Broadband over power lines

Broadband over power lines (BPL) is a method of power-line communication (PLC) that allows relatively high-speed digital data transmission over the public electric power distribution wiring. BPL uses higher frequencies, a wider frequency range and different technologies compared to other forms of power-line communications to provide high-rate communication over longer distances. BPL uses frequencies that are part of the radio spectrum allocated to over-the-air communication services; therefore, the prevention of interference to, and from, these services is a very important factor in designing BPL systems.

History

BPL is based on PLC technology developed as far back as 1914 by US telecommunications company AT&T. 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. More recently there have been attempts to implement access BPL, or the provision of internet services to customers via the grid. The prospect of BPL was predicted in 2004 to possibly motivate DSL and cable operators to more quickly serve rural communities.

The high level of attenuation (or data signal loss) from access BPL power cables had two critical effects:
First, a request to increase signal levels was opposed by groups within the radio community (DOD, FAA, FEMA, amateur radio) that had already documented significant interference. Second, the data rate was greatly reduced when a robust error correction code was added.

Implementation

Generally BPL is described as either In-House BPL to network machines within a building (including power line-based WiFi extenders), or Access BPL which will carry broadband Internet using power lines and allow power companies to monitor power systems.

Because electric current and radio (data) signals oscillate at different frequencies they do not interfere with each other enough to significantly disrupt data transmission.

Medium voltage (MV) lines carry generally up to a few tens of kilovolts, over a few kilometres between the electricity distribution stations and pole-mounted transformers. Low voltage lines transmit a few hundred volts over a few hundreds of metres, usually from pole-mounted transformers into a home or business.

Typically modem couplers embed data signals on to MV lines at the substation, with extractors at the LV distribution transformer feeding power into a group of buildings.

BPL 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 fixed wireless.

Utility companies use frequencies below 490 kHz for their own data applications. Most BPL equipment was built to operate between 1.7 MHz and 30 MHz and occasionally up to 80 MHz.

Technical challenges

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 second major issue is electromagnetic compatibility (EMC). The system was expected to use frequencies of 10 to 30 MHz in the high frequency (HF) range, used for decades by military, aeronautical, amateur radio, and by shortwave broadcasters. Power lines are unshielded and will act as antennas for the signals they carry, and they will cause interference to high frequency radio communications and broadcasting. In 2007, NATO Research and Technology Organisation released a report which concluded that widespread deployment of BPL may have a "possible detrimental effect upon military HF radio communications."

Deployments

There have been many attempts worldwide to implement access BPL, all which have indicated that BPL is not viable as a means of delivering broadband Internet access. This is because of two problems: limited reach, and low bandwidth which do not come close to matching ADSL, Wi-Fi, and even 3G mobile. World major providers have either limited their BPL deployments to low-bandwidth connected equipment via smart grids, or ceased BPL operations altogether.

Australia saw trials of access BPL between 2004 and 2007; but no active access BPL deployments appear to remain there.

In the UK, the BBC
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