The push for more data spectrum
Calls for more spectrum to be freed up for data and telecommunications uses have not fallen on deaf ears in the nation’s capital. Over the past 12 months, both the Federal Communications Commission and members of Congress have put into motion a variety of efforts to provide more of the airwaves for public unlicensed and licensed use. Some frequencies such as 70 GHz are expected to open up with few problems, while others, like television VHF and UHF bands, are likely to run into resistance from current users.
Currently, there are two FCC Notice of Proposed Rule Makings (NRPMs) seeking comment and feedback to open up different spectrum areas.
In addition, U.S. Sens. Barbara Boxer, D-Calif., and George Allen, R-Va., introduced the “Jumpstart Broadband Act” in January 2003 to add another 255 MHz of spectrum in the 5 GHz range. Each effort has its own unique and interesting points.
Broadband in paradise
The most near-term and practically “sure deal” in new spectrum use revolves around millimeter wave technology. Millimeter wave frequencies have been used for radio astronomy, space-based cloud imaging, and various military applications. Experiments have also shown the utility of using millimeter wave to “see” airport runways through fog and smoke. On June 28, 2002, the FCC released an NPRM discussing the use of 71-76 GHz, 81-86 GHz, and 92-95 GHz bands. The NPRM was stimulated in part by a petition by Loea Corporation’s petition to use the 71-76 GHz band and finalized rules on spectrum usage are likely to be issued by the end of 2003.
Based in Lihue, Hawaii, Loea has used the beautiful landscapes of the Hawaiian Islands as a testing ground for their experiments with millimeter-wave high-speed wireless broadband equipment. The company has developed point-to-point gear capable of full-duplex 1.25 Gbps (yes, that’s gigabits per second) data rates at distances of around a mile for reliability of 99.999 percent and distances of up to 8 miles at a reliability of 99.9 percent. Performance reliability is dependent on humidity and distance between transmitters, but fog is not a factor as it would be with free space optical (i.e. laser) systems.
Loea’s system uses two-foot and four-foot Cassegrain dish antennas with up to 56dB of gain. It has a rain fade margin of up to 30 dB. The equipment only uses 10 volts of standard AC power and have an optical interface capable of operating at OC-3, OC-12, and Gigabit Ethernet speeds, as well at the non-standard rate of 1.25 Gbps, called OC-24 by the company. Clocking speeds are software selectable. Loea is working on a solution to mux together a pair of OC-12s to fully drive the equipment at its top OC-24 speed rate.
In real world operations, Loea’s equipment has already been used in several installations. One of the first demonstrations was a 2.7 mile gigabit data link linking the Hawaii Institute of Marine Biology on Coconut Island in Kane’ohe Bay to Oahu. Surrounded by 64 acres of coral reef, the institute was reluctant to pull fiber out to the island for both ecological and cost reasons. More urban installations have been put into operation in downtown Manhattan between 55 Broad and 80 Pine Street and at the 2003 Super Bowl to move raw HDTV footage.
Currently, the 71-76 GHz band is currently co-licensed for both government and commercial use, but commercial links must receive FCC Special Temporary Authority prior to implementation on a limited test basis.
According to Tom Wetmore, Loea’s vice president of strategic relations, the company expects the FCC will adopt rules for commercial use of the spectrum sometime in the second half of 2003. The U.S. Government can use the spectrum today and Loea’s equipment is available for purchase off of GSA schedule.
Congressional efforts to free up more spectrum in the 5 GHz area started rolling in the fall of 2002, when Sens. Boxer and Allen announced they would introduce a bill in the 108th Congress to expand Internet broadband technology. While the partnership of a long-time Democrat from California (Boxer) with a first term Republican of the South would appear to be an odd one at first glance, these particular bedfellows are on the same page. Boxer represents Silicon Valley while Northern Virginia was a keystone to the state’s high-tech growth over the last decade. Allen also serves as the chair of the Republican High Tech Task Force.
Both Senators are touting The Jumpstart Broadband Act as a way to facilitate broadband access in both urban and rural areas. The bill requires the FCC to allocate another 255 MHz of continuous spectrum under 6 GHz for unlicensed use by wireless broadband devices.
It also requires the FCC to make sure Department of Defense usage isn’t compromised while the National Telecommunications and Information Administration (NTIA) will be responsible for establishing guidelines to prevent interference with existing government applications.
Explicitly mentioned twice in the Act, the Department of Defense (DoD) is likely to have a significant impact on the form of the final NTIA guidelines. DoD has expressed concern over the international use of future WiFi products and presented a position paper requesting limits on the future use of 5 GHz to the World Administrative Radio Conference. A broader discussion will take place at the June meeting in Geneva.
The U.S. military also would like to see more stringent implementation of dynamic frequency selection in current and future devices to prevent interference. European governments are opposed to the proposals.
Battle royale on shared TV spectrum?
The most intriguing and likely to be the most heated battle for new spectrum will concern the potential usage of VHF and UHF television bands by unlicensed devices.
Quietly released Dec. 20, the FCC’s latest NPRM on spectrum is seeking comment in an arena that will likely provoke the ire of television broadcasters already being forced into moving over to digital television technology.
At first glance, analog television bands have significant potential for data. TV stations currently operate in 6 MHz chunks in the ranges of 57-72 MHz, 76-88MHz, 174-216Mhz, and 470-806 MHz. To prevent interference, FCC rules require distance separations between co-channel and first-adjacent-channel TV stations.
In addition, distance separations are required between UHF TV stations up to 15 channels apart. As a result, there are a number of vacant TV channels at any given location in the country, with more UHF spectrum available because of no existing licensee at a particular location. Even after a transition to digital television, there will be a number of available channels in a given geographic area not being used for interference avoidance reasons.
Needless to say, smaller cities and rural areas will have more available spectrum.
For instance, new digital TV allotments require minimum distance separation ranging from 196 to 273 kilometers for co-channel stations and separations of 110 kilometers for adjacent channel stations not collocated or in close proximity, based upon the assumption that stations will operate at maximum power.
Lower power transmitters could operate on vacant channels at closer distances and avoid interference with licensed operating stations.
The FCC cites advances in technology that would make it feasible to design new types of unlicensed equipment to share spectrum in TV bands without causing interference to either TV broadcasts or other licensed services operating within the bands.
A next-generation unlicensed device could have enough on-board intelligence to scan and monitor spectrum to detect frequencies already in use and insure transmissions only occur on open frequencies.
The NPRM also discusses the idea of using an on-board GPS location function in combination with an online database to compare the transmitter’s location to licensed operations within the vicinity.
Agreeing upon use of this spectrum for unlicensed devices is liable to encounter commentary from parties other than television broadcasters.
A variety of other applications already use parts of the aforementioned spectrum, ranging from wireless microphones, medical telemetry transmitters, radio astronomy, private land mobile radio service, and commercial mobile radio service.
There also are concerns about possible interference with channels 2, 3, and 4, used by VCRs and other set-top boxes.
A 3650 MHz footnote
In addition to kicking the hornet’s nest of using television spectrum, the Dec. 20, 2002, NPRM also opened up discussion for use of spectrum at 3650-3700 MHz in unlicensed devices at “at power levels significantly higher than the maximum permitted for unlicensed devices in other frequency bands” with “minimal technical requirements” to avoid interference with other services.
The 3650 MHz band was previously allocated to the Federal Government for location services and the private sector for satellite transmissions.
In 1997, the NTIA identified the band as one that could have other uses, with a grandfathered condition that gives the government the ability to operate to three existing sites with a broadcast radius of 80 kilometers per site.
The FCC notes other usage caveats may be tied to the use of the band, but seems to think there’s plenty of potential as well. Since it is a large 50 MHz block of recently vacated spectrum, it is not heavily used in most parts of the country. Current users of the band — satellite services and the three government sites — are all at fixed locations at known geographic coordinates.
To avoid interference, unlicensed devices could use a combination of GPS database reference and frequency agility capability.