High-Speed, Reliable Networking Over Powerline: Sigma Designs Tries One More Time

For the moment, at least, my hybrid-technology LAN is stable and robust (and yes, I realize I’ve just jinxed myself by writing those words). CAT6 cable runs between the house’s living room (containing the DSL modem and router) and the garage’s studio, as well as between the living room and my office. Shorter runs of CAT5e cable connect clusters of wired network clients to their associated switches. Mobile clients (phones, PDAs, and laptops) connect to the network via a Wi-Fi-inclusive router along with two dedicated access points. And HomePlugAV powerline implements the remainder of the intra-house network backbone (aside from the aforementioned two CAT6 spans).

The latter LAN spurs are the focus of this particular post. As regular readers know, I’ve been experimenting with powerline networking for many years now, through multiple hardware, software and underlying silicon generations’ worth of adapters based on HomePlug 1.0, HomePlug 1.0 Turbo, HomePlug AV, HD-PLC (Panasonic) and UPA (DS2). Right now, I’m using three of NETGEAR’s XAV1004 four-port switch-inclusive adapters:

plus a single XAV2001:

all based on Intellon’s (now Atheros’) third-generation INT6400 HomePlug AV transceivers. Ironically, just before starting to write this post, I noticed that the XAV2501 (which enhances the XAV2001 with a pass-through outlet) was on sale for $106.99 in a two-adapter bundle. A Google search on the product name brought me to Amazon’s and Newegg’s review pages, where I was happy to encounter mostly-five-star feedback. Oh, how the times have changed from the early HomePlug 1.0 days…

My experiences with INT6400-based devices are similarly mostly-solid. The XAV1004s and XAV2001 can, with near-100% reliability, pass a single ~20 Mbps video stream from my router to an Xbox 360 acting as a Media Center Extender. And unlike some of their predecessors, they also seem to handle the occasional residence power loss with aplomb, automatically re-handshaking once the juice is flowing again. But attempting to simultaneously run a second ~20 Mbps stream over the power grid, originating from my Windows Vista-based laptop (acting as a Media Center Server) and going to the router, sometimes is too much for the HomePlug AV topology to tackle in a glitch-free fashion…thereby explaining why a dedicated 5 GHz ‘wide’ 802.11n wireless link instead implements the laptop-to-router span.

I had tried (several times, in fact) to improve the powerline performance situation, using Belkin’s ‘Gigabit Powerline HD’ adapters:

based on Gigle Networks’ GGL541 transceivers, albeit without success. My first stab at testing the devices produced sub-HomePlug AV speeds. My second evaluation produced even worse results. The company again got the adapters back from me and, at January’s CES, promised to give me a third crack at them after the bugs had been ironed out…but as mentioned back in April, my subsequent repeated attempts to contact the company via both email and telephone voicemail have been unsuccessful. Then again, I’ve noticed that the bulk of the company’s announced design wins in recent months have been for the HomePlug AV-only GGL301; perhaps I wasn’t the only one who found the GGL541 underwhelming.

The GGL541’s supposed speed boost over ‘vanilla’ HomePlug AV relied on two fundamental technology premises:

• Mediaxstream, a marketing moniker for a second broadcast channel operating between 50 MHz and 300 Mhz (versus HomePlug AV, which uses a 2 to 28 MHz spectrum swath minus notches to avoid destructive interference with ham radio systems), and
• Xtendnet, a fancy name for an optional node-to-node repeater mode

The GGL541, while minimally operating in a HomePlug AV-compliant baseline mode, was supposed to intelligently enable one or both enhanced functions when communicating with other GGL541-based devices and when switching into a Gigle-proprietary mode would be performance-beneficial. Yet, at least in my case, the ultra-high frequency Mediaxstream channel was seemingly attenuated below the threshold of usefulness even over the relatively short power cable runs of my diminutive residence. And the GGL541s’ endless personality schizophrenia, back and forth between HomePlug AV and proprietary operating modes, was seemingly at the core of their sub-HomePlug AV resultant performance.

This background technical information is, I think, crucial to understanding the environment in which Sigma Designs’ CG511x powerline networking chipset will be competing next year (PDF):

The CG5111 and CG5113 had already ‘taped out’ when I spoke with the company last week, and first silicon was expected back from the foundry by the end of this year. Sigma Designs may not be a familiar name to those of you following the networking application space, but any confusion will likely lift when I tell you that the company acquired Coppergate Communications (which had previously inherited Conexant’s powerline networking expertise) a few weeks shy of a year ago.

An understanding of the powerline market also requires comprehension of the status of industry standards. IEEE P1901, as I’ve explained in past writeups, optionally supports a dual-PHY (OFDM for HomePlug AV, and wavelet for HD-PLD) strategy, along with coexistence mechanisms between the two formerly dueling competitive technologies. What I haven’t mentioned before is that it also extends the broadcast frequency range beyond the earlier mentioned 2-28 MHz and all the way up to 50 MHz. Similarly, according to Sigma Designs’ Michael Weissman, competitor Atheros’ latest AR7400 chipset (formerly known as the INT7400) employed in NETGEAR’s ‘500 Mbps’ powerline adapters runs all the way up to 70 MHz. The real-life relevance of these frequency extensions is limited-to-nonexistent in my opinion, at least over power grids. However keep in mind that the P1901 backers are also participants in markets which use coaxial cable as a physical media, for which transport at high frequencies over reasonable distances is more feasible.

Then there’s G.hn, the ITU-sanctioned approach that also comprehends multiple physical media transport options (coax, phone line, and power line) over a common protocol suite. It was the standards ‘horse’ that DS2 bet on in the form of a dual UPA-plus-G.hn PHY strategy. DS2 unfortunately went bankrupt earlier this year, but the company’s technology lives in at Marvell, who subsequently acquired it. And the importance of ITU standardization shouldn’t be underestimated, given that ITU-favoring telecom providers’ IPTV services represent a key market opportunity. Right now, according to Weissman, the telecom operators are spending hundreds of dollars per new customer installing new coax infrastructure in homes, with powerline topologies restricted to HomePlug 1.0 or 1.0 Turbo for data since HomePlug AV was deemed insufficiently bandwidth-robust. He believes that G.hn over powerline, inexpensively self-installed by IPTV customers, will make IPTV providers’ costly coax rollouts unnecessary in the bulk of residence setups.

Intellon-now-Atheros is backing HomePlug AV and its IEEE P1901 follow-on, DS2-now-Marvell is seemingly solidly behind G.hn, and everyone’s waiting to see what (if anything) Broadcom and Intel do. More generally, worldwide powerline single-technology standardization remains elusive. Sigma Designs has therefore taken the pragmatic tack of supporting all three standards (over multiple physical media options, too) in the CG511x, an approach which Weissman claims consumes “minimal” incremental die area over a single-standard baseline stance thanks to the CG5111’s 40 nm process technology (the analog-heavy CG5113 conversely leverages a 130 nm lithography). And further upping the technology ante, the CG511x chipset supports across all three standards a (currently, at least) company-proprietary approach called ClearPath (PDF).

Powerline networking normally only uses the phase and neutral wires of the three-wire AC cable bundle for communications purposes. However, according to Sigma Designs’ Chief Technology Officer Rami Verbin, crosstalk invariably also couples a variant of the signal onto the earth wire, one which may ironically end up being ‘cleaner’ than the phase-plus-neutral original. By monitoring all three wires for incoming packets, Verbin claims that the CG511x chipset can potentially boost received SNR versus competitors’ devices even in fully standards-compliant operating modes. In an all-CG5110 networking topology, the device can not only receive but also transmit over not only the traditional phase-plus-neutral pair but also optionally either the phase-plus-earth or earth-plus-neutral combo. And for G.hn, a further extension of the concept (which the company brands as ClearPath Extreme) enables simultaneous ‘MIMO’ broadcast and reception of multiple signals over multiple AC wire pairs.

Weissman and Verbin espouse a seductive pitch, complete with statements such as “we’re fundamentally focused not on making the already-best powerline networking environments even better but in making the currently-worst setups sufficient”, “our goal is to deliver at least 50 Mbps bandwidth through 99.9% of AC outlets” and “up to 15dB higher SNR”. If Sigma Designs delivers on its promises, I’ll be ecstatic, especially if G.hn and/or IEEE P1901 licenses the company’s ClearPath patents for broader vendor implementation purposes. However, having heard similar (albeit ultimately unfulfilled) promises from other companies many times in past years, I’m admittedly cautious from a “fool me once, shame on you, fool me twice, shame on me” standpoint. The proof of the pudding, as the saying goes, will be in the eating…Sigma Designs plans to start sampling the CG511x chipset to tier-one potential customers in Q1 2011, with production-worthy silicon to follow in the third quarter. I look forward to trying it out for myself next year, and to passing along my results to all of you here.