Interference Suppression Algorithm For Broadband Access Networks

With the rapid development of Internet and the widespread use of computers, the Internetis gradually coming into millions of households. By the end of July2011, the global numberof broadband Internet users has reach to48,500million, two thirds of which is surfing theInternet through the digital subscriber line xDSL. On the other hand, with the rapiddevelopment of broadband services, new value-added services such as video, video phone,distance education, electronic commerce, telemedicine and other services continue to emerge,requiring large bandwidth. Although through broadband fiber to the home will be the ultimategoal, due to high costs, broadband access based on xDSL is still the main access technology.Typically, in digital subscriber line transmission systems, when signal transmitted fromoptical networks unit or the central office to the the client, the various lines in the same leadcable have crosstalk problems because of the electromagnetic coupling. Crosstalk is the mostimpact factor which can affect the data rate in DSL systems. For the VDSL system, since thetransmission distance is short, the signal interferenced by the crosstalk is particularly severe.Therefore, how to suppress crosstalk interference and increase system data rates in VDSLbroadband access networks is an important research area. This paper focuses on crosstalksuppression for VDSL systems. The main results are summarized as follows:(1) A special transmission channel matrix structure splitting method based on upper andlower triangular splitting is proposed. The new method compared with the existingsuppression algorithms algorithm in the current VDSL upstream transmission systemmaintains good performance while the complexity is not high.(2) A new improved algorithm which is based on J.Louveaux’s adaptive sign algorithmfor VDSL downlink pre-coding is proposed. Currently adaptive algorithms have largecomputation for VDSL downlink pre-coding. The new algorithm has low computationalcomplexity and also has a faster convergence.(3)A single-user VDSL symbol of LMS adaptive algorithm which is based on stable cyclecharacteristics is proposed. This paper analyzes the characteristics of cycle autocorrelationfunction of DMT modulation and then proposes single-user VDSL symbol of LMS adaptive algorithm. Compared with the existing channel estimation algorithms, the new algorithmsignificantly reduces its complexity.