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Power up your digital home

Posted: 04 Feb 2009 ?? ?Print Version ?Bookmark and Share

Keywords:digital home? home network? powerline technology?

Today's home networking applications, which include gaming and high-definition (HD) video streaming across all rooms of the home, put high demands on existing home networks, and not just in terms of connectivity, but also in QoS.

This, in conjunction with consumer expectations of zero latency in every application, set the scene for the debatewireline or wireless; Ethernet, coax, wireless, phoneline, or powerline.

However, performance and availability vary greatly among the technologies available for each of these media, with data rate the most obvious limiting factor for many types of service. As a rule of thumb however, if a technology cannot support a 20Mbit/s data stream, it will not be able to support streaming of HDTVthe next major incremental step that such technologies must bridge in order to build a truly digital home.

Another key determining factor is coverage. All technologies are limited in some way by range, and some more than others. Yet, regardless of which technology is chosen, whole home coverage will be a key element for digital home applications.

The best choice?
Wired networking has a number of demonstrable advantages over wireless: better coverage, where coverage is defined as the likelihood of achieving a certain speed in the deployment location, better availability and faster overall speeds.

Recent internal tests by DS2 revealed that today's 200Mbit/s PHY powerline technologies achieve 30Mbit/s in 95 percent of test locations in a home depending on the house's size and layout. Even the recent draft wireless technologies cannot guarantee bit rates above 10Mbit/s in such a high proportion of test locations.

This is due to the complex nature of wireless propagation where reflections cause signal nulls due to high levels of wireless absorption intrinsic in many building materials such as bricks, metals and reinforced concrete. Therefore the better coverage that wireline provides means that higher speeds can be achieved with greater reliability.

Another area where wireline outperforms wireless is in terms of availability, or its ability to guarantee an individual link over time. Whilst the configuration of the home wiring remains static over time, the wireless environment is constantly changing. For example, as doors are opened and closed, changes in wireless availability ensues. Whilst all communication media can be affected by interference, wireless communication in the 2.4GHz band is especially vulnerable to microwave radiation, so just using the microwave can imply a drop in service that is unacceptable for real-time applications, such as video streaming.

Question of quality
One area where wireless has traditionally suffered has been in QoS. This is because these wireless protocols were developed before the QoS requirements for multimedia streaming received high levels of interest. As a result the QoS extensions, such as Contention Free Slots, have had to be shoe-horned into a primarily data oriented Carrier Sense Multiple Access (CSMA) medium access protocol.

Simply put, it's the quality of the QoS that matters for multimedia applications. Wireline designs are based on TDMA rather than CSMA. TDMA has deterministic behavior when multiple data streams contend for the same resource, greatly increasing QoS performance. This ability to ensure deterministic channel resolution leads to excellent low-latency performance. Two milliseconds latency per link is easily within reach of modern wireline protocols, whilst wireless adds tens of milliseconds to the latency budget. This is of special interest to gamers obsessed with the "ping-time" of their ISP and for VoIP applications where excess latency generates an annoying echo effect.

Of the wireline technology options available today, high speed powerline communications technology offers the speed, coverage and QoS for digital home applications. Powerline has far greater penetration than coaxial or phone line technologies and there are far more power outlets available per room, offering greater connectivity. Powerline technology has also been developed to survive the very hostile environment of electricity lines. As a result, powerline technology performs well not only over powerline but also over coaxial cable.

- Lance Watson is strategic marketing manager at DS2.

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