G.fast Takeoff Through Innovations and Applications

The emergence of OTT videos and 4K TV is accelerating ultra-broadband network deployments. Fiber to the home (FTTH) is suitable for greenfield areas to offer high bandwidth, but is costly and difficult to deploy in brownfield areas due to complicated civil works inside the home. G.fast, which reuses existing copper resources to reach speeds comparable to FTTH (1,000 Mbit/s), is well-suited to brownfield areas. Featuring faster access, faster deployment, and faster return on investment, G.fast is attracting increasing industry attention.

G.fast — benefit highlights

G.fast brings copper access into the gigabit era by delivering fiber-like speeds. G.fast is easier to deploy than FTTH and faster than traditional DSL, and allows for quick return on investment (ROI).

• Fiber-like access, easy deployment, and quick ROI

By introducing G.fast technology at fiber to the building/door (FTTB/FTTD) sites, operators can reuse existing copper infrastructure such as telephone lines to deliver gigabit access.

An important feature of G.fast is "self-installation". In G.fast projects, remote distribution point units (DPUs) support plug-and-play, and G.fast customer premises equipment (CPE), similar to ADSL CPEs, can be easily installed by customers at home. This significantly reduces service Time To Market (TTM) and engineering costs.

In addition, reusing copper lines avoids problematic engineering construction inside houses (as required by fiber deployment), which may involve drilling holes and open wiring. This simplifies engineering delivery and reduces customer complaints.

The combined FTTB/D+G.fast solution enables operators to quickly extend ultra-broadband coverage at lower costs. According to cost analysis of FTTH construction in China, in-building civil works of FTTD is only 50% of the cost and TTM than FTTH solution. In developed countries such as those in Europe and North America, where labor costs can be much higher, further savings can be made by deploying G.fast.

• Cloud-oriented traffic model, flexible upstream/downstream bandwidth definition

G.fast allows operators to define the upstream/downstream bandwidth ratio. Traditional fixed access technologies (such as GPON, EPON, and ADSL) provide higher downstream bandwidth than upstream bandwidth. For example, for ADSL2+, the typical downstream bandwidth is 2M-8M and upstream bandwidth is 512k-1M. In the cloud era, low upstream bandwidth is a bottleneck for end users wanting to share large videos and photos.

With G.fast, the upstream/downstream bandwidth ratio can be flexibly set to a value between 1:9 and 1:1 (for example, 900M downstream and 100M upstream; or 500M downstream and 500M upstream). The flexibility helps enhance network capability and allows operators to provision new services such as home video communication, remote video surveillance for home security, and video surveillance in urban areas.

Innovations to deliver technology breakthroughs

Key technologies of G.fast include modulation optimization and synchronized time division duplex (TDD). G.fast currently works at 106 MHz, which will scale to 212 MHz for faster access speeds in the future.

Using an optimized modulation technique based on VDSL2, G.fast is backward compatible with VDSL2 and evolution friendly.

Traditional DSL adopts frequency division duplex (FDD), whereas G.fast adopts TDD. TDD empowers greater spectral efficiency and a more flexible upstream/downstream bandwidth ratio, meeting symmetric access requirements of enterprise users as well as asymmetric access requirements of home users.

G.fast is prone to severe crosstalk in high-frequency band. For multiple user lines within the same cable bundle, vectoring technology must be used to cancel crosstalk and restore normal G.fast speeds.

Applications to empower commercial readiness

The ITU-T released a G.fast draft standard for consent in December 2013, and related chipset and product design has started across the industry. Huawei unveiled the first G.fast technical prototype in the industry at the end of 2011, proposing and verifying the G.fast concept. In August 2013, Huawei launched the world's first pre-standard G.fast product. Huawei also took the lead in G.fast commercialization and engineering delivery with world-leading operators.

To date, Huawei has conducted lab tests on G.fast with France Telecom (FT), Deutsche Telekom (DT), M-Net, Orange Poland, eircom, Vodafone, etc. and completed G.fast field trials with British Telecom (BT), TeliaSonera in Finland and Swisscom. G.fast is no longer confined to the lab.

BT: World’s first G.fast live customer trial

In September 2013, Huawei successfully conducted the world's first G.fast trial with BT in a residential community in Ipswich, UK. The G.fast distribution point unit (DPU) was deployed in a manhole near the community and connected to an optical line terminal (OLT) upstream through a fiber splice closure and to user homes downstream through a copper closure. The DPU and manhole closures, were IP68 waterproof.

Upstream transmission used 10G-PON to guarantee no bandwidth congestion for multiple G.fast users. The 10G-PON shared ODN fiber infrastructure with GPON to the OLT in the central office (CO).

Downstream transmission reused existing copper lines leading from the manhole into three user homes. One user home was across a street from the G.fast DPU, which in a traditional FTTH deployment would have required complicated civil works. However, thanks to reusing the existing copper cables, civil works were unnecessary.

To prevent interference from ADSL2+ users (below 2.2 MHz) from the CO, the G.fast trial adopted a working frequency band between 2.2 MHz and 106 MHz. Total G.fast bandwidth is over 1 Gbit/s, which is the sum of upstream and downstream bandwidth.

Dr. Tim Whitley, Managing Director of Research and Innovation at BT, said, "The G.fast trial has the potential to demonstrate how ultrafast bandwidth access may be more efficiently delivered to consumers and businesses. We will be observing the results of the trial with interest to see whether G.fast technology could play a role in ensuring BT has the best network in the short, medium, and long term."

In November 2013, the G.fast workgroup of ITU-T visited the G.fast trial office in Ipswich and experienced G.fast-based ultra-broadband services (of BT Sport) during their meeting in the UK. Director of the G.fast workgroup Les Brown commented, "The success of the G.fast trial verifies some new technologies being discussed by the workgroup. Such application significantly promotes G.fast standardization, accelerates G.fast commercialization, and ushers in the gigabit era of ultra-broadband networks."

Finland TeliaSonera: first G.fast live customer trial in North Europe

In February 2014, TeliaSonera, the largest telecom operator in North Europe, conducted a G.fast trial in a multi-storey apartment in Helsinki, the capital of Finland. Local loop unbundling is required which means access to physical copper lines is open in North Europe. Therefore, the basement of the apartment also housed VDSL2 equipment (besides the G.fast DPU), and the cable also carried ADSL2+ users from the CO (in addition to G.fast and VDSL2 users).

The starting frequency of G.fast was set to 23 MHz to prevent G.fast signals from affecting DSL performance in the same cable, and the cutting frequency set to 88 MHz to avoid interference from FM radio. Due to a narrower working frequency range, G.fast bandwidth totaled 500 Mbit/s. Line performance was sacrificed to assure interference-free coexistence of G.fast and existing DSL signals.

During the initial commissioning phase, user links were frequently interrupted, severely affecting G.fast performance. The cause was diagnosed (using a signal analyzer) as instantaneous high-amplitude pulse interference from an electrical power control system located near the basement. Huawei solved the problem by enabling anti-pulse interference processing through optimizing G.fast software.

The trial proved for the first time that in an open access environment, G.fast services could be transmitted together with VSDL2 and ADSL2+ over one cable bundle without affecting each other. The trial also accumulated engineering construction experience for mass G.fast deployment.

"We continue to drive innovation to provide the best experience for our customers and build the digital society. The technology to deliver ultra-high-speed broadband connections over old copper lines makes it possible for us to improve the experience for more customers faster and thus making the most of our copper network," said Isto Pasanen, Head of Consumer Services in Networks at TeliaSonera.

Swisscom: 400m long-haul G.fast transmission over paper-insulated cables (Strong crosstalk)

Swisscom is deploying outdoor integrated equipment for fiber to the street (FTTS) in manholes and has planned to deploy G.fast DPUs also in the manholes for bandwidth upgrades. In the lab test, Swisscom verified long-haul transmission of multi-port G.fast. Test results indicated that total G.fast bandwidth reached 250 Mbit/s over a distance of 400 m and more than 600 Mbit/s on loops up to 100m. On paper-insulated cables the performance is lower because of higher attenuation.

Another challenge for Swisscom is severe crosstalk from paper-insulated cables, which are adopted by many user lines. This causes difficulty in activating G.fast CPEs and requires software optimization.

Swisscom started a G.fast field trial in Riggisberg which is 27 km away from capital city Berne in June 2014. G.fast DPU was installed in outdoor manhole. The 10G PON fiber is used for uplink and connected to the exchange head end OLT, waterproof cable connectors are used to enable a quick exchange of the DPU in case of failure or migration to new hardware variants. The trial site can demo both the current Vectoring access technology and the future evolution of G.fast technology, together with IPTV etc. ultra-broadband based services. Swisscom G.fast technical director Oliver Lamparter said: "On short loops G.fast technology can dramatically increase the existing DSL access speed, which will undoubtedly make Swisscom’s broadband network very competitive, we are willing to contribute our efforts to accelerate the technology maturity and the solution deployment."

G.fast takeoff fueled by Huawei's innovations and applications

G.fast technology unleashes the potential of copper, helping operators make the most of existing copper resources and speed up ultra-broadband network deployments. In the G.fast arena, Huawei has been pioneering innovations and applications by proactive technological research as well as field trials and lab tests with 10 plus operators, effectively advancing the development and maturity of the industry.

Huawei unveiled the world's first G.fast prototype back at the end of 2011, demonstrating the feasibility of high-speed gigabit access over twisted pairs. Huawei has also played a proactive role in developing G.fast standards and products. The proposals contributed by Huawei to ITU-T G.fast standardization cover a wide range of G.fast core technologies, including TDD, the basic frame structure, forward error correction (FEC) channel coding, line activation negotiation mechanism, multi-line crosstalk offset, online reconfiguration, and a power-saving working mode. In August 2013, Huawei launched the first pre-standard multi-port G.fast product supporting IP68 waterproofing in the industry. In addition, Huawei conducted G.fast trials with BT, TeliaSonera and Swisscom as well as lab tests with multiple operators, catalyzing G.fast readiness for commercial use and accumulating rich engineering construction experiences.

Copper is an important infrastructure for fixed network operators. The combination of copper reuse and innovative G.fast technologies, which can speed up access, deployment, and ROI, is embraced by a growing contingent of operators. Huawei will continue innovating in copper technologies to further release its potential. Huawei is currently working on improving spectral efficiency and transmission speeds for VDSL2/vectoring, optimizing linear and non-linear algorithms for G.fast, and started the 5G broadband (5GBB) research, which is expected to deliver an access speed of up to 5 Gbit/s over copper in future.