Uplink cross-polarization interference canceller using correlation calculator and stepwise tracking controller

摘要

In a satellite communications system, a rotatable 90^o phase shifter (4) and a rotatable 180^o phase shifter (3) 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 (19) 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^o and 180^o 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 (16) provides fine mode interference cancellation by stepwisely varying the 90^o and 180^o 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 substantialy reduced to a minimum.