One of the biggest challenges for 5G and last mile 10 Gig deployments is not raw data speeds, but middle mile and core networks. The wireless industry is talking up tens of gigabits for 5G, but what feeds the cell sites and neighborhoods? Currently, top speeds for core networks are between 200 Gbps and 400 Gbps, depending on the carrier and day of the week. CableLabs says it has a cost-effective solution to transmit up to Tbps (Terabits per section) to 4 Tbps in the near-term over a single strand of optical fiber using off-the-shelf electronics, with the potential to go up to 50 Tbps.
CableLabs President and CEO Phil McKinney, conducting interviews at CES 2018, says the path forward to boost fiber capacity is by borrowing techniques from long-haul networks and getting rid of unnecessary overhead to increase speed. Coherent optics utilizes the ability to transmit multiple bits of information using light, including amplitude and phase modulation, instead of a simple binary on-off approach. Adding QPSK and QAM, plus polarization means you can move a lot more data onto a single strand of fiber.
The cable community has been steadily running out of fiber strands and bandwidth, seeing fiber bundles being slowly tapped out for such things as dedicated business services and private networks. Adding in a plan for full duplex DOCSIS 3.1 10 Gbps service for residential subscribers only adds to a need for more capacity.
Coherent optics have been in use for long-haul undersea networks for over 30 years, but it has been expensive, requiring lots of error correction and repeaters to correct for distances of thousands of kilometers. Local metro networks are 30 kilometers or less, so there's no need for repeaters or a lot of overhead to ensure signal.
Last year, CableLabs demonstrated the ability to deliver 256 Gbps over 80 kilometers on a single wavelength with 16 QAM "using electronics bought on eBay," said McKinney. By multiplexing eight wavelengths, speeds of 2048 Gbps -- 2 Tbps -- were achieved. By tweaking up encoding and modulation, 4 Tbps should be reachable in the near term while speeds of up to 50 Tbps are possible. This means existing fiber networks can be used to deliver faster speeds by effectively rebalancing capacity on strands rather than having to pull more fiber.
McKinney says CableLabs is working to establish open standards for coherent optics, which should provide lower costs and interoperability for equipment. And since the coherent optics work isn't embedded into any specific cable technology, it can just as easily be adopted by any fiber-to-the-whatever operator to boost metro and last-mile delivery speeds as well. Will wireless and traditional phone companies be able to swallow their pride for a significant speed and fiber efficiency increase? Given the rush to deploy 5G, coherent optics using the CableLabs specs or something similar is likely to show up soon.
Edited by Mandi Nowitz