System and method for channel assignment in a satellite telephone system

Abstract

A system and method for making channel assignments in a low earth orbit satellite telephone system wherein Doppler effect is utilized as a parameter in channel assignment. In a first embodiment the satellites orbit in a fixed grid pattern, and in a second embodiment the satellites move in orbits that appear random relative to each other.

I claim:  
     
       1. A method for making channel assignments in a satellite communications system comprising a plurality of low earth orbiting satellites, a plurality of land bases each including transmitter and receiver means operable in plurality of communication channels, and a plurality of mobile units (remotes) each having transmitter and receiver mean which are selectively assigned to operate in said plurality of channels; said method being effective to make interference free channel assignments for remotes incoming into said system to communicate with selected proposed satellites without the use of central controllers, said method including the steps of: 
       a) making tentative channel assignments between remotes and proposed satellites based on actual signal strength;  
       b) testing by a proposed satellite as to whether its transmission on a tentative channel would interfere with a transmission on a channel which a previously assigned remote is utilizing which channel may be different from said tentative channel due to Doppler shift, wherein the proposed satellite includes means for sensing Doppler effect;  
       c) determining by an incoming remote being assigned to said tentative channel whether it would be interfered with by a previously assigned satellite utilizing said tentative channel;  
       d) determining by said incoming remote whether it would interfere with a previously assigned satellite on the channel that the previously assigned satellite is utilizing which channel may be different from said tentative channel due to Doppler shift,  
       e) determining by said proposed whether it would be interfered with by a previously assigned remote, and  
       dependent on the results of said tests, initiating communications.  
     
     
       2. A method as in claim  1  including the step of making channel assignments dependent on the Doppler shift, and making said assignments on a priority hierarchy starting from the most positive Doppler shift and moving to the most negative Doppler shift. 
     
     
       3. A satellite communications system comprising a plurality of low earth orbiting satellites which satellites are orbiting in paths which are random relative to each other, a plurality of land bases each including transmitter and receiver means operable in a plurality of communication channels, and a plurality of mobile units each having transmitter and receiver means which are selectively assigned to operate in said plurality of channels; 
       a) means for making tentative channel assignments between mobile units and proposed satellites based on signal strength;  
       b) each satellite including means for sensing Doppler effect and means for testing whether its transmission on a tentative channel would interfere with a transmission on another one of said channels which a previously assigned mobile unit is utilizing, which said another one of said channels may be different from said tentative channel due to said Doppler effect.  
     
     
       4. A system as in claim  3  wherein, 
       a) said bases include means for sensing Doppler shift, and each base including means for testing whether its transmission on said tentative channel would interfere with a transmission on another one of said channels which a previously assigned satellite is utilizing which said other one of said channels may be different from said tentative channel due to Doppler shift.  
     
     
       5. A system as in claim  3  wherein 
       a) said mobile units include means for sensing Doppler shift, and each mobile unit includes means for testing whether its transmission on said tentative channel would interfere with a transmission on another channel which a previously assigned mobile unit is utilizing which other channel may be different from said tentative channel due to Doppler shift, and said mobile units can select the base with which said mobile units with which they will communicate.  
     
     
       6. A method for making channel assignments in a low earth orbit satellite telephone system wherein Doppler shift is utilized as a parameter in making communication channel assignments, said system including a plurality land bases each having transmitter and receiver means, a plurality of satellites operable in a plurality of communication channels, and a plurality of mobile units each having transmitter and receiver means which are selectively assigned to transmit and receive signals in said communications channels, said method comprising the steps of: 
         a )  making tentative communication channel assignments between mobile units and proposed satellites based on signal strength;    
         b )  calculating the Doppler shift on said signals and communication channel assignments;    
         c )  determining whether, due to said Doppler shift, transmissions on said tentative communication channels would interfere with transmissions on previously assigned communication channels; and,    
         d )  initiating communications dependent on said determinations.   
     
     
       7. A method for making channel assignments in a low earth orbit satellite telephone system wherein Doppler shift is utilized as a parameter in making channel assignments, said system including a plurality land bases each having transmitter and receiver means, a plurality of satellites operable in a plurality of communication channels, and a plurality of mobile units each having transmitter and receiver means which are selectively assigned to transmit and receive signals in said communications channels, said method comprising the steps of: 
         a )  determining signal strengths between selected mobiles and satellites;    
         b )  making tentative communication channel assignments between said selected mobiles and satellites based on the determined signal strength;    
         c )  calculating Doppler shift to determine whether a transmission on a tentative communication channel would interfere with a transmission on another one of said communication channels which a previously assigned mobile is utilizing.   
     
     
       8. A method as claimed in claim  7  further including the step of: 
         a )  programming mobile units to direct communications to selected land base sites, such as for the purpose of minimizing call charges.   
     
     
       9. A method as claimed in claim  7  further including the step of; 
         a )  dividing the area below a satellite into different sectors;    
         b )  assigning a portion of the channels on each satellite to each sector; and,    
         c )  utilizing directional antennas to transmit and receive said signals.   
     
     
       10. A method as in claim  7  wherein as the Doppler shift progresses from positive to negative, the steps include making channel assignments on a priority hierarchy starting from positive Doppler shifts and moving to negative Doppler shifts. 
     
     
       11. A satellite communications telephone system comprising a plurality of low earth orbiting satellites operable in a plurality of communication channels which satellites are orbiting in either random or set patterns, a plurality of land bases each having transmitter and receiver means, a plurality of mobile units each having transmitter and receiver means which are selectively assigned to transmit and receive signals in said communications channels, said system comprising: 
         a )  means for making tentative communication channel assignments between mobile units and proposed satellites based on signal strength;    
         b )  means for calculating the Doppler shift on said signals and utilizing said Doppler shift as a parameter in making communication channel assignments; and,    
         c )  means for determining whether transmissions on said tentative communication channels would interfere with transmissions on previously assigned communication channels due to said Doppler shift.