes. The radionavigation service in the United States is jointly planned by DOD and DOT with input from the user community. Every two years, DOD and DOT jointly issue major navigation policy statements and a strategic radionavigation plan published in the Federal Radionavigation Plan (FRP).[EN364] The FRP presents the major goal of DOD and DOT in radionavigation planning, which is the selection of a mix of common-use civilian/military systems which meets diverse user requirements. The user community and its requirements vary widely, e.g., from single-engine aircraft to large commercial airliners; from small pleasure boats to large ocean-going-vessels, and military ships and aircraft. There are numerous user requirements, but the most significant ones are accuracy, reliability, and cost. Two organizations in DOT provide radionavigation services: the USCG, and the FAA. The USCG has the statutory responsibility to provide for safe and efficient maritime navigation; the FAA has the statutory responsibility for aeronautical navigation. Some modern navigation services are used by both maritime and aviation, so there is some overlapping interest. The FAA has the responsibility for the development and implementation of aeronautical radionavigation systems for safe and efficient air navigation, as well as control of all civil and military aviation within the National Airspace System (NAS), and for international airspace under the control of the United States.

DOD develops and operates some its own navigation systems. A number of these systems are used by both military and civilian users. Furthermore, DOD ensures that military ships and aircraft have the necessary civilian and military navigational capabilities.

Many radionavigation services require international standardization to provide for the orderly flow of ships and aircraft across borders. Equipment and operating standards are established in the ITU that primarily deals with radio spectrum matters, in the International Maritime Organization (IMO) for maritime systems, and in the ICAO for aviation systems. The ITU, IMO, and ICAO are specialized treaty organizations of the United Nations, with some overlapping spectrum-related interests. Although the IMO and ICAO consider some radio spectrum matters, their main emphasis is in the standardization and interoperability of equipment and standardizing operating procedures. The United States participates in these organizations to plan and provide for the international standardization of navigation for U.S. ships and aircraft.


Current Radionavigation Uses

This section presents a brief description of the major radionavigation systems currently operating, and their long-term spectrum requirements.

Omega

The Omega system is a worldwide CW radionavigation system used for both maritime and enroute aeronautical navigation. The Omega system operates in the 9-14 kHz VLF band on four discrete frequencies There are eight transmitters in the United States along with about 16,200 civil aviation users, 6,900 civil maritime, and 1,000 DOD users. The number of Omega users is expected to decline steadily for the next 10 years down to 800 civil aviation, 1,200 civil maritime, and no DOD users.[EN365]

The long-term projection of the FRP is that the existing Omega transmitters will continue in operation through 2005,[EN366] and thus the corresponding spectrum requirements for the Omega system will continue through at least 2005. Although the number of U.S. users may decline to essentially zero sometime beyond 2005, the United States may continue to operate Omega systems for a period of time to provide navigation for foreign ships and aircraft as required by international treaty obligations.

LORAN-C

LORAN-C operates on 100 kHz and is a maritime and aeronautical radionavigation system operated by the USCG. It is a long-range radionavigation system that possesses an inherent high degree of accuracy at ranges up to 1,900 kilometers. LORAN-C was originally developed for military use, but was selected for civil maritime use because of its high accuracy and relatively inexpensive receiving equipment.

LORAN-C has been designated by the FAA as a supplementary system in the NAS. The FAA will incorporate LORAN-C in the NAS by approving non-precision approaches at selected airports that have adequate LORAN-C coverage.[EN367]

The FRP estimates for LORAN-C for 1994 are 180,000 civil aviation users, 530,000 civil maritime users, and 29,300 civil land users. The FRP long-range projection shows 33 percent growth from 180,000 to 230,000 civil aviation users from 1994 to 2005; a slight increase in the civil maritime users from 530,000 to 550,000; and a decline in the civil land users from 29,300 to 24,000.[EN368]

The USCG operates 27 LORAN-C transmitters with some joint U.S. and Canadian operations. The 27 transmitters are projected to continue operation through 2005, and there are more current and projected users of LORAN-C than any other service.[EN369] Thus, the corresponding long-range spectrum requirements in the 90-110 kHz band will continue for at least the next 10 years.

Aeronautical Radiobeacons

Aeronautical nondirectional radiobeacons (NDB) operate in the 190-535 kHz part of the spectrum and serve the civilian aircraft and DOD user community with low-cost navigational aids. They are used for transition from enroute to precision terminal approach facilities and as non-precision approach aids in many airports. The NDB's also provide weather information to pilots; and in Alaska, the NDB's are used for enroute navigation. The FAA operates over 700 NDB's; the military operates about 200; and there are 800 privately operated NDB's. There are about 180,000 civil aviation users of these beacons, and about 10,000 military users.[EN370]

The FRP mid-range projections indicate that the number of NDB's will remain about the same for the next five years. Over the long term, the FRP projects a decline of over 50 percent by 2005 to 300 FAA beacons, 400 private, and 20 DOD beacons. Furthermore, during the next 10 years, the FAA expenditures will be limited to replacement of older NDB's and an occasional relocation. Although there is a projected over-50 percent decline in the number of beacons, the numbers of civil aviation users is projected to increase from today's 180,000 to 210,000.[EN371]

Since the number of beacons is projected to decline by over 50 percent, the spectrum requirement is expected to decline a corresponding amount.

Maritime Radiobeacons

Maritime radiobeacons provide a backup to more sophisticated radionavigation systems and are the primary low-cost, medium accuracy system for ships equipped with only minimal radionavigation equipment. The beacons are used for direction finding.

Approximately 150 marine radiobeacons are operated by the USCG in the 190-535 kHz band serving an estimated 500,000 users. The number of beacons is projected to decline down to 50 by 2005, although the number of users is projected to remain large at 290,000.[EN372] Since the number of maritime radiobeacons is projected by the FRP to decline by 67 percent from 150 to 50, the corresponding long-range spectrum requirements are expected to be reduced.

On the other hand, the Institute for Telecommunication Sciences, a unit of NTIA (NTIA/ITS), conducted a study of the use of various methods to provide the differential Global Positioning System (DGPS) signal to make the satellite-based GPS systems more accurate.[EN373] The NTIA/ITS recommended the use of "Coast Guard-like" beacons to provide the signal.[EN374]

If the Department of Transportation decides to implement the recommended national system of beacons to provide the differential GPS signal, there may not be an increase in spectrum requirements as the beacons may be accommodated in the existing spectrum allocations. However, the concept of nationwide deployment of such beacons may require additional study to determine if additional spectrum is necessary.

VOR, DME, and TACAN

The VHF Omnidirectional Range (VOR) provides azimuth readings to aircraft. A collocated Distance Measuring Equipment (DME) System (VOR/DME) provides the distance from the aircraft to the DME transmitter. The VOR system operates in the 108-118 MHz band, and the DME and its military version, tactical air navigation (TACAN), operates in the 960-1215 MHz band.

VOR/DME is the primary radionavigation aid in the NAS, and it is the internationally designated standard short-distance radionavigation aid for air carrier, business aviation, and general aviation instrument flight operations. Its use is an integral part of the air traffic control procedures.

The FAA operated 962 VOR/DME facilities in 1992, and the long-range projection is 1,020 in 1993 through 2000, followed by a projected decline down to 800 in 2005. The FRP estimates that there were 196,000 users in 1992, and the projected number of users is expected to peak at 204,000 in 2000, and decline slightly to 198,000 in 2005.[EN375] The VOR/DME is projected to remain a short-range aviation navigation system through the year 2010.[EN376] The FAA has indicated that beyond the year 2010, the need for air-ground voice and data communications is expected to require the use of spare capacity in the adjacent VOR navigation band as the requirement for VOR's may decrease.[EN377]

At some sites, the DME function is provided by the TACAN system which also provides azimuth guidance to military users. These facilities are called VORTAC stations. The DOD operated 85 facilities in 1992 and had 12,500 users. The DOD requirement will diminish when aircraft are properly integrated with the satellite-based GPS, and when GPS is certified to meet Required Navigation Performance (RNP) for national and international controlled airspace. The GPS certification is expected in the year 2000.[EN378] The DOD has indicated that their "... use of TACAN will continue as a backup to GPS even if GPS is certified to meet the RNP and all aircraft are fitted."[EN379]

Extensive use is projected for the VOR/DME systems for at least the next 10 years, and the corresponding long-range spectrum requirements are expected to continue. The GPS may eventually supplant the VOR/DME and TACAN systems, but this is not expected for at least 10 years until the GPS is certified as an approved sole means navigation system within the NAS. (For additional information, see the sub-section on GPS.)

Joint Tactical Information Distribution System

The Joint Tactical Information Distribution System (JTIDS) is a military system used by United States and NATO forces that provides both communications and navigation functions. JTIDS has been an on-going program for over 20 years, reaching operational status in 1981. The JTIDS is deployed on aircraft and ships of all three military Departments. Man-transportable versions are also used. Operations are expected well into the next century.

JTIDS operates on 51 frequencies in the 960-1215 MHz band under the provisions of Footnote US224.[EN380] The 960-1215 MHz band is also used by air traffic control radar beacon system (ATCRBS), Mode S, the Traffic Alert and Collision Avoidance System (TCAS), DME and TACAN systems. JTIDS operation is allowed on the condition that no harmful interference will be caused to current or future users authorized to operate in the band. An extensive test program was initiated to assure that JTIDS, employing spread spectrum modulation (frequency hopping and phase coding) techniques, can operate compatibly with other navigation systems operating in the band. The issues involving the 960-1215 MHz band will not be resolved until compatibility testing with the Precision DME and MODE-S systems are completed in 1996. (MODE-S is discussed under the Air Traffic Control Beacon System sub-section.)

The JTIDS is expected to operate well into the next century, and thus, the long-range spectrum requirements for its operation in the 960-1215 MHz band are expected to continue.

Instrument Landing System

The Instrument Landing System (ILS) provides aircraft with precision vertical and lateral navigation guidance information during approach and landing. The ILS consists of a localizer operating in the 108-112 MHz band, and a glideslope operating in the 328.6-335.4 MHz band, and associated marker beacons operating at 75 MHz. Federal regulations require U.S. air carrier aircraft to be equipped with ILS avionics. ILS is also extensively used by general aviation and military aircraft. ILS is the ICAO standard landing system, and is used extensively worldwide.

There were 974 ILS sites in the United States in 1992, and the FRP projected growth peak is 1,094 in 2000-2003, with a slight decline to 1,020 projected in 2005. The FRP estimates the number of ILS users in 1992 as 131,000, and it projects about a 15 percent decline to 110,000 in 2005.[EN381]

There were 165 DOD ILS facilities in 1992, and the FRP projects a substantial decline down to 40 in 2005. The DOD had 10,500 users in 1992, and the long-range projection is a decline down to 1000 in 2005.

The FRP points out that even though the present 50 kHz frequency spacing in the 108-118 MHz band has nearly doubled the number of usable ILS channels, frequency congestion in some areas of the United States has limited the number of ILS requirements can be satisfied. The FAA has estimated, that by the year 2000, approximately 100 requirements for ILS's in high density areas of the United States will not be implemented because of ILS frequency congestion.[EN382]

Microwave Landing System

The Microwave Landing System (MLS) was a joint development of DOT, DOD, and NASA under FAA management. Its purpose was to provide a civil/military, Federal/non-federal standardized airport approach and landing system with improved performance. The MLS operates in the 5000-5150 MHz band with associated DME in the 960-1215 MHz band.

In 1978, the ICAO selected the MLS as the international standard precision approach system, with implementation targeted for 1998. The MLS was expected to gradually replace the ILS in national and international civil aviation.[EN383] Furthermore, the ICAO scheduled the MLS to be deployed at all international airports by early 1998.[EN384] The MLS has a number of advantages over the ILS because the MLS signals are minimally affected by surrounding terrain, structures, and weather; and MLS signals can be used to support curved approaches.

The FAA indicated that approximately 464 MLS systems were planned for procurement through 2000, and procurement of an additional 786 were planned after 1999. The DOD had planned to procure up to 405 MLS's through the FAA.[EN385] The FRP projects MLS operations beyond the year 2025.[EN386]

In June 1994, the FAA announced the cancellation of the MLS contracts, indicating that it will focus on buying "off-the-shelf" technology to lower costs.[EN387] The FAA later indicated that it canceled only MLS research and development contracts supporting certain landing categories, indicating that it will purchase the needed equipment on the open market.[EN388]

The Air Force has indicated that although the FAA has canceled further MLS development, "... DOD still plans on using the MLS and has begun installation of both air and ground based equipment."[EN389]

In conclusion, there are a number key aeronautical radionavigation activities in the 5000-5150 MHz band:

Air Route Surveillance Radar

The FAA and the Air Force jointly operate the Joint Surveillance System (JSS) for air defense and air traffic control. Thus the JSS operates in both the radiolocation service and the aeronautical radionavigation service. The newest upgrade to the JSS is the Air Route Surveillance Radar (ARSR-4) radar located at the periphery of the United States, and which provides long range surveillance for air traffic control centers to monitor enroute aircraft. The JSS is also used by air traffic controllers to guide aircraft to smaller airports that do not have their own radar systems. In addition to the JSS, the FAA maintains an extensive network of radars supporting the FAA's air traffic surveillance requirements.

The long-term air traffic surveillance requirements and the availability of large frequency bandwidth make the 1215-1400 MHz band very attractive for air traffic control radars. Both the newer ARSR-4 and the older ARSR radars operate in the 1215-1400 MHz band, with radionavigation services confined to the 1240-1370 MHz band, with the older radars limited to 1350 MHz. The ARSR-4 radars are new and are expected to operate for more than 20 years, and the older upgraded radars could also operate for at least 10 years. Thus, long-term spectrum requirements for long-range air traffic control radars within the 1215-1370 MHz band can be expected for at least 10 years.

Airport Surveillance Radar

The FAA operates airport surveillance radars (also called terminal radars) at over 250 airports for management and control of the aircraft as they approach the airport for landing.

All of the ASR radars operate in the 2700-2900 MHz band. They are the mainstay of air traffic management around major airports, and spectrum requirements are expected to continue for more than 10 years. This spectrum is currently shared with meteorological radars and a variety of DOD radars. The FAA is in the early stages of procuring a new ASR-11 system to replace the older ASR-7's and ASR-8's.[EN390]

Air Traffic Control Radar Beacon System and MODE-S

The Air Traffic Control Radar Beacon System (ATCRBS) operates on 1030 and 1090 MHz at stand-alone sites or in conjunction with the long-range air traffic control and airport control radars to provide identification and other flight information about the aircraft so that it can be tracked and managed by air traffic controllers. The ATCRBS is called a secondary surveillance radar (SSR), and consists of a ground-based interrogator and an airborne transponder. The present system interrogates all transponders in its surveillance area and displays target information on a radar screen.

The MODE-S system, also on 1030 and 1090 MHz, will replace the ATCRBS to provide more accurate position information and to minimize interference. MODE-S is a discrete address beacon system that selectively interrogates only those aircraft in the antenna beamwidth. The MODE-S also provides the means for a digital data-link that will be used to exchange information between the aircraft and various air traffic control functions and weather data bases. The military also operates these systems for air-to-air surveillance.

Spectrum requirements for the ATCRBS and MODE-S on 1030 and 1090 MHz are expected to continue for more than 10 years.

Traffic Alert and Collision Avoidance System

As of December 31, 1993, the Traffic Alert and Collision Avoidance System (TCAS) is required for installation aboard aircraft with a capacity of 30 or more passengers. The TCAS operates on 1030 and 1090 MHz.

TCAS is a family of airborne devices that operate independently of the ground-based ATC system. Three different TCAS control levels have evolved. TCAS I is intended for commuter and general aviation aircraft; and it provides proximity warning only, assisting the pilot in visually acquiring intruder aircraft. TCAS II is intended for commercial airliners and business aircraft; it provides traffic and resolution advisories (recommended escape maneuvers) in a vertical direction. TCAS III, still under development, will provide traffic and resolution advisories in the horizontal as well as vertical direction. The system obtains information from the signals of beacon transponders carried by aircraft for ATC purposes. The level of protection provided depends on the type of transponder carried by the target aircraft. TCAS provides no protection against aircraft that do not have an operating transponder. Major airlines are installing TCAS II systems and plan to install thousands of systems. The TCAS is a new system with widespread deployment expected, and spectrum requirements can be expected for more than 10 years.

Airborne Weather Navigation Radars

All commercial aircraft and many private business aircraft use radars to avoid serious weather during their flights. Most of these radars operate in the 9300-9500 MHz band, and usage is expected for at least 10 years as no immediate replacement system has been identified. Thus, spectrum requirements are expected to continue in the 9300-9500 MHz band for at least 10 years.

The long-term spectrum requirements for weather radar navigation use of the 5350-5470 MHz, 8750-8850 MHz, 13.25-13.4 GHz, and 15.4-15.7 GHz bands are not expected to change in the next 10 years.

Airborne Radar Altimeters

Many aircraft use radar altimeters during flight to determine height above the Earth. Most of the radar altimeters operate in the 4200-4400 MHz band reserved exclusively for this function by international agreement. Because of the capability to achieve increased precision and accuracy at altitudes of 1,000 ft. or less, they are used as a height controlling function in aircraft automatic approach and landing systems. In many aircraft, radio altimeters are also directly coupled to Ground Proximity Warning Systems (GPWS) designed to give warning when an aircraft falls dangerously below its desired descent path. Frequency modulated CW altimeters are used in practically all civil aircraft, including many general aviation aircraft. For higher altitude measurement, pulsed type radio altimeters are in extensive use. Some Federal Government agencies operate these pulsed systems at 1600 and 1630 MHz.

In response to a 1987 Mobile WARC Question, the ICAO studied the issue and concluded that the whole 4200 to 4400 MHz band currently allocated for radio altimeters is required up to at least the year 2015.[EN391] The International Radio Consultative Committee (CCIR) also conducted a study of the altimeter use of the 4200-4400 MHz band, and made a similar conclusion.[EN392]

In conclusion, there are long-term spectrum requirements for altimeters in the 4200-4400 and 1600-1630 MHz bands.

Precision Approach Radar

The 9000-9200 MHz band is used extensively by the military for Precision Approach Radars (PAR's). Newer technologies may eventually be developed that would supplant the PAR's. However, the PAR's can be expected to be used for at least the next 10 years, and thus, long-range spectrum requirements will continue.

The FAA has indicated that it is investigating the use of this band for other aeronautical functions.[EN393]

Global Positioning System

The Global Positioning System (GPS) is a DOD-developed, worldwide, satellite-based radionavigation system operating in the 1215-1240 MHz and 1559-1610 MHz bands. It will be the DOD's primary radionavigation system well into the next century. Twenty-four GPS satellites are available. The GPS is proposed to be used extensively worldwide by the civilian community. As an international system, it is expected to be a principal part of a Global Navigation Satellite System (GNSS). Other possible satellites for GNSS may include the Russian Global Navigation Satellite System (GLONASS) and some geostationary satellites.

The GPS was officially integrated into the U.S. National Airspace System on February 17, 1994. The FAA indicated that the action paves the way for satellites to eventually become the sole means navigation system in U.S. airspace.[EN394] In its comments, DOD noted that radionavigation systems often perform "safety-of-life" services, and are thus less amenable to sharing. DOD indicated that navigation systems, such as the GPS, LORAN-C, and TACAN, provide somewhat competitive functions. DOD also pointed out a current trend to satellite-based navigation systems. Moreover, DOD expects that GPS will replace such systems as Omega, LORAN-C, and perhaps VOR/DME. TACAN will be replaced by GPS for airborne use, but will probably remain in use aboard Naval and USCG ships.[EN395]

The FRP has developed projections for the future use of the GPS system. In 2005, the FRP projects 38,000 DOD users, 500,000 civilian aviation users, 2,500,000 civilian users on land, and 180,000 civilian maritime users. The largest projected growth of GPS usage is in the civilian land sector. Automobile usage of GPS is a major component of the large land use projection.[EN396]

Differential GPS (DGPS) improves the accuracy of the basic GPS. The DGPS process uses differences between the known surveyed location of the DGPS station and the derived location from the DGPS signal received at that location. A "delta" differential correction factor is then calculated which is transmitted to users over a separate radio link. DGPS is necessary for some civil applications such as very accurate position location requirements; for example, off-shore oil drilling. In these position location activities, the GPS is actually providing a radiolocation service that may be supplanting CW radiolocation systems operating in the MF band. Examples of radionavigation applications are trans-oceanic navigation, and precision landing approach for aircraft.

There are two types of differential signals: wide area, and local area. The wide area DGPS could achieve improved accuracies over large areas, e.g., for aeronautical navigation purposes. Local differential signal areas could be used, for example, by a ship looking for the exact location to drill for oil. Various methods are being considered for delivering the differential signal. A geostationary satellite could be used for the wide area differential correction signal; an FM broadcasting sub-carrier could be used for the local area differential correction signal in those cases where integrity, continuity, and availability are not important factors.

The NTIA/ITS conducted a study under contract to the Department of Transportation (DOT) to analyze various methods of providing the differential GPS signal. The study was conducted by the DOT, with the support and assistance of the DOD and the Department of Commerce. Radionavigation beacons operating in frequency bands below 500 kHz similar to maritime radio beacons were recommended for national deployment for the addition of the differential signals.[EN397]

Various architectures and security concerns were analyzed in the study, and it was determined that either of the two preferred architectures will meet aviation user requirements for all phases of flight user requirements, marine user requirements for all modes of operation, and most land user needs including ITS, railroad and survey applications. However, neither architecture will satisfy highway collision avoidance because of the high degree of accuracy (1 meter) required nationwide.[EN398]

The NTIA/ITS study recommended that the FAA should continue to implement its Wide Area Augmentation System and local area differential GPS programs as currently planned and the DOT, in coordination and cooperation with the Department of Commerce, should plan, install, and maintain and expanded LF/MF beacon system modeled after the USCG system."[EN399]

The large growth projections together with the general trend away from other navigation systems to the GPS indicate that spectrum requirements for GPS in the 1215-1240 MHz and 1559-1610 MHz bands will continue well into the next century.

GLONASS

The Russian GLONASS navigation satellite system provides navigation services similar to the GPS. The FAA has a planned research effort to examine the combined use of both GPS and GLONASS for a navigation system which meets the required navigation performance within the NAS.[EN400] Research to date indicates that opportunities exist to develop receiver avionics to take advantage of the GPS and GLONASS radionavigation signals to improve the navigation performance over that available from a single system.[EN401]

The GLONASS operates within the 1215-1260 MHz and 1559-1626.5 MHz bands. The present GLONASS system occupies approximately 24 MHz. The Russian Federation, in discussions with the United States, has indicated that the GLONASS frequency usage will be modified so that by the year 2005, only about 17 MHz will be occupied below 1610 MHz. The United States is playing a key role in ensuring that the GLONASS system will be able to be used, in conjunction with GPS, as a viable global navigation satellite system (GNSS) for international use. This involves ensuring that GLONASS utilizes aeronautical radionavigation radio spectrum which is suitably protected worldwide as well as limiting spurious emissions from MSS mobile earth stations using adjacent frequencies.[EN402]

Shipborne Navigation Radars

Ships with large displacements are required to be equipped with a radionavigation radar system that enables them to navigate in coastal areas and near docks. The 2900-3100, 5460-5650, and 9300-9500 MHz bands are allocated for this purpose. The 9300-9500 MHz band is the most frequently used band because radars using it can provide a very high resolution. Furthermore, the 9300-9500 MHz radars use interference-rejection circuitry to eliminate harmful interference even though several radars may be operating on or near the same frequency in the same geographical area.

The requirement for maritime radionavigation radars is contained in the IMO Safety of Life At Sea (SOLAS) treaty. The radars will continue operating well into the next century; thus, long-range spectrum requirements are expected to continue.

Radar Transponder Beacons

Radar Transponder Beacons (RACON's) are short-range navigation devices that provide target images on a ship's maritime navigation radar operating in the 9300-9500 MHz band. RACON's are used to identify specific locations such as hazards. Although most RACON's are operated by the USCG, private users are permitted to operate RACON's. The USCG expects to have 110 frequency agile RACON's operating by 1994.[EN403]

RACON's provide important navigation information that is difficult to provide by other means, and spectrum requirements for RACON's in the 9300-9500 MHz band can be expected for at least the next 10 years.

Vessel Traffic Systems

The USCG operates vessel traffic systems (VTS) around harbors and coastal areas with large amount of ship traffic. There are eight VTS locations including New York, Puget Sound, Houston, and San Francisco. The radars serve port management and vessel control functions by providing "video pictures" of ship activity at various locations that are then transmitted to a central port control facility. The VTS radars operate in the 9300-9500 MHz band. The usage and corresponding spectrum requirements are expected to continue for at least the next 10 years.

Other Research Activities

Although the FAA and other agencies conduct a great deal of research to improve the performance of existing systems, research into entirely new concepts is also being conducted. The Air Force and the FAA have jointly sponsored research into systems, such as head-up displays and synthetic vision systems, which will supplement existing navigation systems. Many of these systems operate in frequency bands around 30 and 90 GHz. One area of research is high resolution systems for landing applications.

Hughes Aircraft is conducting research into a terminal landing aids radar operating in the 34-35 GHz band.[EN404] Although these bands are not allocated to the radionavigation service, they are near bands that are. If the research progresses towards development or production, then the systems would have to operate in properly allocated bands.

Related Issues

The FAA indicated that its mission can be accomplished within the allocated spectrum, and that no additional spectrum is needed.[EN405]

In addition to filing comments on our Inquiry, the FAA provided its spectrum management concerns in a 1989 correspondence to NTIA.[EN406] The FAA commented on three specific areas:


Trends

The are several major trends in radionavigation that are technology-driven. There is a major trend towards increased use of the GPS satellite-based system for many navigation applications. The GPS is expected to be used for even more applications in the future as the more accurate DGPS becomes available throughout the United States. Conversely, a decline in the number of Omega users indicates a trend away from some of the older technologies.

The increased use of GPS is expected to promote long-term reduced use of traditional radionavigation systems. There will be a period of testing and transition when both GPS and the replaced system will need to be used simultaneously. Gradually, systems such as LORAN-C, ILS, and VOR will be replaced by GPS-bases systems. Spectrum for current systems will need to be retained on a case-by-case basis until GPS has been accepted as the sole source of location information for a given function.


Development of Spectrum Requirements

There are numerous aeronautical and maritime radionavigation systems currently operating providing service to hundreds of thousands of users. There are tens of thousands of radionavigation systems deployed on ships, aircraft, and other mobile platforms. These systems will continue to have spectrum requirements for at least 10 years.

Improved radionavigation systems have been and are being developed using new technologies, emphasizing the satellite-based technologies. Although some of these new systems are expected to supplant many of the older systems, the transition may take at least 10 years.


Spectrum Requirements for the Radionavigation Service

The long-term spectrum requirements for the radionavigation service are generally driven by requirements to support specific radionavigation systems. Although there are trends towards more accurate and reliable satellite-based technologies, the spectrum requirements for both aeronautical and maritime radionavigation services for at least the next 10 years can be satisfied within the existing allocated bands.

Radiolocation Service

The radiolocation service is used by pulsed and CW radar systems for a number of vital functions. The specific functions are: determining precise location, search or surveillance, target tracking, weapons control, ground mapping and target identification, or combinations of these functions. The radars can be fixed or operating on ships, aircraft, missiles or land vehicles, or on space platforms.

By far, the largest user of radar systems in the radiolocation service is the DOD for its national defense mission. Other radiolocation service users are the USCG, Customs Service, FAA, NASA, and the private sector.

Unlike some other radio services that can use alternatives such as commercial resources or non-spectrum techniques, the radiolocation service, especially radars, has few, if any, alternatives to the use of the radio spectrum. Thus, the important mission of the radiolocation service must be achieved using the spectrum.


Radiolocation Frequency Bands

There are 55 frequency bands allocated to the radiolocation service in the United States. Table 4-1 presents the broad categories of the spectrum, and why geophysical and mechanical limitations make one region of the spectrum preferable to another for a particular radar application. These limitations are the reasons why operational compromises are necessary for multi-function radars.

TABLE 4-1

RADAR OPERATIONS AND LIMITATIONS

===========================================================================
70-90 and		Allocations provided but no radiolocation usage or
10-130 kHz (LF)		applications identified.

300-3000 kHz (MF)	Used by CW radiolocation systems for accurate
			position locations. High noise levels are
			characteristic.

 3-30 MHz (HF)		Very long range surveillance possible via
			ionospheric waves. Very large antennas necessary
			for good resolution.  High noise levels. No primary
			frequency allocations; only a small secondary
			allocation at 3230-3400 kHz.

 30-300 MHz (VHF)	Long range surveillance possible.  Large antennas
			required for good angular resolution. Few frequency
			allocations except for a narrow band at 216-225 MHz.

 300-3000 MHz (UHF)	Good for long range surveillance and tracking.
			Narrow bands allocated to radiolocation below
			1 GHz.  Large antennas required, especially below
			1 GHz.

 3-30 GHz (SHF)		Low external noise.  Above 8 GHz, small antenna
			sizes provide good performance leading to various
			airborne and missile-borne applications. Weather
			effects begin above 10 GHz.

30-300 GHz (EHF)	Weather and atmospheric effects seriously effect
			range performance. Good performance obtainable
			with very small antennas.

Current Uses

Radiolocation Usage and Requirements in the 30-300 kHz Band (LF)

The FCC has made frequencies available to the civil radiolocation service in the 70-90 and 110-130 kHz bands under Part 90.103. However, no radiolocation service activities were identified in the 70-90 and 110-130 kHz bands, and no comments were received in response to our Inquiry concerning radiolocation requirements in these bands.

The FCC provides radiodetermination frequencies on a number of channels in the 285-325 kHz band for ship stations for the purpose of cable repair. No comments were received concerning spectrum requirements for this activity.

Radiolocation Usage and Requirements in the 300-3000 kHz (MF) Band

The radiolocation systems using the MF band are CW "lane-counting" types using the precise phase differences of several signals for determining accurate position locations. A typical application is the determination of the precise position of an oil-drilling ship in the Gulf of Mexico. Such MF radar systems have been operating for over 30 years. The private sector and the Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) are the main users of CW radar systems in the MF band.

The 1605-1705 kHz band was reallocated to the broadcasting service on an exclusive basis by WARC-79. A two-part ITU regional conference subsequently planned the band for Region 2, and AM broadcasting should begin in the next few years. Sharing is virtually impossible because broadcasting signals could disturb the necessary phase precision of the CW radar systems; conversely, the possible harmful interference that the radiolocation signals can have on the broadcasting signals. The radiolocation allocation is secondary to broadcasting in the 1605-1700 kHz band, and it is expected that the radiolocation systems' use of the 1605-1705 kHz band will substantially decline because of interference problems.[EN408]

Some of the systems operating in the 1615-1700 kHz band also require a transmitted signal at the second harmonic, in the 3210-3400 kHz band. As the usage of the 1615-1700 kHz band will decline with the inception of broadcasting, use of the 3230-3400 kHz band should also decline.

According to a navigation industry executive, the MF systems operating in this band can provide a position accuracy of 5-10 meters, and the GPS system must use a DGPS for better accuracy. The DGPS can provide an accuracy from 2-3 meters. The inception of the GPS and DGPS has resulted in a 50-percent decline in MF radiolocation service usage over the past five years.[EN409] There are a large number of assignments in the 1705-1800 and 1900-2000 kHz bands, and operations can be expected at least for the next five years. Many of the systems currently operating in the 1705-1800 and 1900-2000 kHz bands will most likely continue to operate over the next five years. However, long-range spectrum requirements for the radiolocation service in the 1705-1800, 1900-2000, and 3230-3400 kHz band are expected to decrease over the next five years as activities are shifted to GPS. The requirements beyond five years are unclear, but nevertheless, are expected to decrease even more because of the increased use of GPS.

Radiolocation Usage and Requirements in the 3-30 MHz Band (HF)

Although some of the very earliest radars used the HF (3-30 MHz) band for radar, the band was not used extensively for operational radars until about the 1970's. Prior to the 1970's, HF radars were primarily used for research and experimentation. One of the main reasons for the lack of extensive activity in HF radars in the post World War II era was the shortage of spectrum allocations, as there are no primary or large allocations made to the radiolocation service in the HF bands.[EN410] Secondly, the radar R & D during that period emphasized the UHF and microwave frequency bands.

The HF bands are highly congested with many users and numerous radio services. Furthermore, skywave propagation frequently permits signals to propagate for long distances, even intercontinentally, which may be desirable for some radio services such as broadcasting, but present sharing and compatibility problems to others such as fixed service communications users. In order to avoid interference, HF over-the-horizon (OTH) radars usually choose transmitting frequencies dynamically by monitoring for other signals and avoiding frequencies that are in use.

OTH radars use signals reflected from the ionosphere to detect targets at long ranges, up to 5,000 km. One of the main uses is the detection of aircraft, although the detection of ships and sea conditions are also applications. Some HF radars also use ground wave signals, although the useful range is much less.

Some future civilian applications of OTH radars could be air traffic control, monitoring ships at sea, interdiction of drug trafficking, and oceanographic applications such as monitoring of sea states and wind patterns over oceans. For example, there are northern Pacific air routes where aircraft must navigate on their own for a large part of the flight, and an OTH radar could fill the void.[EN411]

The Navy operates a HF radar in Whitehall, VA in the 5-30 MHz band, and has also developed and deployed the Relocatable Over-the-Horizon Radar (ROTHR). The ROTHR will be land-based, and will provide early warning of naval and airborne threats.[EN412]

NTIA recently certified that spectrum was available for the Navy Mirage OTH radar system for development in California.[EN413] Following development and testing, the Mirage will enter production followed by deployment aboard Navy ships worldwide. The Mirage operates in the 5-40 MHz band using surface wave and near-horizon propagation to provide OTH target acquisition, identification, and tracking information.[EN414]

Although there are no appropriate allocations, the HF spectrum is used for radiolocation. Furthermore, there are military requirements for HF radar spectrum, and there are a number of civilian applications. However, there are many other users and extensive unsatisfied requirements for HF spectrum, and future allocations to the radiolocation service in the HF spectrum are unlikely. Thus, future HF radar systems must be carefully designed with a dynamic channel occupancy analyzer to minimize harmful interference to other systems.

Radiolocation Usage and Requirements in the 30-300 MHz Band (VHF)

The use of the VHF band for radiolocation systems is limited because the allocations are narrow. Furthermore, high performance is difficult to achieve because very large antennas are required for good angular resolution.

Footnote NG148 provides that the frequencies 154.585, 159.480, 160.725, and 160.785 may be authorized to maritime mobile stations for offshore radiolocation and associated telecommand operations.[EN415] The FCC has developed rules and regulations in section 80.375 concerning these applications. No comments were received on the use of these frequencies for the radiolocation service.

Footnote US239 provides for protection of the Navy's Space Surveillance (SPASUR) system operating in the southern part of the United States in the frequency band 216.88-217.08 MHz.[EN416] The Navy has modernized its SPASUR system, and has operated since 1965. The NAVSPASUR system provides data on satellites and other space objects as they pass over the continental United States. The system uses three transmitter sites and five receiver sites positioned on a great circle in the southern part of the United States. It is a bistatic system, locating objects by triangulation.[EN417]

The DOD indicated in its comments that it is conducting advanced research in radiolocation in the 137-225 MHz band.[EN418] Furthermore, DOD indicated that the VHF or UHF spectrum is needed for development of radiolocation systems for the detection of, and defense against, aircraft employing low-observable (stealth) technology. DOD also indicated that it had a critical need for radars in the VHF or UHF region for foliage penetration since the physics of penetration through foliage requires such wavelengths.[EN419]

The only allocations to the radiolocation service in the VHF band are to a few discrete frequencies in the 154-161 MHz part of the spectrum and the secondary allocation in the 216-225 MHz band. In the near future, 5-10 years, new radiolocation service allocations are unlikely even though new radar spectrum requirements may develop as a result of the DOD advanced research activities. If developed, such VHF radars would be without primary allocation status, and would have to be designed to minimize interference, or used outside the United States.

Radiolocation Usage and Requirements in the 420-450 MHz Band

The 420-450 MHz band is excellent for long-range search and surveillance and, to a lesser extent, target tracking. The large antennas required for good angular resolution generally limit operations to land or ship-based installations.

The Air Force Ballistic Missile Early Warning System (BMEWS) has been the backbone of the U.S. missile defense system for over 30 years. The BMEWS radars are located in Clear, Alaska; Flyingdales, UK; and Thule and Sonderstrom AFB, Greenland, and are used for search and tracking. The radars operate in the 420-450 MHz band, and they have been modernized over the years. Technical improvements on the BMEWS radars may continue over the next 5-10 years. Spectrum requirements will continue over the next 10 years for the BMEWS. In the future, the BMEWS spectrum requirements for the 420-450 MHz band may be reduced if spaceborne radars can perform the early warning function.

The Air Force Pave Paws, or AN/FPS-115, radars are used for detection and tracking of submarine launched ballistic missiles (SLBM), and for satellite tracking. Four phased array radars were installed between 1982 and 1987 in the United States. Other elements of the Pave Paws system are the Perimeter Acquisition Radar which was developed in the 1960's and 1970's as a Safeguard anti-ballistic missile (ABM) radar and the AN/FPS-85 SPACETRACK radar.

The AN/FPS-115 Pave Paws radars and the Perimeter Acquisition Radar use the 420-450 MHz band, and are expected to operate for the next 10 years. The older AN/FPS-85 may be phased out. Some modernization may occur to these radars, and the spectrum requirements will likely continue.

The shipborne AN/SPS-40(V) is an older radar used by the Navy and USCG for air search and surveillance of air targets at long-ranges. The AN/SPS-40(V) radar has been modernized, and it can be expected to be used for the next 10 years.

The frequency 449 MHz is allocated for use by wind profiler radars to measure the atmosphere near the surface of the Earth. The radars measure wind speed and direction as a function of time and altitude, information that is useful to aviation. NOAA is planning a network to cover the United States.[EN420]

The DOD indicated in its comments on our Inquiry that "[A]dvanced research in radiolocation is being performed in the bands ... 400-500; 390-940 ...MHz."[EN421] As discussed in the VHF sub-section, DOD has long-range spectrum requirements for UHF radars for anti-stealth and foliage penetration radars. When considering all of the classified and unclassified current and planned systems, it can be concluded that the military agencies are expected to continue their extensive use of the 420-450 MHz band for long-range search and surveillance radars for at least the next 10 years.

Radiolocation Usage and Requirements in the 902-928 MHz Band

The 902-928 MHz band allocation is shared by Federal and non-Federal users. Both military and non-Federal radiolocation services use the band, sharing with the fixed service, the amateur service, Part 15 devices, and ISM.

The Navy operates the AN/SPS-49(V) as a shipborne air search radar onboard a variety of ships including all aircraft carriers and the AEGIS Ticonderoga class cruisers. The AN/SPS-49(V) is a modern all-solid state radar, and since a large number have been deployed in the fleet, it is likely that operations will continue through the next 10 years. Thus, the 902-928 MHz band will be a spectrum requirement for this radar over the next 10 years.

As noted above, DOD indicated in its comments that "Advanced research in radiolocation is being performed in the bands ...390-940... MHz."[EN422]

The Air Force has indicated that it "... uses the 902-928 MHz band to track missiles at test ranges, a capability that is important because it provides real-time tracking capability of manned and unmanned vehicles in test and training areas."[EN423]

The predominant radiolocation activity in the 902-928 MHz band is non-Federal LMS operations, licensed by the FCC. Whereas there were very few assignments in 1980, there are now over 6,800 frequency assignments. The adoption of final rules and standards by the FCC in 1994 should provide for more LMS growth in the band. There are two basic LMS systems:

These systems were in operation under interim rules under Part 90 for about 15 years. The FCC issued a NPRM on automatic vehicle monitoring in April 1993 to finalize the rules that had been used on an interim basis since 1974. The NPRM was issued in response to a petition for rule making filed by an operator of LMS systems. The new rules would create a more stable environment in which LMS systems operate.[EN424]

The subsequent Report and Order renamed the AVM service by defining and establishing a new service, the location and monitoring service (LMS), defined as "[t]he use of non-voice signaling methods to locate or monitor mobile radio units. LMS systems may transmit and receive voice and non-voice status and instructional messages related to such units."[EN425] This definition expands the service to encompass the location of all objects, animate and inanimate, and to permit licensees to provide service on a private carrier basis to individuals, the Federal Government, and those entities eligible under Part 90.

The FCC expects that in the coming years, LMS systems will play an integral role in the development and implementation of the variety of radio advanced transportation-related services known as Intelligent Vehicle Highway Systems (IVHS) or Intelligent Transportation Systems (ITS). The ITS is a collection of advanced radio technologies that promise to improve the efficiency and safety of our nation's highways, reduce harmful automobile emissions, promote more efficient energy use, and increase national productivity.[EN426]

The FCC is proposing to permit operation of non-Federal profiler radars in the 902-928 MHz band, specifically at 915 MHz. Similar to systems operating at 449 MHz, these wind profilers are sensitive Doppler radars that measure wind speed and direction at a variety of altitudes to collect atmospheric data usable in aviation to detect severe wind conditions. In meteorology, the radars improve weather forecasts and warn of severe weather conditions, and in environmental studies to analyze movement of air masses and pollutants. The FCC issued a NPRM to solicit comments on accommodating wind profiler radar systems at 915 MHz, in response to a proposal by the Radian Corporation.[EN427] NOAA and the National Science Foundation currently operate wind profiling radars on 915 MHz.

The Navy requirements for shipborne search radars should continue for at least the next 10 years; the LMS systems are expected to proliferate; thus, there are radiolocation service spectrum requirements for the 902-928 MHz band for at least the next 10 years.

Radiolocation Usage and Requirements in the 1215-1400 MHz Band [EN428]

The 1215-1400 MHz band is excellent for radars used for long-range search, surveillance, and tracking, and it is used extensively for these purposes.

The JSS is a joint Air Force/FAA system used for air defense and air traffic control. The JSS ARSR-4 is a 3-dimensional radar system using the 1215-1400 MHz band. The radar development began in 1984, and it is a major new system; 40 are expected to be deployed on the periphery of the United States; operations and spectrum requirements are expected well into the 21st century.[EN429] The Air Force has indicated that the ARSR-4 must retain access to the 1215-1400 MHz band in order to support national air defense surveillance and air traffic control missions.[EN430]

The Air Force AN/FPS-117(V) radars and the aerostat version, the L-88, operate in the 1215-1400 MHz band. Thirteen AN/FPS-117's will be deployed to replace the Distant Early Warning (DEW) air defense system. The Customs Service is deploying four of the aerostat L-88 radars in the Caribbean and southwestern U.S. border in a $51 million contract.[EN431] In addition, the FAA operates AN/FPS-117 radar at Murphy Dome, Alaska.

The Air Force is now responsible for the L-88 radars. These radars are currently being replaced by the new L-88A radars. While the L-88 is electrically identical to the FPS-117, the two radars are not similar in operation. The L-88A frequencies are crystal-controlled, while the FPS-117 is more easily tuned and has the ability to frequency hop.[EN432] Since the AN/FPS-117 and L-88 are new radars, and the mission requirements will most likely continue, operations in the 1215-1400 band can be expected for at least the next 10 years.

The AN/TPS-59 radar is a joint Air Force and Marine Corps sponsored system operating in the 1215-1400 MHz band. It will most likely remain in operation through the next 10 years, requiring spectrum in the 1215-1400 MHz band.

The AN/TPS-63 is a transportable radar system used by the Marine Corps for detection of small, low-flying aircraft. It operates in the 1250-1350 MHz band. Improvements have been made to this radar since 1987. The radar is expected to be used at least for the next five years, and if it is modernized, it may be used for 10 years. An aerostat version of the AN/TPA-63 is also in use. Spectrum requirements in the 1250-1350 MHz band will continue for at least five and perhaps 10 years or more. The Air Force operates the Cobra Dane radar (AN/FPS-108) in the Aleutian Islands for space track support and for inter-continental ballistic missile (ICBM) early warning. It was deployed in 1977. The Cobra Dane operates in the 1215-1400 MHz band using a 29m phased array antenna.[EN433] Spectrum requirements will likely continue for the next five years.

There are numerous radar systems currently operating in the 1215-1400 MHz band, many of which are relatively new, and whose operations can be expected for at least the next 10 years. The total of the investments made into the JSS, L-88, AN/TPS-59, AN/TPS-63, and Cobra Dane (AN/FPS-108) are over $1 billion. Without being specific, the DOD indicated in its comments that "[A]dvanced research in radio location is being performed in the bands ... 1215-1400...MHz."[EN434]

In conclusion, the relatively new radars and their important missions indicate that substantial spectrum requirements for the radiolocation service in portions of the 1215-1400 MHz band will remain for at least the next 10 years.

Radiolocation Usage and Requirements in the 2-4 GHz Frequency Range

The 2-4 GHz frequency range has a number of bands allocated to the radiolocation service. The radiolocation service is allocated on a primary or secondary basis in the lower part, 2300-2450 MHz, and to five bands in the upper part, 2700-3700 MHz. NTIA has recently transferred the 2390-2400 MHz and 2402-2417 MHz bands to the FCC.

Although the DOD indicated that advanced radiolocation research was taking place in the 2300-2550 MHz band,[EN435] no other information on this activity was provided by commenters nor were any activities identified by NTIA.

Adequate spectrum space is available in the 2700-3700 MHz bands, and good radar performance and angular resolution can be obtained by radars in this band with reasonably sized antennas. The external noise level is low, enabling long-range air search and surveillance radars to operate in the band. The good angular resolution and narrow antenna beams make the band attractive for military radars for the ability to reduce hostile jamming. The band can be used for multi-function radars for medium-range aircraft detection and tracking.[EN436] The overall good radar performance and the reasonable-sized antennas make the band very attractive for transportable military radars used for air search and surveillance.

The Air Force uses the 2900-3100 MHz band for a transportable land-based three-dimensional air search and surveillance radar system. Overall, the Air Force investment is approximately over $1 billion.

The Air Force Airborne Warning and Control System (AWACS) radar is used for specialized surveillance and identification and control. The radar operates in part of the 2-4 GHz part of the spectrum, but the operating frequency band is classified. Through 1991, a total of 68 AWACS have been produced of which 34 are operated by the Air Force. The estimated cost per aircraft is $112 million.

The Army uses the 2900-3100 MHz band for a major transportable radar used to provide accurate information on artillery and/or rockets.[EN437] Through 1992, an estimated 134 radars have been produced at a cost of $10 million each for a total of $1.34 billion invested.[EN438] The radar is expected to be in use for at least the next five years, and it may see use through the next 10 years.

Cobra Judy, or the AN/SPQ-11, is a shipborne phased array radar designed to detect and track ICBM's launched by Russia in their west-to-east missile range. It collects data for SALT treaty verification. The Cobra Judy operates in this band, and a 9-GHz band capability was added in FY85. The spectrum requirements for Cobra Judy are expected to continue for at least the next five years.

The Navy uses the 2900-3100 MHz band for shipborne radars used for long-range air surveillance using a combination of mechanical and electronic scanning. The radars are deployed onboard a variety of ships, with the total estimated cost over $1.9 billion.[EN439] The Navy continues to modernize the radars, and operations and spectrum requirements will likely continue for the next 10 years.

The AN/SPY-1(V) is part of the Navy shipborne AEGIS weapon system, and considered the Navy's premier fleet air defense system. The AN/SPY-1(V) is a 3-D phased array air defense radar used on guided missile cruisers and destroyers. Through 1992, a total of 35 systems have been produced at a cost of approximately $20 million each for a total of $700 million.[EN440] The AN/SPY-1(V) operates in the 3100-3500 MHz band. Operations and spectrum requirements are likely to extend for at least 10 years.

The Navy has an extensive investment in the 3.5-3.7 GHz band. Navy air traffic control radars are deployed worldwide. The radars utilize 15 or more channels throughout the 3.5-3.7 GHz band for optimum operation. The requirement for operation of these radars will continue throughout the 10-year planning period.[EN441]

NTIA conducted an analysis of the radiolocation service bands in 1987. One of its recommendations was: "Since there is no use of the aeronautical radionavigation service in the 3500-3600 MHz band, consideration should be given to making this band an exclusive radiolocation band."[EN442] The DOD comments indicated that it is performing advanced research in radiolocation in the 2300-2550 MHz and the 2700-3700 MHz bands.[EN443] The DOD indicated that frequencies between 1 and 10 GHz may be needed for spaceborne radar, but operational deployment is not expected until after the year 2000.[EN444]

A review of radar R & D in the 2700-3700 MHz band did not identify any major new radar systems being developed for the band. However, the general trend is towards modernizing existing radars as new technology becomes available, although revolutionary trends sometimes result from the new technologies.

The important national security missions carried out by the many classified and unclassified military radars operating in the 2-4 GHz frequency range indicates that spectrum requirements will be needed for at least the next 10 years.

Radiolocation Usage and Requirements in the 4-8 GHz Frequency Range

The 5250-5925 MHz frequency range is allocated to the radiolocation service on a primary or secondary basis in six bands. These bands have some physical limitations that reduce their usefulness for long-range air search and surveillance. On the other hand, these bands are used extensively for test range instrumentation radars to track missiles and other targets.

The upper band, 5850-5925 MHz, is allocated to the fixed-satellite service (Earth-to-space) on a primary basis, and is shared with the radiolocation service, also allocated on a primary basis. Footnote US245 limits the satellite activities in the United States to international intercontinental systems and such activities are subject to case-by-case electromagnetic compatibility analysis.[EN445]

The 5400-5900 MHz band has been a mainstay for test range instrumentation radars since the early days of the space age. The AN/FPS-16 and its transportable or mobile version, the AN/MPS-25, provided service for many years on the Eastern Test Range, the Western Test Range, White Sands Missile Range NM, Wallops Island, VA, on tracking ships and other test ranges.

Although test range radars remain in use, there is an emerging trend towards use of the new Range Applications Joint Program Office (RAJPO) system. Accurate locating of platforms such as missiles is accomplished via a GPS receiver on the platform and an air-to-ground data link. Use of the RAJPO system may lessen the future spectrum requirements for test range instrumentation radars.

The RAJPO data link operates in the bands 1350-1400 MHz and 1427-1435 MHz. It is scheduled to be used at 18 different test and training ranges throughout the United States. The Air Force has stated that this system is critical to ensuring the safety of personnel during test and training systems operation. Radar tacking of aircraft, etc., will still be required at test and training areas." [EN446]

The AN/SPG-55(V) radar is a Navy fire control radar used with the Terrier and the Standard SM-1 and SM-2 ER (extended range) missiles. The New Threat Upgrade (NTU) program provided for some improvements, but the radars will likely leave service throughout the 1990's.[EN447]

The Navy uses the shipborne AN/SPS-67(V) radar for surface search and navigation, and it is the Navy's primary surface search radar. Operations and spectrum requirements in the 5350-5850 MHz band will likely continue for the next 10 years.

The Navy uses the bands for a surface search and navigation radar. An estimated 133 units have been produced through 1992, and deployment is on a variety of ships, including guided missile cruisers and destroyers.[EN448] The radar has been deployed on newer ships, and operations, and spectrum requirements in the 5450-5825 MHz band can be expected for at least the next 10 years.

The Army's Patriot surface-to-air-missile (SAM) defense system includes the AN/MPQ-53 5-GHz band radar incorporating several phased array antennas. The multi-function radar provides search, surveillance, tracking, and missile guidance.

The DOD indicated that it was performing advanced research in radiolocation in the 5255-5925 MHz band.[EN449]

In summary, the 5250-5925 MHz band is used extensively for test range instrumentation radars, a spectrum requirement that is likely to continue for at least 10 years. The Navy shipboard search and surveillance radars are likely to continue in operation, through upgrades, for the next 10 years.

Taking all classified and unclassified systems into consideration, the radiolocation spectrum requirements are expected to continue for at least 10 years.

Radiolocation Usage and Requirements in the 8-10.55 GHz Bands

Good radar performance is achieved in the 8-10.55 GHz band with small antennas permitting numerous mobile applications on aircraft, missiles, ships, tanks, and other vehicles. Small hand-held radar systems are also used extensively. The band is well suited for short range search. The frequency band allocations are wide, permitting the use of narrow pulses with wide emission bandwidth to achieve good target resolution.

The 8.5-10.55 GHz frequency range is allocated in eight bands, some of which are as large as 500 MHz. Over 2 GHz of spectrum is available for radar usage. Some of the bands are used extensively for radionavigation by the private sector. For example, the 9300-9500 MHz band is used by both aircraft weather navigation radars, and by shipborne navigation radars. Since the FCC uses fleet licenses for ships and aircraft, an accurate count is not available. However, since almost all commercial aircraft and larger ships employ such radars, there must be at least 5,000-10,000 installed navigation radars.

The Army and Marine Corps use the band for transportable ground-based radars for weapon locating. A total of 382 units have been produced at a cost of $6.5 million each for a total cost of nearly $2.5 billion.[EN450] Units have been modernized with new technology, and operations are likely to continue for the next 10 years.

The Navy uses the band for a radar for a fire control system on frigates and small ships. Approximately 94 units of two different models have been produced at a cost of $8.5 million each for a total of about $800 million.[EN451] Operations will likely continue for at least the next 10 years, and spectrum requirements continue.

The Army's Ground Based Radar (GBR-X) is a new radar evolving out of the Upper Tier Theater Missile Defense Program which is part of the Ballistic Missile Defense (BMD) program, known as the Strategic Defense Initiative (SDI) prior to May 1993.[EN452] The GBR-X, also referred to as the GBR-T and formerly referred to as the Terminal Imaging Radar, is a transportable radar operating in the 8.55-10 GHz bands. The radar will search and track enemy tactical ballistic missiles, cruise missiles, and other air-breathing threats. It will have fire control capability against such threats.[EN453] The GBR Theater Missile Defense Radar requires spectrum in the 8.55-10 GHz band, and with adequate funding will likely require spectrum for at least the next 10 years and beyond. Additional information is needed on the National Missile Defense radar and the guided missile interceptor radar to adequately develop their future spectrum requirements.

"Speed gun" radars used by state and local police to measure the speed of autos frequently use 10.525 GHz. FCC license records indicate 2,895 licenses in the 10.5-10.55 GHz band attributed to the many state and local law enforcement agencies that operate such radars for traffic control. This number is probably extremely low since law enforcement agencies are no longer required to obtain a separate license to operate a speed gun. The authority to operate such devices is covered under their normal "two-way" license, regardless of what frequencies that license specifies. (See discussion of "blanket" licenses under the sub-section "The 24.05-24.25 GHz Band.")

The Hughes Aircraft Co. is conducting R & D into a passenger bus warning system called FORWARN at 10.5 GHz. This activity is considered to be part of the ITS activities. Furthermore, 20 MHz of spectrum was identified as a requirement for an ITS lateral collision avoidance radar above 10 GHz.[EN454] Another 200 MHz was identified as needed by ITS for longitudinal collision avoidance radars operating in bands above 20 GHz.[EN455]

Military land-based radars also use the 8.5-10.55 GHz bands for search and surveillance. New radars are being developed that use the bands, and given a typical life cycle of 15-20 years between concept and deployment, spectrum requirements should continue for at least 20 years.

New technologies and military requirements are leading towards multi-function systems capable of simultaneously supporting communications, navigation, and identification functions as well as missile guidance, radar, and electronic warfare functions. Hughes indicates that while much of the multifunction nature of the waveforms will be a result of faster processors and enhanced algorithms, the multiplicity of compound waveforms to support the multiple functions implies that instantaneous bandwidth will be much wider, on the order of 50-60 percent in the 8.5-10.55 GHz bands. Hughes expects to see such multifunction systems in the 10-25 year time frame.[EN456]

In summary, the 8.5-10.55 GHz bands are prime bands for military weapons control radars installed onboard aircraft, and spectrum requirements for such activities should continue well beyond 10 years.

Radiolocation Usage and Requirements in the 10.55-30 GHz Bands

The major application of radars in the 10.55-30 GHz radiolocation bands is on mobile platforms such as fighter aircraft, military unmanned aerial vehicles (UAV's), etc., where physical limitations require small antennas. Good performance can be obtained over short ranges, but precipitation attenuation can limit the useful range.

There are three frequency bands between the 10.55-30 GHz band that are allocated to the radiolocation service. Some of these bands have a large number of frequency assignments. The DOD stated that advanced research in radiolocation is being conducted in the 8.5-10.7 GHz bands.[EN457]

The 13.4-14.0 GHz Band

The 13.4-14.0 GHz band has over 300 assignments most of which are to Federal agencies. The Navy has about 86 percent of the assignments, most of which are to one system. The USCG also uses a weapons control system on a number of ships for protection against anti-ship missiles.

Although the Navy radars are 15-20 years old, continued operations are expected for at least the next five years. No other systems are being developed, and they may operate more than 10 years into the future. Thus, radiolocation spectrum requirements are needed for at least the next 10 years.

The 15.7-17.7 GHz Bands.

The 15.7-17.7 GHz portion of the spectrum is divided into five frequency bands allocated to the radiolocation service. The 15.7-16.6 GHz band is the most used of the five bands.

Military uses of the 15.7-17.7 GHz bands include radars employed for guided weapons systems, combat surveillance, mortar locating, airborne weapons control radars, and unmanned air vehicles.

A segment of the 15.7-17.1 GHz band, 15.7-16.2 GHz, has been approved for use by the FAA for their Airport Surface Detection Equipment (ASDE) on a coequal basis with military radars subject to prior coordination with the military. This usage was accomplished with the addition of Government Footnote G59 to the allocation table.

The FAA operates older ASDE systems in the 23.6-24.4 GHz band dating back to 1969-70. There were 15 systems at one time but only eight systems are currently operating. The FAA is slowly phasing out these systems, and replacing them with systems operating in the 15.7-16.2 GHz band. As the management and control of aircraft on runways is a very important safety issue, ASDE is expected to continue in operation for at least the next 10 years. Thus, spectrum requirements for ASDE in the 15.7-16.2 GHz band are expected to continue.

In summary, there are substantial long-term spectrum requirements for the radiolocation service in the 15.7-17.7 GHz bands to support the military and FAA activities.

The 24.05-24.25 GHz Band

The 24.05-24.25 GHz band is used extensively for automobile traffic speed measuring (speed guns) operating in the radiolocation service. Under Part 90.19, the FCC uses a "blanket" authority to license speed gun operations regardless of whether the radar operates in the 10.5-10.55 or 24.05-24.25 GHz bands. Federal policy for authorization of speed guns is similar, therefore, there may be thousands of authorized Federal and non-Federal speed gun users in the 24.05-24.25 GHz band. These activities are expected to continue for at least the next 10 years, and thus, the corresponding radiolocation spectrum requirements will continue.

The FAA operates older ASDE systems in the 23.6-24.4 GHz, but it is phasing them out and replacing them with systems in the 15.7-16.2 GHz band. The 24.05-24.25 GHz band is available for other radiolocation operations.

Radiolocation Usage and Requirements above 30 GHz

The 30-300 GHz or EHF part of the spectrum is designated the millimeter wave (mmw) region. Advances in solid state and signal processing technologies in recent years have made the millimeter wave part of the spectrum more attractive for a number of applications. Small diameter antennas are possible offering some advantages such as narrow beamwidths. The narrow antenna beamwidth leads to other operational advantages such as increased immunity to interference and improved resolution.

The mmw radars have a number of attractive military applications: surveillance and target identification and acquisition, tracking and fire control, seekers and terminal guidance on missiles, instrumentation and measurements and ground mapping. One of the major disadvantages to operations at millimeter waves is the increased atmospheric attenuation, particularly from water vapor and oxygen. The atmospheric attenuation characteristics in the 10-300 GHz range vary widely and influence the choice of frequency bands. However, there are troughs or atmospheric "windows" of lower attenuation around 35, 90, 140, and 240 GHz, coinciding with some radiolocation service band allocations.

There is extensive R&D on radiolocation service radars, and to a lesser extent, on radionavigation service radars, at millimeter waves. Although the activities are primarily research rather than development, the research results may eventually lead to the development and extensive production of equipment at some time in the future, and spectrum will be needed for equipment at the operational stage. The DOD has indicated that it is performing advanced research in radiolocation in the 33-36 GHz, 42-46 GHz, 59-62 GHz, and 92-100 GHz bands.[EN458] Open literature searches of recent research activities revealed that the military agencies are also sponsoring radiolocation research in the 140 GHz, 215 GHz, and 225 GHz bands. Furthermore, the DOD indicated that it is funding research at 215 GHz and 225 GHz, but both frequencies are in bands that are not allocated to the radiolocation service.[EN459]

In summary, there is a great deal of DOD-sponsored radar R&D taking place in the millimeter wave bands. The R&D applications stress ground mapping, including precise resolution and target identification. Some of the radar R&D will most likely evolve into the production and deployment of radar systems.

General Motors has conducted research into the use of automotive radar systems in the 76-77 GHz band, and has petitioned the FCC to amend their rules to permit such a service. GM indicated that the band has been proposed in Europe for radar and road guidance systems.[EN460] The FCC subsequently proposed to amend its rules to limit non-licensed Part 15 use of the 76.0-77.0 GHz band to vehicular radar systems.[EN461]

In conclusion, radiolocation long-term spectrum requirements may evolve in the 33.4-36 GHz, 59-64 GHz, 92-95 GHz, 95-100 GHz, and 134-142 GHz bands.

Radiolocation Usage and Requirements Above 300 GHz

Although frequencies above 300 GHz are not allocated at the present time, research is taking place, and allocations may have to be considered in the future. A majority of the research in the 300-3000 GHz (3 THz) band emphasizes components such as oscillators, mixers, amplifiers, etc. As currently envisioned, the main applications are radio astronomy and remote sensing. The remote sensing application leads to radiolocation service applications. Long-range spectrum requirements for the radiolocation service above 300 GHz may evolve as the R & D continues.

Long-range Spectrum Requirements for Ultra-Wideband and Synthetic Aperture Radars

Although ultra-wideband (UWB) radars date back to the early 1960's, there has been a strong interest in UWB in recent years, particularly for potential military applications. UWB radars are characterized by very wide bandwidth and the commensurate fine range resolution. There are military applications such as the imaging of typical tactical targets where resolutions on the order of 30 cm are desired. Other potential military applications include counter-stealth capabilities, low probability of intercept (LPI), and the detection of relocatable targets in camouflage and foliage.

UWB radars can be generally categorized into impulse radars and non-impulse radars. The non-impulse radars are generally extrapolations and extensions of conventional radar systems. An impulse radar is defined as a radar with a waveform of a single-cycle sine wave that has a bandwidth of approximately 100 percent, or approximately equal to the numerical value of its center frequency.[EN462]

The DOD recognizes that there is no possibility of exclusive or even sufficient properly allocated shared spectrum for UWB radars, and thus, spectrum sharing is required. DOD also recognizes that support for these systems must be based on demonstrated electromagnetic compatibility. Furthermore, DOD asks that flexibility should be allowed to permit their operation in bands where such compatibility can be shown.[EN463]

There has been extensive research and experimentation on UWB radars over the past five years. The results indicate that the UWB radars are useful for certain applications. It is possible that one or more of these systems may move forward to a production phase within the next five years. The wide emission bandwidth of UWB radars transcend many bands, including passive bands, that are used by many services. Although spectrum requirements are apparent, spectrum allocations to accommodate UWB systems are virtually impossible to obtain.

The Navy and NASA are experimenting with synthetic aperture radar (SAR) systems which operate in several radiolocation bands simultaneously and may be able to accomplish many of the applications of UWB radars while operating within allocated radiolocation bands.

Radiolocation Service Requirements for Multi-Band Radar Systems

Radar target identification is valuable in applications such as remote earth sensing and for military uses. Research has been conducted on radars that operate simultaneously in two or more bands to determine if the data provides more accurate target identification. The following provides brief descriptions of some of the recent research.

The MIT Lincoln Laboratory has conducted research and experiments on target identification in foliage using radars operating simultaneously at UHF, in the 1215-1400 MHz band, and in the 5 GHz band, fully polarimetrically.[EN464] The system was an airborne synthetic-aperture-radar (SAR).[EN465] NASA has a established a tri-band radar at the Jet Propulsion Laboratory (JPL) for research. The radar is the airborne synthetic aperture radar (AIRSAR) operating at 410-450 MHz with a 40 MHz chirp bandwidth; 1220-1260 MHz with a 40 MHz chirp bandwidth; and 5270-5310 MHz also with a 40 MHz chirp bandwidth.[EN466]

The ARPA and Navy have funded research into a tri-band radar for target identification. The radar was a polarimetric SAR using the 8-10 GHz, 1215-1400 MHz, and 5 GHz frequency bands. The radar could change transmit and receive polarization on a pulse-to-pulse basis. The system provided very high image quality.[EN467]

In summary, the overall mission requirement for improved and very accurate target information is the driving force behind the increased interest in tri-band radars. This application is for an airborne radar "mapping" the ground and identifying targets. Spectrum requirements will likely be accommodated within existing allocated bands.

Radiolocation Service Spectrum Requirements for Spaceborne Radars

Spaceborne radars (SBR's) can provide wide area surveillance of the Earth for commercial, law enforcement, and military applications including national defense and the detection of drug smuggling traffic. Satellite radars have two major advantages over surface or airborne radars: an essentially unrestricted line-of-sight view to any point on Earth, and an extremely large field of view. The disadvantage is that their location is always known, and a given satellite is within the view of a jammer for substantial periods of time.

In their comments, DOD stated that "there is a known and documented requirement for deployment and operation of a DOD spaceborne radar system." Furthermore, the DOD indicated that basic research is presently underway to determine optimum frequencies, modulation, and other parameters.[EN468]

The DOD further indicated that while the specific spectrum requirements for a spaceborne radar are not yet available, it believes that frequencies between 1 and 10 GHz will be needed. Operational deployment is not expected until after the year 2000.[EN469]

The Naval Electronic System Command funded research into spaceborne radar in 1985-1986 to identify the optimum radar architecture for air surveillance. After an extensive study weighing various advantages and disadvantages, Brookner and Mahoney concluded that "[t]he choice of frequency for a satellite air surveillance radar quickly can be narrowed to a choice between the 1215-1400 MHz and 3 GHz bands."[EN470]

Rockwell International has conducted research into spaceborne radars for various applications in the radiolocation service and other services. One application where substantial future commercial growth is expected is SAR image interpretation. Rockwell indicates that requirements for higher resolutions, e.g., about one meter, will provide the impetus to go to frequencies in the 8.55-10 GHz range where bandwidth in the hundreds of Megahertz will be needed. Rockwell also indicates that the associated space-to-Earth communications radar data link requirement will likewise run to hundreds of MHz.[EN471]

Many of the SAR space applications are for imaging radars for remote Earth sensing. Although not a radiolocation service per se, remote sensing could lead to military applications. NASA has used three Shuttle Imaging Radars (SIR-A, SIR-B, and SIR-C). All three operate in the 1215-1400 MHz band, and the SIR-C also operates in the 5-GHz band. A future system, the X-SAR, will operate at 9.6 GHz.[EN472]

The Earth Observation Satellite (EOS), a joint U.S., Japanese, and European effort will use the 5.3 and 9.6-GHz bands in 1997.[EN473] The only SBR system identified to be using the 3-GHz band is the Soviet ALMAZ SAR system launched in 1991.[EN474]

The existence of radiolocation stations onboard spacecraft is recognized in International Footnote 713 that has been incorporated into the National Table of Frequency Allocations:

"In the bands 1215-1300, 3100-3300, 5250-5350, 8550-8650, 9500-9800 MHz, and 13.4-14.0 GHz, radiolocation stations installed on spacecraft may also be employed for the earth exploration-satellite and space research services on a secondary basis."[EN475]

Technology trends and available bandwidth appear to be focusing on 8.55-10 GHz for space-based radar systems. Based on the information received from industry, space-based radar systems may proliferate in the future although there may be other applications in addition to the radiolocation service.

The Air Force has received Congressional budget approval for the Alarm early-warning satellite.[EN476] The Alarm is believed to use radars onboard low-Earth orbiting satellites, and will transmit its collected data via communications satellites to ground control stations. Spectrum requirements for the Alarm system will be needed as the system becomes more clearly defined.


Trends

The review of ongoing R & D, interviewing experts, analyses of existing and planned operations, and the DOD comments reveal numerous trends:


Spectrum Requirements for the Radiolocation Service

A review of the R & D indicated that the future spectrum needs of the radiolocation service can be accommodated within existing allocations. Those new systems developed in heavily used bands where there are no allocations must use engineering and operating techniques to minimize the interference potential.

With the following exceptions, the radiolocation service long-term spectrum requirements can be accommodated within the existing allocations:

Radiodetermination-Satellite Service

The radiodetermination-satellite service (RDSS) is defined as "[A] radiocommunication service for the purpose of radiodetermination involving the use of one or more space stations."[EN478] The RDSS can provide both radionavigation and radiolocation services, and its long-term spectrum requirements are considered separately from that of the radionavigation-satellite service. There has been considerable private sector interest in developing and operating a radiodetermination satellite or a radiodetermination-satellite type of service that could provide position locating services. A typical application would be from the long-haul trucking industry, where the headquarters or central control facility could easily determine the precise location of its trucks.

Although not a true RDSS system or service, one approach uses another radionavigation service to determine position which is then communicated to a central location. A remote unit calculates its position from a separate navigation system such as GPS or LORAN-C, and then transmits its location via a communications satellite system operating in either the fixed-satellite or mobile-satellite services. One example of this pseudo-RDSS system is the Qualcomm Company use of LORAN-C and a communications satellite to provide positioning and locating services to long-haul trucking companies. A true RDSS system would be a self-contained navigation and satellite system using the frequency bands allocated to the RDSS.

True RDSS systems use the timing provided by radio signals transmitted by multiple satellites and a participating vehicle (or remote ground station) to a central control point. In a supplementary service, using appropriate radio frequency spectrum, the positions can be communicated to the vehicle or remote station for navigation and/or locating.

Following the proposals of the United States and other nations, the ITU allocated frequency bands to the RDSS at the 1987 Mobile WARC and at WARC-92. The U.S. proposals advocating RDSS allocations resulted from industry requirements. One system that was never fully implemented was developed by the GEOSTAR Corporation. While GEOSTAR operated a satellite messaging system in the radiodetermination satellite service using two satellites for a few years, the positioning capability was never implemented.

The relatively low cost of GPS receivers has reduced the impetus for separate RDSS satellites. Thus, no additional RDSS spectrum requirements are anticipated for at least the next 10 years.


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Proceed to Chapter 5, Other Space Services and Radio Astronomy.