By Phil Miguelez and Dr. Robert Howald, Motorola Mobility
As upstream services have become more sophisticated, so too has the technology that supports it. Simple, robust modems were developed to enable STB communications.
Later, more sophisticated DOCSIS® modems complemented these for high-speed data services. Similarly, in the plant, return optics adequately supported the robust physical layer of STB communications using low-cost Fabry-Perot (FP) lasers. For DOCSIS®, laser technology advanced to meet the new challenges. This included higher power FP lasers, isolation techniques to mitigate noise, and the introduction of Distributed Feedback (DFB) lasers into the return transmitter portfolio.
DOCSIS®, of course, has continued to advance. Deployment of DOCSIS® 3.0 began in earnest in 2010 and will continue through 2011 and beyond. A key challenge is the demands that this places on the return channel – yet more sensitive modulation of wider bandwidth, the addition of new DOCSIS® channels, and potentially the addition of new spectrum. Together, it adds up to a much more aggressive use of available dynamic range. Nonetheless, the promise of DOCSIS® 3.0 must be met upstream for consumers whose speed and QoE expectations continue to rise. Next generation systems also may ultimately impose additional high performance requirements on the HFC upstream.
As the deployments of DOCSIS® 3.0 have increased, so too has new confusion over technology options to cost-effectively support this new DOCSIS® era. The new crossroads, replacing the debate over FP and DFB lasers, is around DFB technology options and Digital Return systems. Digital Return, developed now over ten years ago, offers an intriguing set of benefits that all MSOs should consider when planning future HFC migration. However, it also comes with some important constraints. This paper will take a comprehensive look at the use of DFBs and Digital Return technologies for supporting DOCSIS® and new potential upstream requirements in the context of anticipated traffic growth and expansion.
We will delve into the comparable digital return parameters that will help operators compare these systems to the capabilities of their analog counterparts, as well as among the various incarnations of Digital Return systems themselves. Finally, we will weigh the pros and cons of each and provide recommendations.