Downstream broad beam diversity
View Patent ↗A satellite communication system is provided according to one embodiment of the invention. The satellite communication system includes a plurality of satellites, a gateway and a plurality of subscriber terminals in communication with the gateway through the satellites. The gateway includes a plurality of antennas pointed toward a specific satellite. Each antenna may transmit the same signal to the satellites. The signal may be an OFDM signal. The subscriber terminals may include an antenna pointed toward at least one of the satellites and configured to receive OFDM signals. The OFDM signal time is proportional to the longest transmission time difference of all subscriber terminals within the geographic area serviced by the satellites. The transmission time difference is a measure of the difference between the transmission time of a signal over the longest transmission path and the transmission time of a signal over the shortest transmission path at a subscriber terminal.
1. A satellite communication system comprising:
a plurality of satellites;
a gateway with a plurality of antennas, wherein one or more of the plurality of antennas is pointed toward more than one of the plurality of satellites, and the gateway is configured to transmit data using orthogonal frequency-division multiplexing (OFDM); and
a plurality of subscriber terminals, wherein each of the plurality of subscriber terminals include an antenna pointed toward at least two of the plurality of satellites and are configured to receive an OFDM signal from the gateway through the plurality of satellites,
wherein, for each subscriber terminal, the gateway determines the longest transmission time between the gateway and each subscriber terminal through each of the plurality of satellites;
wherein, for each subscriber terminal, the gateway determines the shortest transmission time between the gateway and each subscriber terminal through each of the plurality of satellites;
wherein, for each subscriber terminal, the gateway determines the transmission time difference between the longest transmission time and the shortest transmission time for each subscriber terminal;
wherein the gateway determines the largest transmission time difference among the transmission time differences for each of the plurality of subscriber terminals;
wherein the gateway determines an OFDM symbol time that is greater than the largest transmission time difference;
wherein the gateway receives a data stream;
wherein the gateway converts the data stream into a plurality of data symbols multiplexed over a plurality of orthogonal sub-carriers to create an OFDM symbol stream, each data symbol, exclusive of the cyclic prefix, having the same symbol time as the OFDM symbol time; and
wherein the gateway transmits the OFDM symbol stream to the plurality of subscriber terminals through the plurality of satellites.
2. The satellite communication system according to claim 1 , wherein the number of orthogonal sub-carriers within the OFDM signal is proportional to the OFDM symbol time.
3. The satellite communication system according to claim 1 , wherein the gateway is configured to modulate the signal using quadrature amplitude modulation.
4. The satellite communication system according to claim 1 , wherein the gateway is configured to modulate the signal using phase-shift keying.
5. The satellite communication system according to claim 1 , wherein the plurality of satellites comprise three satellites.
6. The satellite communication system according to claim 1 , wherein the plurality of antennas comprise three antennas.
7. The satellite communication system according to claim 1 , wherein the plurality of satellites are in adjacent orbital slots.
8. The satellite communication system according to claim 1 , wherein the subscriber terminals are mobile.
9. The satellite communication system according to claim 1 , wherein the subscriber terminal antenna is a broad beam antenna.
10. A method occurring at a gateway for communicating with a plurality of subscriber terminals through a plurality of satellites using orthogonal frequency-division multiplexing (OFDM), wherein the plurality of subscriber terminals are located within a geographic area, the method comprising:
determining the longest transmission time between the gateway and each subscriber terminal through each of the plurality of satellites;
determining the shortest transmission time between the gateway and each subscriber terminal through each of the plurality of satellites;
determining the transmission time difference between the longest transmission time and the shortest transmission time for each subscriber terminal;
determining the largest transmission time difference among the transmission time differences for each of the plurality of subscriber terminals;
determining an OFDM symbol time that is greater than the largest transmission time difference;
receiving a data stream;
converting the data stream into a plurality of data symbols multiplexed over a plurality of orthogonal sub-carriers to create an OFDM symbol, each data symbol having the same symbol time, exclusive of the cyclic prefix, as the OFDM symbol time; and
transmitting the OFDM symbol to the plurality of subscriber terminals through the plurality of satellites.
11. The method according to claim 10 , wherein the number of orthogonal sub-carriers within the OFDM signal is proportional to the OFDM symbol time.
12. The method according to claim 10 , further comprising modulating the data stream with quadrature amplitude modulation.
13. The method according to claim 10 , further comprising modulating the data stream with phase-shift keying.
14. The method according to claim 10 , wherein the plurality of satellites comprises three satellites.
15. A satellite communication system comprising:
a plurality of satellites;
a gateway with a plurality of antennas, wherein one or more of the plurality of antennas are pointed toward more than one of the plurality of satellites; and
a reference terminal with one or more antennas pointed toward the plurality of satellites and configured to receive signals from the gateway through the plurality of satellites,
wherein the gateway determines an OFDM symbol time that is greater than the largest transmission time difference between the gateway and the reference terminal through the plurality of satellites;
wherein the gateway receives a data stream;
wherein the gateway converts the data stream into a plurality of data symbols multiplexed over a plurality of orthogonal sub-carriers to create an OFDM symbol, each data symbol having the same symbol time, exclusive of the cyclic prefix, as the OFDM symbol time; and
wherein the gateway transmits the OFDM symbol to the reference terminal through the plurality of satellites.
16. The satellite communication system according to claim 15 , wherein the relative transmission delay are transmitted over the Internet.
17. The satellite communication system according to claim 15 , wherein the reference terminal is configured to transmit signals to one or more subscriber terminals.
18. The satellite communication system according to claim 15 , wherein the plurality of satellites comprises three satellites.
19. A gateway comprising
an input port configured to receive a data stream; and
a plurality of antennas pointed toward more than one of a plurality of satellites, and configured to communicate with a plurality of subscriber terminals through the plurality of satellites,
wherein the gateway is configured to transmit the data stream to one or more of the subscriber terminals using orthogonal frequency-division multiplexing (OFDM),
wherein, for each subscriber terminal, the gateway determines the longest transmission time between the gateway and each subscriber terminal through each of the plurality of satellites;
wherein, for each subscriber terminal, the gateway determines the shortest transmission time between the gateway and each subscriber terminal through each of the plurality of satellites;
wherein, for each subscriber terminal, the gateway determines the transmission time difference between the longest transmission time and the shortest transmission time for each subscriber terminal;
wherein the gateway determines the largest transmission time difference among the transmission time differences for each of the plurality of subscriber terminals;
wherein the gateway determines an OFDM symbol time that is greater than the largest transmission time difference;
wherein the gateway converts the data stream into a plurality of data symbols multiplexed over a plurality of orthogonal sub-carriers to create an OFDM symbol, each data symbol having the same symbol time, exclusive of the cyclic prefix, as the OFDM symbol time; and
wherein the gateway transmits the OFDM symbol to the plurality of subscriber terminals through the plurality of satellites.
20. A satellite communication system comprising:
a plurality of satellites;
a gateway with a plurality of antennas, wherein one or more of the plurality of antennas is pointed toward more than one of the plurality of satellites, and the gateway is configured to transmit a data stream using orthogonal frequency-division multiplexing (OFDM); and
a plurality of subscriber terminals, wherein each of the plurality of subscriber terminals include an antenna pointed toward at least two of the plurality of satellites and are configured to receive an OFDM signal from the gateway through the plurality of satellites,
wherein each subscriber terminal determines the longest transmission time between the gateway and the subscriber terminal through each of the plurality of satellites;
wherein each subscriber terminal determines the shortest transmission time between the gateway and the subscriber terminal through each of the plurality of satellites;
wherein each subscriber terminal determines the transmission time difference between the longest transmission time and the shortest transmission time for each subscriber terminal;
wherein the gateway determines the largest transmission time difference among the transmission time differences for each of the plurality of subscriber terminals;
wherein the gateway determines an OFDM symbol time that is greater than the largest transmission time difference;
wherein the gateway receives a data stream and converts the data stream into a plurality of data symbols multiplexed over a plurality of orthogonal sub-carriers to create an OFDM symbol, each data symbol having the same symbol time, exclusive of the cyclic prefix, as the OFDM symbol time; and
wherein the gateway transmits the OFDM symbol to the plurality of subscriber terminals through the plurality of satellites.