Adaptive depolarization-interference-compensator

Abstract

An adaptive depolarization-interference-compensator for a digital radio relay system using multi-level quadrature amplitude modulation (QAM) with co-channel operation of the orthogonally polarized signals which is not necessarily synchronous with the clock frequency and/or carrier frequency and produces good compensation of depolarization effects. The receiving branch of the two receivers (3, 4), which use the same RF-local oscillator (5) or separate RF-local oscillators are synchronized for the differently polarized signals and each contain a quadrature demodulator (8, 14) for two signal components (I- and Q-channel). A canceller is provided which consists of two quadrature demodulators (20, 23) for the two polarization directions, which are each supplied at with an IF-received signal of one polarization and the IF-carrier (9, 15) of the respective other polarization, and which consist of complex transversal filters (21, 22, 24, 25) (I- and Q-channel) in the signal paths to the two quadrature demodulators (20, 23). The transversal filters (21, 22, 24, 25) have their outputs coupled into the receiving branch of the respective other polarization. The delay time .tau..sub.0 between the tappings of the transversal filters corresponds at the maximum to half the reciprocal value of the frequency of the highest spectral component of the base-band signal with a rational ratio m/n which preferably supplies a delay time which is shorter than or equal to .tau..sub.0 (m/n=ratio of the symbol period of the interference signal to the transit time between the tappings of the transversal filter; m, n whole numbers).