We ran an optimistic piece before Christmas, saying that perhaps the digital home was finally sorting itself, out and that the fact that a standard had occurred in record time for Homegrid’s G.hn might mean that everyone was going to agree this time.
A reader immediately emailed in to highlight some potential difficulties with this analysis, pointing out that the PHY physical layer had been agreed upon, but the MACs remained a million miles apart. The PHY for each of the different media which Homegrid runs on ‘ coaxial cable, phone line twisted paid and powerline ‘ are all variants of OFDM. All that each proponent had to do was to argue about the 10% to 15% of differences between their PHY layers and agree on some form of compromise, but the MAC is totally different. The biggest differences in the PHY were the forward error correction used and they ended up using LDPC due to it’s license free status, despite it being a 45 year old piece of technology (it is being used on DVB-T2 for much the same reason).
The MAC has been broken out of the spec for the standard because this is where the majority of the conflict is likely to be. Homegrid had agreed it would have a spec by the year end, and we failed to notice that what was achieved by year end was only a PHY. So no-one can start designing equipment yet in 2009 after all.
Apparently the guys at DS2 have proposed, and had their proposal accepted to use 16,384-QAM on Powerline and our reader thought this was a tad optimistic. The 200 mbps DS2 chipset has 1,536 sub-carriers, and this is more than ten times that number and it may not ever be achievable and is certainly not achievable now.
The main proponents within G.hn are Intellon (which makes chips for Homeplug), DS2 (which makes chips for Power) and Panasonic and they all have their own proprietary MAC’s and there is very little in common between them.
Other key members including Pulse~link (which uses a different PHY entirely), Texas Instruments, Intel and Infineon and they each have their own idea about what makes a good MAC. So we apologize if perhaps we gave the impression that suddenly a converged MAC and PHY was about to appear for all types of cabling. It now looks like it remains an indeterminate distance off.
Meanwhile DS2, the Spanish based chip designer for Powerline has cut a deal this week with D-Link, to use Aitana, DS2’s 2nd generation 200Mbps Powerline chipset. D-Link is a distributor of virtually ALL of these discrete technologies now, along with many more.