By Jorge D. Salinger, VP, Access Architecture, Comcast Cable
The success and growth in narrowcast services continues to require MSOs to expand the capacity dedicated to those services. Most MSOs have deployed 4 and 8 DOCSISTM QAMs and considering expanding beyond that. Deployment of VOD and SDV QAMS continue to expand with HD and network DVR. And, even more QAMs are needed as service groups are segmented further in the network.
As the narrowcast service growth continues, MSOs are putting emphasis in the evolution of the access technologies to make them more efficient. DOCSIS 3.1 was created to enable more efficient use of spectrum, especially by using higher modulation orders and by taking advantage of newer technologies such as better LDPC codes and OFDM modulation.
MSOs and suppliers alike are considering one more aspect of the evolution: moving the RF modulation downstream into the network. By moving the RF modulation from the headend to the node, known as Remote PHY, it is possible to achieve important gains, such as:
Performance increase: by eliminating the analog laser and reducing cascades as segmentation naturally progresses it is possible to support significantly higher order modulations as SNR performance increases both in the DS and US.
Cost reduction: it seems quite clear that replacing the analog forward link and the analog or digital return link for an Ethernet optical link will be less expensive both from a capital and operational perspective.
Operational improvements: undoubtedly, the Ethernet optical link will be easier to set-up and maintain than the current HFC links, and should carry a lot more capacity at longer distances.
To that end, this paper will cover the following areas:
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Overview of the rational for Remote PHY
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Elaborate on the options available to implement Remote PHY, and
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Explain ways in which it could be implemented.