Vectoring Helps Copper Taste the Fast Life

It's assumed by the cable industry - and many of their competitors in the telephone industry, no doubt, though more quietly - that coaxial cable is inherently superior to twisted-pair copper wiring.Game, set and match, right? Perhaps not. The fact that the base technology is better doesn’t mean that ways of stretching the copper soup aren't evolving. It also doesn't mean that the gap, in many cases, is particularly large considering the relatively short distances that each has to traverse.That fight has been going on for years. The cable industry is upgrading its DOCSIS technology on an ongoing basis. The big news of the past year has seen the birth of DOCSIS 3.1. The telephone industry is not surrendering, however. The most recent advance - G.vector for VDSL2 - is a big deal.The impact is significant, said Khin Sandi Lynn, an industry analyst for ABI Research. "VDSL2 can deliver download speed[s] around 80 Mbps for a distance of about 500 meters," she wrote in response to emailed questions. "By using vectoring performance, that will be improved to [a] download speed of 100 Mbps over the same length of copper line."It is an interesting time in the history of copper wiring. The USTelecom reports that traditional voice line shrinkage is occurring at a "breathtaking pace." It says that from 2000 to the end of this year, traditional phone lines will have receded by 62% and traditional residential voice lines by 70%.At the same time, however, technology aimed at speeding the copper that survives are ongoing. VDSL2 has a head of steam in the United States and abroad. Earlier this week, reports were that Deutsche Telekom had committed to rolling out ADSL2 with vectoring to 44 cities in Germany. The carrier had made a significant investment in the technology late last year.It's easy to see why the telcos are so eager to push DSL and the attraction of vectoring. Frank Engel, the senior marketing manager for VDSL (CPE) for semiconductor vendor Lantiq, said the technique can double the throughput of VDSL2 from 50 Mbps to 100 Mbps over a distance of 500 meters. Bonding two twisted pairs can double that capacity yet again, to 200 Mbps.Vectoring is a noise cancellation technique. Lincoln Lavoie, the senior engineer for broadband technologies for the University of New Hampshire Interoperability Lab, describes vectoring as a noise cancellation technology similar to the multiple in, multiple out (MIMO) antenna technology used in advanced 802.11 scenarios.In both instances, the system takes lemons and makes lemonade. Tightly bundled copper pairs create crosstalk, or cross-coupling between the pairs. This shows up as noise. But at its heart, the noise is identical signals to the main signal. It becomes disruptive because they arrive late: in the case of 802.11, because it has bounced around the room a few times and is delayed; in the case of DSL signals, because of the time it takes to travel between the pairs.Vectoring - as in MIMO - is a way to capture these redundant signals and manage them in such a way that they bolster, not hinder, the main signal. "Vectoring is pre-modulating or pre-shaping the signal so that when it arrives at other side with original noise adding, rather than it distorting the signal, it bolsters it," Lavoie said. “The crosstalk becomes part of the communication channel."The Broadband Forum has run several plugfests in conjunction with the UNH Interoperability Lab. Lavoie said there are two types: One aims at ensuring that the chipsets and firmware can interoperate. Those switch off with events that look at whether whole systems can interoperate. The most recent plugfest, which was in late February, was the second focused at the systems level, Lavoie said. Fifteen companies, including Broadcom, Cisco, Alcatel-Lucent and Technicolor, participated.The race will continue. Cable operators, of course, are working overtime on DOCSIS 3.1. The telcos currently are employing at least one similar concept - channel bonding - to further push DSL. The next big push will be to combine vectoring, bonding and other techniques in a nascent technology called G.fast. Trials on G.fast likely will begin at the end of this year and extend into next, said Lantiq's Engel.At the end of the day, relatively few service providers - on the cable or telephone industry side - immediately use the latest technology. Rollouts are driven by need and the amount of investment, if any, that is stranded by making significant changes. That suggests that the bottom line is that both industries have effective last-mile technologies now and will for the foreseeable future.Carl Weinschenk is the Senior Editor of Broadband Technology Report. Reach him at [email protected].