What is powerline technology PLT?

In the 1930s, ripple carrier signalling was introduced on the medium (10-20 kV) and low voltage (240/415V) distribution systems. For a many years the search has been going on for a cost effective bi-directional technology suitable for applications such as remote meter reading. For example, the Tokyo Electric Power Co was running experiments in the 1970’s which reported successful bi-directional operation with several hundred units . Since the mid-eighties there has been a surge of interest in using the potential of digital communications techniques and digital signal processing. The drive is to produce a reliable system which is cheap enough to be widely installed and able to compete cost effectively with wireless solutions. The narrowband powerline communications channel presents many technical challenges. A mathematical channel model and a survey of work can be found in reference no. 5.