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Simulation of DSL systems


This report contains simulations of performance for different versions of ADSL, VDSL and SHDSL in 0.4 mm twisted pair cables. An important part of the work has been to investigate the compatibility between different DSL systems.
The range of SHDSL system compliant with ITU G.991.2 Annex G has been analysed. These systems allow for bitrates up to 3.848 Mbit/s and 5.696 Mbit/ for 16-PAM and 32-PAM systems respectively.
The overall conclusion is that downstream ADSL and ADSL2+ is compatible with both SHDSL Annex G and HDSL systems. The degradation in bitrate of downstream ADSL due to these systems is moderate, less than 13% compared to a cable containing only ADSL systems.
ADSL subloop means that an ADSL DSLAM is installed between the local exchange and the subscriber. The purpose is to reduce the loop length between the DSLAM and the subscriber in order to increase the bitrate. This subloop signal will represent a strong interference in the downstream direction of the ADSL systems from the local exchange. As is shown in Section 7 in this report there is a severe degradation in the downstream direction of the ADSL system from the local exchange. The remedy to reduce this degradation is to use power backoff in the subloop systems. Use of power backoff regimes is not analysed in this report.
The potential bitrates for VDSL2 systems have been analysed for bandplans 997 and 998. The simulations show that bandplan 997 will give almost symmetrical up- and downstream bitrates for the cables less than 800 meters, whereas for bandplan 998 the downstream/upstream ratio is close to 2:1. Three different bandwidths have been analysed, 12 MHz, 17 MHz and 30 MHz. The frequency bands above 12 MHz are used only for loop lengths less than 800 meters. The frequency bands above 17 MHz are used only for loop lengths less than 650 meters. Bandplans that makes use of the lowest upstream band U0 can still provide adequate upstream capacity (1 Mbit/s) even for loop lengths in excess of 2 km. The downstream bitrate is significant (17-18 Mbit/s) for both 997 and 998 at these lengths.
A discussion of the use of ADSL in equalisation cables is given in Section 9. Alternative ways to install ADSL in pairs that contain 1+1 systems are presented in Section 10.

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