Overhead power lines

Whatever happened to Broadband over Power Line?

It looked like a meeting of technologies that promised much in principle, but the marriage of high-speed data and mains electricity supply has proved to be a challenge too far for the engineers hoping to channel broadband over power lines.

Access Broadband over Power Line (BPL) is a technology that looked a highly promising proposition on paper: piggyback data communication signals on to existing power cables which already deliver electricity into homes and businesses, saving the provider the effort of digging up the environment or erecting wireless masts to provide the same Internet connections to computers and other connection devices. The technology was once lauded by national governments, the European Union (EU), and even the Organisation for Economic Cooperation and Development (OECD), given its apparent ease of deployment and negligible environmental impact.

Alas, the plaudits ended there. After numerous, global trials of the technology spanning the last decade, access BPL initiatives have – or appear to have – petered out. Telecommunications companies and Internet service providers failed to prove that it could deliver the reach and bandwidth required to formulate a cost-effective customer proposition for the consumer broadband market.

So how did this otherwise intriguing technological proposition, which seemed to have plenty going for it, and would have brought together the ICT and power professions in an unprecedented way, come up against such stumbling blocks?

BPL is in fact based on power-line communications (PLC) technology developed as far back as 1928 by US telecommunications company AT&T, and that heritage and global implementation has seen it defined by a range of acronyms in the intervening years, including Power Line Telecoms (PLT), Broadband Power Line Communications (BPLC), and Internet over Power Line (IPL); although to confuse matters somewhat all labels have been applied to in-house BPL (whereby data signals are run over in-building electrical wiring), as well as access BPL that delivers both broadband and power from the electrical sub-station to a given premises.

The theory seemed feasible. Electricity companies have been bundling radio frequency on the same line as electrical current to monitor the performance of their own power grids for years, the theory being that because electric current and radio signals vibrate at different frequencies they do not interfere with each other – or at least not enough to significantly disrupt data transmission. Only low-voltage (LV) and medium-voltage (MV) power cables are suitable to carry data signals; high-voltage (HV) cables transmitting hundreds of kilovolts over distances measured in tens of kilometres do not vibrate at a consistent frequency, causing regular spikes which cancel the data signal and lead to dropped packets that severely interrupt the transmission.

MV lines carry less power, generally up to 100 kilovolts, over a few kilometres between the electricity distribution stations and pole-mounted transformers, with LV lines transmitting a few hundred volts over a few hundreds of metres, usually from pole-mounted transformers into the home or business they connect. Specific configurations vary, but typical access BPL networks use injector devices (or substation modem couplers) to embed data signals on to MV lines at the substation, with extractors (or customer access units) providing the interface between the MV lines carrying BPL signals and the customers within the service area, usually located at the LV distribution transformer feeding power into a group of buildings. Some extractors boost BPL signal strength sufficiently to push the data signal through the transformer; others relay the signal around it by using a coupler on to adjacent MV or LV power lines.

Other extractors connect to non-BPL devices, such as Wi-Fi access points, to beam the data signal into the customer premises. Depending on the distances involved, power companies often have to install repeaters to maintain signal strength repeaters (or regeneration units) to regenerate those signals over distance and prevent attenuation and therefore data loss. The frequencies used have a major effect on the speed and reach of BPL services, as does the encoding scheme used to turn data packets into radio signals. Electric cables have been optimised to transmit between 50-60Hz Extremely Low-Frequency (ELF) band and up to 400Hz, with utility companies using frequencies below 490KHz for their own telemetry, monitoring, and control applications – although most BPL equipment was built to operate between 1.7MHz and 30MHz and occasionally up to 80MHz.

Most power companies, meanwhile, have used Orthogonal Frequency Division Multiplexing (OFDM) – a method of encoding digital data on multiple carrier frequencies – to split radio signals into multiple, smaller sub-signals which are then transmitted at different frequencies to the receiving station, with increased bandwidth and reliability made possible by transmitting along several different signals simultaneously. BPL also uses Direct Sequence Spread Spectrum (DSSS), a modulation technique that also spreads data over the full spectrum of the available frequencies using a chipping code to break information bits into shorter pieces which can then be transmitted more quickly before being reconstructed at the receiving end of the link.

Trials and outcomes

Trials of access BPL technology to date have been prolific and widespread. They have spanned everywhere from the UK and most European countries to the US, Australia, Egypt, Ghana, India, Indonesia, Malaysia, the Philippines, Saudi Arabia and South Africa – to name but a few global instances. Despite all these initiatives, all the trials appear to have resulted in power companies and/or Internet service providers deciding that the technology is not viable as a means of delivering broadband Internet access. This is because of two technological challenges that have impeded progress: limited reach, and low bandwidth which do not come close to matching ADSL, Wi-Fi, and even 3G mobile broadband services that have steadily expanded their own coverage areas over time.

"They just could not get the speed, and the further they want to reach, the bigger the speed challenge becomes... There are additional problems with contention ratios," says Don Beattie, director of the Radio Society of Great Britain (RSGB). "By the time you have shared [access] BPL with a number of subscribers down a particular mains cable, you get nowhere near the speed you get with ADSL, say."

Given the degree of interest in developing the technology up until relatively recently, it seems somewhat odd that projects should have wound up so abruptly. Scottish Power, for example, was reported to be trialling 200Mb/s access BPL connections to around 1,000 homes in Liverpool in 2011, partnering local house builder Plus Dane Homes to overlay broadband provision on the back of a broader smart grid initiative designed to connect smart meters in domestic premises. The power company has remained conspicuously silent on progress, but it is understood that the trial was not successful, and that the two companies are now focusing solely on the smart-meter part of the arrangement.

Of related interest elsewhere in the UK, Virgin Media partnered Surf Telecoms (a subsidiary of Western Power which owns power infrastructure reaching over 2.5 million homes in Wales and England) to offer 50Mb/s and IPTV service to a small village in Wales in 2010-11. The trial was somewhat of a hybrid approach to the broadband/power concept. It did not actually attempt to channel broadband signals through power cables – rather, it pinned fibre optic cables to electricity pylons in order to eliminate one of the biggest costs of broadband fibre provision, which is getting planning permission from local councils to dig up thoroughfares to lay the fibre optic cables. Again, no announcement as to whether the trial was successful was ever made, with Virgin Media having subsequently switched its focus to indoor BP.

Meanwhile, US telecoms firm Gridline Communications teamed up with Electricity Northwest, Cable and Wireless Worldwide and T-Systems (T-S) in the UK in 2011 to access BPL in rural village of Shap in Cumbria, but has yet to published the results of the trial nor any notice of intention for a commercial deployment.

Stumbling blocks

The same pattern of stalled or discontinued trials has become evident across the world as major providers have either limited their BPL deployments to low-bandwidth connected equipment via smart grids, or ceased BPL operations altogether. One of the world's most ambitious BPL companies, International Broadband Electric Communications (IBEC) in the US, ceased trading in January 2012, encouraging its existing customers to pursue other options for their Internet service as soon as possible.

IBEC had scored a deal with IBM to install BPL networks on power lines operated by seven US regional electricity suppliers, aiming the service at 200,000-340,000 rural homes in Alabama, Maryland, Pennsylvania, Texas, Virginia and Wisconsin – although it remains unclear how many customers were actually connected by the time the company ceased operations. (The company attributed its plight on the physical and financial damage caused by tornadoes which affected its major service areas during 2011.)

Australia too saw regional and national electricity providers such as Aurora Energy, Energy Australia, Essential Energy, and the Woomera Consortium, trial access BPL at various times between 2004 and 2007; but no active access BPL deployments appear to remain in the country.

Though the electricity companies could extend the reach of access BPL by inserting repeaters at regular intervals in the power grid to push signals further down the line, this is an expensive process – and the shaky commercial proposition presented in some geographies, notably the US, was undermined further by the need to install additional couplers and bridges in order to transmit information over transformers. The high level of attenuation (or data signal loss) from access BPL power cables – which are often unshielded – had two critical effects. First, it limited bandwidth, and second, it attracted opposition from groups within the radio community.

These included radio amateurs, shortwave broadcasters, emergency radio services, and Citizen's Band radio users. A report published in 2010 by the UK Department for Business, Innovation and Skills specifically recognised the potential for access BPL to cause interference; and after receiving 200 complaints, UK regulator Ofcom recognised the potential for interference of in-house BPL in its report 'The Likelihood and Extent of Radio Frequency Interference from In-Home PLT Devices' (June 2010), although it did not explicitly cover access BPL because 'it is not deployed commercially in the UK'. The report examined the priority for investigating the potential for interference with many different types of radio users, and identified three 'high priority' types or 'victim receivers' – shortwave radio listeners, radio amateurs, and aeronautical ground station professional users. It concluded that equipment modified to use frequency notching and power control techniques would result in a 'negligible probability of interference' in each case.

Its detractors have maintained that all forms of power-line communications cause not only interference to existing radio broadcasts using the same frequencies, but also that high levels of radioactivity in the near vicinity of access BPL lines have the opposite effect of slowing or interrupting data transmission within the power infrastructure. Similar opposition surfaced Stateside from the American Radio Relay League (ARRL) in 2010.

"We did not get into any large-scale trials, but we ran some tests and took measurements in some places," recalls the RSGB's Don Beattie. "We found that there were emissions, but that broadband signals were hugely sensitive to any form of local radio transmitter, or any other form of transmission within the spectrum of the signal being sent down the cable, and that caused the broadband signal to fail."

The RSGB estimates that each BPL device, such as an in-house power-line adapter, generates as much noise or interference as 10,000 other devices operating in the same unlicensed radio frequency bands, emissions strong and widespread enough to also interfere ADSL connections using overhead, rather than underground, telephone cables. Other complaints centred on the high levels of electromagnetic compatibility emissions caused by access BPL, suggesting that pylons and other tall structures effectively amplify the interference. Norweb trialled access BPL in Manchester during 1998/1999, using street lights near the test site that served to act as antennas for the 2-10MHz band. This reportedly caused interference to the BBC World Service, Civil Aviation Authority, and GCHQ.

The failure to properly define clear international standards for BPL technology also probably played its part in its demise. Because they used unlicensed frequencies and voltages which varied from one country to another, early standardisation initiatives were fragmented, and it was generally up to individual power companies to decide how they implemented their transmission facilities, leaving the possibility of problematic interconnection. 

Sign up to the E&T News e-mail to get great stories like this delivered to your inbox every day.

Recent articles