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  • Research Article
  • Open Access

Error Sign Feedback as an Alternative to Pilots for the Tracking of FEXT Transfer Functions in Downstream VDSL

EURASIP Journal on Advances in Signal Processing20062006:094105

  • Received: 1 December 2004
  • Accepted: 22 August 2005
  • Published:


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.


  • Impulse Response
  • Error Variance
  • Downstream Signal
  • Estimation Scheme
  • Simple Algorithm

Authors’ Affiliations

Delft University of Technology, Delft, 2600AA, The Netherlands


  1. Latsoudas G, Sidiropoulos ND: On the performance of certain fixed-complexity multiuser detectors in FEXT-limited vectored DSL systems. Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP '05), March 2005, Philadelphia, Pa, USA 3: 889–892.Google Scholar
  2. Cendrillon R, Moonen M, Verlinden J, Bostoen T, Ginis G: Improved linear crosstalk precompensation for DSL. Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP '04), May 2004, Montreal, Quebec, Canada 4: 1053–1056.Google Scholar
  3. Ginis G, Cioffi JM: Vectored transmission for digital subscriber line systems. IEEE Journal on Selected Areas in Communications 2002, 20(5):1085–1104. 10.1109/JSAC.2002.1007389View ArticleGoogle Scholar
  4. Leshem A, Youming L: A low complexity coordinated FEXT cancellation for VDSL. Proceedings of 11th IEEE International Conference on Electronics, Circuits and Systems (ICECS '04), December 2004, Tel-Aviv, Israel 338–341.Google Scholar
  5. Honig ML, Crespo P, Steiglitz K: Suppression of near- and far-end crosstalk by linear pre- and post-filtering. IEEE Journal on Selected Areas in Communications 1992, 10(3):614–629. 10.1109/49.127783View ArticleGoogle Scholar
  6. Ginis G, Cioffi JM: A multi-user precoding scheme achieving crosstalk cancellation with application to DSL systems. Proceedings of the 34th Asilomar Conference on Signals, Systems and Computers (ACSSC '00), October 2000, Pacific Grove, Calif, USA 2: 1627–1631.Google Scholar
  7. Cendrillon R, Moonen M, Van den Bogaert E, Ginis G: The linear zero-forcing crosstalk canceller is near-optimal in DSL channels. Proceedings of IEEE Global Telecommunications Conference (GLOBECOM '04), November–December 2004, Dallas, Tex, USA 4: 2334–2338.View ArticleGoogle Scholar
  8. Tong L, Perreau S: Multichannel blind identification: from subspace to maximum likelihood methods. Proceedings of the IEEE 1998, 86(10):1951–1968. 10.1109/5.720247View ArticleGoogle Scholar
  9. Zeng Y, Ng T-S: A semi-blind channel estimation method for multiuser multiantenna OFDM systems. IEEE Transactions on Signal Processing 2004, 52(5):1419–1429. 10.1109/TSP.2004.826183MathSciNetView ArticleGoogle Scholar
  10. Morelli M, Mengali U: A comparison of pilot-aided channel estimation methods for OFDM systems. IEEE Transactions on Signal Processing 2001, 49(12):3065–3073. 10.1109/78.969514View ArticleGoogle Scholar
  11. Coleri S, Ergen M, Puri A, Bahai A: Channel estimation techniques based on pilot arrangement in OFDM systems. IEEE Transactions on Broadcasting 2002, 48(3):223–229. 10.1109/TBC.2002.804034View ArticleGoogle Scholar
  12. Love DJ, Heath RW Jr.: Limited feedback precoding for spatial multiplexing systems. Proceedings of IEEE Global Telecommunications Conference (GLOBECOM '03), December 2003, San Francisco, Calif, USA 4: 1857–1861.View ArticleGoogle Scholar
  13. Heath RW Jr., Giannakis GB: Exploiting input cyclostationarity for blind channel identification in OFDM systems. IEEE Transactions on Signal Processing 1999, 47(3):848–856. 10.1109/78.747790View ArticleGoogle Scholar
  14. Louveaux J, van der Veen A-J: Downstream VDSL channel tracking using limited feedback for crosstalk precompensated schemes. Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP '05), March 2005, Philadelphia, Pa, USA 3: 337–340.Google Scholar
  15. Sayed AH: Fundamentals of Adaptive Filtering. John Wiley & Sons, Hoboken, NJ, USA; 2003.Google Scholar
  16. Moeneclaey M: On the true and the modified Cramer-Rao bounds for the estimation of a scalar parameter in the presence of nuisance parameters. IEEE Transactions on Communications 1998, 46(11):1536-1544. 10.1109/26.729398View ArticleGoogle Scholar
  17. Sidiropoulos ND, Karipidis E, Leshem A, Youming L: Statistical characterization and modelling of the copper physical channel. Deliverable D2.1. EU-FP6 STREP project U-BROAD No. 506790, 2004,
  18. ETSI : Transmission and Multiplexing (TM); Access transmission systems on metallic access cables; Very high speed Digital Subscriber Line (VDSL); Part 2: Transceiver specification. ETSI TS 101 270-2, 2000Google Scholar
  19. Bingham JAC: ADSL, VDSL, and Multicarrier Modulation. John Wiley & Sons, New York, NY, USA; 2000.View ArticleGoogle Scholar


© Louveaux and van der Veen. 2006