Globalstar.info, Globalstar Satellite Phone Background Information, Globalstar Satellite Telephone, Globalstar Satellite Communications

Globalstar is a Low Earth Orbit (LEO) system, with 40 satellites arranged in eight planes of 5 satellites each. The satellites are placed in an inclined orbit of 52 degrees at an altitude of 1414 km. The Globalstar satellites act as a “bent-pipe” transponder, which simply pass along satellite signals from the Globalstar user terminals to the nearest gateway.

The following distinct advantages are inherent in this simple “up-down” call routing:

Path Diversity

Path diversity is a method of signal reception that combines multiple satellite signals of varying power strengths into a single coherent signal. Globalstar satellite phones communicate with as many as three satellites simultaneously and combine those signals into a single, static-free signal. Globalstar satellite phones also alter power levels to compensate for shadowing and interference as needed.

As satellites move in and out of view, they will be seamlessly added to and removed from the calls in progress, reducing call interruptions. This enables the Globalstar system to provide superior service to a wide variety of locations with less potential for signal blockage from buildings, terrain, or other natural features. If buildings or terrain block a phone's signal, a "soft-handover" takes place, and the call's transmission is switched to an alternate satellite with no interruption.

Due to Globalstar's path diversity feature, multiple satellites (redundancy) are visible to users even on high latitudes as Anchorage (approx. 60 degrees North Latitude) and in some cases further north up to Fairbanks (approx. 64 degrees North Latitude).

When a Globalstar satellite antenna has an open line of sight to the southern horizon in Alaska, the user will have 100% visibility to at least 1 satellite up to 70 degrees North Latitude, with partial satellite visibility as high as 74 degrees.

The failure of any single satellite is actually a “soft” failure, which results in one less satellite being available to a relatively small portion of the globe for a short time during the satellite's orbital pass overhead, about 12 minutes, at the user's location. The out-of-service satellite quickly moves out of view and an operational satellite replaces it in the user's field of view. Therefore, a “hard” failure of “no satellites available” to a given user is .999997.

The expected life span of the Globalstar satellite constellation is 10-12 years, and Globalstar has additional spare satellites on the ground which can be launched to replenish the satellite constellation.

Redundancy in the Globalstar phone receiver. Globalstar phones feature a rake receiver to combine digital channels from a number of satellites simultaneously to form a stronger received signal. The combination of Globalstar's patented satellite path diversity, and the rake receivers in both the user terminal and the gateway yield superior call quality and fewer dropped calls.

Ground Segment

The Globalstar ground segment includes a network of 25 fully operation gateways around the world, a Globalstar Data Network (GDN) linking all the gateways, and a redundant Ground Control Operations Centers.

Each gateway, which is owned and managed by the host country service provider, receives transmissions from orbiting satellites, processes calls, and switches them to the appropriate ground network.

Gateways offer seamless integration with local and regional telephony and wireless networks. The gateway connects directly into the local Public Switching Telephone Network (PSTN) It also connects the Globalstar satellite-based wireless network with the Public Land Mobile Network (PLMN), such as AMPS and GSM.. As such, the gateway is the termination point for network transmission and network signaling.

The gateway is connected to the existing PSTN using standard E1/T1 trunk supporting a variety of signaling protocols. Inter-operability between the Globalstar system and telephone/cellular companies enables the subscriber to maintain a convenient single point for billing. Encoding ensures voice and signaling security for individual transmissions.

Ground Operations Control Centers (GOCC)
The Ground Operations Control Centers (GOCC) are responsible for planning and controlling the use of satellites by gateway terminals and for coordinating this utilization with the Satellite Operation Control Center ( SOCC ). GOCCs plan the communications schedules for the gateways and control the allocation of satellite resources to each gateway.

Satellite Operations Control Center ( SOCC )
The Satellite Operations Control Center ( SOCC ) manages the Globalstar satellite constellation. The SOCC tracks satellites, controls their orbits, and provides Telemetry and Command (T&C) services for the constellation. Globalstar satellites continuously transmit spacecraft telemetry data that provides on-board health and status reports for the satellite. The SOCC also oversees satellite launch and deployment activities. The SOCC and GOCC facilities remain in constant contact through the Globalstar Data Network (GDN).

Globalstar Data Network (GDN)
The GDN is the connective network which provides wide-area intercommunications facilities for the gateways, the Ground Operations Control Centers, and the Satellite Operations Control Centers.

Redundancy in the Globalstar Ground Segment. Neighboring Globalstar gateways can provide back up services to one another in the event of a service outage of other technical failure on the ground. All Globalstar gateways are equipped with back up power sources to ensure uninterrupted gateway service in the event of a terrestrial power failure, as was recently witnessed on August 14, 2003 on the East Coast of the U.S.

Further, Globalstar has a 24/7 fully operational back up Ground Control Operations Center in El Dorado Hills in the event of an outage at its primary GOCC facility.

Globalstar Background...

Path Diversity

Ground Segment