By John Ulm, Dr. Zoran Maricevic & Dr. Frank O’Keeffe, CommScope
As of April 2020, all the 1,000+ pages of the Data Over Cable Service Interface Specification (DOCSIS) 4.0 PHY and MULPI specs, combined, are out and about. That’s step one in making the 1,794 MHz top frequency in the downstream, combined with up to 684 MHz for the top frequency in the upstream, a new reality for the hybrid fiber-coax (HFC) plants. As part of the greater 10G initiative, this is what will be needed to support the many Gbps in both the upstream and the downstream for nodes with amplifier cascades (a.k.a. N+X). The multiple system operators’ (MSOs’) successful business model and existing HFC broadband networks are our starting point. All that’s needed is a simple upgrade to get from here to there, easy peasy! Not so fast?! Well, OK, there are some “minor details” to sort in the process of getting there: Where is the Goldilocks zone – not too little but not too much either – for the RF amps gain and power? There are many items to consider.
With a comprehensive network model of a node + 6 cascade, should the “unity gain” concept be extended all the way up to 1.8 GHz? Once modeled, what would an optimal power spectral density (PSD)distribution across the forward spectrum look like? What happens as the distance between the amps increases? Does the tap position on a link make a difference? What is the impact of the drop cables? Should we continue to use end-of-line (EoL) throughput as our capacity benchmark? There are many, many questions and this paper will start to look at some of the considerations with rolling out 1794 MHz HFC plants. All of this is distilled into conclusions and best practices guidance – to help make 10G and the DOCSIS 4.0 networks a reality for the time to come!