tailieunhanh - Báo cáo hóa học: "Error Sign Feedback as an Alternative to Pilots for the Tracking of FEXT Transfer Functions in Downstream VDSL"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Error Sign Feedback as an Alternative to Pilots for the Tracking of FEXT Transfer Functions in Downstream VDSL | Hindawi Publishing Corporation EURASIP Journal on Applied Signal Processing Volume 2006 Article ID 94105 Pages 1-14 DOI ASP 2006 94105 Error Sign Feedback as an Alternative to Pilots for the Tracking of FEXT Transfer Functions in Downstream VDSL J. Louveaux and . van der Veen Delft University of Technology 2600AA Delft The Netherlands Received 1 December 2004 Revised 11 August 2005 Accepted 22 August 2005 With increasing bandwidths and decreasing loop lengths crosstalk becomes the main impairment in VDSL systems. For downstream communication crosstalk precompensation techniques have been designed to cope with this issue by using the collocation of the transmitters. These techniques naturally need an accurate estimation of the crosstalk channel impulse responses. We investigate the issue of tracking these channels. Due to the lack of coordination between the receivers and because the amplitude levels of the remaining interference from crosstalk after precompensation are very low blind estimation schemes are inefficient in this case. So some part of the upstream or downstream bit rate needs to be used to help the estimation. In this paper we design a new algorithm to try to limit the bandwidth used for the estimation purpose by exploiting the collocation at the transmitter side. The principle is to use feedback from the receiver to the transmitter instead of using pilots in the downstream signal. It is justified by computing the Cramer-Rao lower bound on the estimation error variance and showing that for the levels of power in consideration and for a given bit rate used to help the estimation this bound is effectively lower for the proposed scheme. A simple algorithm based on the maximum likelihood is proposed. Its performance is analyzed in detail and is compared to a classical scheme using pilot symbols. Finally an improved but more complex version is proposed to approach the performance bound. Copyright 2006 Hindawi Publishing Corporation. All rights .