Architecture of powerline communication (PLC) devices

Indoor architecture

Homeplug is the PLC solution in commercial use today for indoor installations, these are ideal for extending a local area network and sharing existing broadband Internet access, mainly for domestic or small business use, with easy installation. PLC units usually come with an ethernet or USB port and an electrical plug.

Minimum requirements for Indoor PLC installation are a PC with either an Ethernet card or a USB port depending on the model. Check for the availability of drivers for specific operating systems (for USB versions).

• Setting up an Ethernet unit is similar to installation for a local Ethernet cable network.
• Setting up a USB unit is done using the supplied drivers, a virtual network adapter is then configured just like an Ethernet local area network adapter.

At the electric level, the installation does not pose any concerns inside a housing behind a single-phase current meter insofar as the adapters connect directly to the electrical plugs. On the other hand installation is more complex for large buildings, than it is for homes, with a three-phase entrance point and various meters, or in large buildings such as colleges, hospitals or administrative buildings. The setting up of a "wide area" PLC solution requires a two-fold skillset: expertise in electrical supply network and computer networking, as well as the use of hardware different from the Homeplug units sold for the indoor market.

The widespread solution currently on sale, Homeplug, has a theoretical bandwidth of 14Mbps. Other solutions also exist with bandwidth ranging from 2Mbps to 45Mbps. A 100Mbps solution has been laboratory tested.

Real bandwidths are reduced by the overhead required for management of the system. However, the available bandwidths are sufficient for the majority of domestic applications taking the Homeplug rate of 14Mbps as an example.

PLC network security

Role of the electric phase: the signal passes along the phases by induction, but the signal is rapidly weakened from one phase to the next. Role of the electricity meter: the PLC signal passes through the electricity meter, this does not however cause any barrier for the PLC network.

Local area network security: any PLC network must be protected like any other local area network, through the installation of a firewall, however there are two intrinsic levels of security in PLC equipment:

• a DES encryption (using a 56 or 128 bit key)
• the possibility of setting up separate networks on the same electric circuit with two different encryption keys that can be configured using software usually provided with the equipment.

Outdoor architecture

Experiments are ongoing for external installations, with a link between Broadband Internet and the electrical mains network via a HTA/BT transformer creating a local electric loop.

Pros and cons

Advantages of PLC:

• Mobility
• Flexibility
• Ease of installation for indoor setup
• Stability
• Complements both cable and wireless solutions

Disadvantages of PLC:

• Installation and high performance depend on the architecture of the electrical network
• Lack of standards and guidelines
• Interoperability problems with various types of equipment.
• Current price, market needs to be developed

Conclusion

PLC solutions may be seen as complementary or alternative solutions to traditional fixed line networks, wireless networks and VDSL networks.

According to existing network architectures, buildings or technical constraints, either solution can be chosen, but one can also consider one solution to complement another!

PLC bandwidths are set to increase, the Hompelug AV standard is being considered for broadcasting digital television.

Many research projects are ongoing into these solutions and their applications, it is all to come, one should pay close attention to news about this technology!

Written by Françoise Cacciaguerra – November 2003