Abstract:
This invention concerns improvements in the efficiency and flexibility of multi-beam communications satellites connected by intersatellite links. It will increase the number of customers serviced and hence the revenue generated when intersatellite links are employed by multibeam satellites which use the currently available technology in a bent-pipe microwave architecture. Existing multibeam systems use the bent-pipe microwave architecture. Information from one geographic region uplinked to one satellite can be transferred to a second satellite via intersatellite link and then downlinked into a second geographic region. These multibeam systems waste available bandwidth capacity by tying up complete intersatellite link transponders even if the channels are not full because information switching is conducted at a full transponder level. Further, if information is broadcast, as in news-gathering applications, to several downlink beams, the system ties up, in the receiving satellite, one transponder per downlink beam. In future systems using on-board digital-processing technology, it is theoretically possible that information can be switched at a much finer bandwidth level. Hence, one intersatellite channel could handle traffic originating from several uplink beams on the first satellite with destinations to several downlink beams on the second satellite which avoids the inefficiency of a partially full transponder. However, customer terminals have to be designed for the modulation and coding architecture specific to that system and cannot be used with any other system. The present invention solves spectral flexibility and inefficiency problems of existing systems, and is transparent to all modulation and coding architectures while still allowing for communication with all terminals currently in use with communications satellites. The approach used is to combine switching at a subchannel level (solving flexibility and inefficiency problems) while using technologies compatible with bent-pipe architecture (solving terminal-compatibility problems) with an intersatellite link. Technologies used include Surface Acoustic Wave (SAW) filtering and solid-state switching. This invention will provide spectral efficiency and flexibility approaching but not equalling the theoretical efficiency and flexibility of future systems employing digital signal processing. It will, however, be significantly more efficient than future digital satellite systems in terms of the two most expensive satellite resources, power and mass.
Abstract:
A repeater for a multibeam communications satellite combines the features of coaxial channel interbeam switching and subchannelization of some of the channels. In one embodiment described, the input radio-frequency signals from the input beams are fed through the input multiplexers to form channels. Some, but not all, channels are subsequently subchannelized for interbeam switching. In another embodiment of the invention, a portion of the incoming radio frequency signals bypasses the input demultiplexer and is filtered for noise-limiting reasons, converted down to an intermediate frequency and then subchannelized using SAW filters. The specification also teaches that digital techniques can be used to obtain the same results. Especially in the case of satellites with a large number of beams and a large number of channels, it is not necessary to have full interbeam switching of all the subchannels derived from one channel: instead, the specification proposes the use of parallel configurations of smaller, less complex switching networks.