Uplink cross-polarization interference canceller using correlation calculator and stepwise tracking controller
First Claim
1. An uplink cross-polarization interference canceller of a satellite communications earth station, the earth station including a rotatable 90°
- phase shifter and a rotatable 180°
phase shifter connected in circuit for introducing variable phase shifts to a pilot signal, means for transmitting said phase-shifted pilot signal to the satellite, means for receiving said pilot signal returning from said satellite, and means for detecting downlink cross-polarization interference cancellation control signals from a beacon signal transmitted from said satellite, comprising;
pulse generator means for generating a pulse sequence;
amplitude modulator means for modulating the amplitude of a carrier with said pulse sequence to produce an ASK signal as said pilot signal;
correlation calculator means for estimating uplink cross-polarization interference components from said downlink cross-polarization cancellation control signals and adjusting the angle settings of said 90° and
180°
phase shifters in accordance with the estimated interference components;
synchronous detector means for synchronously detecting the received pilot signal with said pulse sequence and generating a DC signal representative of an uplink cross-polarization interference; and
stepwise tracking control means for stepwisely varying the angle settings of said rotatable 90° and
180°
phase shifters by predetermined amounts, detecting previous and recent values of said DC signal resulting from the stepwise variations of said angle settings, and repeating the stepwise variations of said angle settings until a difference between said previous and recent values is substantially reduced to a minimum.
1 Assignment
0 Petitions
Accused Products
Abstract
In a satellite communications system, a rotatable 90° phase shifter and a rotatable 180° phase shifter introduce variable phase shifts to a single pilot signal, which is transmitted to the satellite. Downlink cross-polarization interference cancelling control signals are derived from a beacon signal received from the satellite. A pulse sequence is generated to modulate the amplitude of a carrier to produce an ASK signal as the pilot signal. A correlation calculator provides coarse mode interference cancellation by estimating uplink cross-polarization interference components from the downlink cross-polarization cancelling control signals and adjusting the angle settings of the 90° and 180° phase shifters with the estimated components. The pilot signal is transmitted back to the earth and synchronously detected with the pulse sequence to derive a DC signal which represents an uplink cross-polarization interference. A stepwise tracking controller provides fine mode interference cancellation by stepwisely varying the 90° and 180° phase shifters by predetermined amounts an detecting previous and recent values of the synchronously detected DC signal resulting from the stepwise variations, and repeating the stepwise variations until a difference between the previous and recent values is substantially reduced to a minimum.
-
Citations
4 Claims
-
1. An uplink cross-polarization interference canceller of a satellite communications earth station, the earth station including a rotatable 90°
- phase shifter and a rotatable 180°
phase shifter connected in circuit for introducing variable phase shifts to a pilot signal, means for transmitting said phase-shifted pilot signal to the satellite, means for receiving said pilot signal returning from said satellite, and means for detecting downlink cross-polarization interference cancellation control signals from a beacon signal transmitted from said satellite, comprising;pulse generator means for generating a pulse sequence; amplitude modulator means for modulating the amplitude of a carrier with said pulse sequence to produce an ASK signal as said pilot signal; correlation calculator means for estimating uplink cross-polarization interference components from said downlink cross-polarization cancellation control signals and adjusting the angle settings of said 90° and
180°
phase shifters in accordance with the estimated interference components;synchronous detector means for synchronously detecting the received pilot signal with said pulse sequence and generating a DC signal representative of an uplink cross-polarization interference; and stepwise tracking control means for stepwisely varying the angle settings of said rotatable 90° and
180°
phase shifters by predetermined amounts, detecting previous and recent values of said DC signal resulting from the stepwise variations of said angle settings, and repeating the stepwise variations of said angle settings until a difference between said previous and recent values is substantially reduced to a minimum. - View Dependent Claims (2, 3, 4)
- phase shifter and a rotatable 180°
Specification