Multipath echo cancellation in FM transmission using adaptive FIR filters

Multipath propagation in conventional FM broadcasting is a severe problem since this phenomenon results in nonlinear distortions after demodulation. In the present paper a solution is given for equalization of the multipath transfer function using FIR digital filters. The main idea is to take advantage of some a-priori knowledge of the multipath channel which reduces the number of the complex equalizer coefficients to 5 or 6. For adaptive adjustment we apply the well-known gradient algorithm using the absolute value of the complex FM envelope as a quality criterion which has to be minimized. Some examples will be given to illustrate the convergence behaviour of the algorithm and the real-time performance of the digital equalizer.