Satellite communications system and method

A satellite communication system having N satellite communications earth stations, wherein each of the N earth stations are capable of simultaneous transmission of a local transmission signal, and wherein the respective local transmission signals of a desired pair of bidirectionally communicative earth stations are preassigned a predetermined frequency band, each earth station comprising:

• a transmission unit for transmitting a local transmission signal toward a satellite;
• a reception unit for receiving a remote transmission signal transmitted from a remote earth station and a return signal, the return signal being part of said local transmission signal transmitted from the local earth station toward the satellite and partially returned from the satellite and received at the local earth station;
• and
• a canceling unit supplied with part of said local transmission signal and said received return signal, for canceling said received return signal by part of said local transmission signal,
• whereby communications by a plurality of signals sharing the same frequency band becomes possible while partially or wholly superposing respective signal frequencies.

A VSAT satellite system having a large earth station (HUB station) and a plurality of small earth stations (VSAT stations), the HUB station comprising:

• a transmission unit for transmitting a local transmission signal toward the satellite;
• a reception unit for receiving a remote transmission signal transmitted from a remote earth station and a return signal, the return signal being part of said local transmission signal transmitted from the local earth station toward the satellite and partially returned from the satellite and received at the local earth station;
• and
• a cancelling unit supplied with part of said local transmission signal and said received return signal, for cancelling said received return signal by part of said local transmission signal,
• whereby communications by the HUB station and the VSAT stations sharing the same frequency band become possible while partially or wholly superposing respective signal frequencies.

A satellite communications system having a plurality of earth stations for bidirectional communication via a satellite transponder, wherein at least one of each pair of earth stations engaged in bidirectional communication comprises:

• a transmission system comprising:
• local transmission baseband means for digitizing transmission information and error correction coding the digitized transmission information to generate a transmission bit train;
• transmission modulating means for modulating said transmission bit train;
• up-converter means for converting the frequency of said transmission bit train modulated by said modulating means into an RF frequency;
• and transmitting means for transmitting said modulated bit train having the RF frequency as a local transmission signal at a local station toward the satellite transponder via a transmission antenna;
• and
• a reception system comprising:
• receiving means for receiving via a reception antenna a remote transmission wave transmitted from a remote earth station and frequency band converted and a frequency band converted return signal, the return signal being part of a local transmission signal transmitted from the local earth station toward the satellite transponder and partially returned from the satellite transponder and received at the local earth station;
• down-converter means for converting the frequency of a reception signal received by said reception means into an IF frequency;
• remote transmission signal demodulating means for demodulating the reception signal having the IF frequency and converting the reception signal into a reception bit train;
• remote station transmission signal baseband means for receiving said reception bit train and obtaining transmission information sent from the remoter station;
• and
• return signal canceling means for reproducing a carrier wave of the return signal from an output signal of said down-converter means and generating a modulated signal for canceling said frequency band converted signal corresponding to said local transmission signal, said modulated signal being obtained by modulating, in the same manner as said modulating means of said transmission system, said carrier wave with said transmission bit train generated by said local transmission base band means and delayed by a transmission time of said return signal, said return signal canceling means canceling said return signal contained in the output signal of said down-converter means by adding said modulated signal to the output signal.

A satellite communications method for each earth station under bidirectional communication via a satellite transponder, comprising the steps of:

• supplying part of a local transmission signal transmitted toward the satellite transponder;
• delaying said supplied signal by a time generally equal to a time required for a return signal which is part of said local transmission signal returned from the satellite transponder;
• and
• combining said delayed signal and said return signal returned from said satellite transponder and received at the local earth station to cancel said return signal,
• whereby communications by a plurality of signal sharing the same frequency band become possible while at least partially superposing respective signal frequencies.

A satellite communication method for N satellite communications earth stations, wherein each of the N earth stations are capable of simultaneous transmission of a local transmission signal, and wherein the respective local transmission signals of a desired pair of bidirectionally communicative earth stations are preassigned a predetermined frequency band, said method comprising the steps of:

• supplying at least part of a local transmission signal transmitted toward a satellite;
• delaying said supplied signal by a time generally equal to a transmission time required for a return signal which is part of said local transmission signal returned from the satellite;
• and
• combining said delayed signal and said return signal returned from said satellite and received at the local earth station to cancel said return signal,
• whereby communications by a plurality of signals sharing the same frequency band become possible while partially or wholly superposing respective signal frequencies.

A satellite communication method wherein in response to a channel setting request from two earth stations A and B, a bidirectional satellite channel is assigned for predetermined time, the method comprising the steps of:

• in each of earth stations A and B,
• supplying part of a local transmission signal transmitted toward a satellite;
• delaying said supplied signal by a time generally equal to a transmission time required for a return signal which is part of said local transmission signal returned from the satellite;
• and
• combining said delayed signal and said return signal returned from said satellite and received at the local earth station to cancel said return signal, whereby a wider band between two bands occupied by communications from station A to station B and from station B to station A is assigned, allowing the narrower band to share the wider band.

A satellite communications method wherein in response to a channel setting request from two earth stations A and B, a bidirectional satellite channel having a predetermined single band is assigned for a predetermined time, the method comprising the steps of:

• in each of stations A and B,
• supplying part of a local transmission signal transmitted toward a satellite;
• delaying said supplied signal by a time generally equal to a transmission time required for a return signal which is part of said local transmission signal returned from the satellite;
• and
• combining said delayed signal and said return signal returned from said satellite and received at the local earth station to cancel said return signal,
• whereby stations A and B are allowed to share the band at the same time while superposing part of the whole of frequency spectra.

A satellite communication method for a VSAT satellite system having a large earth station and a plurality of small earth stations, the method comprising the steps of:

• in the large HUB earth station,
• supplying part of a local transmission signal transmitted towards a satellite;
• delaying said supplied signal by a time generally equal to a transmission time required for a return signal which is part of said local transmission signal returned from the satellite;
• and
• combining said delayed signal and said return signal returned from said satellite and received at the local earth station to cancel said return signal,
• whereby the same frequency band is shared by both transmission signals from the large HUB earth station and small VSAT earth stations while partially or wholly superposing respective signal frequencies.

A satellite communications method for a VSAT satellite system having a large earth station and a plurality of small earth stations, the method comprising the steps of:

• in each small VSAT earth station,
• supplying part of a local transmission signal transmitted toward a satellite;
• delaying said supplied signal by a time generally equal to a transmission time required for a returned signal which is part of said local transmission signal returned from the satellite;
• and
• combining said delayed signal and said return signal returned from said satellite and received at the local earth station to cancel said return signal,
• whereby the same frequency band is shared by both transmission signals from the large HUB earth station and small VSAT earth stations while partially or wholly superposing respective signal frequencies.

A satellite communications method for bidirectional communications, comprising the steps of:

• supplying part of a local transmission signal transmitted toward a satellite;
• delaying said supplied signal by a time generally equal to a transmission time required for a return signal which is part of said local transmission signal returned from the satellite;
• and
• combining said delayed signal and said return signal returned from said satellite and received at the local earth station to cancel said return signal,
• whereby the same frequency band is shared by a plurality of signals while partially or wholly superposing respective signal frequencies.

For use in a satellite communication system, a return signal canceling circuit which receives a supplied part of a local transmission signal comprising:

• a delay circuit for delaying said supplied signal by a transmission time required for a return signal which is part of said local transmission signal returned from a satellite;
• a circuit reproducing a carrier wave from the returned signal;
• a circuit for modulating said reproduced carrier wave with the signal delayed by said delay circuit;
• a circuit changing the amplitude and phase of the modulated carrier wave;
• and
• a circuit for combining said modulated wave with the changed amplitude and phase and a reception signal from the satellite.