System and method for selecting a ground station in an air-ground data network

1. A method of selecting a ground station in an air-ground communications network, comprising:

initiating radio communications between an aircraft and a first ground station;

determining an altitude of the aircraft while monitoring the signal strength value of the first ground station;

comparing the altitude of the aircraft to a first reference value, a second reference value, and a third reference value; and

discontinuing radio communications with the first ground station and initiating radio communications with a second ground station when the monitored signal strength of the first ground station is weaker than a threshold value associated with the reference value,

wherein a first threshold value is associated with the first reference value, a second threshold value is associated with the first and second reference value, a third threshold value is associated with the second and third reference value, and a fourth threshold value is associated with the third reference value,

wherein the third reference value is greater than the second reference value, which is greater than the first reference value, and

wherein a fourth threshold value is less than the third threshold value, which is less than the second threshold value, which is less than the first threshold value.

2. The communication system of claim 1 , wherein the

the first reference value is approximately five thousand feet;

the second reference value is approximately twelve thousand feet;

the third reference value is approximately twenty-four thousand feet;

the first threshold value is approximately five relative to a full scale response of ten;

the second threshold value is approximately four relative to the full scale response of ten;

the third threshold value is approximately three relative to the full scale response of ten; and

the fourth threshold value is approximately two relative to the full scale response of ten, wherein the full scale response of ten indicates a strong signal and a monitored signal strength value of zero indicates a weak signal.

3. A communications system for an aircraft, comprising:

a communications device operable to maintain bi-directional data communications between the aircraft and a selected ground communications station; and

a communications processor coupled to the communications device that is configured to switch ground stations from a first ground station to a second ground station when one of the following occurs:

a) a channel occupancy of the frequency channel shared by the ground stations is less than a first reference number and a monitored signal of the first ground station is weaker than a first threshold value;

b) the channel occupancy of the frequency channel shared by the ground stations is greater than or equal to the first reference number and is less than a second reference number and the monitored signal of the first ground station is weaker than a second threshold value; and

c) the channel occupancy of the frequency channel shared by the ground stations is greater than or equal to the second reference number and the monitored signal of the first ground station is weaker than a third threshold value,

wherein the second reference number is greater than the first reference number, and

wherein the third threshold value is greater than the second threshold value, which is greater than the first threshold value.

4. The communications system of claim 3 , wherein the communications processor is further configured to maintain communications with a first ground station if the limitations of a), b), and c) are not met.

5. The communication system of claim 3 , wherein the the first reference number is approximately 0.25 relative to 1.0 for full capacity;

the second reference number is approximately 0.50 relative to 1.0 for full capacity;

the first threshold value is approximately one relative to a full scale response of ten;

the second threshold value is approximately two relative to the full scale response of ten; and

the third threshold value is approximately three relative to the full scale response of ten, wherein the full scale response of ten indicates a very strong signal and a monitored signal of zero indicates a very weak signal.

6. A method of selecting a ground station in an air-ground communications network, comprising:

initiating radio communications between an aircraft and a first ground station;

determining a channel occupancy of the frequency channel shared by the ground stations while determining a signal strength value of the first ground station;

comparing the channel occupancy of the frequency channel shared by the ground stations to a first reference number and a second reference number, until the channel occupancy of a frequency channel shared by the first ground stations is greater than one of the first reference number and the second reference number;

comparing the determined signal strength value of the first ground station to threshold values, wherein each threshold value is associated with at least one reference number, wherein a first threshold value is associated with the first reference number, a second threshold value is associated with both the first and second reference number, and a third threshold value is associated with the second reference number,

wherein the second reference number is greater than the first reference number, and

wherein the third threshold value is greater than the second threshold value, which is greater than the first threshold value; and

discontinuing radio communications with the first ground station and initiating radio communications with a second ground station when one of the first reference number and the second reference number is greater than the channel occupancy of the first ground station and when the determined signal strength value is weaker than the associated threshold value.

7. The communication system of claim 6 , wherein the

the first reference number is approximately 0.25 relative to 1.0 for full capacity;

the second reference number is approximately 0.50 relative to 1.0 for full capacity;

the first threshold value is approximately one relative to a full scale response of ten;

the second threshold value is approximately two relative to the full scale response of ten; and

the third threshold value is approximately three relative to the full scale response of ten wherein the full scale response of ten indicates a strong signal and a determined signal strength of zero indicates a weak signal.