A filterbank structure for voice-band PCM channel pre-equalization

A non-maximally decimated filterbank structure for pre-equalizing channels with intersymbol interference (ISI) is investigated. The impulse response of the channel is assumed to be known at the transmitter. Compared with the classical Tomlinson-Harashima (1971) precoding technique, the proposed pre-equalizer compensates for the channel without increasing the number of the received signal levels (channel alphabet). The proposed technique does not require the channel to be minimum-phase. The filterbank structure adds redundancy to the input signal to compensate for the channel ISI while keeping the transmitted power bounded. The proposed pre-equalization is particularly useful for data transmission over voice-band PCM channels. The upstream PCM channel is bandlimited, causing severe ISI at the output of the front-end receiver filter. By using the pre-equalizer at the transmitter, channel ISI can be mitigated