Crosstalk Study In Multi-user Vdsl Systems

The broadband and IP-based access network is an inevitable trend. Digital Sbuscriber Line (DSL) technology uses existing copper twisted-pair as a transmission medium to provide users with broadband access services. Due to the high transmission rate and low access cost, DSL technology becomes the mainstream broadband access technology.Generally, tens of copper twisted-pair are in the same bind from the centre office or optical network unit to end-users. When signals transmission in the pairs at the same time, each pairs may cause crosstalk interference to each other because of the electromagnetic coupling. Crosstalk is the the most important factors affecting the data rate of DSL system.VDSL system suffers more severe crosstalk interference in high frequency and lower distance transmission. How to suppress crosstalk interference and increase data rates of VDSL system is an important research topic in the area of acess network.The research in this paper is focused on the crosstalk problems in VDSL systems, especially on crosstalk channel estimation and crosstalk cancellation. The primary work and innovations of this paper are:1,We describe the research background and significance of the subject. Discuss the principle of discrete multi-tone (DMT) modulation and the Cyclostationarity of DMT modulation signals. Furthermore, we discuss the data data transfer model of Multi-user VDSL systems.2,most crosstalk cancellation algorithms need crosstalk channel information. So crosstalk channel estimation is an essential step for crosstalk cancellation. In this paper, we first analyze the characteristics of the cycle of auto-correlation function of DMT modulation signal, and then propose a simplified blind crosstalk channel estimation algorithm. Compared with the existing blind crosstalk channel estimation algorithm, the complexity of our new algorithm is significantly reduced while the performance is maintained.3,alien crosstalk cancellation is a tough question. In this paper, we propose an adaptive blind crosstalk cancellation method from time domain.The method can cancel both in-domain crosstalk and alien crosstalk without crosstalk channel information.4,most of crosstalk cancellation mehods in frequency domain are involving two stages: crosstalk channel estimation and crosstalk cancellation. In this paper, we propose a crosstalk cancellation method without channel estimation. The method can self-update the filter coefficients based on transmission data. The proposed algorithm has lower complexity with a good performance.