In December 1996, Square Peg Communications Inc. (SPCI) of Ottawa, Ontario completed the installation of a five-channel Inmarsat Aero Evolution Test Ground Earth Station (GES) at Teleglobe Canada’s Laurentides earth station located in Weir, Quebec. The Test GES is a key component of Inmarsat’s current and ongoing plans to introduce new aeronautical services.
The Inmarsat Aeronautical system currently provides voice, fax, and data services to aircraft with high gain antennas (Aero-H) and a low-rate data-only service to aircraft with low gain antennas (Aero-L). In 1994, Inmarsat convened a forum of users, service providers and manufacturers to plan the next steps in the evolution of the system. The resulting enhancements to the Aero system included a spot-beam based service to aircraft with intermediate gain antennas (Aero-I) and a new, lower-rate speech codec. The Aero-I specification provides for lower terminal size and cost and will therefore allow the benefits of in-flight telephone service to be extended to short and medium haul airliners and mid-range corporate aircraft. The new lower-rate speech codec used by Aero-I aircraft earth stations (AESs) can also be utilized by Aero-H AESs. Such upgraded terminals have been designated as Aero-H+. Since the reduced-rate codec requires less power and bandwidth than the existing codec, it will reduce space-segment utilization costs and increase system capacity. In 1995, Inmarsat commissioned a system design and proof-of-concept implementation of the Aero-I C-channel modem from CAL Corporation, the Canadian Communications Research Centre (CRC) and Calian Communications Systems Ltd. After initial laboratory and over-the-satellite testing of the CRC modem, a comprehensive flight test program was performed by CRC (see ASN, Dec 1995-Jan 1996). The results of this extensive testing confirmed the objective and subjective performance of the design (see ASN, June-July 1996).
To help reduce the lead time involved in introducing the new service, Inmarsat contracted Square Peg Communications in April 1996 to perform a quick turnaround design and manufacture of a GES which could bring the Aero-I/H+ service on-line prior to the availability of the corresponding GES upgrades from Nera and Toshiba. The complete five-channel system was installed in December 1996. The installation will permit Aero-I and evolved Aero-H terminals to be tested and operationally demonstrated in AOR, prior to the start of global commercial Aero-I service in the first quarter of 1998. The GES provides all functionality required to support AES-initiated (air-to-ground) calls into the PSTN. This includes system table and spot beam map broadcasts, AES log-on/off and handover functions as well as all call processing associated with the C-channel calls. The system supports up to five simultaneous voice calls; calls can be set up in the global beam or any of the spot beams supported by the new Inmarsat-3 satellites. Upgrades to support ground-to-air or data calls are straightforward and can be added if required.
The core of the GES is a network of rack-mount PC-compatible computers. One PC is used as a Management Unit and acts as the central controller for the GES. It provides the primary monitoring and control interface to the system, implements the P/R-channel protocols and interfaces to the P/R-channel unit, switching matrix controller, and power management units. Five additional PCs are used as identical Channel Units. Custom hardware is utilized to meet Inmarsat signal-in-space requirements in the conversion between baseband and the 70 MHz IF required by host LES. All other functions are performed by commercial off-the-shelf (COTS) hardware.
The GES normally runs unattended, and does not require operator intervention on startup or in normal operation. However, standard Windows 95 operator interfaces are provided by the Management and Channel Units for configuration and monitoring. The operator interfaces are accessible locally via a keyboard/display/mouse multiplexer The GES can also be monitored and controlled from Inmarsat’s headquarters in London. This is accomplished by using a commercial remote control software package (MARC) and then bridging the LAN at the GES to a LAN at Inmarsat. A LAN bridge is used to link a PC at Inmarsat to British Telecom’s earth station at Goonhilly, UK. From there, a 64 kbps C-band to C-band link (available on the new Inmarsat-3 satellites) is used to connect to a companion LAN bridge at Teleglobe’s earth station. The remote control facility allows the video display, keyboard, and mouse of the remote control computer to act as if they were directly connected to the Management unit or to any of the Channel units. This is completely transparent to the GES software. In addition, the remote control facility supports file transfers between the GES and the remote control computer, allowing (for example) system tables to be uploaded to the GES and log files to be downloaded. The GES utilizes Power Management Units (PMUs) which allow the power on any piece of GES equipment to be cycled either remotely from Inmarsat or automatically by the system. If a software fault occurs, a watchdog within one of the PMUs will automatically reset the system. Introduction Of Aero-I/H+ The first Aero-I antennas are expected to be fully access-approved by mid-1997, with the development of Aero-I or Aero-H+ channel unit equipment completed shortly thereafter. The GES will aid manufacturers in the development of their equipment. For example, the GESs P-channel will be available for manufacturers wanting to verify reception of spot beam map information. The GES will also be available for demonstrations and beta trials of the Aero-I/H+ service.
The Aero Evolution Test GES, now operational, will facilitate the introduction of Inmarsat’s new Aero-I/H+ service. Its modular design coupled with its programmable digital signal processing (DSP) based modem architecture allows for straightforward incorporation of new channel types, providing Inmarsat with an ongoing platform for evaluating future aeronautical communications services.
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