What is PLC?

        The main idea of powerline communications (PLC) is the usage of electrical grids.  PLCs are extremely important because they would allow for a network to be set up on existing infrastructures.  This is needed because 50% of investments for telecommunication access networks are needed for building the hardware.  Also, the usage of existing infrastructures does not only reduce cost, but also reduces the amount of time until the system is fully functional.  DSL and cable are two other methods of establishing network connections through existing communication lines. 

        In the case of a PLC access system a low-voltage power supply network is used for the connection of end-users/subscribers to a communication network.  There is a number of subscribers in a low-voltage electrical power supply network who have to share the transmission capacity of a PLC access network.  Therefore a high gross data rate on the medium is necessary to ensure a sufficient Quality of Service (QoS), making PLC systems competitive to other access technologies.

        PLC networks have to work with a limited signal power that makes PLC systems more sensitive to disturbances from the electrical power supply network and from the PLC network environment.  Error handling can correct these disturbances, ut will add overhead and decrease the already limited data rates of PLC systems.

Network Structure

        The communication between the users of a PLC network and a wide area network is carried out over a base station, usually placed in a transformer unit.  (Fig. 1)  The base station is also used for internal communications between users of a PLC network, so there are two transmission directions:

                            1.  Downlink - transmission from base to the network users

                            2.  Uplink - transmission from each user to the base

BUS LIKE CHARACTERISTIC:  Downlink and uplink transmissions are broadcasted to all users on the PLC network, which means that the networks holds a logical bus structure.

Planning of the PLC Access Networks

                            1.  Maximize number of subscribers to be connected to a PLC network providing a sufficient QoS.

                            2.  Specification of QoS to be guaranteed by a PLC provider and design of a suitable service offering

                            3.  Network utilization and network economic efficiency 

        PLC networks have to provide a very good network utilization keeping also a sufficient QoS that can only be reached by using efficient methods for the network capacity sharing - Media Access Control (MAC) protocols.