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Multiroom Audio over Powerline: The Fiction and the Facts about HomePlug (1/5/2009)

By Rick Kukulies, NuVo Technologies

No product is truly wireless. Your mobile phone, notebook computer and iPod may be wireless most of the time, but sooner or later it will be temporarily tethered to a power supply. Solar is, of course, truly wireless, but your iPhone would need a solar panel the size of a small umbrella.

Multiroom audio systems, of course, require a lot more power than an iPhone does. These systems can take many forms, and new variations appear regularly. Traditionally, their source devices, such as tuners, audio servers, and iPods; a routing matrix; and amplification are centrally located, then connected to each zone with speaker wire and control wire, usually CAT5. This method has been widely adopted, and with good reason. It is easy to understand and install and, if done properly, is very robust.

Another popular scheme is to distribute amplification, with the source equipment still in a centralised location, but amplifiers in each zone. Of course, instead of a speaker wire to each zone, there would need to be a low-level signal and control cable, usually CAT5.

Wireless versus wired

So how do we take the next step, into wireless multiroom audio? It certainly sounds like an attractive alternative and several basic methods exist. You can use your already-existing 802.11g/n home router and stream audio, or you can use a proprietary wireless technology. Either method has advantages and disadvantages. Obviously, both have the advantage of requiring no home run wiring, but remember that you still need to wire the in-room amplifier to the speakers (if separate), possibly wire a controller, and then you need to connect the amplifier to a source of power. That's quite a number of wires for a wireless solution.

And then there are the real-world problems of bandwidth limitations, networks competing in the same frequency space, and the usual difficulties inherent in network configuration and management. Most troubling of all is that things in the environment change over time. What happens when a new router or additional Wi-Fi devices are installed? What happens when a new mobile phone tower goes up on your street? What happens when your neighbour gets onto your network and discovers that you listen primarily to Britney Spears? What then?

Let's face it - a wired solution is more reliable, more secure, more robust and altogether less potentially messy. So, back to a wired solution we go. We need power, we need to get audio and control from one or more locations in the house. But what if we don't want to run wires throughout the house?

The Powerline option

Power Line Communication (PLC) offers a compelling solution. PLC has been around for a long time - X10 was first released in the mid-1970s, and several PLC systems have come and gone over the years. Early PLC systems were notorious for their unreliability, and many early-adopter installers got burned. As a result, many remain sceptical of any powerline-based solution, not to mention wireless systems.

Until recently, PLC technology could only address control; its bandwidth was not sufficient to handle one audio stream, much less multiple audio streams. That drawback has been eliminated. Now, with the advent of powerful microprocessors and sophisticated technologies, high-bandwidth PLC solutions are, for the first time, practical and affordable.

In 2000, the HomePlug Powerline Alliance was founded with the goal of developing a standard for using AC mains wiring for high-speed data transmission. For this market to truly develop, a worldwide standard is necessary, and the Alliance is delivering it. The current sponsors of the HomePlug Powerline Alliance include Cisco, GE, Intel, Motorola, Texas Instruments and others. Companies with HomePlug products in production include Belkin and NETGEAR (USA), Develo (Germany), Solwise (UK) and LEA (France). To date, over 25 million HomePlug products have been shipped. This technology is ideally suited to multiroom audio. In fact, it is well beyond the early adopter phase in that regard.

How PLC works

The technology in concept is quite simple but, like any sufficiently sophisticated technology, the details separate success from failure. A digital data stream is coupled to the AC mains, and then one or more receivers are connected elsewhere on the AC mains. The AC mains, however, is a challenging environment. Firstly, there is the 120-240VAC at 50-60Hz (and a lot of harmonics); secondly, there is noise caused by devices such as motors, fluorescent lights, computer power supplies and more; and thirdly, the PLC signal becomes weaker over distance. Low-bandwidth (control) PLC systems typically operate between 50kHz - 200kHz, but unfortunately, many noise sources also produce significant energy at these frequencies and therefore compete with the PLC signal.

The HomePlug standard

The HomePlug standard addresses and solves these problems. HomePlug operates between 4.5MHZ and 21MHz and uses 84 separate subcarriers (or bands). Its high operating frequency is above many noise sources, and excessively impaired carriers can be turned off when connection reliability would be improved. HomePlug technology continually adapts itself to the changing environment on a moment-by-moment basis. In extreme cases of noise, the offending piece of equipment or machinery can be isolated with a simple, commercially-available filter.

The NuVo Renovia system uses HomePlug technology and a wireless control pad to deliver multiroom audio around the home as a retrofit solution.

The benefits of PLC and Homeplug

PLC offers a compelling solution to multiroom audio, and the list of benefits is significant. Firstly, since you need power anyway, the AC mains is a convenient place to send audio and control data. The operating environment is problematic, but potentially easier to deal with than 801.11 wireless, especially when a dozen or more networks are in the same space. Secondly, PLC signals are not blocked by concrete walls or floors, or attenuated by steel framework construction. Thirdly, the installation is easy - just plug and play - there is no Ethernet network to setup or manage. Fourthly, latency is not an issue; because each room or zone is synchronised, no echoes will be heard in acoustically-coupled spaces.

As mentioned earlier, HomePlug is a worldwide standard that has been adopted by many companies. HomePlug technology is rapidly increasing in bandwidth, costs are decreasing, and partnerships with complementary technologies are in development. Currently, the HomePlug AV standard supports 200MHz, and HomePlug AV2 (now in development) will support 600MHz. Soon, HomePlug devices from different companies will talk to each other, and last year, HomePlug announced a liaison partnership with the ZigBee Alliance.

HomePlug has also expended substantial efforts to ensure that products designed to the HomePlug specification meet the radiation limits imposed in the U.S. by FCC part 15 rules, which limit the maximum signal level that can be injected onto the power line. Tests conducted by FCC-certified labs in various regions of United States show that the maximum signal levels incorporated in the specifications result in emissions that are below the part 15 limits.

HomePlug also limits its power spectral density around the amateur radio bands by inserting 30dB notches for the HAM bands in the 4.5M to 21MHz HomePlug frequency range. Due to this notching of HAM bands, only 76 OFDM carriers are usable in HomePlug products operating in United States. Joint testing conducted by HomePlug and ARRL showed that, in general, with a moderate separation of the antenna from the structure containing the HomePlug signal, interference was barely perceptible. HomePlug is also compatible with other low-speed powerline technologies such as CEBus, X10 and LonsWorks, as they operate in different frequencies.


HomePlug is robust technology supported by a worldwide list of reputable companies. Both NuVo Technologies and Russound recently announced multiroom audio products based on HomePlug, and several traditional AV companies such as Pioneer and Sharp are active HomePlug members.

In an era in which we all are being asked to do more with less, the ability to run audio and data over existing electrical infrastructure within the home makes perfect sense, for so many reasons.

Rick Kukulies is the Chief Technology Officer for NuVo Technologies, a leading innovator in multiroom audio.


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