On the performance of an asymmetrical digital subscriber lines QAM transceiver

The author presents an analysis of an asymmetrical digital subscriber line (ADSL) transceiver that uses the quadrature amplitude modulation (QAM) passband transmission system. Output signal-to-noise ratio curves versus carrier and guardband frequencies are presented for the 16-, 64-, and 256-point rectangular constellations, assuming ADSL impairments consisting of self-far-end crosstalk, thermal noise generated by the loop, and receiver noise that is generated primarily by amplifiers in the front-end of the receiver. The simulation results show that an ADSL system with these impairments is viable even on loops that are at the extreme range of the loop plant. In addition, 16-QAM signaling generally performs better than any of the other constellations. The study assumed perfect timing and carrier recovery