Socket to 'em: It's the HomeGrid vs HomePlug powerline prizefight
Rival mains LAN standards go mano-a-mano for a place in your home network
Signal to noise
Ranck’s most important pitch, however, is that HomePlug has momentum that will carry AV2 forward, whether through consumers upgrading their existing HomePlug adaptors or with service providers who have already handed out HomePlug kit to their subscribers. The service providers aren’t going to want to have to get their engineers up to speed on G.hn, he says, when they already know HomePlug for powerline, HomePNA for networking over phone cabling and the MoCA standard for the co-ax links that are popular in US homes.
But there is an advantage for HomeGrid here: G.hn can operate over all three of these media, all connectable through single PHY. Why worry about MoCA and other standards, asks the Forum’s Matt Theall, when a G.hn-equipped box can be run over any or all of these wire types? The standard was designed not merely to operate over all of these, but to connect them together. One product can connect to any ord all the wires in a house, proponents say. That’s one of the reasons why many service providers are so keen on G.hn, he says. Rather a lot of them are members of the Broadband Forum, yet another industry association charged with overseeing standards; it too has given G.hn the thumbs up.
But not so the world’s radio hams, who disapprove of powerline technology period, claiming it is a source of electromagnetic pollution in the bands they and others favour, and fear the impact of the next-generation technologies even on FM transmissions. To avoid the FM band, HomeGrid cuts out at 80MHz rather than 86MHz, where HomePlug AV2 draws the line. To obtain HomeGrid certification, a product must not intrude into the FM band at all, though this is a widespread regulatory requirement in any case. G.hn also follows Comité International Spécial des Perturbations Radioélectriques (CISPR) recommendations for notching frequencies to prevent powerline noise affecting ham and other bands, and - as does HomePlug - provides the tools product makers need to ensure their kit doesn’t contravene local EMC regulations.
Where you notching is one thing, how well you do it another matter entirely. In Europe, the EN50561-1:2012 standard put in place by European electronics regulator CENELEC (Comité Européen de Normalisation Electrotechnique) is intended to deal with this kind of powerline interference issue, though some hams say the standard is tainted because some members of the Working Group that defined it have close connections with the powerline industry.
It's certainly a compromise to allow powerline kit to get away with not meeting the EN55022 baseline EMC standard. Powerline proponents say that doesn't apply to their technology - hams say it does. The argument isn't going to go away, but neither is powerline. “Significant protection is provided [in EN50561-1] for the Amateur HF bands, as the standard specifies fixed notching for these and other safety of life bands, reducing conducted emissions from PLC devices to the levels of EN55022,” says the Radio Society of Great Britain (RSGB). So that's as good as it gets until there's more consistent, more replicable evidence than a few YouTube videos, or tests of specific adaptors - blame the brand not the technology? - for tougher action to be taken.
For its part, the HomePlug Alliance says: “We think EN50561-1 represents a decent compromise amongst the various stakeholders.” But that’s no consolation to stakeholders who fear the impact of kit that hasn’t passed HomePlug or HomeGrid certification, or who question the efficacy of the mandated notching. HomeGrid numbers show that notching the FM band and the ham radio frequencies reduces G.hn’s peak PHY data rates from 959.12Mb/s to 475.12Mb/s (SISO) and from 1.9Gb/s to 807.7Mb/s (MIMO), so there’s a strong incentive for vendorsto push out kit that’s not notched. How much further these numbers fall in real-world usage - as fall they will - will remain an unknown factor until adaptors are released for independent testing.
HomeGrid and HomePlug say its not the job of standards bodies like the ITU-T and IEEE to enforce good neighbourliness in a world of different territories with different radio regulations. It’s for local regulators to set suitable standards, they say, and to police them. That task isn’t going to become any easier as the number of devices that make use of the technology increases, and the installed base expands, on the back of vendors pushing the connected home concept and multi-technology networks.
Both HomeGrid and HomePlug unsurprisingly each suggest their favoured standard is better at noise reduction, though with no kit available to buy, the EMC credentials of G.hn and AV2 will again not be certain until independent tests can be taken. Device makers have three years’ grace period before they can be taken to task for not meeting the specifications of EN50561-1.
In the meantime, G.hn and AV2 will be slugging it out for the hearts and minds of service providers, of users keen to shift more HD content around their homes, and of set-top box, media streamer and TV makers looking for easy home networking beyond Wi-Fi. Both standards are evenly matched, but one must emerge as the leader if equipment makers are to be able to implement the technology safe in the knowledge that their smart TVs will talk to other vendors' routers and content stores. If they don't, and implement Ethernet to be fed by whatever powerline adaptor the user has in place, the fight will be set go on for a long time indeed. ®