The outlook is golden for copper because innovations in localized technologies and network architecture are providing zippier broadband rates on copper-wire networks.
The arrival of Fiber to the Home (FTTH) promised to be the next big thing and supplant the near decade-old Asymmetric Digital Subscriber Line 2/2+ (ADSL2/2+). A brief boom in FTTH deployment caused fixed-line operators (FLO) to realize that FTTH was a good fit for residential areas, but not for upgrading older areas with new ultra-broadband networks. Enthusiasm for FTTH construction was low for a number of reasons.
Coaxial and wireless carriers also began competing with FLOs, with multi-service operators (MSO) claiming that coaxial networks are faster than VDSL2 copper networks. Moreover, mobile operators could deliver high-speed 3G and, in some areas, 3.5G data services.
The VDSL2 17a used by many FLOs theoretically enables download speeds of 150 Mbps, though the reality is much lower due to crosstalk between lines. Simply using a higher frequency band doesn’t solve the problem of crosstalk or lift rates, and that’s why solutions like VDSL2 30a were ineffective and not adopted.
Vectoring maturity around this time was a lifeline for FLOs because it solved crosstalk. Vectoring can take VDSL2 to up to 100 Mbps, and it’s quick, easy, and inexpensive to roll out. In Fiber to the Cabinet (FTTC) solutions, carriers can just upgrade DSLAM in roadside cabinets and customer premises equipment (CPE) without re-laying lines or building new stations. Vectoring, therefore, enabled FLOs to quickly wrestle back the lead in broadband access markets.
Huawei acted quickly to push ITU to set vectoring standards, and brought out the market’s first 384-line vectoring product. Vectoring also solved the impact of crosstalk due to a higher frequency band, enabling operators to offer higher speeds on copper networks.
Fiber speeds on copper with G.fast
After ramping up speeds with vectoring, operators set their sights on the next goal – access speeds of 1 Gbps over copper wire.
But was that possible? This question had two parts: First came whether DSLAM could be moved to a Distribution Point (DP) close to user homes in a Fiber to Distribution Point (FTTdp) scenario that, in many cases, could bring DPs closer to homes than roadside cabinets. Even in places without fiber cable at the DP, deployment would be far simpler than with an FTTH solution. Low investment, quick construction time, and enough space for small DSLAMs – the FTTdp scenario was sound.
The second part of the question was whether access rates of 1 Gbps could be achieved in the FTTdp-copper wire scenario. Released in 2011, Huawei's G.fast prototype aimed to open the FTTdp market with Gigabit speeds across 100 meters of telephone wire, after proving fiber optic speeds on legacy telephone wires were possible without an FTTH solution.
In October 2013, Huawei and BT successfully held the industry's first G.fast trial. Then, in August 2014, Huawei and Swisscom signed the first commercial contract for G.fast, with the system going live at the end of 2015.
How does G.fast achieve Gigabit access? First, it brings fiber optic cable closer to the home, shortening the length of the copper wire leg. Second, it uses a wider frequency band – about 106 MHz. Third, improved vectoring cancels out crosstalk and inherits Discrete Multi-Tone (DMT) modulation. Moreover, reverse power feed and time division duplexing (TDD) flexibly adjusts the ratio of upstream and downstream rates, simplifying G.fast rollout.
Tailoring with SuperVector
FLOs plan copper networks using specific construction and maintenance models that can be flexibly formulated. Variations in different networks typically increase closer to the user end of the network, necessitating custom solutions for local conditions.
Developed specifically for a German operator, Huawei's SuperVector is one such solution. When deploying G.fast in Germany, engineers found that the network had no obvious DPs, unlike most operators’ networks.
Both possible solutions – a large-scale network upgrade or extending G.fast to between 500 and 800 meters – were not possible. However, Huawei’s VDSL2-based SuperVector increases the working frequency band from 17 MHz to 35 MHz, boosting the power of the transmission signal and optimizing vectoring for crosstalk cancellation. SuperVector is two to three times faster for users in FTTC scenarios than vectoring alone, and reuses existing FTTC sites and equipment, with only the service board needing to be replaced.
A future win with NG-Fast
G.fast maturity in 2014 prompted Huawei to start researching the next-gen solution – NG-Fast. With innovative technology and infrastructure, NG-Fast meets operator needs for high bandwidth, low latency, low cost, and ease of deployment.
Each successive generation of DSL is five to ten times faster, and so NG-Fast can meet the ultra-high bandwidth needs of 8K streaming at rates of 5 Gbps to 10 Gbps.
Providing such massive bandwidth over copper in single-pair line access scenarios requires a frequency band of 500 MHz alongside advanced coding and modulation techniques for better spectral efficiency. To use the legacy copper network, Phantom Mode and MIMO crosstalk cancellation can be used in home scenarios that involve multi-pair wiring like Cat5. Phantom Mode creates a virtual third pair from two pairs and seven pairs from four pairs, either ramping up speeds or lengthening transmission at the same speed.
Lower latency is crucial to maximize bandwidth for 4K video over DSL. Single-session TCP/IP throughput is determined by the Round Trip Time of the response packet, as well as physical bandwidth. In turn, DSL latency arises from wide-spread interleaving and DSL code length.
NG-Fast needs to slash transmission latency to carry services such as 8K video, which require lower latency than 4K services; avoid interleaving; and reduce code length to suit ultra-low latency services.
It also has to be cheaper than FTTH or there’s no reason to choose it. DSL construction costs are lower than FTTH for equipment as well as deployment, which is several times cheaper. However, NG-Fast brings DP much closer to the home, sharply increasing deployment costs and therefore requiring innovations in technical architecture.
A key aspect of deploying NG-Fast is coping with differences near the user end of the network between the copper networks of different operators. Huawei’s virtual DSLAM improves the economy and convenience of deploying NG-Fast, because it requires far less space and moves the digital signal processing module up the network. Therefore, it can be deployed almost anywhere, and doesn’t need a pre-arranged location on the telephone network.
NG-Fast’s OPEX is lower because, unlike DSL which continuously transmits data, NG-Fast only transmits signals sent by data services, which uses less electricity. The position of the digital signal processing module also means it’s maintenance-free.
Since ADSL arrived in 2000, constant tech and network infrastructure advances and innovations to tailor solutions for local conditions have accelerated broadband rates on copper wire networks.
NG-Fast is poised to take the baton from G.fast, and set new records for ultra-high-speed broadband access on copper networks.