A frequency-domain training approach for equalization and noise suppression in discrete multitone systems

Abstract

In discrete multitone (DMT) transceivers, a time-domain equalizer (TEQ) is used to shorten the effective channel impulse response such that a shorter cyclic prefix can be used. In this paper, we pose the TEQ design problem completely in the frequency domain by defining a frequency-domain weighted least-squares cost function. The definition of the frequency-domain TEQ design criterion, we show, allows for the introduction of a weighting function to control the spectral shape of the TEQ, and facilitates important extensions particularly useful for the DMT system. The TEQ can be used to suppress the noise and interference in the DMT system, a feature especially useful in the frequency division multiplexing-based DMT system. Also, in the echo-cancellation-based DMT system, the TEQ can be used to jointly shorten the echo response thus reducing the complexity of the echo canceler. We present corresponding algorithms for these two objectives and simulation results, which show that the weighted frequency-domain least-squares algorithm and the two extensions we derive can achieve the shortening (channel or channel and echo) as well as noise suppression objectives effectively.