Overlaying an Air to Ground Communication System on Spectrum Assigned to Satellite Systems

Abstract

An air to ground communication system provides internet access to aircraft from ground based stations. The air to ground system shares spectrum with uplink portions of a satellite communication spectrum. Interference mitigation techniques are employed to avoid interference between the ground based communications and satellite communications. Fade mitigation techniques are employed to provide communication to aircraft at low angles of elevation in the presence of rain.

1 . A ground base station comprising:
 a transceiver configured to transmit and receive signals on a satellite uplink band; and   a controller configured to reduce interference with satellite communications on the satellite uplink band, the controller further configured:   to handoff an aircraft transceiver to another ground base station when the ground base station and aircraft transceiver are aligned with a non-geostationary satellite when the other ground base station is available for handoff, and   to control transmit power of the transceiver to use a reduced power for maintaining a communication link while reducing interference with satellite communications.   
     
     
         2 . The ground base station of  claim 1 , in which the controller is further configured to spread transmit power across a frequency band to reduce power spectral density of transmissions. 
     
     
         3 . The ground base station of  claim 1 , in which the ground base station is further configured to direct transmissions away from a geostationary arc of Earth. 
     
     
         4 . The ground base station of  claim 1 , in which the controller is further configured to reduce interference with satellite communications by directing ground base station antennas away from the equator. 
     
     
         5 . The ground base station of  claim 1 , in which the controller is further configured to reduce interference with satellite communications by reducing a data rate on the communication link between the ground base station and the aircraft transceiver until the ground base station and the aircraft transceiver are no longer aligned with the non-geostationary satellite. 
     
     
         6 . The ground base station of  claim 1 , in which the controller is further configured to select the other ground base station based at least in part on a data rate available from the other ground base station and whether the other ground base station and the aircraft transceiver are aligned with the non-geostationary satellite. 
     
     
         7 . The ground base station of  claim 1 , in which receiving antennas and transmit antennas are configured separately by beam forming on a single antenna. 
     
     
         8 . A method of avoiding signal degradation in a wireless air to ground communication system, comprising:
 monitoring a signal strength between a ground base station and an aircraft transceiver communicating in a satellite uplink band;   determining based on the signal strength whether a signal is subject to excessive rain fade according to a predetermined criteria; and   in response to determining that the signal strength is subject to excessive rain fade, handing off the communication from the ground base station to a second ground base station.   
     
     
         9 . The method of  claim 8 , further comprising:
 returning the communication to the ground base station in response to determining the signal strength is no longer subject to excessive rain fade.   
     
     
         10 . The method of  claim 8 , further comprising:
 searching for signals being transmitted from neighboring ground base stations away from a geostationary arc of Earth;   determining a best ground base station with which to communicate based on the signal strength; and   in response to determining the best ground base station, establishing communication with the best ground base station.   
     
     
         11 . The method of  claim 8 , further comprising:
 controlling transmit power of the ground base station and the aircraft transceiver to use a reduced power for maintaining a communication link while reducing interference with satellite communications.   
     
     
         12 . The method of  claim 8 , further comprising:
 estimating a received Signal to Interference plus Noise (SINR) at the ground base station and the aircraft transceiver; and   adjusting data rates of the ground base station and the aircraft transceiver to a highest rate that the transceiver may still correctly decode a signal with a predetermined probability.   
     
     
         13 . The method of  claim 12 , in which a beam of the ground base station is directed toward the aircraft transceiver based upon position location information indicating a location of the aircraft transceiver. 
     
     
         14 . The method of  claim 8 , further comprising:
 adjusting a beam of the aircraft transceiver to be directed toward a ground base station serving the aircraft transceiver.   
     
     
         15 . The method of  claim 8 , further comprising:
 assigning time slots to system wide control channels on a downlink direction to the aircraft transceiver;   transmitting on a wide beam in the assigned time slots to enable signal strength measurements; and   transmitting data on a narrow beam directed to the aircraft transceiver in other time slots.   
     
     
         16 . An apparatus for avoiding signal degradation in a wireless air to ground communication system, comprising:
 means for monitoring a signal strength between a ground base station and an aircraft transceiver communicating in a satellite uplink band;   means for determining based on the signal strength whether the signal is subject to excessive rain fade according to a predetermined criteria; and   means for handing off the communication from the ground base station to a second ground base station in response to determining that the signal strength is subject to excessive rain fade.   
     
     
         17 . The apparatus of  claim 16 , further comprising:
 means for returning the communication to the ground base station in response to determining the signal strength is no longer subject to excessive rain fade.   
     
     
         18 . The apparatus of  claim 16 , further comprising:
 means for searching for signals being transmitted from neighboring ground base stations away from a geostationary arc of Earth;   means for determining a best ground base station with which to communicate based on the signal strength; and   means for establishing communication with the best ground base station in response to determining the best ground base station.   
     
     
         19 . The apparatus of  claim 16 , further comprising:
 means for controlling transmit power of the ground base station and the aircraft transceiver to use a reduced power for maintaining a communication link while reducing interference with satellite communications.   
     
     
         20 . The apparatus of  claim 16 , further comprising:
 means for estimating a received Signal to Interference plus Noise (SINR) at the ground base station and the aircraft transceiver; and   means for adjusting data rates of the ground base station and the aircraft transceiver to a highest rate that the transceiver may still correctly decode a signal with a predetermined probability.   
     
     
         21 . The apparatus of  claim 20 , in which a beam of the ground base station is directed toward the aircraft transceiver based upon position location information indicating a location of the aircraft transceiver. 
     
     
         22 . The apparatus of  claim 16 , further comprising:
 means for adjusting a beam of the aircraft transceiver to be directed toward a ground base station serving the aircraft transceiver.   
     
     
         23 . The apparatus of  claim 16 , further comprising:
 means for assigning time slots to system wide control channels on a downlink direction to the aircraft transceiver;   means for transmitting on a wide beam in the assigned time slots to enable signal strength measurements; and   means for transmitting data on a narrow beam directed to the aircraft transceiver in other time slots.   
     
     
         24 . An apparatus for wireless communication comprising:
 at least one processor; and   a memory coupled to the at least one processor, the at least one processor being configured:
 to monitor a signal strength between a ground base station and an aircraft transceiver communicating in a satellite uplink band; 
 to determine based on the signal strength whether a signal is subject to excessive rain fade according to a predetermined criteria; and 
 to hand off the communication from the ground base station to a second ground base station in response to determining that the signal strength is subject to excessive rain fade.