Mobile satellite communication system utilizing polarization diversity combining
View Patent ↗The present invention utilizes a dual polarization reception system ( 200 ) that utilizes the energy available in orthogonal polarizations to effectively increase link margin, thereby allowing for adequate signal quality reception in difficult environments. A co-polarized and a cross-polarized signal are separately downconverted and demultiplexed. The signals from each demultiplexed output are then sampled and weighted. The weighted samples for each polarity are combined in soft decision combining/decoding circuitry ( 255, 360 ), and this circuitry determines the most likely state of a received symbol's transmitted value.
1. A method of operating a satellite in a dual-polarization reception system, said method comprising the steps of:
acquiring a signal from a subscriber unit via an access channel;
detmnnining a location for said subscriber unit, wherein said satellite receives message information comprising location data;
determining if a dual-polarization beam exists at said location;
measuring received signal power, when said dual-polarization beam exists at said location;
determining whether said received signal power is greater than a first threshold value;
converting from a single polarization beam to a dual-polarization beam, when said received signal power is greater than said first threshold value; and
updating a beam allocation table.
2. The method as claimed in claim 1 , wherein said method further comprises the steps of:
measuring average received signal power, when a beam does not exist at said location;
comparing said avenge received signal power to a second threshold;
assigning a single polarization beam to said location when said average received signal power is greater than said second threshold;
assigning a dual polarization beam to said location when said average received signal power is not greater than said second threshold; and
updating said beam allocation table.
3. The method as claimed in claim 2 , wherein said method further comprises the steps of:
lowering said second threshold, when the number of available dual polarization channels is less than a first limit; and
raising said second threshold when the number of available single polarization channels is less than a second limit.
4. A method of operating a subscriber unit (SU) in a dual-polarization reception system, said method comprising the steps of:
acquiring a signal from a satellite via a broadcast channel;
determining a location for said subscriber unit, said SU self-determining said location;
determining from a beam allocation table a beam assignment at said location;
measuring co-polarized signal power and cross-polarized signal power at said location;
determining whether said measured co-polarized signal power and said measured cross-polarized signal power are consistent with said beam assignment;
modifying said beam assignment, when said measured co-polarized signal power or said measured cross-polarized signal power is not consistent with said beam assignment; and
updating said beam allocation table.
5. The method as claimed in claim 4 , wherein said method further comprises the step of transmitting beam assignment modifications to a satellite.
6. The method as claimed in claim 4 , wherein said method further comprises the step of reporting said measured co-polarized signal power and said measured cross-polarized signal power to a system control center.
7. The mcthod as claimed in claim 4 , wherein said method further comprises the step of storing said measured co-polarized signal power and said measured cross-polarized signal power in a history file for said location.