DOCSIS 3.1 is an expansion of the Data Over Cable Service Interface Specification (DOCSIS) standard that can stretch even more bandwidth out of existing HFC plants. As such, DOCSIS 3.1 implementations are allowing cable operators to compete on nearly equal footing with fiber installations.
Every version of the specification added new features, including the latest workhorse for IP video, DOCSIS 3.0. DOCSIS 3.1 takes a dramatic leap forward in functionality with two new technologies: orthogonal frequency domain multiplexing (OFDM) and low-density parity check (LDPC).
Together, OFDM and LDPC can add as much as 50 percent more data capacity, with signal speeds up to 2 Gbps on the upstream and 10 Gbps on the downstream, while being backwards-compatible with the large installed base of earlier DOCSIS gear.
For multiple system operators competing with all-fiber builds or trying to keep ahead of accelerating consumer broadband usage, it’s a great tool. Yet, only proper deployment and testing of your DOCSIS 3.1 rollout will ensure that you optimize your investment—keeping costs in line with projections and providing customers with a higher-quality experience.
Testing for peak performance first requires an understanding DOCSIS 3.1’s two critical new technologies.
OFDM and LDPC
In short, OFDM has boundaries ranging from 24 MHz to 192 MHz, within which it can run as many as 8,000 subcarriers running at 25 KHz or 50 KHz over the entire bandwidth. Compare this with DOCSIS 3.0’s 6 MHz boundaries and a single carrier. Whereas DOCSIS 3.0 symbols must run through the same carrier in sequential order, DOCSIS 3.1’s symbols carry codewords and are spread across multiple subcarriers and time slots.
Modulations are where OFDM makes significant improvements in network performance, as it can allow different modulations for each subcarrier. Instead of modulations being optimized for the worst part of the plant—as with DOCSIS 3.0—they can now be optimized for the best part of the plant at any given moment. Even where multiple QAMs are being used at the same time, DOCSIS 3.1 is 35 percent more efficient than its predecessor—without changing the HFC plant.
DOCSIS 3.1 uses LDPC for error correction, as the form of error correction used on earlier versions—bit errors as a ratio—was only relevant for single carrier systems. LDPC is able to look across the entire bandwidth for codeword errors instead of bit errors, greatly reducing the need for retries and keeping subcarriers working at optimal levels.
LDPC’s one downside, however, is that it makes real-time adjustments, which means it can reach its limits regarding power levels and modulation error ratio while trying to correct codewords—without much warning. To keep this from happening, testing becomes very important.
Click here for step-by-step testing best practices that will keep DOCSIS 3.1 operating at peak performance.