Cable providers have spent years trying to solve a dilemma: “Do we spend money to completely upgrade the plant or do we make due with incremental improvements to our existing plant?”

Fiber is able to transport more data at higher speeds than cable, but completely replacing a cable network with fiber is cost prohibitive. Until now, providers have added fiber to new parts of the plant and tried to make the most of DOCSIS over existing cable networks. DOCSIS has made incremental improvements over time, but has never been able to compete head-to-head with fiber.

With the introduction of DOCSIS 3.1, this all changes. One of the main changes to DOCSIS 3.1 is orthogonal frequency domain multiplexing (OFDM). OFDM makes quantum leaps in the amount of data capacity and speed available – sometimes as much as 50 percent more capacity over the same spectrum. Running at peak performance, DOCSIS 3.1 has the ability to provide 10 G on the downstream and 2 G on the upstream – speeds that can rival fiber.

But how is this possible? And what major changes need to be made to take advantage of OFDM?

Components of OFDMOFDM moves away from the single carrier QAM (SC-QAM) model, and instead, uses multiple modulations running over as many as 8000 subcarriers. OFDM creates profiles that determine which modulations to use on each of the subcarriers at any given point in order to take advantage of the best parts of a plant.Mixing Modem Profiles

For example, each of the profiles are assigned a letter such as A, B, C, D and so on. Each profile adjusts the modulations of the subcarriers for different signal to noise conditions. If one part of the plant is clean, a higher profile (and modulation) would be used such as 4096 QAM. If there is some noise in another part of the plant, a lower profile (and modulation) would be used in that part of the plant such as 1024 QAM.

The main take away is that DOCSIS no longer needs to be optimized for the worst part of the plant. OFDM is able to use the highest QAM possible that any specific part of the plant can handle at any given point in time for each of the subcarriers. Although OFDM is much more complex that this, the main point is that OFDM can change the profiles in real-time to optimize modulations to the best parts of the plant – dramatically increasing speed and throughput.

One of the best aspects of OFDM is that providers can immediately take advantage of speed and throughput increases without making major upgrades to existing networks. Where DOCSIS 3.0 was able to achieve 6.3 max bits/Hz, DOCSIS 3.1 is able to achieve 10.5 max bit/Hz at 4096 QAM. In a more typical situation where multiple QAMs are being used at the same time, DOCSIS 3.1 is still able to achieve 8.5 bits/Hz – making it 35% more efficient without changing the HFC plant.

Providers will need to make some upgrades to their networks to reach the highest levels of performance, but because of the inherent capabilities of OFDM, DOCSIS 3.1 provides immediate performance enhancements. This can give providers some time to make those upgrades, while increasing quality of experience for their customers in the near term. Once upgrades are made, DOCSIS 3.1 will give providers speeds that can compete with fiber.

OFDM and profiles are much more complex than we can describe in a single blog post. For more in depth information, see the white paper “DOCSIS 3.1: Best Practices for Peak Performance”. For a quick overview of how DOCSIS 3.1 works, this infographic is a great place to start.

Are you planning to deploy DOCSIS 3.1 into your network? If so, what are the main questions you have concerning OFDM and profiles? Let us know in the comments below.

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1 Comment

  1. Any estimates of cost per sub to upgrade to Docsis 3.1?

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