Broadband over power line, also called power line communications, refers to communicating over the existing aluminum and steel wire network, built by the power industry to provide electricity to businesses and homes, by transmitting data at medium and high frequencies. In the US, electric power is transmitted as a 60 Hz signal at various voltages over varying sized wires to our homes and businesses . BPL introduces the concept of communicating information over medium voltage lines, around 12 – 64 kilovolts, at frequencies excluding 60 Hz, typically 1.6 – 30 MHz . This technique allows broadband Internet service to be provided to anyone connected to the electric grid. The power grid network far surpasses the existing high-speed telecommunications network in the US. Using OFDM, BPL can deliver theoretical speeds of up to 130 Mb/s from end users to the nearest power substation .
BPL works by incorporating the utility companies into the telecommunication loop by running higher-speed connections, typically fiber, to substations throughout a designated area and having those substations serve users via the power lines. Multiplexing and de-multiplexing equipment is then installed into the substation to allow the transmission of the data onto the power lines leaving and entering the station . The customers will also need hardware equipment on their end, but it will be on a smaller scale, typically the same size and functionality of a DSL or cable modem. In addition to multiplexing, impedance matching must be considered and plays an important role in the transmission rate and noise generation of the line. An impedance matching technique was developed using a ferrite toroidal core and a flat cable to create a matching transformer with one of the following impedances: 75 Ω, 200 Ω, 300 Ω, 460 Ω, and 800 Ω . Figure 4 shows a BPL network for a typical residential area with few businesses.
BPL has to overcome the “harsh” environments associated with the noise and chaos on the electrical grid. Large industrial customers introduce this noise to the line because of the abrupt changes in loads when powering on or off their equipment.
For example, when a steel mill is turned on, it produces very disruptive noise onto the power line due to the abrupt change in voltage and current in the mill. This effect can cause the lights to flicker in a residential house several miles down the road. Similarly, this makes it difficult, maybe impossible, to decode a communications signal and retain the transmitted data within a given window of time. Any additional noise on the power line will decrease the overall achievable transfer rates 
Source: Connecting the “Last Mile”: A Comparison
Among Fiber-to-the-Home (FTTH), WiMax,
and Broadband over Power Line (BPL)
Blake Brannon, Georgia Institute of Technology