In this article, we propose a vectored system by using both common mode (CM) and differential mode (DM) signals in upstream VDSL. We first develop a multi-input multi-output (MIMO) CM channel by using the single-pair CM and MIMO DM channels proposed recently, and study the characteristics of the resultant CM-DM channel matrix. We then propose a low complexity receiver structure in which the CM and DM signals of each twisted-pair (TP) are combined before the application of a MIMO zero forcing (ZF) receiver. We study capacity of the proposed system, and show that the vectored CM-DM processing provides higher data-rates at longer loop-lengths. In the absence of alien crosstalk, application of the ZF receiver on the vectored CM-DM signals yields performance close to the single user bound (SUB). In the presence of alien crosstalk, we show that the vectored CM-DM processing exploits the spatial correlation of CM and DM signals and provides higher data rates than with DM processing only. Simulation results validate the analysis and demonstrate the importance of CM-DM joint processing in vectored VDSL systems.
Bibliographical noteFunding Information:
This study was supported by research grants from Conexant Systems Inc. USA, and IIT Delhi. An earlier preliminary version of this study consisting of discussion on the CM channel model was presented at the Annual IEEE Indicon Conference, INDICON 2008, IIT Kanpur, India, in December 2008. The authors would like to thank the anonymous reviewer for useful comments which helped to improve the quality of the article.
- Alien crosstalk
- Common-mode signal
- Crosstalk cancelation
- Diagonal dominance
- Digital subscriber lines (DSL)
- Discrete multi-tone (DMT)
- Far-end crosstalk (FEXT)
- Twisted pairs; vectoring