APPLICATION OF FAST CONVOLUTION ALGORITHMS USING SAMPLING FREQUENCY CHANGE IN DIGITAL HIGH-SPEED MODEMS

This paper deals with effective algorithms of digital signal processing for digital high-speed modems (i.e. 14.4 kBit/s in telephon lines). The advantage of the modem concept is implementation of transmitter filters, modulators, Hilbert filters, demodulators, equalizers and sampling frequency changes in the frequency domain rather than in time domain through the theory of fast convolution and taking advantage of spectral charcteristics of transmitted signals. That yields to addition and multiplication numbers saving up to 35%. The feature of this modem concept is the use of fractionally spaced equalizer providing the simpler design of receiver filter and better equalization in strong amplitude- and phase-distortion environment. Because of the symmetric design of transmitter and receiver the inclusion of an echo canceller in a duplex modem is fairly simple.