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04.21.2003
Originally featured on BroadcastEngineering.com
New types of satellite paths make expanded war coverage possible

With more and more video and audio traffic traveling from uplink to studio, IP traffic uplink crews now often need a good satellite-based ISP. One such satellite ISP provider on the drawing board is SkyBridge, a division of Alcatel. SkyBridge will use a constellation of 80 satellites in the Ku Band, orbiting at an altitude of 913 miles. This low earth orbit allows the short signal propagation time (30 milliseconds) needed for the provision of real-time interactive services. This service will provide Internet connectivity to users via satellite without any on-board processing by the satellites.



Reporters in the field can now send stories via email and possibly attach an edited video piece with it.

Approximately 200 gateway stations are planned for worldwide coverage. Each gateway will have a 234 miles radius coverage. Gateway stations will interface with the existing terrestrial network through an ATM switch. This service will share the Ku Band with current users. It re-utilizes the frequency assignments for Fixed Satellite Services, Broadcasting Satellite Services, and Fixed Services between 10 and 18 GHz. The system will share the spectrum through a technique called geo-stationary arc avoidance. Traffic from a gateway cell is transparently handed over to another satellite whenever harmful interference could potentially affect fixed satellite services. SkyBridge is also designed to avoid interference with terrestrial wireless systems operating in the same frequency bands.

As the satellites move across the sky, the earth stations track one satellite and when it moves into the avoidance arc or falls below the horizon, an automatic hand-over of traffic occurs from one satellite to the next. Both Right Hand Circular Polarization (RHCP) and Left Hand Circular Polarization (LHCP) will be utilized for efficient use of the spectrum.

The target launch mass of each satellite will be about 270 lbs, of which 880 lbs is the communications payload. Each satellite will create 18 spot-beams, i.e. uplink and downlink beams for both the forward and return links. Each beam is continuously steered and shaped inside the Satellite field-of-view to illuminate cells fixed on the ground.

SkyBridge plans to offer access to broadband and narrowband services globally. By space resource sharing between gateways (satellite antennas and power), the initial 80 satellite SkyBridge constellation should be able to handle the traffic exchanged by at least 20 million equivalent users. The equivalent capacity of the system, defined as the cumulative residential and professional instantaneous broadband traffic at respective peak hours is more than 215 Gbps.

Companies such as Stratos, which repackages services from Inmarsat, is providing coverage from Iraq. Stratos provides satellite coverage of most of Europe, the north half of Africa, to Central Asia and the Indian sub-continent, including all of the Middle East. They provide Global Area Networking (GAN) and Broadband GAN (BGAN). Besides the space connectivity the company provides satellite modems/antennas that facilitate data and voice connectivity.

A number of news organizations use this connectivity to connect Video over IP (VoIP) devices for SNG via GAN. Inmarsat satellites can direct spot beams to areas that require additional service. They recently repositioned an antenna on a satellite over the Indian Ocean to put an additional spot beam on Iraq.

While offering very low bit rates, 2.4 Kbps, some are using the Iridium satellite phone system for voice, and for sending still photos. Iridium offers a data kit that allows a PC to be connected to an Iridium phone. The Iridium system is comprised of 66 low altitude satellites operated by Boeing. The Iridium system is able to handle concentrated spikes in usage in a given area by not relaying solely on a specific gateway downlink station to handle the satellites in its service footprint. The satellites are able to send traffic off to adjacent satellites and off to additional gateways if traffic gets too heavy at the closest gateway.

For more information visit www.stratosglobal.com and Inmarsat.com.

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