Echo cancellation in ADSL modems

This Master Thesis report presents a way of enhancing the performance of an ADSL (Asymmetric Digital Subscriber Line) system by canceling out transmitter echoes that occur in the coupling between the AFE (Analog Front End) and the phone lines. This new way of canceling the transmit echoes applies to all systems where the transmitted signal can be modeled by a random noise signal. The idea is to cancel out the transmit echoes in the analog domain before the ADC (Analog Digital Converter) in order to increase the sensitivity of the receiver. With this echo canceling method the echo suppression of the transmitted signal can come close to what is theoretically possible.

The development and simulations are done using a Matlab model of the AFE. To verify the model and show that the performance expectations were fulfilled the echo canceller was implemented in a real time system based on four ADSP-21160 DSPs (Digital Signal Processors) from ADI (Analog Devices). The issues involved with a migration from a simulation model to real systems are also considered.

Author: Overby, Johan

Source: LuleƄ University of Technology

Download Link: Click Here To Download This Project Report (PDF)

Reference URL: Visit Now

Leave a Comment