US Spectrum Requirements: Projections and Trends - Chapter 2

Chapter 2

Fixed and Fixed-Satellite Services

Introduction

The fixed and fixed-satellite services provide communications between two or more fixed locations. The fixed-satellite service involves one or more satellites as intermediate relay points; the fixed services utilize only terrestrial stations.

The use of radio systems for point-to-point communications has gone through several phases, including the use of HF radio after World War I for long-range circuits, especially transoceanic circuits and other routes which were not well served by the early wired telephone and telegraph networks. The next important phase of point-to-point radiocommunications began after World War II, when extensive point-to-point microwave networks were installed by the telephone companies. These microwave networks typically had more than a thousand times the information-carrying capacity of HF radio links, which allowed microwave to carry TV programs and large numbers of long-distance telephone calls. Unfortunately, each microwave link only had a short range (50-80 kilometers) and many links had to be connected in series to achieve transcontinental ran ge.

The development of communication satellites in the 1970's allowed wideband single-hop relay of information across a continent or an ocean. Satellites greatly improved transoceanic communications of many types, and provided improved distribution of television signals across the United States. The half-second transit-time delay for geosynchronous satellites was objectionable to telephone users, however, and satellite-based voice circuits did not gain wide acceptance. Optical fiber became a greatly-improved alternative to copper wires in the early 1980's, and it has become the technology of choice for most new high-traffic capacity communications between fixed points installed in the 1990's.

This chapter describes the present state of fixed radiocommunications and estimates future requirements for radio spectrum supporting these services. Section II describes the (terrestrial) fixed service; Section III describes the fixed-satellite service.

Fixed Services

The fixed service is defined as "a radiocommunication service between specified fixed points."[EN176] This includes those services in which a stationary transmitter communicates with one or more intended stationary receivers.[EN177] Fixed services include operations in frequency bands ranging from below HF (3 MHz) to millimeter-wavelength (above 30 GHz). They can be divided into several very different groups, according to frequency. The lowest range is the HF band (3-30 MHz). HF signals are not restricted to line-of-sight, but can travel for thousands of kilometers, providing a long-range but highly variable narrowband service. At VHF and UHF frequencies (30-1000 MHz), narrowband fixed services are provided over short ranges (up to 60 km), often sharing frequencies in mobile bands but using directional antennas. These services also include the rapidly growing point-to-multipoint multiple address service (MAS). The last group of fixed services uses microwave frequencies (above 1 GHz). Point-to-point microwave systems (often simply called "microwave systems") provide wideband communications over line-of-sight paths. Tropospheric scatter systems provide point-to-point service over paths up to 200 km, using highly directional antennas and high-power transmitters. Point-to-multipoint microwave services are used over line-of-sight paths, often with an omnidirectional master antenna and directional node antennas. These microwave fixed services have been described in a recent NTIA staff stu dy,[EN178] hereinafter called the Fixed Study.

The fixed services will be grouped within seven categories: HF services, VHF/UHF services, and five categories of microwave services. The microwave categories include common carrier, private, auxiliary broadcasting, cable relay, and Federal Government. These five microwave categories represent the licensing categories established by the FCC or NTIA. Within each of these five categories, there are functionally similar uses which cross the category boundaries. For example, the supervisory control and data acquisition (SCADA) functions within private operations are similar to SCADA uses within the Federal Government. Similarly, video signals are carried by stations belonging to all five categories, using virtually identical technology.


Current Uses of the Fixed Service

High Frequency Services

Since HF signals are reflected back to Earth by the ionosphere, they can travel long distances, including transoceanic routes. HF communication users must consider the constantly-changing nature of the ionosphere, high levels of ambient noise, severe crowding and interference, and the need for relatively large antennas. Nevertheless, because of the long-range capability using inexpensive equipment, HF is uniquely valuable for many long-range fixed applications. USCG said that no other portion of the spectrum can "do it all" like HF.[EN179]

The DOD and many other Federal agencies use HF fixed to support priority communications after hurricanes, earthquakes, or other natural disasters have disrupted the existing communications infrastructure. DOD uses HF for command and control communications. In addition, HF communications are often the only way to communicate with developing nations via radio links. The recent development of HF automatic link establishment (ALE) technology has given HF systems improved performance. An ALE system continually monitors the propagation between all stations in the network over a range of HF frequencies. This allows the best frequency to be automatically selected for each message, substantially improving performance and reliability over conventional HF systems. Many Federal agencies have joined the Shared Resource Program (SHARES), which uses HF voice network assets and ALE technology, during emergency conditions.[EN180]

Private industry and Federal agencies use many fixed HF links to offices in foreign countries, partly as backup for sometimes unreliable foreign communications services. The main Federal users are DOD and the Department of State, which maintain many HF links to overseas bases, embassies, and offices.

VHF and UHF Fixed Services

Fixed services are permitted in the mobile bands in the 30-1000 MHz range, though often as a secondary service or only in a limited geographical area. These fixed services include voice circuits (often serving as low traffic backbone between mobile radio sites), supervisory control and data acquisition circuits (SCADA) for control and monitoring of utilities, hydrologic and transportation systems, to replace wired telephone connections in remote areas,[EN181] and to send audio program material from radio studios to radio transmitter sites. Most VHF/UHF fixed services share frequencies (sometimes on a secondary basis) within the VHF and UHF mobile bands—using directional antennas, but otherwise similar technology to the mobile systems. Recently, several bands have been allocated especially for fixed services around 900 MHz. These bands provide for MAS, where a master site can provide two-way data connections to a number of slave sites. This rapidly growing technology is being used for a wide range of services, from verifying checks written at stores to reading residential electric meters.

Common Carrier Fixed Services

These microwave services are licensed by the FCC's Common Carrier Bureau under Part 21 of the FCC Rules. They include fixed radio stations operated mainly for the use of the public, i.e., for the use of parties other than the owner of the station. The telephone companies—local exchange carriers (LEC's) and long distance or interexchange carriers (IXC's)—and cellular telephone companies are the major users.

The telephone companies built networks of point-to-point analog microwave links in the 1950-1970 period in the 4-GHz and 6-GHz bands and short-range links in the 11-GHz band. The original analog circuits carried coast-to-coast TV coverage, as well as long-distance telephone circuits and computer data. Most of the early analog channels have been converted to digital systems in recent years. Narrowband channels in the 2-GHz bands have recently proven ideal to provide a backbone network for rapidly-expanding cellular telephone systems. The 2-GHz links are also used by telephone companies to bring services into smaller towns in remote areas, where the lower equipment costs and the modest bandwidth requirements of a small town make an excellent fit.

Public operations also include a series of "distribution" services. These include the multipoint distribution service (MDS, 2 GHz), the multiband multipoint distribution service (MMDS, 2.5 GHz), digital electronic message service (DEMS, 10.5 GHz) or digital termination service (DTS), and a recently proposed local multipoint distribution service (LMDS) operating at 28 GHz. These distribution services are intended to provide one-way or two-way services for digital messages, but they have been used mainly to distribute TV signals. They feature a "star" topology, i.e., a master station (with an omnidirectional antenna) communicating with multiple slave stations (using directional antennas aimed at the master station). The same bands and services can often be used by private operators.

MDS and MMDS are used as "wireless cable" in rural areas where the subscriber density is too small to support cable TV and in urban areas where they compete with cable. LMDS is planned for crowded urban locations, where multiple short-range master stations would be used.

Private Fixed Services

These microwave services are licensed by the FCC's Wireless Radio Bureau under Part 94 of the FCC Rules.[EN182] They include services that are operated by organizations mainly to carry signals for their own purposes. Major users include private companies, utilities, transportation providers, and state and local governments.

Private companies use microwave to support corporate data and voice circuits serving several local sites. These links are installed to get improved economy or performance compared to the LEC, or to provide backup circuits independent of the LEC central office.

State and local governments use microwave to interconnect various government office complexes. In addition, many cities interconnect police and fire stations with a microwave system backbone, serving as a back-up in case a major disaster destroys normal telephone communications. State government functions use private microwave as backbone to connect remote mobile radio relay sites. These sites provide statewide mobile radio service to state highway patrol, natural resource management, and highway maintenance personnel.

Transportation and utility companies use private microwave for SCADA, which includes monitoring and control applications for pipelines, electrical power lines, railroads, dams and locks, irrigation projects, etc. In many SCADA applications, the data rate is quite low, although high reliability and quick response may be needed. SCADA applications often follow a solitary power line or pipeline through remote areas, where few alternative telecommunication services are available. State and local governments also use SCADA to control water, gas, and electric distribution, traffic signals, etc.

Auxiliary Broadcasting Services

Auxiliary Broadcasting (AUXBC) functions are described in Part 74 of the FCC rules; they include applications that support the TV and AM/FM broadcasting industry. Although TV signals are broadcast to the consumer with a 6-MHz-wide signal in the NTSC[EN183] format, AUXBC video links utilize an analog frequency-modulated point-to-point microwave channel with 17-25 MHz bandwidth. Electronic news gathering (ENG) uses transportable microwave links, usually carried in small vans with telescoping antenna towers, to provide "live" coverage of a local news event or a major sports event. ENG's will typically move several times a day to cover different local news stories, using ENG frequencies that are often coordinated and shared between local TV stations on a tightly scheduled basis.

Fixed AUXBC video applications include studio-to-transmitter links (STL's) and intercity relays (ICR's),[EN184] which carry program material and control circuits between the studio, transmitter sites, and other locations. A large TV station might use 10-15 AUXBC links, including several remotely controlled rooftop ICR's that can be pointed to receive signals from distant ENG's or used with a local camera to provide pictures of weather or traffic conditions.

AUXBC audio links are used by AM and FM stations for temporary live coverage of particular events, as well as for studio-to-transmitter links. Audio STL services are also provided by specially equalized analog or special digital telephone lines.

Cable Relay Service

The cable relay service (CARS)[EN185] is described in Part 78 of the FCC rules; it supports the cable TV industry. CARS and AUXBC use electronic news gathering in identical ways to provide temporary real-time coverage of news events outside the studio. CARS uses studio-to-cable headend links (SHL's) to transmit TV program material from a distribution hub to individual cable headend sites, where the signal is transferred to cable. SHL's can transport individual TV channels (similar to the STL's used by AUXBC services) or they can transmit blocks of up to 42 contiguous NTSC channels from a central distribution hub to multiple cable headend sites.

Federal Government Fixed Services

The Federal Government uses fixed services for a wide variety of functions, in accordance with the regulations found in the NTIA Manual. Many functions (including SCADA, back-up communications for high-priority functions, backbone connection to remote radio sites, etc.) are similar to corresponding civilian functions. Other Federal functions, e.g., military and air traffic control, do not have non-Federal counterparts.

Federal civilian agencies like the Department of Interior and Department of Agriculture use microwave networks to support mobile radiocommunication sites in Federally-controlled remote areas like National Forests and National Parks. These networks are used for natural resource management, firefighting, law enforcement, tourist information, environmental and wildlife control, search and rescue, and general administrative communications. The Departments of Justice and Treasury maintain extensive urban and wide-area radio nets to support national law enforcement and security. The FAA uses a nationwide microwave network to monitor and control the national airways, bringing air traffic information from remote radar sites and navigation sensors, and providing two-way voice and data communications between air traffic controllers and aircraft. USCG provides monitoring and control of maritime traffic in major U.S. harbor areas, using microwave communications to interconnect multiple local vessel traffic service (VTS) radar and radiocommunications sites.

Federal power agencies, such as the Tennessee Valley Authority (TVA), Bonneville Power Administration, the Army Corps of Engineers, etc. make extensive use of microwave SCADA networks to monitor and control the operation of electrical distribution networks, irrigation, flood control, river navigation and lock systems, navigation projects, gas and oil pipelines, and other systems. DOE, for example, has 2.4 million kilometers of telecommunications circuits for SCADA applications.[EN186]

Military test and training ranges use extensive fixed microwave systems to support range safety and security; to relay telemetry data received from airborne, mobile, and stationary platforms to central control sites; for closed circuit TV for safety, security, and performance evaluation; to provide radar tracking and air traffic control information, and to observe other test and training results; and to support a wide range of logistics and administrative support activities on these ranges. The need for extensive communication backbones on some ranges includes the relay to central monitoring sites of real-time updates on the status and exact location of thousands of individual vehicles and soldiers during realistic exercises that cover hundreds of square kilometers of test range.

Military operations and training make extensive use of transportable fixed and fixed-satellite microwave terminals, designed to be transported to an overseas combat or support area, rapidly set up and configured into a communications network, and used for critical operational C3I communications for the duration of the mission. These capabilities are also used domestically to support training and to provide support of disaster relief and similar missions..

Numerous Federal agencies use the fixed service to communicate with a wide range of sensors that keep track of weather, stream flow, geophysical, agricultural, and pollution phenomena. Microwave is also used to provide more economical communications between nearby offices, as well as providing high-reliability backup in case of LEC failures.


Trends

General Market Trends

Although the telecommunications industry as a whole is growing rapidly, the fixed microwave industry is not. Figure 2-1 shows the number of fixed licenses in the non-Government microwave bands above 1 GHz, not counting the 13-GHz CARS band (which is shown separately in Figure 2-7).[EN187] Some reasons for the observed performance of the microwave industry will be examined in this section, with obvious application to predicting future fixed service spectrum requirements.

Figure 2-1. Number (in thousands) of fixed licensed frequencies in the non-Government bands above 1 GHz, excluding the 13 GHz band. Figure 2-1 goes here.

In contrast to the stable, or slightly declining number of microwave licenses, fiber optic systems are growing very rapidly. Figure 2-2 shows the cumulative kilometers of installed by U.S. LEC's and IXC's for the 1987-1992 period.[EN188] The NTIA Fixed Study[EN189] calculated that the amount of new communications capacity (in terms of DS-3 kilometers)[EN190] added in optical fiber in 1991 was about 23 times the capacity added with microwave systems.

Figure 2-2. Cumulative fiber kilometers (in thousands) deployed by LEC and IXC service providers.
Figure 2-2 goes here.

The initial rapid growth in optical fiber systems was produced by the IXC's, whose long-distance networks are now mostly based on fiber. The next wave of fiber growth was by the LEC's, who installed fiber to interconnect central offices, major customers, and neighborhood interface sites. About two years ago, cable TV companies began replacing microwave and coaxial cable with optical fiber networks capable of supplying advanced two-way digital services. Independent fiber providers are currently building fiber systems in dense business and industrial areas. The proposed mergers between cable TV and local telephone companies represent still another possible route to a great expansion of local telephone/TV/data service based on optical fiber.

The rapid expansion of optical fiber systems by multiple vendors is expected to bring a competitive environment for optical fiber services throughout urban areas, although it is not yet clear which of the rapidly-changing business alliances will provide the services. Cellular telephone companies, future PCS providers, cable TV companies, the LEC and non-LEC telephone companies, etc. are all expected to play a role.

Many commenters recognized a strong and continuing trend toward the replacement of long-haul microwave with fiber.[EN191] Motorola asked that the migration to fiber be encouraged, so that spectrum could be freed up for new mobile services.[EN192] Comsat suggested that a shrinkage of the fixed services in the shared 4-GHz and 6-GHz bands would allow greater growth of fixed-satellite services in those bands.[EN193] SBCA wanted to put a freeze on any new fixed assignments in the 4-GHz band, leaving the band more available for television receive-only (TVRO) sites.[EN194]

Fiber Optic vs Microwave Tradeoffs

A single optical fiber can carry 2400 Mb/s of data (48 DS-3 circuits); the maximum capacity of a commercial microwave channel is 135 Mb/s (three DS-3 circuits). Thus, fiber provides much greater capacity than microwave, and this capacity can be increased arbitrarily by simply adding more fibers. Typically, 25-35 individual fibers are installed in a fiber cable.[EN195]

Because the relatively high cost of right-of-way and cable burial, the cost is the same for a cable with one fiber or many fibers. The cost per fiber decreases as more fibers are included in the cable. Thus, fiber tends to be more expensive than microwave for a low-traffic circuit and less expensive than microwave for a high-traffic circuit. The case study in Table 2-1 shows the relative cost of a specific 130-km circuit requiring three microwave hops or one fiber repeater site.[EN196] This table expands a figure in the cited paper to include a larger number of DS-3 links. The relative costs show why microwave is often chosen for routes with less dense traffic and fiber is selected for denser routes. Difficult terrain or a difficult landowner can make it more time-consuming and expensive to install fiber. Microwave circuits can usually be installed much more rapidly than fiber.

The high cost of a fiber optic link is partly due to the cost of optical components, with individual optical repeaters, laser modulators, optical switches, etc. often costing $25,000 to $50,000 apiece. This cost could decrease by 90 percent with economies of scale and improved technology. The cost of placing fiber in the ground will remain an important factor, however, even if component costs decrease.

There is a risk that buried fiber will be accidently damaged. One industry rule-of-thumb points toward one fiber cut/year/500 km of fiber. Alcatel says that typical fiber breaks require 6-12 hours to locate and repair.[EN197] Since the risk of outages are too great for some applications, many fiber networks are beginning to use self-healing ring architectures where the ring must be broken in two places before a segment becomes isolated. Microwave links are also used to back up some fiber circuits.

TABLE 2-1
RELATIVE COSTS OF MICROWAVE AND FIBER OPTICS OPTIONS
                                   
Number of DS-3 Links	Construction Cost per DS-3 Link ($1000's)
				Microwave	Fiber Optics
==================================================================
1				1890		4410
2				945		2205
3				630		1470
6				450		735
12				260		367
24				203		195
36				183		138
60				168		88
96				160		67

Although fiber has substantial advantages for many applications, AT&T has suggested several situations where microwaves are likely to remain preferable over fiber.[EN198] AT&T's list includes circumstances where the circuit needs only a traffic capacity of one DS-3 or less, crosses inaccessible terrain, is needed for disaster recovery, is used as backup for disaster avoidance, is used for rapid deployment, or is used to provide temporary service.

The above list implies that fiber optics have taken over many of the long-haul, high-density markets, but have left several important niche markets to microwaves. Some of these niche markets may remain quite active in future years. Several commenters stated that low traffic density, inaccessible terrain, or cost would prevent complete replacement of microwave with fiber.[EN199] DOD stated that an increased percentage of fixed communications traffic would be shifted to fiber, but that transportable links would continue to need microwave fre quencies.[EN200]

Fixed Use of Higher Frequency Bands (above 15 GHz)

Another major change affecting the use of fixed services is the increasing use of higher frequencies. Although most of the bands below 10 GHz have exhibited growth rates of less than 2 percent a year, the 18-GHz and 23-GHz microwave bands are growing at the rate of 20-30 percent a year, as shown in Figure 2-3.[EN201] The very high apparent growth rate of the 18-GHz band in 1992 is mostly caused by a change in rules that allowed this band to transport television signals to private cable networks (similar to the use of the 13-GHz CARS band). The past use of higher frequencies (greater than 15-GHz) was limited by the high cost of electronic components and by poor performance over long paths. Continued technical development has recently provided much-improved complex gallium arsenide (GaAs) monolithic microwave integrated circuits (MMIC's) capable of operating as high as 30 GHz.

Figure 2-3. Number of licensed frequencies in the 18-GHz and 23-GHz bands, 1987-1993. Figure 2-3 goes here.

The smaller antennas typically used at higher frequencies can be integrated into a compact radio/antenna package and set into a window, avoiding the expense of a separate rooftop antenna. These systems may have an operational range of only 20 to 30 kilometers, but this is acceptable for short-range bypass of the LEC—one of the major uses for the new higher frequency microwave units. Frequencies above 23 GHz are not yet extensively used, and licenses in higher bands are limited mostly to experimental uses. Recently, a number of systems have been built for the 38 GHz band, mainly for use with PCS in Europe.

Since fiber has taken most of the new capacity in the long-haul and heavy traffic uses, the majority of new microwave systems have been short-range, low-capacity systems. Although a modern 23 GHz radio operates in a 50 MHz bandwidth, it provides a maximum capacity of only a single DS-3 link.[EN202] The 23 GHz radio uses simple QPSK modulation, and provides only about one fourth the capacity per MHz as 6 GHz radios using 64-QAM modulation.

In frequency bands well below 15 GHz, there is a movement toward higher frequencies. The FCC has undertaken a series of rulemakings that reallocated 220 MHz of fixed frequency bands near 2 GHz from fixed microwave to various PCS applications.[EN203] The existing 2 GHz microwave links are permitted to move into several migration bands higher in frequency (4 GHz, 6 GHz, 10.5 GHz, and 11 GHz). The process will also provide narrower channelization in the destination bands to more efficiently handle the low-capacity links commonly in use at 2 GHz.

Many commenters believe that microwave will remain attractive for short links, particularly in the 18-GHz, 23-GHz and higher frequency microwave bands.[EN204] Alcatel, however, states that there is a growing demand for high-reliability microwave links, which cannot be met using frequencies above 10 GHz because of weather-related outages. Alcatel suggests reallocation of the 3.6-3.7 GHz band to meet a possible future need for fixed services spectrum.[EN205] AT&T states that there will be a continued need for some long-range microwave links, though new services will tend to use shorter paths.[EN206]

Federal Government Factors

In general, the role of radiocommunications in the Federal Government is expected to continue growing, as it will in U.S. industry and business. However, recent policies often require Federal agencies to procure telecommunications service from commercial suppliers, instead of building and operating their own networks.[EN207] Some Federal fixed radio networks are expected to be discontinued or consolidated with other networks over the next 20 years, slowly decreasing Federal use of fixed services. Since many commercial telecommunication suppliers use fiber networks, there will be a net replacement of fixed radio services with fiber.

At first glance, the military use of microwave might be expected to decrease because of the anticipated military downsizing, as well as the increased use of fiber optics. Many future military communications services will be implemented with fiber or furnished by commercial networks using fiber. However, much of the military use of "fixed" is for transportable stations that are used to rapidly extend wideband communications to any part of the globe. These stations cannot be replaced by fiber. The reduction in permanent overseas bases will tend to increase the amount of temporary communications needed when U.S. forces are deployed overseas. In addition, modern military doctrine depends on a highly mobile force with increased use of C3I as a "force-multiplier." This includes increased use of high-resolution digital imaging data for reconnaissance purposes. DOD stated that the need for transportable fixed stations is expected to increase. However, the existing spectrum for transportable fixed systems is expected to be adequate until the year 2000.[EN208]


Development of Spectrum Requirements for the Fixed Services

Spectrum Requirements for HF Fixed Services

The HF bands have been very crowded, because HF has been the only technology that could provide very long range coverage with a minimum investment in infrastructure. In the past, HF circuits operated by government, industry, and private and common carriers provided the great majority of long range fixed circuits, including most of the transoceanic circuits. All HF services remain extremely crowded today, with strong competition between services for spectrum and a substantial backlog of demand to absorb any frequencies that become available.

However, the availability of alternative technologies may bring a decrease in HF crowding. Communication satellites and greatly improved optical fiber undersea cables have taken over the majority of overseas circuits. Inexpensive VSAT terminals[EN209] and improved wired telecommunications infrastructure in many foreign countries are also reducing the past heavy dependency on HF circuits. Although HF fixed use may decrease, it will remain very important for emergency use within the United States and for backup communications between the United States and foreign countries. ALE techniques have recently made HF communications more reliable and useful.

Spectrum Requirements for VHF and UHF Fixed Services

Fixed services in the VHF and UHF bands (30-1000 MHz) are generally not expected to grow rapidly, though some bands may. In many of these bands, the fixed services share frequencies with the mobile services, though the fixed stations may usually have to meet additional restrictions. The number of fixed assignments in the 406-420 MHz Federal mobile radio band, for example, declined slightly between 1986 and 1992, though the number of mobile stations doubled. On the other hand, the number of MAS stations is growing in some newly-allocated bands near 900 MHz.[EN210]

Spectrum Requirements for Common Carriers.

The common carriers were the first to begin switching from microwaves to optical fiber. Figure 2-4 shows seven years of license data from the four most-heavily used common carrier bands.[EN211] This figure reflects two distinct trends. First, the number of licenses used for general common carrier purposes shows a decrease from the highs of the late 1980's in the 4 GHz, 6 GHz, and 11 GHz bands, probably caused by the replacement of microwave with optical fiber, a trend that is expected to continue. The decrease is especially noticeable in the 4 GHz band, where the presence of numerous TVRO stations has discouraged the licensing of new fixed stations.

Figure 2-4. Number of licensed frequencies in the 2 GHz, 4 GHz, 6 GHz, and 11 GHz common carrier bands, 1987-1993. Figure 2-4 goes here.

The second trend is a recent increase in the use of microwave links to connect new cellular base stations. This trend was first evident in the 2 GHz band, but recently it can be seen in the 6 GHz and 11 GHz bands. Although this is a strong trend now, we expect this trend to become less important in a few years. Fiber and wideband copper are becoming more available in the urban areas where many future additional cellular sites will be established. Simultaneously, the cellular network is changing to carry denser traffic between more closely space sites—conditions that tend to favor fiber. Even if the number of licenses continues to increase in the 6 GHz and 11 GHz bands, this does not necessarily imply increased crowding, since many of these new licenses will be using the newly-created narrowband channels.

Since the 2 GHz bands will be vacated for new PCS applications, it is expected that this growth will stop. Harris suggested that it may be a long time before PCS needs the 2 GHz bands in rural areas[EN212] and that major portions of the 2 GHz bands should be left to point-to-point microwave in the rural areas. Harris also suggested that it would be very helpful to allow some of the displaced 2 GHz microwave systems to use some of the Federal 1710-1850 MHz band. One carrier stated that some of its microwave assignments "can, over time, be released to other services."[EN213]

Although the number of licenses in some common carrier bands is still growing, it is expected that the aggregate number of common carrier licenses in the 2 GHz, 4 GHz, 6 GHz, and 11 GHz bands will decrease over the next five years. Moreover, the remaining users (including the new cellular users) will carry comparatively less traffic, since the routes with the heaviest traffic will tend to be replaced with fiber first. The cellular telephone services will continue to add microwave links in support of new cellular networks and to relocate links from the 2 GHz bands, but will use an increasing percentage of fiber.

The FCC has recently reallocated most common carrier and private microwave bands to make them equally accessible to common carrier and private use.[EN214] Previously, these bands were allocated for specialized use, with certain bands intended for wideband common carrier use and other bands intended for private use with an assortment of narrower bandwidths. The recent reallocation provides a complete assortment of bandwidths in most bands. This gives private carriers access to wideband channels and provides many more narrowband channels (suitable for cellular backbone) to the common carriers. Since all of these microwave bands are now allocated almost identically, the reallocation should also eventually erase the distinctive features that now make some bands crowded and others relatively empty. Therefore, in the future, growth of a particular service might not occur within frequency bands that have traditionally been associated with that service.

These trends are expected to continue over the next ten years, with the major uncertainty being whether support services for cellular telephone and PCS will use microwave or fiber. At the end of 10 years, it is expected that only 30 to 50 percent of the present total number of assignments will be active in the common carrier service.

Spectrum Requirements for Private Operational Services

The private operational services include a number of niche markets, including SCADA, remote operations, and short-range LEC bypass. These services are not particularly subject to competition from fiber, and private operational services have been growing steadily. Growth is slow (less than 5 percent) or negative for frequencies below 10 GHz (Figure 2-5)[EN215] and quite rapid (20 to 30 percent) for frequencies above 10 GHz (see Figure 2-3). Digital Microwave Corporation believes that the 18 GHz and 23 GHz bands will exhibit considerable growth, that higher capacity 16-QAM and 64-QAM modulation[EN216] may be needed, along with spectrum in the 26 GHz, 29 GHz, and 38 GHz bands.[EN217] On the other hand, Alcatel believes that attenuation due to rain and water vapor will curtail effective use of the microwave bands above 10 GHz when high reliability is needed.[EN218]

Figure 2-5. Number of licenses in selected private microwave bands, 1987-1993. Figure 2-5 goes here.

As several commenters noted, SCADA systems often require higher reliability than that obtainable with a single fiber route and require relatively low data rates—situations where fiber is not competitive. SCADA is often located in areas where fiber is not practical or economical to install[EN219]. UTC said that a much more complex regulatory and structural environment (open power distribution systems with multiple independent producers, automatic switching and load management, and tightened environmental controls) will double or triple the spectrum requirements for SCADA in the next five to ten years.[EN220]

The situation for LEC bypass is a little less clear. Although several commenters said that short-range bypass of the LEC was a probable growth area for higher frequency microwave,[EN221] it should also be noted that fiber is likely to be available less expensively in a competitive urban environment.

It is expected that there will be slow and steady growth in the private microwave services, amounting to a three percent growth rate, averaged over the next five years.[EN222] Over the next 10 years, it is difficult to predict the degree to which fiber will displace microwave LEC by-pass in urban areas and SCADA in rural areas. Much of the growth in these services will be in the 18 GHz and 23 GHz bands, with less growth in the bands designated as migration bands from the 2 GHz bands. No additional frequency allocations will be needed, because most bands (including empty bands above 23 GHz) still have adequate room for growth.

Spectrum Requirements for AUXBC Services

AUXBC is currently growing at a moderate rate (Figure 2-6),[EN223] but the industry is undergoing rapid changes, and it is not clear what will be the final outcome. The AUXBC bands are already crowded and will become more so, mostly because of the need to simultaneously transport NTSC[EN224] and HDTV signals and the increasing use of ENG for local news coverage.[EN225] To meet this crowding, digital signal compression will be used to squeeze in some additional ENG and STL links. In addition, many STL and ICR microwave links will be replaced with optical fiber. Nevertheless, broadcasters believe that crowding will be too great in the top 30 markets and intend to ask the FCC to reverse an earlier decision against providing more AUXBC spectrum.[EN226]

Figure 2-6. Number of licenses in selected AUXBC frequency bands, 1987-1993. Figure 2-6 goes here.

NAB believes that the deployment of digital audio broadcasting (DAB) will require additional audio STL's, causing serious crowding in major metropolitan areas, and perhaps requiring an additional 5-8 MHz of spectrum for audio STL's.[EN227]

Spectrum Requirements for Cable Relay Services

CARS is replacing many microwave links with fiber. Beginning in 1992, many cable systems began converting their coaxial cable trunks and feeders to fiber to obtain a larger number of channels with improved quality. Recently, more ambitious plans to provide a broad mix of two-way services have added to the need for networks of fiber or fiber and coaxial cable.[EN228] These rapidly-changing plans include various partnerships between LEC's, cable companies, electrical utilities, and providers of PCS and cellular to provide analog TV, digital TV, telephone, data, TV-on-demand, electrical power management, etc. Irrespective of who the providers of these services are, or exactly what technologies are finally used, it is clear that CARS will be affected by the rapid and significant changes that are likely in this service.

The existing CARS microwave distribution architecture, based on one-way SHL's in the 13 GHz band, is not suited to the new two-way services which the cable companies would like to offer. Therefore, plans to provide two-way services on cable may require the switch to fiber. Figure 2-7[EN229] shows the number of licenses in the 13 GHz CARS band. This band was packed with more than 109,000 SHL assignments and was still growing rapidly in 1991. The growth stopped abruptly in 1992 as cable companies began to switch to fiber. Even if all cable companies do not choose to offer a broad range of 2-way services, most will still convert to fiber networks.

Figure 2-7. Number of licensed frequencies in the 13 GHz CARS band, 1987-1993. Figure 2-7 goes here.

The fiber networks owned by the cable companies could remove microwave stations from more bands than the 13 GHz CARS band. They could become another general-purpose local fiber carrier, offering broad competition to the LEC's and greatly increasing the accessibility to fiber and wideband communications. This could provide substantial competition to microwave for LEC bypass and future cellular and PCS network connectivity. The use of the 13 GHz CARS band is expected to experience a rapid decrease in a few years, after many SHL's networks are replaced with fiber. Cable companies will use more ENG to meet the programming demands of 500-channel systems with a larger number of viewers. There may be considerable opportunity to exploit vacated CARS channels for ENG and STL.

Spectrum Requirements for Federal Government Services

The use of microwave bands by the Federal Government will follow many of the same trends followed by similar non-Federal services. There are, however, several factors unique to Federal use. Figure 2-8[EN230] shows the number of Federal assignments in several of the frequency bands used by the Federal Government for fixed services.

Figure 2-8. Number of assignments in selected Government bands, 1987-1991. Figure 2-8 goes here.

Since HF provides long-range communications with a minimum of infrastructure, Federal use of fixed HF systems will continue to be highly important for emergency and military communications throughout the foreseeable future. However, commercial switched systems and fixed-satellite technology will meet an increasing share of fixed communications needs. Many Federal civilian agencies plan to use HF for communications restoration after natural disasters. The VA, for example, plans to acquire additional HF sites to provide communications in emergency and national disaster situations.[EN231]

The use of telecommunications between fixed geographical locations is expected to continue to grow within the Federal Government, as is it within the society as a whole. However, a smaller percentage of this traffic will be carried by microwave links. Fixed microwave is used to connect Federal offices within the same city for general traffic, often with links to Federal centers in nearby cities. Some agencies also have extensive nationwide nets, but these are more often used to support SCADA or mobile radio operations. Although these general-purpose communications links will continue to have advantages in specific situations, their number will decrease slowly under the competitive pressure of widely available optical fiber in a competitive telecommunications environment.

Fixed networks used to support military test and training ranges will probably be slowly converted to fiber—partly to reduce the cost of maintaining old analog microwave links and partly to increase bandwidth to monitor more complex tests and training exercises. The conversion of existing microwave links to fiber is paced partly by the funds available for the conversion. The replaced microwave links will often continue to be used for backup and for lower priority purposes.

Federal SCADA applications and the use of microwave backbone to support mobile radio nets are expected to slowly decrease over the long run, although temporary increases are presently indicated in support of particular programs. DOE will be using microwave links to replace many of its 3,000 power line carrier (PLC) systems over the next 10 years.[EN232] The FAA is adding up to 300 additional low-density microwave links in the 1710-1850 MHz band.[EN233] The Coast Guard is adding more VTS sites to more closely monitor active harbor areas. Fiber and microwave will be used to tie together radar and communications sites.

SCADA and mobile backbone applications are not easily replaced with fiber because of cost and reliability considerations, but fiber will become continually cheaper and more available, even in rural locations. The use of microwave to support SCADA and mobile agency communications nets is expected to decrease, gradually being replaced with VSAT links, fiber, or commercial services purchased under the FTS 2000 program.

In summary, we expect Federal use of the fixed microwave services to remain at present levels. Although a higher portion of Federal fixed communications will be carried on commercial systems and Federal fiber optic systems, this trend will be partly balanced by continued growth of communication-related functions performed by the Federal Government. The extensive use of transportable systems by the military will continue, and these systems cannot be replaced by fiber systems.


Spectrum Requirements for the Fixed Service

Optical fiber is expected to continue to take market share away from microwave for many point-to-point systems. Especially for the high traffic density markets, such as dense urban common carrier and urban CARS SHL's, the use of fiber is often very advantageous. We believe that some parts of certain microwave bands could reasonably be converted to other uses within the next 10 years. The following bands may have sufficient spare capacity, that they should be considered for reallocation at a future date.

3.7-4.2 GHz Common Carrier Band

The number of common carrier links is rapidly decreasing in this band, and it is expected that 50 percent of the fixed service allocation could be converted to other uses within 10 years. A major limitation on the reallocation of this band is the large number of home satellite dishes (TVRO's) receiving television signals from geosynchronous satellites. A new user may find it difficult to operate compatibly with the existing TVRO's and will tend to choose another band. The common carrier fixed service in this band could reasonably be expected to operate with 50 percent (250 MHz) less spectrum by 2004. Any other use, however, should be compatible with TVRO operation.

12.7-13.25 GHz CARS Band

It is believed that the number of licenses in this band will begin to decrease rapidly as the Cable TV industry changes from microwave distribution of TV programming to optical fiber distribution systems. The use of this band will vary greatly from city to city. In many cities, most cable program material will be transported by fiber; in other cities it will be mostly by microwave. Where microwave is used, however, a large block of spectrum will be needed to fill a 500-channel cable system. In fact, as the total bandwidth in fiber-based cable systems increases, the 550 MHz allocated in this band may be insufficient to handle the required fiber bandwidth. At some future time, it may no longer be in the public interest to allocate this large band to the fixed service if it is used heavily in only a few cities. At that time 50 percent of the band (275 MHz) could be reallocated for other purposes.

The net reduction in fixed service requirements identified above suggests that a significant amount of currently allocated spectrum may not be required in the future. By the year 2004, as much as 250 MHz could be made available, under certain conditions, for use by other services.

Fixed-Satellite Service

The space age opened new opportunities for radiocommunications between widely-separated locations. Instead of HF systems with limited bandwidth or a large number of short-range microwave relays, satellites could link distant locations from a vantage point high above the Earth. By the mid-60's, launch vehicles were delivering communications satellites to locations in the geostationary satellite orbit, about 35,800 kilometers above the equator. In this orbit, the satellites circle the Earth at the same rate as the Earth rotates, making them appear nearly stationary from the Earth's surface.

Today, geostationary communications satellites continue to play a major role in telecommunications. From the geostationary orbit, satellite antennas can illuminate a small area (using "spot beams"), a country, or a larger region encompassing many countries. Thus, satellites can theoretically compete with point-to-point microwave and non-radio media (e.g., optical fiber) in providing communications between fixed points.

The fixed-satellite service primarily involves communications between fixed earth stations via satellite, i.e., uplinks and downlinks, although the service can also include certain inter-satellite links and feeder links.[EN234] The fixed-satellite service can include communications to multiple, specified fixed locations, but not broadcasting functions.[EN235] While current U.S. systems operating in the fixed-satellite service use geostationary satellites exclusively, one commenter has suggested the use of non-geostationary satellites to reduce the time delay.[EN236]

The fixed-satellite service basically involves four frequency bands: 4/6 GHz, 7/8 GHz (for military systems), 11/14 GHz, and 20/30 GHz. Although numerous bands above 30 GHz are allocated to the fixed-satellite service, only one is presently used.[EN237] Microwave frequencies and "stationary" satellites allow the use of high-gain, directional antennas, much like the fixed service.[EN238] This reduces the power requirements for the satellite transmitters.


Current Uses

The fixed-satellite service includes international, domestic, and military systems. Though they often carry the same type of traffic, each group has its own set of users. International and domestic systems operate at 4/6 GHz and 11/14 GHz while military systems use 7/8 GHz and frequencies near 20 GHz and 45 GHz. This section describes each of these applications, as well as the use of the fixed-satellite service for inter-satellite links, feeder links, and power control beacons.

International Systems

In the mid-1960's, satellites began offering a reliable new alternative to submarine cable for intercontinental telephony, along with the promise of intercontinental television transmission. Until recently, the history of international fixed-satellite service satellites was the history of INTELSAT. More recently, private "separate systems" have begun providing an alternative.

International systems in the fixed-satellite service use frequencies at both 4/6 GHz and 11/14 GHz. In the United States, part of the 4/6 GHz spectrum has been reserved for "International inter-Continental" systems.[EN239]

INTELSAT

Created in 1964, the International Telecommunications Satellite Organization (INTELSAT) owns and operates the primary global satellite system. The INTELSAT system provides international voice, data, and video services as well as domestic services for many smaller countries.

The INTELSAT system began with the launch of the "Early Bird" satellite (INTELSAT I) on April 6, 1965 and achieved worldwide coverage with the completion of the INTELSAT III system four years later. Since then, the INTELSAT system has progressed thorough several generations of satellites. The first satellite of the INTELSAT VII series was launched on October 22, 1993 to an orbital location over the Pacific Ocean.[EN240]

Separate Systems

Under Article XIV of the INTELSAT Agreement, members may establish international public telecommunication services separate from INTELSAT. These "separate systems" must be technically compatible with existing and planned components of the INTELSAT space segment and must not cause "significant economic harm" to the INTELSAT system.[EN241]

In June 1988, Pan American Satellite (PanAmSat) launched its PAS-1 satellite into geostationary orbit over the Atlantic Ocean. The first private international satellite, PAS-1 provides services to customers in the Americas and Europe. Although television programming accounts for most of PanAmSat's business, PAS-1 also provides data services to businesses as well as voice services.[EN242] PanAmSat launched its second satellite, PAS-2, into orbit over the Pacific ocean region in July 1994.[EN243]

PanAmSat's plans for a global satellite network suffered a setback with a launch failure that destroyed PAS-3 in early December 1994. A replacement for the satellite, which was intended to provide service to Latin America, is under construction but will not be launched for at least a year.[EN244] PAS-4, covering the Indian Ocean, is scheduled for launch by the end of 1994.[EN245] The completed network of satellites will provide global coverage that will reach 98 percent of the world's population.[EN246]

Another separate systems provider, Columbia Communications Corporation leases 4/6 GHz capacity on NASA's Tracking and Data Relay Satellite System (TDRSS) satellites located over the Atlantic and Pacific Oceans. Columbia plans to eventually launch two satellites of its own.[EN247]

Domestic Systems

While INTELSAT and PanAmSat provide international satellite communications, about 30 privately-owned 4/6 GHz and 11/14 GHz satellites provide U.S. domestic services.[EN248] While the number of domestic satellite owners and operators was higher in the 80's, the limitations of the market in the 90's have reduced the competitors to four: Hughes Communications, AT&T Skynet, GE Americom, and GTE Spacenet.[EN249]

Domestic 4/6 GHz satellites fall into three categories based on the markets they serve. "Cable" satellites distribute television programming to cable headends and, opportunistically, to homes equipped with backyard TVRO "dishes."[EN250] "Broadcast" satellites distribute network programming to affiliates and syndicated programming to affiliates and independent stations. The third category of 4/6 GHz satellites is generally used for point-to-point transmission (as opposed to the point-to-multipoint operation of the other categories) of video and data signals.[EN251]

Satellites operating in the 11/14 GHz band are generally used for private networks, such as those operated by businesses and academia. A typical use of 11/14 GHz satellites is for data networks, carrying voice, facsimile, and compressed video signals in addition to business data. Educational video is another common application.[EN252] Satellite networks in the 11/14 GHz band can use smaller earth station antennas than 4/6 GHz systems and are subject to less interference.[EN253]

Military Systems

U.S. military communications satellites, having both international and domestic applications but serving a very different user, constitute a third group of FSS satellites. Since the success of the armed forces depend upon their mobility, many of their requirements for communications between fixed points involve transportable systems.[EN254] The fixed-satellite service accommodates many of these requirements because military units cannot quickly or economically connect temporarily fixed locations with wires.[EN255]

Unlike commercial systems in the fixed-satellite service, military systems primarily use Federal frequency allocations in the 7-8 GHz range.[EN256] Recently launched or planned systems use frequencies near 20 GHz, 30 GHz, and 44 GHz.[EN257] In addition to satellites in these bands, DOD also uses commercial satellites to satisfy some of its requirements.[EN258]

Since the late 1960's the Defense Satellite Communications System (DSCS) has provided satellite communications for the armed forces. The first of the current generation of satellites, DSCS III, was launched in 1982. Although DSCS III replace DSCS II in January 1994, two DSCS II satellites still provide reserve capabilities. DOD launched the first MILSTAR satellite on February 7, 1994. This system will provide tactical communications in the fixed-satellite service using the 20 GHz and 44 GHz bands.

DOD expects its use of the fixed-satellite service to increase. Data and imaging communications, which require large amounts of bandwidth, will continue to strain communications systems. Commercial systems currently take on some of the burden and the need for additional spectrum is not anticipated before the turn of the century. After that, however, spectrum requirements are expected to increase as data and imaging take on a critical and increasing role in military communications.[EN259]

Other Fixed-Satellite Service Links

Under the U.S. and international definitions, the fixed-satellite service can include some feeder links and inter-satellite links.[EN260] Spectrum requirements for feeder links are discussed in the chapters covering the services they support.[EN261] We expect that 200-400 MHz of additional FSS spectrum allocations may be required for feeder links supporting initial non-geostationary MSS systems. We believe that sharing between these feeder links and some types of terrestrial systems will be feasible.[EN262]

None of the current fixed-satellite service allocations provide for space-to-space (inter-satellite) links, although they can be accommodated in other services.[EN263] Any future requirements for inter-satellite links in the fixed-satellite service would thus require changes to allocations. No such requirements have been identified.

The fixed-satellite service is also used for satellite power control. Because satellite links at 20-30 GHz are subject to significant rain attenuation,[EN264] they can be unreliable. To meet requirements for uplink availability and performance, earth stations monitor a power control beacon on the satellite, which indicates the level of rain attenuation.[EN265] Acting on a U.S. proposal, WARC-92 allocated the 27.5-30 GHz band for space-to-Earth links for this purpose on a secondary basis (except for the bottom and top 1 MHz, in which the allocation is primary).[EN266] No requirements beyond this allocation have been identified.


Trends

The fixed-satellite service competes with point-to-point microwave and non-radio media (wire and optical fiber) for telecommunications traffic between fixed points. As all three have matured, each has captured its own niche in the market. Users (or industries) will generally choose the most economical medium that meets their requirements for availability, capacity, and reliability.

The first satellite communications between fixed points involved international voice (telephony) and television signals. More recently, voice communications has largely returned to terrestrial telecommunications systems and has been replaced by increasingly sophisticated video and data communications. This section discusses trends in the fixed-satellite service including voice communications, video and data communications, VSAT's, and proposed multi-service satellite systems.

Voice Communications

The history of two-way voice telecommunications goes back to the invention of the telephone in the last century. Wire continued as the primary medium for telephone until the 1950's, when microwave links began to carry long-distance calls. With the development of the INTELSAT system in the 1960's, satellites proved more reliable than submarine cable for intercontinental telephone calls. The time delay caused by the distances involved with geostationary satellites, however, made telephone conversations cumbersome. Telephone links via satellite became undesirable when a reliable terrestrial medium was available.

Today, telephony has come full circle, as optical fiber has largely replaced both microwave links and satellite links, once again physically connecting the users. Indeed, most voice applications of the fixed-satellite service in the United States have been replaced by optical fiber.[EN267] The fixed-satellite service, however, may continue to provide a backup capability for voice communications.[EN268]

Video and Data Communications

While their use for voice communications has decreased, satellites have proven cost effective and reliable for video and data signals, which often involve transmission of the same signal to numerous sites.[EN269] Since satellites link multiple, geographically dispersed locations as easily as they link two locations, they are more economical than multiple terrestrial links.

The largest application of domestic and international satellites is video communications, mainly involving programming for cable providers and television broadcasters. Other video communications links are used for distance learning and teleconferencing.

The growth of digital video communications will bring greatly improved efficiency through video compression. Digital video signals are compressed by removing redundant information from the signal, dramatically decreasing the bandwidth required for transmission. Satellite transponders that carry a single analog video signal are able to accommodate several compressed signals. The satellite industry is already using video compression for broadcast and cable television and for educational networks.[EN270] Although this could reduce spectrum requirements for video transmission, some argue that the demand will rise along with the capacity as compression makes satellite communications more economical.[EN271] One commenter believes that video compression will lead to the growth of "new services . . . , such as HDTV, direct to the home applications, and growth in the distance learning market — just to name a few."[EN272]

Private satellite data communications began in 1975 as Dow Jones transmitted facsimiles of The Wall Street Journal from Massachusetts to Florida for sale to that state's retirees.[EN273] With the Information Age in full swing, the United States now has tens of thousands of data terminals using satellite communications.[EN274] Users exchanging modest amounts of data between two sites often find public switched services to be the best suited medium.[EN275] For higher data rates or multiple dispersed sites, however, the choice is more complicated and satellite networks offer a competitive option.

Teleports and VSAT Systems

In the 1980's satellite service providers began assembling earth stations on properties conveniently located near urban areas. These "teleports," numbering in the dozens in the United States, serve as high-tech telecommunications hubs.[EN276] While most began as small operations, "[t]oday's teleport typically includes ten to 20 antennas ranging in size from 3.5 to 11 meters, with an occasional dish for international communications."[EN277] Teleports connect terrestrial telecommunications (microwave and optical fiber) with satellite uplinks, providing access to space telecommunications. Although most teleport traffic is cable and broadcast television programming,[EN278] teleports also provide data communications and communications in other space services.[EN279]

The use of VSAT technology is moving the fixed-satellite service back into crowded urban areas.[EN280] VSAT systems use 11/14 GHz frequencies and higher power satellite transmitters, allowing antennas on the order of a meter or less in diameter.[EN281] Low-cost private networks based on VSAT systems serve diverse applications, including data, voice, and video communications.[EN282] The largest providers of VSAT networks are Hughes Network Systems, GTE Spacenet, AT&T Tridom, and Scientific Atlanta.[EN283]

A typical VSAT network consists of a hub (a central location with a host computer) and multiple VSAT's connected to remote computer terminals.[EN284] If the remote terminals need to communicate with each other, they do so through the hub. A teleport may serve as the hub of several VSAT networks.[EN285] Recently, VSAT systems have been evolving from "hub" to "mesh" architecture, allowing user terminals to communicate with each other without going through the hub.[EN286]

The major users of VSAT systems are the retail and automotive industries.[EN287] VSAT systems have been competitive with private line networks for users requiring an on-line (as opposed to a dial-up) network. Satellite advocates claim that VSAT networks offer better throughput, response time, and system availability than private line networks.[EN288] In the past few years, VSAT's have been replacing dial-up networks as users recognize the need for an on-line system and choose VSAT's over private line networks.[EN289]

While the growth of VSAT networks is expected to continue, the future growth of teleports is less certain. VSAT networks will proliferate because they are economical and because they can operate in a crowded urban environment.[EN290] At the same time, the increased use of VSAT systems could slow the growth of teleports, especially if network architecture becomes more flexible (i.e., if private networks can easily be configured without the use of a hub), if VSAT data capacity increases, and if costs decline.[EN291] The anticipated growth of VSAT networks and the requirements for higher data rates lead some to project additional spectrum requirements for the fixed-satellite service by the end of the century.[EN292] Data compression, however, could reduce or eliminate these requirements.[EN293]

Advanced Satellite Technology

NASA's Advanced Communications Technology Satellite (ACTS) is a major development for the fixed-satellite service. The purpose of the ACTS satellite, launched on September 12, 1993, is to verify new fixed-satellite service technologies and techniques.[EN294] According to NASA, it will serve as a prototype of future multi-function, multi-service satellites, demonstrating, in part, the space segment of an integrated services digital network (ISDN).[EN295]

The ACTS satellite features on-board baseband processing of signals, providing satellite-based routing and switching. This eliminates the need to route traffic through an intermediate earth station. The ACTS satellite features electronically hopping high-gain antenna beams permitting smaller and cheaper earth stations. ACTS has a steerable antenna for flexible coverage throughout the Western Hemisphere. ACTS' microwave switch matrix will allow higher data rates and volume.[EN296]

A major facet of the ACTS technology is the development of new earth stations. One such earth station is the T-1 VSAT, which provides voice, data, and video communications through a standard 64 kbps telephony interface and also a 1.544 Mbps "T-1" interface. In conjunction with other interfaces, the T-1 VSAT will accommodate ISDN and packet switching. Recent earth station developments include high data rate terminals for supercomputing networks and HDTV applications as well as earth stations using ultra-small aperture terminal (USAT) technology in the 11/14 GHz band.[EN297]

NASA believes the continued viability of the fixed-satellite service depends on its compatibility with ISDN. Standards for ISDN, particularly standards for network delay, must be realistic and not preclude fixed-satellite service systems. With the development of compressed voice terminals and aeronautical communications, NASA sees the ACTS system as a prototype of a satellite operating in both the fixed- and mobile-satellite services. NASA further sees the use of fixed-satellite service systems in ISDN as bringing about greater homogeneity between satellite and terrestrial systems, including similar bandwidth requirements.[EN298]


Spectrum Requirements for the Fixed-Satellite Service

Future spectrum requirements for the fixed-satellite service (excluding feeder links supporting other space services) will depend on the overall market for communications between fixed points, the portion of that market for which satellites are the medium of choice, and the efficiency (in terms of bandwidth requirements) with which satellites can provide services. For some applications using optical fiber or terrestrial microwave, the fixed-satellite service will continue to provide a backup capability.[EN299]

Several factors will affect the market share of satellite communications as compared with terrestrial media. As terrestrial switched digital services become more available and economical, they will put increasing competitive pressure on VSAT systems.[EN300] International carriers' increasing investment in fiber optic cable—which has a much smaller time delay than satellite systems—will negatively affect the demand for international voice and data satellite services.[EN301] Improvements in launch vehicle reliability may enhance the growth of the satellite industry.[EN302] In general, while terrestrial systems (mainly optical fiber) will likely capture the point-to-point market, satellite communications may still be the best choice for point-to-multipoint applications.[EN303]

The main source of increased efficiency will be video compression. This technology will permit a dramatic increase in the amount of programming that can be carried by a single transponder. However, as discussed earlier, the spectrum requirements for video distribution may not decrease since the demand may increase significantly as the cost of distributing programming to affiliates and cable headends drops.[EN304] Another source of increased efficiency will be the use of spot beams, orthogonal polarizations, and reverse band working to allow frequency reuse.

While commenters representing international and military users suggested a possible need for additional spectrum after the turn of the century,[EN305] other commenters believe that the spectrum allocated to the fixed-satellite service will be adequate in the short term.[EN306] We believe that the currently allocated spectrum will be adequate to meet requirements for the fixed-satellite service, except for feeder links supporting other space services. We estimate a requirement for 200-400 MHz of additional FSS spectrum for feeder links supporting non-geostationary satellites in the mobile-satellite service.[EN307]


Return to Report Table of Contents.

Proceed to Chapter 3, Broadcasting and Broadcasting-Satellite Services.