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Advanced Return-Path Cable TV Access Technologies

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Cable TV networks have been evolving from one-way broadcast of analog video channels to two-way interactive hybrid fiber/coax (HFC) networks delivering analog/digital video channels and high-speed data. The problem with the current HFC architecture is the upgrading cost of an existing one-way 450 MHz HFC network for premium video and data services. This is because it requires not only additional installation of fiber-optic cables for two-way transmission, but also architectural changes to the HFC network with additional equipment installations at the primary or secondary head ends. Furthermore, the explosive demand for more upstream bandwidth from an increasing number of cable subscribers generates additional pressure on the cable operators to provide larger return-path capacity and/or larger allocated bandwidth per subscriber. Recently, dense wavelength division multiplexing (DWDM) technology has emerged as the most significant and important option for cable TV operators to solve their current bandwidth bottleneck in their HFC network architecture. Two return-path technologies were recently developed and field-deployed: the frequency-stacking scheme (FSS) and the digitized return-path transport. This article first briefly reviews the operating principles of each method and then compares their performance requirements at the cable TV primary or local head ends, using two measurable parameters. These return-path access technologies provide significant cost savings to the cable TV operators while maintaining network transparency and flexibility.
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The return-path dense wavelength-division-multiplexed network architecture using time-division-multiplexing and frequency-stacking methods is reviewed. Digitizing the return-path bandwidth provides significant cost savings while maintaining network transparency and flexibility.

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