Advanced Return-Path Cable TV Access Technologies
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.