OPERA, Broadband Over Power Line (BPL)

Published Fri, 2007-09-21 12:00

Just as we get used to the idea of watching television over a phone line, along comes a new idea: broadband internet, TV and phone services delivered through ordinary power cables. European researchers have solved the formidable challenges of this new technology, and are leading the race to an international standard that could give us cheaper, easier broadband access.

Broadband ‘always on’ internet is taking off. The number of Europeans with high-speed internet access grew by nearly 50 percent between 2005 and 2006, and the popularity of internet-based phone and television services is straining the capacity of existing broadband carriers.

Thanks to the huge data capacity of optical fibres, high-speed communications “backbones” linking towns and cities are economic to set up. More challenging is what the telecoms industry calls the “last mile”: the few hundreds or thousands of metres between the customer’s house or office and the nearest switchbox or telephone exchange.

Co-axial cable and optical fibre provide high bandwidths, but cost too much to install in thinly-populated areas. Phone-based broadband – ADSL – is cheaper, because it uses existing wiring, but performs poorly at more than a few kilometres from the exchange. Even in cities, ADSL is reaching its technical limits. New communications channels are urgently needed.

European researchers believe they have a solution in the technology known as power line communications (PLC). Like ADSL, PLC uses existing cables, in this case the ones installed to carry electric power. Since mains electricity is found almost everywhere, PLC works even in remote areas and countries where phone lines are in short supply. PLC also has great potential for saving energy through better control of the electricity network itself.

OPERA beats the noise
Although PLC of one kind or another has existed for several decades, getting the technology to work reliably at broadband speeds is difficult, explains Javier Arriola of Spanish power company Iberdrola. The electrical grid carries large currents at low frequency, whereas broadband involves low-power signals at high frequencies (up to 30 MHz). The weak data signals are easily overwhelmed by electrical “noise” on the grid, yet paradoxically they can interfere with nearby radio transmissions if special measures are not taken to prevent this.

PLC signals can only travel for a few kilometres before they become too feeble, and they cannot pass through transformers at all. The tree-like structure of the power network also presents problems, especially when lines are switched in and out as demand changes.

This places stringent demands on PLC design. The algorithms used to encode the data must be robust, to avoid problems with noise, and the signals need to be frequently re-amplified and routed around obstacles such as transformers. The management system has to take account of changing network paths, and safety is always an issue when working at thousands of volts.

All these issues have been solved, Arriola says, by an EU-supported project which he coordinates. The OPERA consortium has brought together 26 organisations – power and telecoms providers, equipment manufacturers, technology companies and academics –from 11 countries to create a new PLC system that is practical and affordable.

OPERA has a total budget of €29 million. The project began in January 2004, and two years later it had created a PLC system capable of 45 Mbit/s that was advanced enough for Iberdrola to market. This service still had some teething problems, Arriola admits, but a second phase of OPERA that began in January 2007 has already created a new prototype that is more robust and much faster.

The new system is currently on test at three sites in Spain, Portugal and Austria. Its bandwidth of 200 Mbit/s can be shared by several hundred consumers, to create an economical broadband service, or fewer people when higher speeds are needed. The local equipment is easily installed by power company technicians: a repeater at the electrical substation, smaller repeaters in apartment and office blocks, and a small modem-like box for each customer.

Squaring up to standards
OPERA is by no means the only PLC initiative: between 2001 and 2004 there were more than 100 PLC trials in 40 countries. The main standards body, the Institution of Electrical and Electronic Engineers (IEEE), is now assessing a handful of PLC technologies. An agreed standard is essential, says Arriola, if PLC is to be widely accepted, especially as power companies forge closer links between neighbouring grids. Only large-scale adoption of a single technology will allow the equipment to be made cheaply enough for consumer use.

OPERA is the only PLC technology to have been demonstrated under real conditions in its current form, Arriola says. This lead in testing, plus OPERA’s advantages in terms of speed, robustness and lack of radio interference, put the technology in an excellent position to become a world standard. By the time the project finishes in December 2008, PLC equipment and services based on OPERA should be commercially available, Arriola says.

As well as providing high-speed internet access, video and phone services from any electric socket, OPERA has a great future in controlling the grid. Power companies already use a form of PLC to control their high-voltage lines and switchgear, but until now this has not been possible at the consumer level. PLC could allow remote meter reading and the use of dynamic tariffs to save power and spread demand. “This is a versatile technology that can provide a practical alternative to cable, DSL and wireless broadband,” Arriola concludes.

Source: ICT Results