Among the options available for enabling a home network without having to install new wires, both wireless and powerline communications stand out for their ubiquity. Powerline communications enables a broadband connection to be sent anywhere in a home by using the existing electrical wiring available in every room.

Powerline communications can work regardless of the back-haul technology used to provide a broadband connection. As long as a broadband connection is available, powerline technology can be used to extend this connection to any socket inside a house.

For example, Internet protocol television (IPTV) services, where the technology used for the back-haul technology is xDSL-based, uses powerline communications to create a secure home network. In this case, service providers need a cost-effective and easy-to-use solution to connect a set-top box, located next to a television set, to the broadband modem, which is usually located in a different room somewhere in the house.

Similarly, cable companies are also using powerline communications for broadband extension when the data rate and stability requirements are higher than those offered by wireless technology.

In this case, the back-haul technology used by cable companies is DOCSIS-based. As a result, powerline technology is gaining traction as the preferred solution to extend the service provider's network into the subscriber's home and to guarantee the quality of experience required for a competitive service offering.

Typically, the broadband connection is fed through a powerline adapter, which can be plugged into any socket in the house. By doing this, all the remaining sockets in the house automatically become an interface to the home network.

Every electrical point in the home can now pick up a video stream, digital audio, digital data or a live Internet connection, instantly and without interruptions. By simply connecting a pair of adapters to any existing socket in the house, a home network is created in a matter of seconds.

Powerline communications technology uses electrical wiring for high-speed transmission of data. It is a more competitive solution to the connectivity problem faced by many applications than other wired solutions or wireless technologies. It has the capability of offering the data rate, performance, flexibility, reliability and cost-efficiency required to support whole-home multimedia networking.

The electrical wiring used by powerline communications for data transmission is considered to be a harsh and unfriendly environment and one of the most difficult communications channels. It is a channel known for real-time variations, impulsive and periodic noise sources, sudden impedance changes and several bifurcations creating reflections and other undesirable effects.

OFDM: Modulating the powerline
Most powerline communications technology implements advanced OFDM (Orthogonal Frequency Division Multiplexing) modulation, a scheme that overcomes most channel difficulties to achieve high data rates while keeping power transmission levels low.

OFDM was selected as the most suitable modulation scheme for the powerline channel in particular because it is:

1) The most immune to interference, being able to cope with severe changes in channel conditions;

2) Provides the highest level of spectral efficiency and performance.

Several leading powerline communications technology providers use OFDM modulation based on the simultaneous transmission of more than one thousand carriers over a frequency band of 30MHz, usually starting at 2MHz and ending at 32MHz. The data to be transmitted is divided between all sub-carriers which are independently modulated based on the available SNR of the channel.

A number of bits are assigned to each sub-carrier depending on the situation in the communications channel at that very instance. SNR measurements are continuous and the OFDM signal changes the bit loading to adapt to any changes in the channel instantaneously, avoiding line errors (by decreasing the bits/carrier), or increasing efficiency (by increasing the bits/carrier).

One of the great advantages of some OFDM implementations is that the signal strength and the frequency spectrum used are fully adaptable and configurable. This means that commercial products can be tuned, taking into account any type of regulation either by adding notches to allow for coexistence with Radio Amateur signals, reducing the signal strength or limiting the frequency spectrum that is used.

At the same time, powerline communications uses some of the most advanced forward error correction (FEC) algorithms. These algorithms enable semiconductor vendors to add redundant bits to every data frame and thus allow for the information recovery to be possible even with the presence of errors in received frames.

Similarly, most noise sources found in the electrical network are synchronous to the ac cycle, which allows powerline communications technology vendors to design synchronous algorithms to improve performance. Synchronizing to the ac cycle and not transmitting when a known noise source will be present ensures that block errors are minimized and higher effective data rates are achieved.

All these very complex algorithms and their corresponding silicon implementations are required to transmit in one of the most complex mediums if high data rates, in the order of 200+Mbit/s data rates, are desired.

The best of wired and wireless
Powerline combines the best of wired and wireless connections. Consumers have a fast, reliable and secure connection, anywhere in their home. Since transmissions are sent over a wired medium, lower latencies can be achieved benefiting real-time streaming applications like VoIP and IPTV and interactive services.

The powerline connection does not experience interference from 'line of sight' issues, because it is a direct connection to every outlet within the home. At the same time, it also has strong encryption and a push-button secure network configuration to enable a secure data connection.

Wireless can offer benefits as well, though. Like powerline, it does not require any additional wiring and can extend a broadband signal through the house. However, it is less stable and secure and the level of bandwidth that it can deliver also limits it. It rarely has the capability to deliver triple play services (video, voice and data) simultaneously. Another limiting factor for wireless technology is full coverage.

Every time a wireless signal encounters an obstacle, signal strength is lost. This means that full coverage can be a problem depending on the construction materials used and the size of the house. Powerline technology can help improve wireless coverage by acting as a backbone for wireless connectivity increasing coverage and available data rates.