Satellite communications for public safety
Satellite communications-once considered an exotic and forbiddingly expensive method of mobile communications-is becoming a viable option for public safety agencies for several reasons. The size, weight and cost of portable and mobile satellite terminals have dropped considerably in recent years, as have the usage costs for the satellite services. At the same time, the range of mobile satellite services has blossomed, with new capabilities such as fax, data, position tracking and dispatch radio becoming readily available at an affordable cost.
This article examines some of the current and projected mobile satellite communications technologies, the range of satellite services available and the cost-benefits of satellite communications for public safety applications.
LEOs and MEOs and GEOs-oh my! The satellite communications industry is rapidly developing and growing. Industry news reports are full of the fortunes and misfortunes of companies such as Iridium, ICO, AMSC and Globalstar. It can all be baffling for the layperson, who simply wants to get the best products and service at the best price.
We’ll start with a quick overview of the different choices in satellite communications. The satellite systems are normally grouped by the height of orbit for the “birds” in space.
* Low-orbit systems – Low-earth-orbit satellite systems (LEOs) are relatively small and low-powered. They orbit the earth rapidly. Because they are close to the earth’s surface, they do not require as much power. This also means that the mobile transceiver requires only a relatively small omnidirectional antenna. LEO satellites are cheaper to build and to put into orbit. On the other hand, with LEOs you need more satellites to provide global coverage. The switching scheme is more complex because the rapidly moving satellites are constantly having to hand off calls to each other, and a worldwide infrastructure of ground stations is required. Iridium, Teledesic and Globalstar are LEO systems.
* Medium-orbit systems – The next group of satellites are medium-earth orbit (MEOs). They are also sometimes called ICOs, for “intermediate circular orbit.” With a MEO system, you can cover the earth with fewer satellites, but the higher-powered spacecraft are more expensive to build and to launch into orbit. Spaceway and ICO Global Communications are both examples of MEO systems.
* Geosynchronous systems – Finally, there are geosynchronous satellite systems (GEOs). The GEO systems are based on the premise that a satellite placed in orbit over the equator at precisely the right altitude has an orbital speed exactly the same as the earth’s rotation on its axis. This means that the satellite’s position in the sky relative to a fixed point on the ground will always be the same. This has obvious advantages for fixed antenna systems such as home TV systems. It also has the benefit of being able to offer nearly global cover age with only a few satellites. On the other hand, the orbital distances are such that much larger, high-powered satellites are required, and they are far more difficult and expensive to launch into orbit.
Probably the best-known GEO system in mobile communications is Inmarsat, which was originally created for maritime communications with ships on the high seas. The Inmarsat system has also won a considerable share of the land-mobile market with the latest generation of relatively small briefcase-size satellite terminals. Inmarsat provides worldwide coverage, except for the extreme polar regions.
There are also a number of regional GEOs, such as the MSAT satellites, over North America, and other similar systems for the Far East, Australia, South America, Europe and Africa. These regional systems typically use spot beams to maximize power into specific areas.
MSAT-1 is a good example of a regional GEO system. The MSAT-1 satellite is in geostationary orbit at 106.5 degrees west longitude and operates in the L-band frequency range. The footprint of the satellite covers all of North and Central America, extending from the Arctic Circle to the northern portion of Ecuador. The satellite system is operated by TMI Communications, a Canadian consortium. SatCom Systems has been providing MSAT-1 services to the U.S. market under a Special Temporary Authority (STA) from the FCC since July 1998. Full License Authority was granted to the company by the FCC in November 1999. A similar service is also provided by American Mobile Satellite Corporation (AMSC) through the MSAT-2 satellite.
The recent bankruptcies of Iridium and ICO should in no way be taken as a sign that the technology is faltering or slowing down. On the contrary, these pioneering systems have led the way into an exciting new world of mobile communications, and the prospect of hand-held cellular-like satellite phones is on the verge of becoming a reality. The next generation of satellites, such as Teledesic, will provide a true high-speed data bus permitting wireless Internet and electronic connectivity worldwide.
Meanwhile, back to today Satellite communications systems (whether they are LEOs, MEOs or GEOs) provide a wide range of services, including voice, fax and data. Other services typically include vehicle tracking and differential GPS data broadcasts for precise positioning. For instance, MSAT-1 users in the United States have a choice of dial-up telephony, fax, circuit-switched data, packet-switched data and push-to-talk (PTT) two-way dispatch radio. The latter service, marketed by SatCom Systems under the trade name NetRadio, is supporting applications in the public safety sector, especially in remote rural areas.
The service uses dedicated satellite channels to provide two-way, half-duplex, point-to-multipoint dispatch communications. Subscribers get unlimited satellite usage at a fixed monthly rate. Functionally, it is identical to a terrestrial, trunked, two-way radio system, with channels, talk groups and familiar PTT microphones. The only difference is that the repeater is some 22,000 miles in space instead of on a tower.
Supporting rural EMS A glance at any political map of the United States reveals that large portions of the country are thinly populated. Yet, residents of these rural regions rightfully expect that they will have access to the same sort of police, ambulance and fire service as their counterparts in metropolitan areas. This expectation presents a challenge to public safety organizations.
Take, for example, Emergystat Ambulance Service, which operates a fleet of about 65 vehicles across a sparsely populated region of Alabama and Mississippi. Founded in Vernon, AL, in 1988, Emergystat has steadily expanded into a major regional EMS company. Today, the company provides paramedic services for 34 locations in Alabama and Mississippi, with more than 400 employees and 65 primary vehicles. More than 50 of these vehicles are typically in service at any given time. Cellular and two-way radio coverage is unreliable or unavailable in much of this rural region. Emergystat recently deployed a NetRadio system, installing satellite terminals on 15 vehicles and one fixed terminal at its dispatch center in Vernon. The units are all tied together in a private, dedicated talk group. Initial results are being evaluated, but it is believed that Emergystat can save more than $10,000 annually, per location, by switching to the satellite dispatch radio system.
Satellite communications technology will play an important role in Emergystat’s plans to expand its business. Every time the company moves into a new location, it can cost more than $20,000 in capital outlay to set up a mobile radio network, including tower rentals, repeater purchase, leased landline connections and labor-not to mention the inevitable headaches of securing licenses. Many of the towns and counties in this part of the country renew agreements with EMS providers on an annual basis. It is difficult to justify the large capital and operating expenditures needed to establish and maintain modern trunked special mobile radio (SMR) networks for a thin-route area in a competitive marketplace.
The satellite network offers inherent flexibility in fleet management, permitting Emergystat to deploy vehicles rapidly from one service area to another. They can communicate via satellite with the dispatch center in Vernon no matter where they are.
Last year, for instance, when a hurricane hit the Gulf Coast, Emergystat had to deploy a number of vehicles on short notice to evacuate people from hospitals. Much of the time they were not in range of the installed SMR networks and were outside of cellular coverage, so the drivers were often completely out of touch with the dispatch center. This is one time that the satellite networks could literally have been lifesavers.
Not just for rural agencies The benefits of mobile satellite communications for rural areas is obvious, but important benefits exist for urban areas as well, where satellite systems can provide essential backup for existing terrestrial systems. In a metropolitan area, where there are multiple layers of excellent, modern communications facilities, there is still an inherent vulnerability to disruption from natural disasters, such as earthquakes in California, hurricanes in Florida, ice storms in Massachusetts and tornadoes in Kansas.
For these places, mobile satellite communications can provide a low-cost backup communications network for disaster relief and recovery. For instance, SatCom Systems deployed a large number of satellite terminals to Honduras and Nicaragua in the aftermath of Hurricane Mitch in 1998. In many cases, this was the only link with the outside world. The U.S. Army Corps of Engineers has been a major user of the system in its rebuilding efforts in that heavily devastated region.
What’s next? Mobile wireless satellite technology is now a practical and cost-effective alternative for public safety communications, but that’s just the beginning. In the next few years, as new satellite services such as Iridium, Globalstar, ICO and Teledesic come into service, a large portion of terrestrial communications will migrate naturally to satellites. Moreover, the satellites will open exciting new possibilities for vehicle tracking, asset management, precise positioning and high-speed data transfer.
Tom D. Soumas Jr is president of SatCom Systems and Dave Robertson is vice president of Energystat.
