Working Group on Power Line Communications

PLC (Power Line Communications) technology consists in the utilization of power lines as a transmission medium. Actually, this technology exists since long time ago, although, it was restricted to low bit-rate applications of utility companies, mostly focused on the control and management of their distribution networks. However, at the Nineties, two interesting applications boosted the interest for this technology:

1. Internet access. The utilization of the low voltage power network as a last mile solution, that is, to integrate power lines as the access part of a WAN (Wide Area Network). PLC technology is a good opportunity to offer internet, telephone and television services, especially in non-developed countries or in isolated areas in industrialized countries.

2. Home networking. The use of power lines as a LAN (Local Area Network) at homes and small offices. The objective is not only to interconnect PCs, but also multimedia equipment like TV and recorders/players using only their power cables.

Our group has put their effort in the second application. In home networking, the use of the power grid presents a valuable advantage against some other wired systems: it is already installed wherever a communication equipment is used. Regarding wireless technologies, PLC offers a better signal quality and more capacity, so that the common lack of coverage of WiFi networks can be avoided. Moreover, the bit-rate that current PLC modems provide is much higher than the one given by WiFi.

Nowadays, PLC systems are complementary to other technologies like ADSL. Actually, there are many telecom providers that offer to their customers PLC modems to distribute their signal inside homes. This application is usually known as the triple play, that is, to cast the signals for telephone, digital television and internet that comes from the ADSL modem/router into the whole dwelling by means of PLC modems.

PLC systems can also become an opportunity to complement wireless systems by serving as a backbone that connects different transceivers or base stations in the rooms, what extends their coverage.

Simultaneously, the use of the existing in-vehicle power lines for communication purposes, the so-called in-vehicle power line communications (PLC), is attracting considerable attention in the last years. It provides several benefits. Firstly, reduces the cost of the wiring itself and of its installation. Secondly, it allows the plug and play idea for the implementation of aftermarket systems, e.g. nowadays, installing additional fog lights requires drilling holes in the fire wall that separates the engine and passenger cabin. And finally, it allows reducing the vehicle’s weight, which in turns reduces the energy consumption. During the last two years our group has been investigating in this scenario, by means of a project publicly funded. In a first instance, our efforts have concentrated on channel characterization. However, at this stage, we have already started transmission techniques studies. The following video (in spanish), broadcasted in the Andalusian TV Canal Sur 2, shows a brief description of this application. The QuickTime plugin is required to watch the video. You can download it from here.

PLC systems comprise at least a pair of modems with two interfaces: on one side, they are plugged in the sockets at home or office (this interface share both the supply and the transmission link) and, on the other side, they have an Ethernet or USB interface to which connect our computer or multimedia player.

The transmission technique mostly employed in PLC is the multicarrier modulation OFDM (Orthogonal Frequency Division Multiplexing, or DMT, Discrete Multitone), the one also used in other applications like ADSL, DVB, fourth generation mobile telephony (LTE), etc.

Currently, the frequency band used in PLC extends from 1 MHz and 30 MHz, approximately, although an extension up to 200MHz it is expected. Due to electromagnetic compatibility reasons, there are banned sub-bands to avoid creating interference to other telecommunications systems like amateur radio or broadcasting.