Online Journal of Space Communication


This paper describes the Gigabit Satellite Network (GSN) being developed under joint sponsorship of NASA and ARPA. The system will use the wide-band Satellite Switched Time Division Multiple Access (SS-TDMA) capability and hopping beam antennas of NASA's Advanced Communications Technology Satellite (ACTS). The GSN network will provide full-duplex SONET services over satellite at OC-3 (155.54 Mb/s) and OC-12 (622.078 Mb/s) rates. Typical applications will include connection of distributed SONET/ATM fiber "islands" over satellite, wide-area distributed supercomputer networking, high-definition digital TV, and high-speed file transfer.

The RF link consists of 30 GHz uplink and 20 GHz downlink signals transmitted using a 3.4 meter offset-fed antenna and 120 Watt helix-type TWTA. The burst modem uses offset QPSK or offset-BPSK modulations for transmission at 696 Mb/s and 348 Mb/s, respectively. Transmissions to the satellite are protected using Reed-Solomon encoding, providing almost error-free clear-sky performance and, in the case of rain-fade, bit error rates better than 1099% of the time.

The terrestrial side of the ground station will function as standard SONET Line Terminating Equipment (LTE), with OC-3 and OC-12 fiber interfaces, and is capable of multiplexing and demultiplexing the SONET signals down to the STS-1 (51.84 Mb/s) level. These STS-1 signals can be routed independently through the satellite between various ground stations.

Management of the network is performed using a Network Management Terminal (NMT) and is based on standard SNMP and Internet protocols. The earth stations can also be remotely monitored and controlled via the satellite channel or via the terrestrial Internet.



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