Broadband over power lines: Difference between revisions

Broadband over power lines (BPL) is a method of power line communication that allows relatively high speed digital data transmission over the public electric power distribution wiring. BPL uses different technologies from other forms of power-line communications to provide high-rate communication over long distances. BPL uses parts of the radio spectrum allocated to other over-the-air communciation services. Interference to, and from, these services is a limiting factor in the introduction of BPL systems.

While some have been in widespread use for a decade, integrated circuits implementing one standard were introduced in May 2011.

Applications

Internet access

Internet access service through existing power lines is often marketed as broadband over power lines (BPL), also known as power-line Internet or powerband. A computer (or any other device) would need only to plug a BPL modem into any outlet in an equipped building to have high-speed Internet access. International Broadband Electric Communications or IBEC and other companies currently offer BPL service to several electric cooperatives.

Smart grids and use of BPL by power companies

Power providers are also standardizing their internal and external communications including use of BPL technologies to provide direct links to power system components like transformers. In North America another IEEE standard group is supervising these activities.

Unlike home users, power providers are more able to consider widespread deployment of fiber optic cables immune to electromagnetic interference (and which do not generate any) and for which mature devices (switches, repeaters) are available. Accordingly there is no one single compelling reason to carry data on the existing power lines themselves as there is in homes, except in remote regions where fibre optic networks would not normally be deployed at all. Power network architectures with many transformers are more likely to be served using fibre.

Even if a home is using BPL it may not necessarily connect to the Internet using a BPL-based gateway (typically a smart meter), although this would have major advantages to both the consumer and provider. NIST and IEEE have considered whether requiring smart meters to all be fully functioning BPL gateways would not accelerate demand side management and create a uniform market into which security, home control and other providers can sell.

Application concerns

BPL may offer benefits over regular cable modem or digital subscriber line (DSL) connections: the extensive infrastructure already available appears to allow people in remote locations to access the Internet with relatively little equipment investment by the utility. Cost of running wires such as Ethernet in many buildings can be prohibitive; Relying on wireless has a number of predictable problems including security, limited maximum throughput and inability to power devices efficiently.

But variations in the physical characteristics of the electricity network and the lack of standards mean that provisioning of the service is far from being a standard, repeatable process. And, the bit rate a power line system can provide compared to cable and wireless is in question. The prospect of BPL was predicted to possibly motivate DSL and cable operators to more quickly serve rural communities.

PLC modems transmit in medium and high frequency (1.6 to 80 MHz electric carrier). The asymmetric speed in the modem is generally from 256 kbit/s to 2.7 Mbit/s. In the repeater situated in the meter room the speed is up to 45 Mbit/s and can be connected to 256 PLC modems. In the medium voltage stations, the speed from the head ends to the Internet is up to 135 Mbit/s. To connect to the Internet, utilities can use optical fiber backbone or wireless link.

Deployment of BPL has illustrated a number of fundamental challenges, the primary one being that power lines are inherently a very noisy environment. Every time a device turns on or off, it introduces a pop or click into the line. Switching power supplies often introduce noisy harmonics into the line. And unlike coaxial cable or twisted-pair, the wiring has no inherent noise rejection. The system must be designed to deal with these natural signaling disruptions and work around them. For these reasons BPL can be thought of as a compromise between wireless transmission (where likewise there is little control of the medium through which signals propagate) and wired transmission (but not requiring any new cables).

Broadband over power lines has developed faster in Europe than in the United States due to a historical difference in power system design philosophies. Power distribution uses step-down transformers to reduce the voltage for use by customers. BPL signals cannot readily pass through transformers, as their high inductance makes them act as low-pass filters, blocking high-frequency signals. So, repeaters must be attached to the transformers. In the U.S., it is common for a small transformer hung from a utility pole to service a single house or a small number of houses. In Europe, it is more common for a somewhat larger transformer to service 10 or 100 houses. This makes little difference for power distribution. But delivering BPL in a typical U.S. city requires an order of magnitude more repeaters than in a comparable European city. On the other hand, since bandwidth to the transformer is limited, this can increase the speed at which each household can connect, due to fewer people sharing the same line. One possible solution is to use BPL as the backhaul for wireless communications, for instance by hanging Wi-Fi access points or cellphone base stations on utility poles, thus allowing end-users within a certain range to connect with equipment they already have.

The second major issue is signal strength and operating frequency. The system was expected to use frequencies of 10 to 30 MHz, which has been used for many decades by amateur radio operators, as well as international shortwave broadcasters and a variety of communications systems (military, aeronautical, etc.). Power lines are unshielded and will act as antennas for the signals they carry, and they will interfere with shortwave radio communications. Modern BPL systems use orthogonal frequency-division multiplexing (|OFDM), which allows them to mitigate interference with radio services by removing specific frequencies used. A 2001 joint study by the American Radio Relay League (ARRL) and HomePlug Powerline Alliance showed that for modems using this technique "in general that with moderate separation of the antenna from the structure containing the HomePlug signal that interference was barely perceptible at the notched frequencies" and interference only happened when the "antenna was physically close to the power lines" (however other frequencies still suffer from interference). What the effects of large scale deployment on PLT modems in house will do to the notching has still to be defined, however in lab tests the notches appear to fill in due to intermodulation between modems.

Failure scenarios

There are many ways in which the communication signal may have error introduced into it. Interference, cross chatter, some active devices, and some passive devices all introduce noise or attenuation into the signal. When error becomes significant the devices controlled by the unreliable signal may fail, become inoperative, or operate in an undesirable fashion.

1. Interference: Interference from nearby systems can cause signal degradation as the modem may not be able to determine a specific frequency among many signals in the same bandwidth.
2. Signal Attenuation by Active Devices: Devices such as relays, transistors, and rectifiers create noise in their respective systems, increasing the likelihood of signal degradation. Arc-fault circuit interrupter (AFCI) devices, required by some recent electrical codes for living spaces, may also attenuate the signals.
3. Signal Attenuation by Passive Devices: Transformers and DC-DC converters attenuate the input frequency signal almost completely. "Bypass" devices become necessary for the signal to be passed on to the receiving node. A bypass device may consist of three stages, a filter in series with a protection stage and coupler, placed in parallel with the passive device.

Ultra-High-frequency (≥100 MHz)

Even higher information rate transmissions over power line use RF through microwave frequencies transmitted via a transverse mode surface wave propagation mechanism that requires only a single conductor. An implementation of this technology is marketed as E-Line. These use microwaves instead of the lower frequency bands, up to 2-20 GHz. While these may interfere with radio astronomy [3] when used outdoors, the advantages of speeds competitive with fibre optic cables without new wiring are likely to outweigh that.

These systems claim symmetric and full duplex communication in excess of 1 Gbit/s in each direction. Multiple Wi-Fi channels with simultaneous analog television in the 2.4 and 5.3 GHz unlicensed bands have been demonstrated operating over a single medium voltage line conductor. Because the underlying propagation mode is extremely broadband (in the technical sense), it can operate anywhere in the 20 MHz - 20 GHz region. Also since it is not restricted to below 80 MHz, as is the case for high-frequency BPL, these systems can avoid the interference issues associated with use of shared spectrum with other licensed or unlicensed services.

Government promotion and regulation

US FCC

On 14 October 2004, the U.S. Federal Communications Commission adopted rules to facilitate the deployment of "Access BPL", the marketing term for Internet access service over power lines. The technical rules are more liberal than those advanced by the US national amateur radio organization, the American Radio Relay League (ARRL), and other spectrum users, but include provisions that require BPL providers to investigate and correct any interference they cause. These rules may be subject to future litigation. One service was announced in 2004 for Ohio, Kentucky, and Indiana.

On 3 August 2006 FCC adopted a memorandum opinion and an order on broadband over power lines, giving the go-ahead to promote broadband service to all Americans. The order rejected calls from aviation, business, commercial, amateur radio and other sectors of spectrum users to limit or prohibit deployment until further study was completed. FCC chief Kevin Martin said that BPL "holds great promise as a ubiquitous broadband solution that would offer a viable alternative to cable, digital subscriber line, fiber, and wireless broadband solutions".

'Notching out' and dynamic adaptation to contention

New FCC rules (and the IEEE standards) require BPL systems to be capable of remotely notching out frequencies on which interference occurs, and of shutting down remotely if necessary to resolve the interference. BPL systems operating within FCC Part 15 emissions limits may still interfere with wireless radio communications and are required to resolve interference problems. A few early trials were shut down, though whether it was in response to complaints is debatable. The need to deal with signals that inevitably will propagate through thick metal wires hanging above crowded areas was always an issue in BPL standardization and the technologies to resolve it are those already used for wireless, so the issue was primarily one of thresholds and agreement on who had priority for spectrum.

In the US, simply ignoring wireless users was apparently not legal. The ARRL sued the FCC, claiming that the FCC violated the Administrative Procedure Act in creating its rules. On 25 April 2008, a US Court of Appeals agreed with the ARRL that the FCC violated the APA, especially by redacting data from the public that could have shed doubt on the FCC's decision.

"It is one thing for the Commission to give notice and make available for comment the studies on which it relied in formulating the rule while explaining its non-reliance on certain parts", D.C. Circuit Judge Judith Rogers wrote. "It is quite another thing to provide notice and an opportunity for comment on only those parts of the studies that the Commission likes best."

US power and telecommunications companies had meanwhile started tests of the BPL technology, over the protests of the radio groups. After claims of interference by these groups, many of the trials were ended early and proclaimed successes, though the ARRL and other groups claimed otherwise.

Some of the same providers conducting those trials later began commercial roll-outs in limited neighborhoods in selected cities, with some level of user acceptance but also many documented cases of interference reported to the FCC by amateur radio users. Some wireless users filed a petition for reconsideration with the FCC in February 2005.

In 2010, the AARL posposed a required 35 dB "notch depth".

United Kingdom and Europe

In the United Kingdom and many other countries, power line communication is often called power line telecommunication (PLT). Concern of radio users about the proliferation of PLT technology was acknowledged by the European Commission who, in August 2001 issued a Harmonised Standard. A Harmonised Standard can be used by manufacturers to demonstrate compliance with the Electromagnetic Compatibility (EMC) Directive (but is not mandatory) and will act as a benchmark for enforcement authorities across Europe.

The UK communications regulator Office of Communication commissioned a study into PL, published in June 2010.

Ofcom also investigated alleged complaints of interference attributed to PLT apparatus. Complaints are from radio amateurs, CB radio users and shortwave listeners and are normally [httpresolved]. No other radio service has been affected.

The independent study said it was "important that mitigating features are implemented in future PLT devices." Newer PLT products adopted interference mitigation in their design.

An ‘adjournment debate’ on PLT took place on 18 May 2011, Mark Prisk (Minister for Business and Enterprise) responded on behalf of the government to a question tabled by Mark Lancaster) the adjournment debate can be viewed here, the transcript is here.

A draft European Standard (FprEN 50561-1) for PLT has been developed by CENELEC.

The Electromagnetic Compatibility Industry Association (EMCIA), formed in March 2002 for the benefit of companies involved in the supply, design, test or manufacture of EMC products, or the provision of EMC Services and is a UKTI Accredited Trade Organisation, submitted a stern report to the Parliamentary Committee overseeing broadband, stating that they "..very strongly recommend that the Committee specifically excludes the use of PowerLine Telecommunication (PLT*)..."

The Radio Society of Great Britain is extremely concerned over PLT and has established a Spectrum Defence Fund.

Other governments

Austria, Australia, New Zealand and other locations have also experienced early BPL's so-called "spectrum pollution" and raised concerns within their governing bodies. In the UK, the BBC has published the results of a number of tests (The effects of PLT on broadcast reception,PLT and Broadcasting, Co-existence of PLT and Radio Services) to detect interference from BPL installations. It has also made a video (Real Media format), showing broadcast of data and interference from in-home BPL devices.

In April 2009 the Wireless Institute of Australia reported that radio amateurs in Australia appear to be safe from the rollout of a nationwide Broadband over Powerline or BPL system. Australia's government announced that it will be building a system based on fibre optic technology for its backbone - though it would likely still rely on BPL on high-voltage lines in remote areas. This decision would appear to remove the possibility of widespread interference to radio communications from any network-wide adoption of BPL technology, but still leaves as a concern the possibility of interference from in-home use of G.hn over AC.

In June 2007, NATO Research and Technology Organisation released a report titled HF Interference, Procedures and Tools (RTO-TR-IST-050) which concluded that widespread deployment of BPL may have a "possible detrimental effect upon military HF radio communications and COMINT systems."

See also

• Broadband