Can VDSL2 bring 100 Mbps to subscribers? That’s the question service providers (SPs) need to know because cable providers advertise high broadband speeds and various national broadband targets often call for 100 Mbps by 2020. Can extending the life of copper wire meet the challenge?
The answer is yes. With VDSL2 vectoring, that is.
The magic number of 100 Mbps downstream bit rates are achievable over copper wire in the 400m to 500m range when vectoring is used, according to an Alcatel-Lucent (News 
- Alert) TechZine article, “VDSL2 Vectoring Delivers on its Promise.”
As noted in the article, Alcatel-Lucent (ALU) ran 17 VDSL2 vectoring trials with various SPs around the world, most in the 300m to 600m loop length range and with the typical fiber to the node (FTTN) topologies that SPs are considering for vectoring. ALU says the results were very positive in that it was able to get up to 130 Mbps.
This is partially explained by the G.inp coding that now provides a retransmission-based error-handling mechanism for VDSL2 vectoring which results in significantly lower overhead. By replacing the Forward Error Correction (FEC) mechanism, G.inp avoids the FEC-associated fixed overhead of about 12 percent, and G.inp only kicks in when there’s actually an error to correct. ALU also found that cable diameter played a role, but that SPs can achieve good gains with vectoring whatever the cable type used.
“The good news is vectoring delivers greater gain on poorer cable that is heavily impacted by crosstalk, because the crosstalk can be canceled by vectoring,” noted the authors Dr. Stefaan Vanhastel and Jan Verlinden.
Upstream VDSL2 vectoring bitrates also were good, in the 40 Mbps range. In fact, the authors state that upstream rates benefited twice from the VDSL2 vectoring.
“First, VDSL2 vectoring cancels the crosstalk in the upstream direction, which increases the bit rate. In addition, VDSL2 vectoring allows SPs to relax their upstream power back off (UPBO) settings, which can boost upstream bit rates from the 20Mbps-range to the 40Mbps-range,” they note. UPBO works by reducing the transmit power on very short VDSL2 lines so they don’t interfere with weaker signals on longer loops, according to the paper. But because VDSL2 vectoring eliminates crosstalk, UPBO settings can be relaxed.
Vectoring also equalizes performance. At the article highlights, “VDSL2 vectoring delivers consistent and predictable performance across all lines by removing unpredictable cross-talk and making loop attenuation (and thus accurately measurable loop lengths) the determining factor.”
Further DSL acceleration can be added with VDSL2 bonding. Alcatel-Lucent reports up to 200Mbps downstream and 50Mbps upstream if bonding is used for speed. Bonding also can be used to extend reach instead, and Alcatel-Lucent found that VDSL2 bonding can deliver 75Mbps downstream and 17Mbps upstream at 800m if distance is more important than speed.
“These rates provide DSL service providers with strong differentiators in their competition with cable, while enabling them to reach the broadband targets defined in various national broadband agendas and plans,” noted the article.
With ubiquitous fiber deployments still years away in many parts of the world, the ability to leverage existing outside copper plant to provide competitive broadband services is becoming an increasingly attractive solution for SPs, particularly in place like Europe where VDSL2 vectoring has already drawn significant traction.
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Edited by
Peter Bernstein
