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Concern over power lines for HD

The use of power cables to transmit TV services around the home is now well-established in a number of countries including several in Europe and has been proven to work well in most cases for SD services. But questions are being raised again by some home networking system vendors over power line's ability to scale up to HD, and especially to multichannel HD, which will become a standard requirement over the next few years. This does not mean that vendors, and by implication their customers, including pay TV operators, will be giving up on power line, but it does mean they may reappraise its role. In countries where coax is already widely installed in homes, such as the U.S., there may be little room for power line, but given the antipathy among operators and their customers to unnecessary installation of new wires in the home, it will continue to appeal where there are no suitable existing wires for data. This then leaves two options, power cables, since they are always there, and Wi-Fi.

The latter will certainly be used for video transmission within the home, driven by increased demand for access to content and services from tablets devices such as the iPad, which are predominantly wireless devices. But it looks unlikely that in the foreseeable future Wi-Fi will be able to provide guaranteed HD delivery within larger homes in particular, or those with walls that are thick or contain a substantial amount of metal.

Unfortunately, power line cannot provide guaranteed service throughout all homes either, also being subject to varying conditions. The fact that power cables were not installed with data transmission in mind means that the HomePlug AV consortium has had to come up with some clever algorithms to mitigate some of the effects. But there are still signs that interference can significantly reduce the effective bandwidth under certain conditions; unlike coaxial cable or Ethernet, performance cannot be guaranteed.

Out of concerns that power line cannot deliver that guaranteed performance, some vendors of home networking products like residential gateways, such as Turkey-based AirTies, are advocating systems that combine Wi-Fi and power line. This they hope will overcome the limitations of each and provide a robust high-performance "no new wires" system for multichannel HD delivery within the home. One possibility is to connect several Wi-Fi routers into outlets in different rooms, but without relying totally on power line for the backbone. In effect, each acts as cover for the other.
Whether this will gain ground remains to be seen, with one issue being to make such a combined system plug and play, given the need to plug coverage gaps and guarantee high bandwidth everywhere. Meanwhile, improvements in signal processing bring hope that power line can at least be made to work for HD in a large majority of homes, despite the fears over its ability to guarantee the required bit rates, up to say 500Mb/s. After all, the history of communications tells us that it is foolish to predict that a communications medium has hit an insurmountable performance barrier. Ethernet was once thought to be incapable of speeds above 10Mb/s over twisted-pair copper wires. Now it can reach 10Gb/s, 1000x as much, over short distances, through a combination of improved structured cabling and signal processing.

In the case of new homes, power cables could be installed in an optimal way for broadband communications, but in those cases it costs little extra to add coax or Ethernet Cat 5 wiring during construction, which will always perform better since they are dedicated and can be shielded against interference. The role of power line is likely to be confined therefore to existing homes lacking dedicated data cabling.