Waterfilled VDSL echo limitation for rate-reach performance improvement

Digital subscriber line (DSL) deployment is evolving to ever higher bit rates resulting in the use of broader spectra. The DSL flavor using the broadest spectrum today is known as VDSL. The reach performance of VDSL is upstream limited as the upstream bands use the highest frequencies. These high frequencies experience more channel attenuation, resulting in smaller signal-to-noise ratio (SNR) values. In this paper, a way of increasing the upstream reach performance is described. After investigating the VDSL transceiver, the reach performance of a VDSL modem is identified to be dominated by the echo power. Therefore, limiting the downstream echo yields a better upstream receive signal. This results in trading off downstream bit rate for more upstream bit rate. The way to optimally limit the echo is derived and high performance gains can be achieved. Finally, the optimal solution is approximated with a near-optimal solution with considerably less complexity. The near-optimal solution performs very well compared to the optimal solution.