Turbo coding in ADSL DMT systems

Increasing the transmission speed and/or the loop length in asymmetric digital subscriber lines (ADSL) is highly desirable. This can be achieved by employing sophisticated channel coding techniques. We investigate the potential usage of turbo codes in ADSL discrete multitone (DMT) systems to improve the system performance. Using turbo coding in ADSL DMT systems is shown to give a 6 dB coding gain at a bit error rate (BER) as low as 10^-6. To lower the decoding complexity, Gray mapping of turbo coded QAM symbols is proposed and a standard binary decoder is employed at the receiver. To counter impulse noise, another major impairment in subscriber loop transmissions, using turbo codes together with proper interleaving and erasure decoding results in very good performance