Joint optimal impulse response shortening

Abstract

In discrete multitone a cyclic prefix (CP) is inserted between symbols to ensure that samples from one symbol do not interfere with the samples of another symbol. The CP length is determined by the impulse response length of the effective physical channel. The cyclic prefix reduces the throughput of the transceiver. When the transceiver is used in a full-duplex environment the portion of the receive signal arising from echo must be reduced through the use of echo cancellation, the complexity of which is directly related to the length of the echo path impulse response. To alleviate both problems a short time-domain FIR filter can be used to shorten both the effective channel and echo impulse responses. This paper explores a joint optimal algorithm for determining the coefficients of this time-domain filter, resulting in reduced ISI and echo canceller complexity. For the simulations a configuration is chosen which is representative of that encountered by the remote terminal in the asymmetrical digital subscriber lines (ADSL) environment.