Communication protocol for a high data rate satellite communication

Abstract

A communication protocol or method that provides for terminal access, data flow, call monitoring and terminal polling, and call termination between user terminals connected to a high data rate satellite communication system. An 'Aloha' random access channel that forms part of a bent-pipe architecture is used in conjunction with orderwire uplink and downlink channels to permit the system to cleanly and simply establish its data links and thus provide terminal access. A network control center is used to assign a source user terminal to uplink and downlink channels. After the communication link is established, uplinked data is demodulated, and routed to every downlink beam where it is multiplexed with other data channels, then remodulated and downlinked to every user terminal. The orderwire uplink is only from the network control center to the satellite relay system, and uses the channel without demodulation and remodulation. The orderwire downlink is only from the satellite relay system to the user terminals, and uses the channels with demodulation and remodulation. Each user terminal monitors its orderwire downlink channel to recognize and extract messages addressed to it. Data flow, call monitoring and terminal polling is performed once the source and destination user terminals have been assigned their beams and frequency and time slots. Thereafter, data transfer between terminals is generally independent of the network control center. Input data generated at a source user terminal is multiplexed and transmitted to the satellite relay system. The satellite relay system demodulates the data, routes it so that it is retransmitted on a beam that communicates with the destination user terminal, remultiplexes and remodulates the data, and then transmits the multiplexed data to the destination user terminal. The network control center monitors the link so that system resources are not unnecessarily tied up if a connection is lost. This is achieved by causing both terminals to send periodic messages to the network control center indicating that they are active on the network, or the network control center may periodically poll each terminal and terminate a call if either terminal is unresponsive or provides a signal indicating that it has hung up. Several call termination procedures are also provided.