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

摘要

In a satellite communications system, a rotatable 90o phase shifter (4) and a rotatable 180o 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 90o and 180o 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 90o and 180o 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.