The woes of powerline communications

February 26th, 2018, Published in Articles: EngineerIT

Once heralded as the answer to broadband communication, the introduction of communication over powerlines had a rocky start. There was fierce opposition from radio spectrum users as it was seen as a generator of excessive interference, particularly on frequencies between 1 and 30 MHz and, in some instances, stretching into the VHF region of the RF spectrum.

Narrowband powerline communications began soon after electrical power supply became widespread. It is estimated to have first been introduced in 1922 when the first carrier frequency systems began to operate over high-tension lines with frequencies of 15 to 500 kHz for telemetry purposes. Consumer products such as baby monitors became available around 1940.

Due to the dawn of the internet and the increasing need for fast connectivity, companies realised that powerline communication could be a cost-effective method of providing broadband communication. There was a big move towards it in the USA, where is was branded as broadband powerline (BPL). Elsewhere in the world it became known as powerline communication (PLC) and powerline telecommunication (PLT). The academic world tried to differentiate between PLC as the carrier for internet and PLT as a telemetry system for powerlines, smart metering and similar remote control systems for the electricity network.

BPL/PLC/PLT  systems all work by transmitting high frequency data signals through the same power cable network used for carrying electricity power to household users. Such signals cannot pass through a transformer. This requires devices that can combine the voice and data signals with the low-voltage supply current in the local transformer stations to bridge the last mile. In homes, “indoor devices” are used to filter out the voice and data signals and to feed them to the various applications (e.g. PC, internet, telephone).

World-wide trials

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. But after numerous global trials of the technology, access BPL initiatives 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.

PLC trials have been widespread, from the UK and most European countries to the US, Australia, Egypt, Ghana, India, Indonesia, Malaysia, the Philippines, Saudi Arabia and South Africa. Despite 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 did not come close to matching ADSL, WiFi, and even 3G mobile broadband services available at the time.

Many projects ended abruptly. Scottish Power, for example, was reported to be trialling 200 Mbps access BPL connections to around 1000 homes in Liverpool in 2011. It partnered with local home-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 two companies are now focusing solely on the smart-meter part of the arrangement.

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.

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.

The demise of BPL

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

Reports of widespread interference in the radio frequency spectrum emerged in many publications. In the July 2004 edition of Elektron, the forerunner of EngineerIT in an article on PLC it was reported: “There is a worldwide concern about the introduction of power line communication because of its radio interference potential. There are many documented cases that show that interference caused by PLC systems render radio reception unusable. Some manufacturers claim that they have solved that problem and have produced newer designs that produce lower levels of interference. The Tshwane Metro is trialling (in Rooiwal) such a newer system that, according to their spokesperson, looks promising.” Once interference studies were carried out, the Rooiwal trial was abruptly stopped.

Fig. 1: A street installation of the Rooiwal PLC trial at the base of an electricity pole.

PLC was heavily debated in SABS TC 73 committee on EMC which led to the publication of draft PLC regulations by ICASA on 7 February 2008 (Government Gazette 30752). It resulted in a large number of comments, proposals for amendments, and objections. The regulations were never finalised and today remain in draft  form.

PLC never took off as a broadband access technology. Is it completely dead? No, the technology is used in devices like HomePlug used in homes and small offices to extend WiFi systems by using the mains wiring. It is a standard of the HomePlug Alliance that was established in 2000. The latest version of HomePlug is AV2 that uses OFDM over the frequency range of 2 MHz to 86 MHz on the AC line. Using modulation to 4096QAM it can achieve a raw data rate to 1 Gbps or 500 Mbps considering overheads. This is useful for transporting HD video in the home.

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