BPL - Broadband over Powerline
*** see also http://www.powerline-plc.com
BPL enables Internet access via your home power sockets, with a maximum speed of about 2 Mbps. The idea is that you plug your PC into your wall socket - and that's it !! You're powered up . . . and connected. This is a new technology with a huge potential for the future. Because electricity lines run into virtually every room of every home and business, BPL can deliver broadband to many areas where cable or DSL simply cannot reach, or cannot reach economically. However . . . a controversy has ensued, because BPL causes RFI (Radio Frequency Interference). More on that later.
Although the standard is incomplete - a number of BPL trials are underway, and they’re already rolling out commercial BPL services in Cincinnati, Allentown, Pa., and Raleigh, N.C. Big power companies like Cinergy in Ohio, PPL in Pennsylvania and Progress Energy in North Carolina, for example, are teaming up with EarthLink and private BPL providers like Current Technologies and Amperion to offer BPL in test markets. Users connect their computers to power lines outside their homes in two ways:
PCL & BPL - the overall concept of data through power lines is known as PCL (Power Line Communications). BPL is actually a subset of PCL. PCL includes three major areas:
IEEE BPL Standard - IEEE is in the process of finalizing a standard, P1675, for the technology and they have named it BPL (Broadband over Powerline). Here is a snippet from the IEEE P1675 Announcement:
The Power Grid Conversion - BPL's basic physical infrastructure was already in place before the technology was even developed. Everyone has power lines to their home . . . and if you add Internet access to those lines . . . then everyone has Internet access. Sound familiar ?? About 10 years ago, almost everyone had a cable TV line to their home. The cable companies began converting those one-way transmission lines to 2-way, and added a carrier signal for Internet access. As with any huge infrastructure conversion, this was a major undertaking. Similarly, with BPL, even though the power lines are there, and in place . . . the process of adding Internet access to those lines is cumbersome and expensive.
BPL, WiFi, and BPL/WiFi Hybrid Networks - many feel that the cost associated with BPL is not worth it when considering the WiFi alternative. Other companies rolled out BPL, only to conclude that the last mile portion was too expensive, and they created a hybrid network, with WiFi to the residences, and BPL running over the medium and low voltage transmission lines.
The BPL Controversy (HF interference)
Since BPL requires high frequencies to run across low frequency (60 Hz) power lines, it is a source of interference, particularly with the Ham Radio (Amateur Radio) HF bands. This has caused quite a controversy, between the BPL supporters (the big corporations and IEEE) and the HAM radio hobbyists (see the "STOP BPL" website). Their claim is summarized, as follows:
"anyone listening to radio frequencies from VLF up to lower VHF (and possibly higher) will hear a loud noise on their radio receiver similar to the following list. (depending on the BPL system it will sound either like a Geiger counter; noisy carrier waves turning on and off very rapidly; or it will sound like a dial-up modem connecting to a phone line). (For some BPL/PLC sound examples please click here, here, here or here!!)
This sound is permanent and it does not just hit one radio frequency, it wipes out many radio frequencies at one time, in fact, the more BPL users are on-line using the electricity cable for broadband internet, the more radio frequencies will be in use."
Many BPL trials have failed, due simply to the interference. As a recent example, a BPL trial in Cedar Rapids, Iowa ended prematurely, after the location had been a hotbed of complaints over interference issues.
Bottom line, the detractors feel that it's a bad idea and that the only reason it has not been scrapped altogether, is that the BPL folks have invested heavily and want their money back !! Of course, there is little doubt who will win this battle, since the FCC and even President Bush are backing BPL !!.
How it Works
A computer-router combination and a coupler take the signal from an optical fiber cable as it enters a substation and imposes it on the electric current. The signal travels over the medium-voltage lines, with repeaters placed every 0.5 to 1 mile to keep the signal viable.
The customer plugs a small, off-the-shelf, inexpensive "powerline" modem into any wall outlet in the home or business. That modem easily connects to a user's computer via a standard USB or Ethernet cord, or even using a wireless fidelity, or "WiFi," connection.
A signal from the consumer's computer travels the through the consumer's powerline modem, over the 120 volt premises wiring and "low voltage" electricity wire outside the home or business toward the utility company's "step-down" transformer. The utility uses transformers for power, to convert the medium voltage (e.g., 10,000 or more volts) electricity that runs down the street from one of its distribution substations to the 120 volts that can safely come into homes and businesses. THEY DO NOT USE TRANSFORMERS WITH BPL !! In fact, the transformers must be avoided by the BPL signal.
The transformer will not allow digital signals to pass because they contain high frequencies. Transformers are inductors, and inductors present a huge resistance to high frequencies. The workaround is to install special equipment, called a "coupler", that bypasses the transformer. The primary, low frequency, 60 Hz power flow is unaffected, while the BPL (Internet) signal is intercepted on both sides of the transformer, and injected back into the line on the other side. Each company uses their own bypass device, and many are proprietary and non-standard.
The coupler "couples" the two transformer lines together (the high voltage and the low voltage lines) - and allows the BPL signal to bypass the trancformer.
BPL Data Flow Example
- downstream data flow (to the customer):
the downstream Internet signal is received from fiber hookups by a router
the data signal is superimposed (modulated) onto high voltage lines, and becomes a BPL signal
when the BPL signal reaches the High/Low voltage transformer - the bypass device takes data from the high voltage line, reshapes and amplifies it (i.e. signal regeneration), and then modulates it onto the signal at the medium voltage line on the other side of the transformer
the BPL signal on the medium voltage line travels down the wires to an aggregation point
the BPL signal is extracted from the medium voltage wires
then one of two methods are used for the final endpoint:
Method 1 (true BPL) - a bypass device transfers the data from the medium voltage line, to the low voltage customer line. This signal is then available at the customer's wall sockets throughout their home, giving them Internet access.
Method 2 (Hybrid) - a special router converts the medium voltage BPL signals into traditional IP communications packets and they are sent along copper, fiber, or wireless to the customer. This method typically employs WiFi.
Transformer Problem Explained
One of the biggest challenges to BPL, was how to get a digital signal to go through voltage transformers. To counter line loss, the power utilities send out electricity at high voltages. Then just before the power enters the residence, a transformer reduces it down to approximately 110-120 volts AC. But transformers are inductors, and inductors increase their resistance to electricity as a function of frequency. Since a square wave (digital) has sharp edges, it requires very high frequencies. The transformer resistance to these square waves is very high, and would block them altogether (i.e. filter them out). Therefore the transformers simply must be excluded !! What is not shown in the above diagrams is that there is a device that takes the signal from one side of the transformer - and copies it to the other side . . . thereby bypassing the transformer altogether.
A repeater/router near a residence or business extracts the signal off the medium voltage just before the transformer and injects it onto the low-voltage wiring on the other side of the transformer. The signal is now on all of the low voltage wiring within the structure and can be accessed at any outlet by plugging in a modem.