Advertisement
Articles
Advertisement

Sorting out the satellite confusion

Sat, 05/31/1997 - 8:00pm
Jeffrey Krauss, Satellite Skywatcher and President of Telecommunications and Technology Policy
i_krauss.GIF
By Jeffrey Krauss, satellite skywatcher and President of Telecommunications and Technology Policy
Traditional GEO fixed satellites

We are all familiar with C-band and Ku-band satellites that deliver video programming to cable headends, TV stations and home dishes. These satellites are assigned to slots along a band that is located directly above the equator and at an altitude of 36,000 km, at which distance the earth's gravity and the sun's gravity are balanced. This is the geostationary orbit, and these satellites are called geostationary or GEO. C-band satellites operate at 6 GHz (uplink) and 4 GHz (downlink). Ku-band satellites operate at 14 GHz (uplink) and 12 GHz (downlink).

Now there's a new band for GEO satellites, called Ka-band. The frequencies are 28 GHz (uplink) and 18 GHz (downlink). The FCC has just granted construction approval for a whole slew of new Ka-band GEO satellites. Those pursuing Ka-band include names such as Hughes Spaceway, Loral Cyberstar, Motorola Millennium, and new guys such as VisionStar, NetSat 28, Morning Star and KaStar. These systems are called "fixed" satellite systems because they communicate with earth stations that are fixed on the ground (as opposed to mobile).

The FCC has granted permits for U.S. companies to locate their satellites all the way around the world, not just over the U.S. There will be U.S.-owned Ka-band satellites over Europe and Asia. And guess what — Luxembourg has applied for orbital slots over the U.S.!

Very few of these new satellites will be used for distribution of video programming, because they are designed with spot beam antenna patterns that cover a few hundred miles, rather than global beams that cover the entire continent. So they'll probably be used for voice and data networks, rather than video distribution. The FCC authorizations require the start of construction within one year and launch in five years, by May 2002. We'll see whether this schedule can be met.

LEO fixed satellites

Teledesic has received FCC approval for a network of hundreds of non-geostationary satellites, orbiting the Earth at a lower altitude than the GEO satellites; these are low earth orbit, or LEO satellites. The earth stations will be fixed, and will track the satellites as they orbit. This system will operate at Ka-band, using slightly different frequencies than the Ka-band GEO satellites . This is an enormously expensive system, but it will be owned by Bill Gates and Craig McCaw, and they can afford it. It's intended for data communications and for voice communications in rural areas and less developed countries. LEO systems cover the globe as the satellites orbit, and Teledesic plans to have earth stations throughout the world.

Both the Teledesic system and the Ka-band GEO fixed satellites will share the 18 GHz downlink band with a large embedded base of point-to-point microwave systems. These include microwave systems used by railroads, oil companies, local governments, cellular companies interconnecting cell sites, and pay-TV distribution networks such as Liberty Cable in New York. Satellite and microwave services have been able to share the C-band frequencies, using a procedure called frequency coordination, but frequency coordination at 18 GHz will be much more difficult. It may be quite a challenge for these satellite systems to find usable earth station sites.

LEO mobile satellites

A few years ago, the FCC approved the first generation of low earth orbit mobile satellites, systems like Iridium and GlobalStar and Odyssey. These will communicate with moving vehicles like trucks out on the highway, and with aircraft. Iridium just launched the first five of a network of 66 satellites. These systems use frequencies at 2.5 GHz and 1.6 GHz for their mobile communications, as well as "feeder link" frequencies at Ka-band to communicate with a few large gateway earth stations that interconnect with the telephone network and other private terrestrial networks.

The FCC has just reallocated spectrum for a future generation of LEO mobile satellites, around 2 GHz. Because the frequencies are very close to PCS frequencies, watch for proposals for hybrid satellite/terrestrial systems with handheld terminals that communicate with PCS cell sites if there are any nearby, and with satellites everywhere else. One of the major players expecting to use this band is called ICO Holdings, and is a spinoff of INMARSAT, the international maritime satellite organization.

This reallocation will require the relocation of some terrestrial users, both point-to-point microwave links and mobile microwave links used by broadcasters for electronic newsgathering (and by a few cable TV news operations). But the FCC has decided that the satellite systems will have to pay the relocation costs, just like PCS licensees have had to pay the relocation costs of incumbent microwave links. And the satellite folks don't like that one bit. They've come up with a plan that, rather than relocating the broadcasters, will simply kick them out. So we're in the start of a big fight, with satellite interests on one side and broadcasters on the other. But it will eventually be settled, and I'd guess that we might see the first satellites launched in this band around 2003.

With all of these new satellite systems in the works, at new frequency bands, there will be a variety of interesting new technologies coming along. Stay tuned, even if they are mostly non-video technologies.

Advertisement

Share This Story

X
You may login with either your assigned username or your e-mail address.
The password field is case sensitive.
Loading