Node-Based QAM Frees Up the Headend

In order to provide on-demand services like VOD, switched digital video (SDV), and increasing numbers of HD options, cable operators are faced with adding large numbers of QAM channels. Doing so involves both physical and environmental challenges that begin with the problem of shoehorning everything into the existing headend, where space and power are at a premium.Each time more QAM modulators are added into the headend, the operator has to consider the effect on the RF combining network, balance power amplification and readjust for noise, said Rei Brockett, product manager, video products group, Aurora Networks. "How do you add QAMs into the operation without upsetting things that are already there?"In addition, currently the decision needs to be made ahead of time how to apportion the new QAMs to the appropriate service and group. "It is an art to try to match who needs what and when," Brockett said.One way these problems can be mitigated is by putting QAM modulation in the node. "For example, instead of combining services in the RF domain, you use simple IP switching," Brockett said. "This eliminates the need to touch the RF combining network as you move QAMs around. The decision can be made on the fly what to use the QAMs for. You are not tied to the hardwire cascade of combiners and splitters."A QAM channel can be used for VOD in the afternoon and dynamically switched to accommodate data services in the evening. "This is both an operational simplicity by bypassing the RF combining network, and also allows you to blur service silos," Brockett said.Monetary savings come in the form of not overtaxing the headend, but also because the operator is not faced with purchasing QAM channels in bulk, if you will, up front. Since they can easily be added at the node, they can be purchased as needed. And existing equipment is not rendered obsolete by placing QAM modulation in the node. QAM streams can come from the headend over traditional HFC and combine with the new QAMs in the node, Brockett said.As for the much talked-about CCAP, with the benefits of reduced power and headend space, node-based QAM modulation meets the targeted objectives of the CCAP architecture. It can be managed transparently from a CCAP device. "It looks like any other QAM, except it has the benefit of not being in the headend," Brockett said.Brockett will explain these and other ideas further at the Cable Show on a Tuesday panel titled "HFC 2.0: The Evolution of an Architecture."Monta Monaco Hernon is a free-lance writer. She can be reached at [email protected].