Coordinated transmission for two-pair digital subscriber lines

The performance of two-pair dual-duplex systems is substantially improved if the transmission on one pair is coordinated with that on the other, so that the transmitted signals are two-dimensional vector pulses. The advantages of coordination of transmission in an optimal way are quantified. Signal processing gains of 1.8 dB can be achieved in this way by averaging the SNRs on the two pairs constituting the high rate digital subscriber line (HDSL) and by canceling the near-end crosstalk (NEXT) between them. Exploitation of pair-to-pair correlation of NEXT voltages on the constituent pairs provides an additional source of processing gain. Under reasonable assumptions concerning the distribution of NEXT coupling coefficients between cable pairs, there is a better than 50% chance that the signal processing gain achieved by exploiting pair-to-pair NEXT correlation will be greater than 1.5 dB. Coordinated transmission requires the adaptation of four flat gain amplifiers in transmitters to achieve its optimum system configuration