System and Method For Communicating Via A Satellite In an Inclined Geosynchronous Orbit

Abstract

A hub terminal and remote client communicate via a target satellite in an inclined geosynchronous orbit. As the target satellite ascends or descends away from the geostationary arc, the signal strength of the uplink channel is increased without increasing the level of interference with geostationary satellites. The increased angular separation from geostationary satellites also decreases downlink interference. The resulting increase in signal strength permits adjustment of the modulation and coding parameters to increase spectral efficiency. The method permits intermittent communication with an inclined satellite sharing a geostationary slot with a station-kept satellite, or from locations where the geostationary arc is blocked, or while using disadvantaged antennas that would be impractical for use with geostationary satellites. In some circumstances, it is desirable to deliberately mis-steer the antenna slightly away from the target satellite.

What is claimed is: 
     
         1 . A method of communicating via a satellite, the method comprising:
 locating a target satellite in an inclined geosynchronous orbit;   pointing an antenna at an aiming point offset from a geostationary arc, the antenna having a radiation pattern; and   in response to an absolute value of a declination of the target satellite increasing to greater than a first threshold value, transmitting a radio frequency signal to the target satellite using the antenna.   
     
     
         2 . The method of  claim 1  further comprising:
 in response to the absolute value of the declination of the target satellite decreasing to less than the first threshold value, suspending transmission of the radio frequency signal. 
 
     
     
         3 . The method of  claim 2  further comprising:
 in response to the absolute value of the declination of the target satellite increasing to greater than a second threshold value, resuming the transmission of the radio frequency signal, wherein the declination at which the transmission is resumed is opposite in sign to the declination at which the transmission was suspended. 
 
     
     
         4 . The method of  claim 1  wherein an object blocks the antenna and the point at which the satellite crosses the geostationary arc. 
     
     
         5 . The method of  claim 1  wherein the target satellite crosses the geostationary arc within one and one half degrees right ascension of a geostationary satellite receiving transmissions in a same frequency spectrum as the radio frequency signal. 
     
     
         6 . The method of  claim 5  further comprising:
 estimating a maximum boresite Equivalent Isotropic Radiated Power (EIRP) Spectral Density (SD) that complies with a predetermined maximum EIRP SD toward the geostationary satellite based on the radiation pattern and the aiming point wherein the radio frequency signal is transmitted to the target satellite at a transmitted boresite EIRP SD no greater than the maximum boresite EIRP SD. 
 
     
     
         7 . The method of  claim 5  wherein a declination of the aiming point is greater in absolute value than the declination of the target satellite during the transmission. 
     
     
         8 . A method of communicating via a satellite, the method comprising:
 locating a target satellite in an inclined geosynchronous orbit wherein the target satellite shares a geosynchronous slot with a geostationary satellite;   pointing an antenna at an aiming point offset from a geostationary arc, the antenna having a radiation pattern;   estimating a maximum boresite Equivalent Isotropic Radiated Power (EIRP) Spectral Density (SD) that complies with a predetermined maximum EIRP SD toward the geostationary satellite based on the radiation pattern and the aiming point;   encoding information into a radio frequency signal based on an information rate, coding parameters, and modulation parameters; and   transmitting the radio frequency signal to the target satellite at a transmitted boresite EIRP SD no greater than the maximum boresite EIRP SD.   
     
     
         9 . The method of  claim 8  further comprising:
 suspending transmission in response to an angular separation between the geostationary satellite and the target satellite decreasing to less than a threshold value. 
 
     
     
         10 . The method of  claim 9  further comprising:
 resuming transmission in response to the angular separation increasing to greater than the threshold value. 
 
     
     
         11 . The method of  claim 8  wherein a declination of the aiming point is greater in absolute value than a declination of the target satellite during transmission. 
     
     
         12 . A communications transmitter comprising:
 a directional antenna having a radiation pattern;   an antenna pointing control configured to point the antenna at an aiming point with a right ascension and a non-zero declination;   a modulator configured to convert information into a radio frequency signal at an information rate using encoding parameters;   an amplifier configured to amplify the radio frequency signal such that the signal is transmitted from the antenna with a transmitted boresite EIRP SD; and   a processor programmed to determine a maximum boresite EIRP SD that complies with a predetermined maximum EIRP SD toward a geostationary satellite, based on the radiation pattern and the aiming point and to control the amplifier no greater than the maximum boresite EIRP SD, the geostationary satellite having a right ascension within one and one half degrees of the aiming point right ascension.   
     
     
         13 . The communications transmitted of  claim 12  wherein the processor is further programmed to:
 locate a target satellite in an inclined geosynchronous orbit that shares a geosynchronous slot with the geostationary satellite; and 
 suspend transmission in response to an angular separation between the geostationary satellite and the target satellite decreasing to less than a threshold value. 
 
     
     
         14 . The communications transmitted of  claim 13  wherein the processor is further programmed to:
 adjust the aiming point as the angular separation changes; 
 revise the maximum boresite EIRP SD as the aiming point changes; and 
 adjust the transmitted boresite EIRP SD based on the revised maximum boresite EIRP SD.