Multichannel Signal Processing for Data Communications in the Presence of Crosstalk

We consider transmission of data over multiple coupled channels, such as bundles of twisted-pair copper wires in the local subscriber loop, and between central offices in the public switched telephone network. Transceiver designs for such channels typically treat the crosstalk between adjacent twisted pairs as random noise uncorrected with the transmitted signal. We propose a transmitter/receiver pair that compensates for crosstalk by treating an entire bundle of twisted pairs as a single multiinput/multioutput channel with a (slowly varying) matrix transfer function. The proposed transceiver uses multichannel adaptive FIR niters to cancel near- and far-end crosstalk, and to pre- and postprocess the input/output of the channel. The linear pre- and postprocessors that minimize mean squared error between the received and transmitted signal in the presence of both near- and far-end crosstalk are derived. The performance of an adaptive near-end crosstalk canceller using the stochastic gradient (LMS) transversal algorithm is illustrated via numerical simulation. Plots of mean squared error versus time and eye diagrams are presented assuming a standard transmission line model for the channel. A signal design algorithm that maps a vector input bit stream to a stream of channel symbol vectors is also presented. This algorithm is illustrated explicitly for a simple model of two coupled channels. It is shown that the achievable rate using the proposed signaling scheme is very close to the rate attainable in the absence of far-end crosstalk, and is significantly greater than the achievable rate assuming that far-end crosstalk is treated as additive noise with unknown statistics.