D8.16 M I N I M a X Design O F F a C T O R a B L E N Y Q U I S T F I L T E R S

The use of Nyquist f i l ters in data transmission systems is important in avoiding intersymbol interference. Moreover, the Nyquist f i l ters should be factorable into lowpass transmitter/receiver f i l ter pairs. Here, the design problem is formulated so as t o generate zero-phase FIR lowpass Nyquist f i l ters that can be sp l i t in to min imum and maximum phase par ts . Two factorable mtnimax design methods are given. These methods use the McClel lan-Parks algori thm as a first step to control the stopband behaviour. The t ime domain constraints, imposed by solv ing a l inear system of equations, determine the passband response. The flnal filter exhibits equiripple stopband behaviour The advantages of these methods are that the minimum and max lmum phase parts are obtalned without direct factorization and that arbitrary frequency weighting can be easily incorporated to a l low for a nonequiripple behaviour. The new design approach is compared with other methods Final ly, a practical design that conforms to a CCITT voice band modem specification is shown