How the Iridium Network Can Operate with Only Two Gateways

The Iridium network's design allows the system to operate using only two gateways.  Functioning gateways or ground stations are located in Tempe, Arizona and Wahiawa, Hawaii.  There is a non-functioning gateway in Italy.  The gateway in Wahiawa, Hawaii is primarily used by the U.S. military. 

The Iridium satellites communicate with each other using Ka-band intersatellite links.  Each satellite uses four intersatellite links, two to the fore and aft satellites in the same orbital plan and two to the satellites in orbital plane to either side.  These intersatellite links allow calls to be switched and routed across the satellites in the constellation before being transferred to a gateway.  The Iridium intersatellite link design makes the Iridium system impervious to natural disasters like earthquakes and hurricanes which could damage a gateway in the area of the disaster.  Like other satellite networks if a gateway is damaged the Iridium network can route the call to another gateway.    

With 66 satellites in the Iridium constellation, which offer complete planetary coverage, a call can come from a phone near the north pole then it could be switched from satellite to satellite before being sent down to a gateway where it can be switched to the public phone system.

The gateways include the system control segment and telephony gateways which is used to connect to the public phone network.  As an Iridium satellite orbits the earth they can lose line of site as it leaves the area of the gateway.  The routing tables change and frames are forwarded to the next satellite coming in view of the gateway.

The intersatellite links allow Iridium satellite phone to Iridium satellite phone calls to be handled totally by the constellation.  Calls of this type are not sent through the gateway.  The Iridium constellation has intelligence built in the network where an outbound Iridium satellite call from Iridium satellite phone goes to one of the satellites then the call is either sent directly down to the receiving satellite phone.  If the receiving satellite phone is not in the spots beam of the satellite receiving the call then the call is switched from satellite to satellite till it reaches the satellite in area of the receiving phone where it is then sent down to the call destination. 

Iridium network uses more satellites than any other satellite service provider.  With 66 satellites with polar orbits, this gives the constellation coverage to every part of the planet.  With no service gaps, Iridium users place and receive calls from virtually every part of the planet as long as the user has line of site to the Iridium satellites.  Cellular systems only cover 15% of the planet making the Iridium satellite service the only wireless service with total planetary coverage.

Learn More:

• Iridium Satellite Phones
• How the Iridium Network Works
• History Timeline of Iridium
• What is in the Future for Iridium
• Iridium Coverage Map
• Iridium 9555 Video Tutorial: Preparing Your Satellite Phone for Use
• Simulation of Iridium Constellation (SaVi)

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