The ground segment comprises a network of gateways (GESs), satellite control centers (SCCs), OCCs and Globalstar business offices (GBOs) interconnected via a Globalstar data network (see Figure 5). GESs, provide the interfaces between the satellites and the PSTN/public land mobile network to provide telemetry, tracking and command and control links between the SCC and the satellites and to allocate satellite resources on a call-by-call basis.
The Globalstar system has many GESs distributed around the world that receive and transmit feeder link signals from and to the satellites and provide interconnection to the PSTN. GESs are designed for unmanned operation. Each has up to four 5.50 meter antennas and electronic equipment installed in a building or shelter. The GES connects the Globalstar space segment to terrestrial switching equipment, receives telephone calls from the terrestrial switching equipment and generates CDMA carriers to transmit through the satellite. The satellite then retransmits the signal to UTs.
The UT equipment may be either handheld, fixed or mobile and located anywhere within the satellite antenna footprint. In the return direction, the UT transmits to the satellite(s) and the satellite(s) retransmit the signal to the GES. The GES connects the call to terrestrial switching equipment, which can then connect to any subscriber using the standard telephone system. Connections can also be made to terrestrial cellular subscribers or to other Globalstar UT mobile or fixed stations.
The Globalstar system includes two OCCs to manage and control system planning and execution. Each is completely capable of operating the network and managing the satellite constellation. There are two to circumvent the possibility of earthquake, power grid failure or other disasters. One is in San Jose, California and the other is near Sacramento. Each location includes an OCC, SCC and GBO.
The OCC manages the satellites, controls the orbits and provides telemetry and command (T&C) for the satellite constellation. To accomplish this function on a worldwide basis, the OCC communicates with T&C units collocated at selected GESs. The T&C units share the RF links with the GES communications equipment to relay commands and to receive telemetry.
The SCC manages all satellite telemetry, track, command and control functions and launches operations.
To support the GBO, the Globalstar accounting and billing system (GABS) is collocated with the SCC and the OCC. The GABS is responsible for all financial activities associated with Globalstar. 2, 4-6
The user segment includes three different kinds of UT equipment: handheld units, mobile-mounted units and fixed units. UTs with omni-type antennas are designed to support data rates up to 9.6 Kb/s. A variable rate vocoder varies its rate each frame to voice activity. This automatically reduces transmitter power for lower vocoder rates, which means, on average, less interference to other users and higher system capacity.
Satellite diversity is used in the system; if a call is transmitted through multiple satellites, the user terminal and the gateway receive at least two and usually more signals and coherently combine them, which brings diversity gain, reduces the required link margin on each individual link and increases capacity.
Diversity overcomes the adverse effects of propagation such as blocking, shadowing and fading. With the constellation, double satellite coverage is available nearly 100 percent of the time; therefore, UT devices can provide diversity as required. Both forward and reverse link power control is used to adjust GES and UT powers to the minimum required to maintain high performance. Power is increased only as needed, which means less interference to other users and increased capacity.
Handheld Satellite Phone Terminals
The Globalstar handheld terminals look like standard cellular telephones. They can also be used as equipment for alert after emergency grounding of ships and aircraft. Tri-, dual- or Globalstar-only modes of telephone service are available:
1. Tri-mode satellite phone service offers a global phone roaming solution for the U.S.A.-based Advanced Mobile Phone System (AMPS/IS-95), IS-95 CDMA digital phone coverage or the Globalstar satellite service. The tri-mode Qualcomm satellite phone for AMPS/CDMA/Globalstar services is shown in Figure 6a. Calls can be answered with any key for easy access to short messages and voicemail, with a "new message" alert that can be configured by the user. It features standard international dialing (prefix "+"), a mailbox for voice, numeric and text messages, user-configured ringtones (8 modes), side keys for volume adjustment and a 2.5 mm headphone jack.
2. Dual-mode satellite phone service offers global service for the Global System for Mobile Communications (GSM) Cellular Class 4 phones for Globalstar/GSM users, such as the Ericsson and Telit dual-mode GSM/Globalstar phones.
3. The Globalstar phone service mode only satellite phone is one of the smallest and lightest SatPhones with dimensions 16.92 cm (H) x 7.33 cm (W) x 5.79 cm (D). A Qualcomm GSP-1700 satellite phone is shown in Figure 6b.
Fixed Satellite Phone Terminals
The Globalstar network, in general, offers two types of fixed satellite terminals:
1. Payphone Terminals are single line Globalstar fixed units used to connect a payphone service into the PSTN for rural and remote areas used in the U.S.A. out of terrestrial landline or cellular coverage (see Figure 7a). These units can also be installed on mobile platforms, namely onboard aircraft for passenger service with flush mount fuselage antennas. Access to the Globalstar network is via an antenna mounted outside the booth with a clear view of the sky or via a mobile satellite antenna. The antenna is connected to the CDMA radio unit.
2. Fixed Single Line Phones offer communication service in remote office environments. An indoor telephone kit and outdoor antenna are shown in Figure 7b. The antenna can be mounted in a convenient position on the roof, wall or mast with a clear view of the sky and connected to the subscriber’s equipment. The system is compatible with all RJ11 type subscriber equipment such as wall, desk and cordless phones and value-added devices like fax/answering machines. Globalstar also offers a standard trunk interface for compatibility with local switching systems, such as private automatic branch exchanges (PABX).
Fixed satellite phone equipment performance is equivalent to that of a mobile earth station (MES) except that the antenna gain and transmitter power may be even higher. In fact, fixed terminals do not require path diversity to combat fading and blockage and must support seamless beam-to-beam and satellite-to-satellite hand off.
Since there is no hand off between the local cellular system and the Globalstar network, if the user crosses a service boundary between the local cellular system and Globalstar, the call could be dropped and must be placed again. Indicators tell the operator that the mode has changed. The system will not clash in a boundary area, thus all users/MESs can select the preferred mode. The call can be placed in Globalstar mode and will continue until the phone is in an idle state.
The Globalstar system, in general, offers voice, duplex data speeds from 9.6 to 200 Kb/s, circuit switched data similar to dial-up Internet services, packet switched data, Internet, SCADA and integration with GPS for satellite navigation.
3. Multipurpose 9600 Data Satellite Hotspot is the de facto satellite mini router that provides hotspots for users to use a convenient app and seamlessly pair their existing GSP-1700 satellite phone with a smartphone, tablet or laptop to send and receive E-mail and text messages over the Globalstar network (see Figure 8).
With the Globalstar 9600 and Globalstar satellite phones, customers can use their existing Wi-Fi-enabled devices to send e-mails and post on social media over the Globalstar network. Whether on land or at sea, customers can maintain reliable connectivity when beyond the cellular network. The Globalstar 9600 router is compatible with cell phones such as Android, Apple iOS, Windows and Mac. Thus, today’s smartphones provide more options for staying in touch with friends and family.
Customers can take smart phones beyond cellular using the Globalstar satellite hotspot outdoors with a clear view of the sky and horizon without obstructions, buildings and large trees. The phone must be placed on its side and the antenna fully extended, pointing toward the sky and turned on. After 30 seconds, two icons appear on the home screen, which means that unit is registered with the Globalstar satellite network. Globalstar 9600 is then ready to send and receive E-mail and data. This unit is ideal for industries such as: energy, oil and gas, emergency and commercial management, ferries and recreational marine, aircraft, transportation and construction.2,9-11