Investigates the bit error rate (BER) performance of a passband single-carrier QAM transceiver for asymmetric digital subscriber lines (ADSL), with additive white Gaussian noise (AWGN) and self far-end crosstalk (FEXT) as the main disturbances. The major difference with previous contributions on ADSL performance is that the authors present a simple approximate analytical expression fur the signal-to-noise ratio (SNR) margin, which clearly shows the effect of various cable and system parameters (such as loop length, transmit power, QAM constellation size, bit rate, ...) on ADSL performance. From this expression, they determine the optimum constellation size and the maximum achievable bit rate as a function of the loop length.>