The theoretical performance of the next generation High-speed Digital Subscriber Loops (HDSL2) is calculated under the limited latency constraint in the presence of near end crosstalk (NEXT). The concept of having different up-stream and down-stream power spectral densities is highlighted. The noise margin at the central office HDSL terminal unit (HTU-C) can he enhanced by boosting the power output of the remote user HDSL terminal unit (HTU-R). Further improvement in performance can be achieved by reducing the HTU-C NEXT interference, similar to the power control used in wireless systems. The preemphasis/deemphasis can also be used to further reduce the interference levels, and in the mean time cut the power consumption. Combining the techniques leads to at least 6dB SNR margin improvement for the full reach CSA loops.
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