Satellite communications system and apparatus

Abstract

A satellite communication system, which is inherently power limited, employing spread spectrum techniques in order to trade-off bandwidth for small ground station antennas. In a one-way system embodiment a central station transmits data to a satellite for relay to a large number of small antenna receiving stations, the transmissions being spread spectrum encoded with spreading code lengths selected to provide adequate data recovery at the least sensitive station to which the transmissions are directed. Spreading codes may also function to address particular stations. In a two-way system embodiment, the central station additionally functions as a terrestrial relay station. A plurality of small antenna transmitting stations, at least one of which may be at the same site as a receiving station, transmit code division multiplexed data via the satellite to the central relay station using sufficiently long and distinct spreading codes as to permit adequate data error rates and to distinguish the transmissions of the various stations. The central relay station reformats the received data for retransmission to the satellite for relay to the receiving stations.

What is claimed is: 
     
       1. An earth satellite communications system for transmitting data from a plurality of users through a repeating geostationary satellite to a plurality of receiving earth stations, comprising A central transmitting station receiving data from a plurality of users, said station including means for converting the format of said data into a form suitable for transmission to a satellite,   means for spread spectrum processing the converted data, and   means for transmitting the spread spectrum processed converted data to a repeating geostationary satellite, and     A plurality of receiving earth stations, each of said receiving earth stations including .[.wide beamwidth, low gain.]. antenna means, said antenna means including a .Iadd.small, in the sense that a dish antenna with a diameter substantially less than 16 feet operating at 4 GHz in a system if which the orbital spacing of the geostationary satellites is 4 degrees is small, and consequently relatively wide beamwidth and concomitant low-gain .Iaddend.fixed directional antenna .[.having a beamwidth wider than the standard orbital spacing of geostationary satellites, whereby said antenna receives signals from more than one geostationary satellite,.]. .Iadd.having, at its operating frequency, a directional radiation pattern, in the sense that a 2 foot dish operating at 4 GHz has a directional radiation pattern, the beamwidth and gain of which pattern depends on the operating frequency and the antenna size, .Iaddend.and   detection means coupled to said antenna means, said detection means including spread spectrum processing .[.means,.]. .Iadd.means .Iaddend.for recovering data sent to said receiving earth station via said repeating geostationary .[.satellite.]. .Iadd.satellite even if and when the low gain and wide beamwidth of the antenna, resulting from its small size, leads to the reception of signals from said repeating geostationary satellite along with interfering signals from at least one other geostationary satellite, said spread spectrum processing means having a processing gain sufficient to substantially suppress said interfering signal.Iaddend..     
     
     
       2. The combination of claim 1 wherein said detection means further includes means for converting the format of said data into a form suitable for a user. 
     
     
       3. The combination of claims 1 or 2 wherein said .[.antenna means includes an.]. antenna .[.having.]. .Iadd.has .Iaddend.a gain providing a signal level below the thermal noise floor when standard (nonspread spectrum) satellite modulation techniques are used. 
     
     
       4. The combination of claim 1 wherein said spread spectrum processing means in said receiving earth stations includes means storing a local reference code for comparison to signals received for recovering data sent to said receiving earth station. 
     
     
       5. The combination of claims 1 or 4 wherein said spread spectrum processing means includes means for synchronizing said processing means to the received signals. 
     
     
       6. The combination of claim 1 wherein said spread spectrum processing means in said central station includes means for processing data for particular receiving earth stations with a spreading code unique to such stations. 
     
     
       7. The combination of claims 1 or 6 wherein said spectrum processing means in said central station includes means for processing data for particular receiving earth stations with a spreading code having a length commensurate with the sensitivity of the least sensitive station among said particular receiving earth stations. 
     
     
       8. The combination of claims 1 or 6 wherein said means for transmitting transmits said data in a time division format. 
     
     
       9. The combination of claim 6 wherein said means for transmitting transmits data in a time division formast having a plurality of time slots, wherein data processed by each unique spreading code occupies the next available time slot. 
     
     
       10. In a geostationary earth satellite communications system, wherein the signals relayed from a repeating geostationary satellite are power limited spread spectrum signals, a receiving earth station comprising .[.wide beamwidth, low gain.]. antenna means, said antenna means including a .Iadd.small, in the sense that a dish antenna with a diameter substantially less than 16 feet operating at 4 GHz in a system in which the orbital spacing of the geostationary satellites is 4 degrees is small, and consequently relatively wide beamwidth and concomitant low-gain .Iaddend.fixed directional antenna .[.having a beamwidth wider than the standard orbital spacing of geostationary satellites, whereby said antenna receives signals from more than one geostationary satellite,.]. .Iadd.having, at its operating frequency, a directional radiation pattern, in the sense that a 2 foot dish operating at 4 GHz has a directional radiation pattern, the beamwidth and gain of which pattern depends on the operating frequency and the antenna size, .Iaddend.and   detection means coupled to said antenna means, said detection means including spread spectrum processing .[.means,.]. .Iadd.means .Iaddend.for recovering data sent to said receiving earth station via said repeating geostationary .[.satellite.]. .Iadd.satellite even if and when the low gain and wide beamwidth of the antenna, resulting from its small size, leads to the reception of signals from said repeating geostationary satellite along with interfering signals from at least one other geostationary satellite, said spread spectrum processing means having a processing gain sufficient to substantially suppress said interfering signals.Iaddend..   
     
     
       11. The combination of claim 10 wherein said detection means further includes means for converting the format of said data into a form suitable for a user. 
     
     
       12. The combination of claim 10 wherein said .[.antenna means includes an.]. antenna .[.having.]. .Iadd.has .Iaddend.a gain providing a signal level below the thermal noise floor when standard (nonspread spectrum) satellite modulation techniques are used. 
     
     
       13. The combination of claim 10 wherein said spread spectrum processing means includes means storing a local reference code for comparison to signals received for recovering data sent to said receiving earth station. 
     
     
       14. The combination of claims 10 or 13 wherein said spread spectrum processing means includes means for synchronizing said processing means to the received signals. 
     
     
       15. An earth satellite communications system wherein a plurality of stations transmit data through a repeating geostationary satellite and a terrestrial relay station to a plurality of receiving earth stations, the combination comprising a plurality of transmitting stations, each comprising means receiving data for transmission to a repeating geostationary satellite,   means for spread spectrum processing said data, and   means for transmitting said spread spectrum processed data to said repeating geostationary satellite, said transmitting means including .[.wide beamwidth, low gain.]. antenna means, .Iadd.said antenna means including a small, in the sense that a dish antenna with a diameter in the order of 4 feet opeerating at 6 GHz in a system in which the orbital spacing of the geostationary satellites is 4 degrees is small, and consequently relatively wide beamwidth and concomitant low-gain antenna, the beamwidth and gain of which pattern depends on the operating frequency and the antenna size, .Iaddend.and     a terrestrial relay station, comprising antenna means,   detection means coupled to said antenna means, said detection means including spread spectrum processing means for recovering data sent by said transmitting station,   means for spread spectrum processing the recovered data, and   means for transmitting the spread spectrum processed data to said repeating geostationary satellite, and     a plurality of receiving earth stations, each of said receiving earth stations comprising .[.wide beamwidth, low gain.]. antenna means, said antenna means including a .Iadd.small, in the sense that a dish antenna with a diameter substantially less than 16 feet operating at 4 GHz in a system in which the orbital spacing of the geostationary satellites is 4 degrees is small, and consequently relatively wide beamwidth and concomitant low-gain .Iaddend.fixed directional antenna .[.having a beamwidth wider than the standard orbital spacing of geostationary satellites, whereby said antenna receives signals from more than one geostationary satellite,.]. .Iadd.having, at its operating frequency, a directional radiation pattern, in the sense that a 2 foot dish operating at 4 GHz has a directional radiation pattern, the beamwidth and gain of which pattern depends on the operating frequency and the antenna size, .Iaddend.and     detection means coupled to said antenna means, said detection means including spread spectrum processing .[.means,.]. .Iadd.means .Iaddend.for recovering data sent to said receiving earth station via said repeating geostationary .[.satellite.]. .Iadd.satellite even if and when the low gain and wide beamwidth of the antenna, resulting from its small size, leads to the reception of signals from said repeating geostationary satellite along with interfering signals from at least one other geostationary satellite, said spread spectrum processing means having a processing gain sufficient to substantially suppress said interfering signals.Iaddend..   
     
     
       16. The combination of claim 15 wherein said terrestrial relay station receives data from terrestrial sources, in addition to said recovered data, for transmission to said repeating geostationary satellite, said spread spectrum processing means further processing said additional data and said transmitting means further transmitting said processed additional data. 
     
     
       17. The combination of claim 15 wherein said transmitting station transmitting means transmits on different frequencies than said relay station transmitting means. 
     
     
       18. The combination of claims 15 or 17 wherein said transmitting station transmitting means transmits in a code division multiplex format and said relay station transmitting means transmits in a time division multiplex format. 
     
     
       19. The combination of claim 17 wherein there are a plurality of transmitting stations and a plurality of receiving earth stations, and at least one pair of transmitting and receiving earth stations are located at the same geographic site. 
     
     
       20. The combination of claim 19 wherein said transmitting station has a unique spreading code or pair of codes. 
     
     
       21. The combination of claims 19 or 20 wherein sdaid means for spread spectrum processing in said relay station includes means for processing data for particulawr receiving earth stations with a spreading code unique to such stations. .Iadd. 
     
     
       22.  The combination of claim 15 wherein said antenna has a gain providing a signal level below the thermal noise floor when standard (nonspread spectrum) satellite modulation techniques are used. .Iaddend.