In 1963, the 2500-2686 MHz frequency band was reserved for educational institutions for over-the-air transmission of instructional television programs. The transfer was point-to-point, for example, campus-to-campus or campus-to-hospital for continuing education needs. Hence the name: Instructional TV, Fixed Service (ITFS). The allowable power (up to 100 watts) allowed transmission / reception of separations up to 30-40 miles.
In 1972, commercial operators were allowed to use the coexisting commercial band 2150-2162 MHz for over-the-air pay-TV broadcasts for roof antennas on apartment buildings and private homes and for business data transmissions. Transmitters responded to them for ITFS service, and the range for these installations was also 30-40 miles. The transmitter site was centered in the coverage area, usually a city, on a pre-tower or on top of a tall building.
The antennas were usually circular to reach all subscribers in the circular coverage area. The signal was intended for distinct subscriber locations rather than for anyone wishing to retrieve the signals (as in the broadcast services). Therefore, the new service was named Multipoint Distribution Service (MDS). This service was the beginning of what we now know as “Wireless Cable”. MDS was conceived as an alternative or supplement to conventional cable television (CATV). It was more successful in areas not covered by CATV. In areas where both services were available, it was severely challenged: it could only offer one or two TV channels against the dozens of channels offered by CATV. After MDS news went off, MDS revenue fell. Obviously, one means was to use multiple channels, and the commercial wireless operators looked with interest at the easily used ITFS channels reserved for educational purposes.
MDS operators and potential MDS operators filed a regulatory petition to allow commercial use of some of the ITFS channels. As a result, in 1983 the FCC redistributed eight of the ITFS channels (identified as Groups E and F) for use in commercial pay-TV operations over the air. The idea was that each market should have two licenses, each with four channels. As this enabled simultaneous broadcast of many more channels than existing MDS, the newly assigned channels became Multichannel Multipoint Distribution Service (MMDS). Many MDS operators have acquired MMDS channel licenses, and in some cases newly licensed MMDS operators have acquired older MDS operations. Existing ITFS licenses using the E and F channels were not displaced at the time, although the rules allow the MMDS licensee to pay all costs and move such licensee to an alternate channel if available.
Almost at the same time, the FCC assigned three ITFS channels (in Group H) to the relatively new operational fixed service (OFS). This was envisioned as a point-to-point transmission / reception service primarily for the transfer of business information. However, in large numbers, MDS and MMDS licensors began purchasing licenses for the OFS channels in their markets and using them for one-way analog video programming. Since 1998, the FCC has considered these H-channels (H1, H2 and H3) MDS channels.
In order to describe operations, we must consider the MDS, ITFS and MMDS services technically identical. For those interested in the FCC channel allocation plan, it is described in Appendix A to LBA Technical Note 115.
Cable TV operation
Historically, wireless cable has been a one-way analog video service. “One-way analog video service” means it has operated much like commercial TV stations and broadcast a “video stream” such as NBC or CNN over each channel. Viewers used down converters to interrupt transmissions from 2500 MHz frequencies to 65 MHz and then they could watch the programs on traditional TVs.
The MDS operator, which had a channel license, was limited to offering a channel with programming. The MMDS operator, which had a four-channel license, was only slightly better off because four channels were available to cable customers. By consolidating all MDS and MMDS channels in one market, the licensee consortium could operate a wireless cable system with as many as 13 channels. While this may have been viable in the early 1980s, the market in the 1990s required dozens of channels from a cable service. MMDS operators still wanted to use ITFS channels to meet this need.
ITFS operators tended to use their channels for long distance teaching during regular work hours, and the channels lay fallow in the evenings and weekends when the wireless cable demand for programming was greatest. The FCC had placed a provision in its rules that allowed an ITFS licensee to lease its “excess channel capacity”. This meant that as long as the ITFS licensee used its channels for educational purposes for at least 20 hours per week per week. Channel, it was free to lease the channel for commercial use the rest of the time. The FCC rules contain restrictions on Airtime Lease agreements to prevent a naive teacher licensor from giving up many of its rights, but the use of those agreements allowed an explosion in the growth of ITFS operations.
The training costs for the teacher to construct a four-channel transmission system and install reception equipment at the schools to be served could run into six figures. Most school systems did not have this kind of money for an untested technology. Then, under the leasing rules, it worked like this: the commercial wireless cable operator in the market paid all the upfront application costs for legal and engineering to prepare an application to the FCC for a license that the school should possess. The wireless cable operator purchased the equipment, built the transmitter tower, installed the receiver locations in the schools and built a studio. The operator worked with several trainers in its market so that most available channels were used and all shared the transmission facility. Each teacher was a licensee in his own right, but had a contractual agreement to lease his excess channel capacity back to the wireless cable operator. The teacher got the license without spending money, had used the studio and equipment built by the wireless cable operator, and had used the service for many hours each week. In addition, it received monthly leases from the wireless cable operator for use of the channels in the evenings and weekends. This scheme is a classic example of business and education units working together for the benefit of both. This new, untested technology became a financial institution for the school in addition to allowing long-distance education to become a reality. And the wireless cable operator now had access to as many as 33 channels using the ITFS, MMDS and MDS bands. Thirty-one of these channels are immediately adjacent to each other in the 2500 MHz band, and two are at 2100 MHz. The channels designated as the A group, the B group, the C group, the D group and the G group are reserved educational channels. The channels designated as channel 1, channel 2, the E group, the F group and the channels H1, H2 and H3 are available to commercial operators.
Commercial use of ITFS channels
In 1991, the FCC decided to allow wireless cable operators to use ITFS channels for their commercial operations under certain rather stringent conditions. A wireless cable operator is defined as one who has a conditional license, license, or lease on at least four MDS channels or has an unpublished application awaiting at least four MDS channels. The wireless cable operator may request permission to operate on ITFS channels if no additional MDS channels are available on the market and at least eight remaining unused ITFS channels are available for future ITFS use in the community. Entities eligible for ITFS licenses may request from the FCC that they access the commercially used ITFS channels for up to 40 hours per week per channel. These conditions are described in 47 CFR §74.990 to §74.992.
In the early 1990s, the U.S. the economy was down and Congress had discovered the dollar value of the spectrum licenses the FCC granted. It required that licenses for most services be awarded to the highest bidder. This decision greatly changed the wireless cable market.
In 1995, the FCC rules were amended to specify that all remaining MDS licenses would be auctioned. A decision was made to divide the land into geographical areas, each of which could then be auctioned. The Rand McNally Basic Trading Area (BTA) divisions were selected with the addition of a few BTA-like areas to complete coverage of the United States and its territories. Each BTA or BTA-like area is a collection of counties. Physical size varies greatly, although they tend to be smaller in the more densely populated east and west coasts, and tend to be larger in the more sparsely populated areas of the western United States.
What the FCC granted in its BTA license was the right to use any of the 13 commercial channels (see above for a list) anywhere in its BTA if it could do so without causing any interference to an existing licensee or to an adjacent BTA. These pre-existing licenses are called “grandfather” licenses, and their licenses remain in effect and are eligible for renewal at the end of their licensing period. The grandfathered licenses have a protected service area, which is a 35 km circle, centered on the transmitter site used in 1991 when the rules for the protected service area were completed. This area may overlap with more than one BTA and requires protection from all nearby BTA licenses. The interference protection required for these grandfathered stations is also more generous than that given for BTA licenses. BTA licenses are protected against interference at the BTA border, but the irregular forms of BTA boundaries do not reflect the prevalence conditions of reality and make service to areas on the outskirts of the service area more difficult.
The MDS auction took place from November 1995 to March 1996, yielding $ 216.3 million. The auction funds were not allocated to the FCC; they went directly into the U.S. Treasury. A total of 493 licenses, one per. BTA, was awarded a total of 67 licenses.
Two-way digital controls
Recently, the wireless cable technology standards have been eased to allow a one- or two-way digital service. This extends the potential use of the spectrum. A wireless cable operator may be able to use digital compression to place additional “video streams” in the same number of channels, which actually increases its channel capacity without using more bandwidth. It can use the answer channels for ordering payment per. View. Or it may be able to use the two-way service for high-speed wireless internet or other data transfer applications.
This change of rules was the result of a consortium of wireless cable operators, consultants, lawyers, ITFS licenses and equipment manufacturers. This group came together and created a plan to allow bidirectional use of the wireless cable frequencies. They established minimum operating standards that the equipment could tolerate, interference standards with which operators could live, an accelerated processing method, and frequency sharing rules that teachers and wireless cable operators both found fair. Then the whole package was turned into a proposal by the Commission. The FCC allocated significant portions of the package without modifications. The initial filing window for two-way applications was in August 2000. Many of these applications have been awarded and are under construction.
In a two-way digital wireless cable system, each subscriber not only has a receiver but also a transmitter. These transmitters have low power and send a response back to the answering station hub. The black transmission is called upstream transmission and the signal from the main transmitter is called downstream transmission. Initially, the system required a directional response end antenna oriented directly on the response station hub. However, it only meant trained service personnel who could perform the installation. In an effort to reduce operating costs, some wireless cable operators requested the FCC to allow low-gain omnidirectional response antennas to allow users to install the equipment themselves. This request was granted.
In addition, FCC rules allowing booster stations have been eased, allowing an operator to more easily add additional transmitter locations to service areas that were previously out of range. Boosters can be used on the downstream component of the bidirectional system or transmission rate of the one-way system. This allows more “cellularization” of the market to improve coverage with more transmitters.
Line of sight operation
Traditionally, the antennas used for wireless cable have required a line of sight (LOS) between transmission and receiving antennas. This limits service providers to position the hub antenna at a very high central location, often 500 meters above the surrounding area. They also need a high transmission power to reach the coverage area of 35 miles. In addition, the customer’s antennas often have to be mounted at the highest point on the roof, which is ugly from the consumer’s point of view and may also be in violation of restrictive covenants.
Even with these restrictions, the applicable service area is limited to parts of the authorized service area. Any building behind or under the shade of a larger structure cannot receive service. This larger structure can be a hill or a building or even a water tank. On a nationwide average, LOS service is available only between 30% and 80% of an authorized service area.
In addition, using a very high-powered transmitter creates interference problems in adjacent areas. Cooperation between operators in nearby areas is necessary to solve the interference problem. Often, the same company will have activities in adjacent markets, creating problems for themselves. Using a high, high-powered hub antenna also limits the operator’s ability to reuse the same frequencies in its market.
To overcome these problems, several manufacturers are working with technology to allow unopened operation. This is defined as reliable operation in the absence of a clear LOS path. Although the signal is not expected to penetrate large terrain obstacles, it can be expected to penetrate walls and leaves and bend around buildings. The signal must be robust enough to operate in a multi-way fading environment and despite some obstruction and interference. The goal is to achieve coverage of 90% of the authorized service area. Non-LOS (NLOS) paths are not as effective as LOS paths, but they allow the use of shorter, lower powered transmitters. This allows more frequency reuse.
The areas that have blocked paths still receive a signal, but it is a weak signal. The NLOS areas receive signal that has traveled along paths that reflect (are rejected from an obstacle) or break (bend as they pass over an obstacle). There are any number of such paths that start at the hub site and end at the customer site. The signal received along any such path is weak or attenuated. In addition, the paths have different lengths, which means that the time delay along them varies. Intelligent customer room equipment can use error checking routines to combine the signals from the various paths and correct the errors in the data sufficiently to have a usable signal. There are ways to predict attenuation and multi-path effects, and these calculations indicate the path loss that can be expected from an NLOS path. The wireless cable operator may include this loss in its scheduling, thereby allowing NLOS operation.
Self-installation of equipment for customers
One of the major costs of a wireless cable operation is the provision and installation of equipment in the customer’s premises. As long as the requirement exists to “fine-tune” each installation to optimize LOS, trained installers must be sent to each new subscriber. Since wireless cable systems are designed to allow higher loss budgets, customers can install equipment themselves. The goal is to have universally compatible equipment available in consumer electronics stores that consumers can purchase and install themselves. The DirecTV model is the one the wireless cable industry wants. Consumers buy the DirecTV equipment themselves, and most install it themselves. Professional installation is available for a fee if the customer desires. If this could be achieved in the wireless cable service, an operator’s costs would be greatly reduced.
Airtime Lease Agreement. The agreement between the teacher and the commercial wireless cable operator to allow the wireless cable operator to use the teacher’s frequencies at specific times of the week. These agreements are discussed in 47 CFR §74.931.
Booster Station. An additional transmitter used by the wireless cable operator to replicate the signals from the MDS station or trunk MDS signals. Booster stations are intended to extend service in areas poorly served by the main transmitter.
BTA. Basic trading area. A Rand-McNally term for a geographical unit consisting of one or more counties, which Rand McNally has certainly some properties in common.
BTA license. A license issued to a commercial wireless cable operator. BTA licenses were auctioned in 1995 and 1996. A BTA license authorizes an operator to use all commercially available channels within a BTA, as long as no interference is made to any authorized station that existed at the time of the auction.
Cable TV (CATV). A multi-channel subscription offer available from a single device, but CATV usually indicates traditionally wired cable.
Customer Location Equipment (CPE). The system of antenna, transmission line and downconverter or modem installed on the customer’s website to allow the use of wireless cable broadband technology.
Excess channel capacity. Anytime during the week when the ITFS licensee channels are not needed for educational activities. The spectrum that used to lie fallow during those hours; now, FCC rules allow the leasing of the use of the channels during this time to commercial operators, generate revenue for schools and increase spectrum efficiency. See Airtime Lease Agreement.
Federal Communications Commission (FCC). The federal agency authorized by Congress to regulate the use of the radio spectrum.
Instructional TV Fixed Services (ITFS). The frequencies devoted to the use of educational units in the course of their educational mission. The channels are six MHz each. The reserved channels range from 2500 MHz to 2686 MHz. The service is “fixed” in that the transmitter and receiver locations are identified to the FCC and specified in the license. The purpose of this service is to allow long distance education. For example, a hospital may be a licensed reception location and use the service for continuing education. The FCC rules for ITFS stations can be found in 47 CFR §74, subsection I (beginning at §74,900).
Line-of-Sight (LOS). There is a clear, unobstructed microwave path between transmitter and receiver antennas. LOS propagation of microwave not only requires that the direct path between the two antennas is unobstructed, but that an area around the path is also clear. This area is sausage-shaped and surrounds the direct path in all three dimensions. It is larger in diameter (extending farther from the direct path) in the middle than at the end points and varies in diameter with frequency and with the length of the total path. It is called Fresnel zone clearance after the French mathematician who developed the formula.
Multipoint Distribution Service (MDS). A domestic public radio service provided from one or more fixed transmission sites to multiple reception locations. These channels are six MHz each. An MDS licensee may operate either as a joint carrier or as a non-joint carrier, but must specify such to the FCC. The frequencies initially assigned to this service are in the 2150-2162 MHz band. The frequency bands 2596-2644 MHz and 2650-2680 MHz were added when the need for more spectrum became apparent. The FCC rules for MDS stations can be found in 47 CFR §21, subsection K (which begins at §21.900).
Multichannel Multipoint Distribution Service (MMDS). An MDS service that uses multiple broadcast channels. The FCC rules for MMDS stations can be found in 47 CFR §21, subchapter K (which begins at §21.900).
Response Station. In a two-way digital wireless cable system, the customer site is the answering station. It communicates back to the wireless cable system and communicates directly with the answering station hub.
Response Station Hub. A fixed system operated by the licensee or wireless cable operator for receiving information transmitted by one or more response stations. The response station must use digital modulation with uniform power spectral density.
Wireless cable. Using microwave frequencies to aggregate multiple channels of video programming, which are then offered to subscribers. Using microwave frequencies instead of wires makes it much easier to operate homes in less dense areas. In addition, the cost of wiring is removed.