Electronic Design

G.hn Standard Promises Compatibility At Home

Wired communications is a very mature sector, so there are rarely any major revolutions. But G.hn from the International Telecommunications Union-Telecommunications (ITU-T) attempts to consolidate all of the various home networking standards into one common worldwide format.

This complex new standard offers interoperability and backward compatibility with the multiple technologies that have been competing in this space for the past several years. It also offers the hope of producing a technology that all designers can agree upon and use to work toward everyone’s benefit.

Like Wi-Fi in the home, G.hn is designed to provide PC connectivity to a broadband Internet connection and distribute it throughout the home. But that’s not all. Other services include IPTV, HD video distribution, and connectivity between the HDTV set, DVD player, and other devices.

Music and gaming distribution are potential applications. G.hn also can be used for the new Smart Grid utility application for energy monitoring and savings. And, it forms a network for intelligent communication and control in the home (see the figure).

A LOOK AT G.HN
When it comes to home networking, wireless still dominates. Thanks to the Wi-Fi Alliance, all IEEE 802.11 wireless local-area products (WLAN) products work with one another. Using one standard with its interoperability and backward compatibility makes it easy for consumers to set up, use, move, and change all of their devices with minimal problems.

But that’s not the case with wired communications. We have a real mix of wired standards that use the existing telephone wiring, coax from the cable connections, or the ac powerline. There are multiple variations for each of those media, too. Furthermore, none are compatible (see “A Dizzying Mix Of Standards”).

G.hn is short for the ITU-T’s G.9960 standard effort. This worldwide project is designed to generate a wired home networking standard that all companies, or at least most, can agree upon. The ITU-T’s objective is a single next-generation physical-layer/media access controller (PHY/MAC) technology that runs over coax, phone lines, and powerlines.

The G.hn working group was founded in 2006, and major accomplishments have been achieved on the way to a final standard. The organization consented to a PHY and general architecture in October, so silicon vendors can begin their product designs. The data-link layer (DLL) standard, which is the step just before final consent, is frozen.

The ITU also recommended that G.9972 receive consent. This standard provides for coexistence between G.hn products and specifies a process by which G.hn devices can coexist with other powerline standard devices that also adopt the coexistence standard.

In G.hn, the PHY is a generic orthogonal frequency-division multiplexer (OFDM) operating from 2 to 30 MHz, which should work over any wired medium. G.hn also provides data rates greater than 100 Mbits/s and ultimately to 1 Gbit/s. It offers up to 250 nodes on each network. And, it supplies programmable OFDM to a select number of subcarriers, subcarrier spacing, center frequency, and window size.

G.hn’s forward error correction (FEC) is a quasi-cyclic low-density parity check (QC-LDPC). Note that this is one of the major differences with other powerline and coax standards that use turbo code or Reed Solomon.

The DLL’s time-division multiple access (TDMA) MAC guarantees bandwidth and low latency for applications that have strict quality of service requirements, such as IPTV. G.hn’s MAC also supports multiple priority levels to ensure that an application such as peer-to-peer file transfer does not impact the performance of higher-priority applications like IPTV, Voice over Internet Protocol (VoIP), or online gaming.

Also, the DLL’s logical link control (LLC) sublayer ensures delivery of data over home electrical wiring. The LLC employs an advanced selective automatic retransmission request (ARQ) protocol that automatically retransmits data affected by noise and provides error-free end-toend Ethernet services to any G.hn device on the network connected to powerlines, phone lines, or coaxial cables.

A procedure for efficient aggregation of multiple Ethernet messages over a single MAC protocol data unit (MPDU) significantly increases network throughput to support applications such as highdefinition IPTV that have large bandwidth requirements. G.hn specifies line data rates up to 1 Gbit/s, which is much higher than current wired networking technologies.

THE SMART GRID EFFORT
The Smart Grid is the name for the effort by the U.S. and state governments and utilities to better monitor and control energy usage. With increased knowledge of usage types and schedules, consumers can reduce their energy usage and utilities can conserve energy to minimize the need for future power plants.

The idea is to have products that plug into the outlet between the ac mains and the appliance that will monitor the power usage and time and report back to the utility. With consumer approval, the utility could even control the appliance with an improved energy algorithm to save energy in some cases.

This effort, now under way with experiments in the U.S. and Europe, implies a communications capability. Appliances to be monitored and controlled would be connected to a home network that would in turn be connected to the utility via the Internet or possibly by wireless.

G.hn fits into this scheme nicely. Just recently, the National Institute of Standards and Technologies (NIST) approved G.hn for Smart Grid applications. Smart electric meters, heating and air conditioning systems, major electrical appliances, lighting systems, big TV sets, and other heavy power-consuming products all could be connected to G.hn.

HOMEGRID FORUM
The HomeGrid Forum is a worldwide, non-profit trade group promoting the International Telecommunication Union’s G.hn standardization efforts for next-generation home networking. It also promotes the adoption of G.hn through technical and marketing efforts, addresses the certification and interoperability of G.hn-compliant products, and cooperates with complementary industry alliances.

By developing a worldwide standard using a unified MAC/PHY for coaxial, phone line, and powerline networking, ITU G.hn enables operators to deploy home networks most cost-effectively. It also enables consumer electronics manufacturers to develop cost-effective connected home equipment for the worldwide market. And, it gives consumers a range of interoperable products.

HomeGrid will develop testing and certification programs to ensure product compatibility among vendor products. Key members include Best Buy, British Telecom, Coppergate, DS2, Gigle, Ikanos, Infineon, Intel, Panasonic, and Sigma. Home- Grid also has liaisons with the Consumer Electronics Powerline Communications Alliance, Continental Automated Buildings Association, Digital Living Network Alliance, HomePNA Alliance, and Universal Powerline Association.

BEST IS GOOD ENOUGH
The success of G.hn is not a sure thing. Yet it does offer hope for a wired home networking standard that a consolidated industry can get behind. There will be two keys to its success. First is its adoption by the major carriers as the home distribution system of choice for their broadband, TV, and related services. Second is consumer acceptance, which requires educating consumers about the technology and the interoperability and compatibility it can offer. The HomeGrid Forum has its work cut out for itself.

What will all the present companies do given their already huge investments in current products? Entrenched standards like HomePlug and MoCA could continue to build on their current situations. Together, they claim more than 55 million home networking devices in the field. Others are leaning toward building multi-mode chips and products, meaning they will implement their own existing standard but also include G.hn with provisions for coexistence. That seems promising.

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