HIGH BIT-RATE ASYMMETRIC DIGITAL-COMMUNICATIONS OVER TELEPHONE LOOPS

Asymmetric digital subscriber lines (ADSL) transmit high bit rate data in the forward direction to the subscriber, and lower bit rate data i n the reverse direction to the central office, both on a single copper telephone loop, This paper provides a comprehensive description of th e performance of ADSL's that use currently available technologies with optimized parameters, Passband ADSL's encounter no self-near-end cros stalk (NEXT) since the forward and reverse channels are separated in t he frequency domain. The absence of NEXT allows reliable transmission at high bit rates on long loops, The passband ADSL is disturbed by bac kground noise, self-far-end crosstalk (FEXT), and NEXT from other digi tal transmission systems that share its spectrum, such as Basic Access DSL, HDSL, and T1 lines, This paper determines the performance of DS1 rate passband ADSL's in the presence of each of these impairments. Al though baseband ADSL's are disturbed by NEXT from the reverse channel, they are suitable for data rates at 3 Mb/s or above since they experi ence less high frequency loss than passband ADSL's. The range of relia ble baseband ADSL transmission is determined for forward data rates be tween 1.5 and 9 Mb/s, and reverse data rates up to 1.5 Mb/s. An analys is and comparison of different codes that could be applied to an ADSL is also presented, The performance of forward error correction codes a nd trellis codes is found for ADSL's in the presence of crosstalk and impulse noise.