Per tone shaping filters for DMT transmitters

Discrete multitone (DMT) modulation has been widely adopted for wideband transmission over digital subscriber loop (DSL) channels. In the conventional DMT system, the transmitting filters are the DFT filters. DFT filters suffer from poor frequency responses. Hence, the resulting transmit signal has a large spectral sidelobe and its power spectral density (PSD) decays at a rate of 1/f only. In this paper, we propose a modified DMT scheme with improved transmitting filters. In the proposed system, shaping filters are applied to improve the frequency responses of the transmitting filters. Moreover, an efficient implementation of the proposed system is derived. Experiment shows that for VDSL applications, the proposed system has a very satisfactory spectral efficiency.