When it comes to access networks, fiber is the technology that’s getting all the attention these days, and for good reason, as it offers superfast speeds for the latest broadband services. Yet for all the talk of fiber, the reality is that the majority of the world’s existing access wireline infrastructure is copper based, and service providers everywhere are looking to make the best use of this installed infrastructure.
We, as consumers, do not need to worry about where this bandwidth is coming from, but for network operators it is creating quite a conundrum. Most established telcos are sitting atop massive copper networks and are slowly moving to fiber to deal with our insatiable appetite for bandwidth and services. They walk a tightrope of trying to satisfy growing subscriber demand while maintaining their own need for return on investment. If they do not upgrade, they won’t be able to offer next-generation services and will lose customers as a result. If they upgrade too fast, there may not be a critical mass of subscribers who are willing to pay for extra bandwidth and services and the investment will be difficult to justify. This has brought the telcos to a critical decision point: replace their copper plant with fiber altogether now, or optimize the infrastructure that is already in place.
Building out an all-fiber network can require large capital outlays, some claim up to $2,000 per subscriber, making it cost prohibitive for many operators. The deployment cycles can be long as well, particularly in residential areas, resulting in delayed ROI.
With competition from the cable companies and other alternative service providers intensifying, many wireline carriers are finding themselves in need of a more immediate solution that will allow them to buy time as they transition to fiber.
Copper networks have been reliably providing telecommunications services for decades. Over the years, various technologies have been used to increase the capacity and reach of these networks, and one in particular, VDSL2 (very-high-speed DSL 2), showed great promise. Standardized by the ITU in 2005, VDSL2 was specifically developed to support the deployment of triple-play services at near-fiber speeds – up to 100 Mbps. Problem was, though, that real-life performance did not reach theoretical speeds due to a phenomenon known as ‘crosstalk.’
Crosstalk is the electromagnetic interference created by copper pairs that are adjacent to one another. This interference, or noise, degrades the quality of the signal being transmitted through the wire and reduces the actual speed of VDSL2 to only 24 Mbps at 1000 meters.
Recognizing the potential of VDSL2 to extend the life of copper infrastructure, a group of DSL researchers formed the iSmart Consortium in 2006 to find a solution to the crosstalk limitation. The group conducted research on DSM (dynamic spectrum management), a technology that uses advanced signal processing to mitigate crosstalk. The result of their work is DSM Level 3, or ‘VDSL2 vectoring’ (ITU‑T G.993.5, or G.vector).
Simply put, VDSL2 vectoring works by mitigating the noise (crosstalk) that occurs between twisted copper pairs. In doing so, it enables broadband speeds and reach far beyond what is possible with standard VDSL2. For example, in one scenario, field trials have shown that vectoring could improve DSL data rates by 100%, to 50 Mbps or more, and subscriber coverage area by 300%.
Let’s take a closer look at the enhancements in downstream reach and rate that are possible with vectoring. Figure 1 shows a scenario where vectoring can increase the 50 Mbps service radius from 400 meters to 800 meters over 0.4 mm copper wire. Super-premium 85 Mbps services would be possible at distances of up to 400 meters. With 0.5 mm copper wire, data rates would improve to 100 Mbps at 800 meters.
In a similar case, by doubling the 50 Mbps service radius from 400 meters to 800 meters, the potential premium-service subscriber base would increase by 300%, as illustrated in Figure 2.
With its ability to boost the speed and reach of DSL, VDSL2 vectoring is quickly becoming the technology of choice for enhancing deployed copper networks. According to Broadbandtrends, there has been growth in VDSL shipments over the last year as many operators pushed fiber deeper into the network via hybrid architectures. VDSL ports represented 20% of total DSL ports in 2011, and this is expected to grow to 45% of total ports by 2017.
It’s inevitable that one day the copper network will be supplanted by the all-fiber network. In the meantime, wireline carriers are seeking out ways to prolong the life of the copper plant and stay competitive as they make this transition. For many, VDSL2 vectoring will be the solution. This copper-enhancement technology enables telcos to get the most of their existing infrastructure by improving their broadband offerings and reaching more subscribers more quickly.