Capacity and cutoff rate of the digital subscriber loop with near end crosstalk noise

It is shown that most twisted-pair local loops within a 12000-ft range of the central office, i.e., within the standard carrier serving area, could potentially support high-rate services at rates exceeding 800 kb/s, even in the presence of worst-case crosstalk interference. Because the crosstalk noise increases as the input power increases, the capacity of the channel asymptotically reaches a finite limit. While capacity indicates the ultimate channel performance with infinite coding complexity, the cutoff rate of the channel suggests the maximum performance of a finite-complexity system. The cutoff rates for twelve different local loops are calculated and shown to exceed the T1 transmission rate (1.544 Mb/s). With sufficient sophisticated coding techniques and equalization many local loops could potentially support service at this rate. Significant transmission capacity also requires using the high-frequency portions of the channel spectrum, thereby requiring a high symbol rate and lower bit rate per symbol to achieve the desired throughput.<>