Interference suppression in DMT receivers using windowing

Abstract

A new receiver structure for improving the performance of conventional Discrete Multitone (DMT) based Digital Subscriber Line (DSL) transceivers is described. In this method, the conventional demodulator consisting of a FFT followed by a scalar frequency-domain equalizer is augmented by an additional data-path utilizing windowing. Time-limited receiver windowing is done independently for each symbol over the orthogonality interval while the transmitter is unchanged. Windowing can be carried out efficiently in the time or frequency domain. A decision feedback equalizer is used to cancel the resulting inter-bin-interference. Computer simulation results are presented for ADSL with realistic interference conditions which show that this method is most effective against narrowband interference and other impairments which lead to diminished inter-bin orthogonality. The overall technique is also applicable to other multicarrier modems such as VDSL and wireless OFDM.

An Interference Cancellation Algorithm for Fourier-based and wavelet-based OFDM systems

“…The Interference Cancellation Algorithnl (ICA) has been discussed by [8], this work included the use of windowing techniques to suppress thl' interference. however.…”

Combining per tone equalization and windowing in DMT receivers

“…However, if the window is limited to the DMT symbol, the windowing itself leads to the loss of orthogonality [6]. One can either take this into account [7] or avoid it alltogether by extending the win dow beyond the boundary of, the symbol, but still within a cyclic extension. Because these window functions ren der the demodulator more spectrally contained, they help counter NEXT and RFI.…”

Intra-Symbol Windowing for Egress Reduction in DMT Transmitters

“…The narrowband signals from, for example, an AM broadcast station can be picked up by the receiver and, due to the sidelobes, be smeared out over a broad frequency tone range. This problem has been recognized, and various schemes have been developed to tackle it (see [6][7][8]). On the other hand, the same poor spectral containment of transmitted signals makes it difficult to meet egress norms, for example, the ITU-norm [9] specifies that the transmit power of VDSL should be lowered by 20 dB in the amateur radio bands.…”