Wireless Systems Design

60 GHz Of Promise Land . . . Or Is It?

Each week I hear more about products and plans for the unlicensed 60 GHz spectrum. Yes, that is 60 gigahertz, or 60 billion cycles per second. Very high frequency indeed. What can you do with frequencies that high? Well, with all the progress in 60 GHz semiconductors, we are about to find out. A 60 GHz wireless product is probably in the near future.

What the Physics Portends
We call that part of the spectrum—from 30 to 300 GHz—extremely high frequencies (EHF). Another designation is millimeter (mm) waves as the wavelength of 60 GHz is 0.005 meter or 5 mm. You will see the name V-band applied to this range as well. Beyond 300 GHz is no-man’s-land for all intents and purposes. It extends from 300 GHz to 300 THz. That's terahertz, or 1012 Hz. Beyond 300 THz are the low infrared frequencies. The spectrum from infrared through the narrow visible range and through ultra violet is known as the optical band. I was never really sure where the transition from radio wave to light wave occurs but it appears to be around 300 THz. In any case, all such waves, radio or light are electromagnetic waves.

I am a big believer in working the numbers when you are evaluating any new technology. So let's take a look. Millimeter wave circuits seem great for semiconductor technology. Small, though. If inductors and capacitors are involved (as in filters or tuned circuits), you can only imagine how small the values are—something like femto Henries or atto Farads, or whatever. About the only way you can realize these small values is with fully integrated designs which are apparently no big problem. And the transistors in regular CMOS now have feature size down in the 65 or 90 nm region, and they’re getting smaller every day as Intel has demonstrated with its 45 nm technology. There’s no problem in hitting 60 GHz there. So, the good news is that we can indeed make some 60 GHz transceivers, in CMOS.

As for antennas, size poses no problem. Your typical half-wave dipole at 60 GHz is about .1-inch long, or roughly 2.5 mm. A quarter wave-ground-plane antenna would be half that size. The antennas are so small you can integrate them right on the chip with the transceiver. In fact these antennas are so small you can create arrays that will give gain and directivity to the signal, reducing the need for higher power. One vendor already has integrated a phased array on its chip so it can steer the signal beam. This is difficult to do at lower frequencies—not to mention expensive because of the large, cumbersome antennas. So it is good news for antennas as well.

As for data rate you need to look at available bandwidth. With 7-GHz bandwidth available at 60 Hz (57 to 64 GHz in the U.S.), you can really get some great data rates (4 to 5 Gb/s to be conservative), and that is using the simpler BPSK and QPSK modulation methods. Obviously even higher rates are possible with multilevel modulation schemes. With QAM in OFDM you can probably get to the 20 Gb/s range. That is plenty for just about any application and certainly much more than what’s available anywhere else today.

Low Tide Radio Waves
Now let's take a look at the basic RF range equation (called the Friis equation) that factors in antenna gains, wavelength, and transmit power and an assumed receive power. Using one mW transmit power, antenna gains of one at both receiver and transmitter, and a desired receive power of 10 nW, I get a range of about 5 inches. Not too useful. Bumping up the transmit power, adding gain antennas and making the receiver sensitivity greater should yield a range of multiple meters. Still pretty poor as it severely limits the application. No doubt manufacturers will work to get that range well up—otherwise why bother? The target is probably 10 meters, which is useful. The problem is the range prediction above assumes an unblocked line-of-sight (LOS) signal path. Any practical usage will encounter walls to penetrate and many obstacles that will create horrible multipath conditions. Under such conditions, assume a maximum range of only a few meters. Is that good enough? Maybe.

One final note about the propagation. As it turns out, 60 GHz is at that part of the spectrum where the absorption of the signal by water molecules is at a peak. That's probably why they made 60 GHz the unlicensed band. The frequencies directly above and below are more useful. What that means is that when it rains or snows signal amplitude will be severely decreased even blocked. That attenuation is in the 10 dB/km to 15 dB/km or about 1.5 dB/100 meters. Luckily, most applications will probably be of the indoor variety, so we won't have to worry about that.

Two really good arguments for high water-vapor attenuation are interference mitigation and security. Signals won't travel far beyond their intended targets with this technology so interference to others will be minimal and the chance for illegal reception significantly less.

The solution to the range problem is more power. The IC transceivers can only generate so much say up to 100 mW or so. But the real solution lies with antennas. By using gain antennas, the effective isotropic radiated power (EIRP) can be boosted significantly giving the transmitter an EIRP from say 10 to 100 watts. Phased arrays of dipoles, patches or slots are ideal. For a real power and range boost use a parabolic dish. A "big" dish at 60 GHz isn't all that big (several inches in diameter) but the gain is huge. The downside is a very narrow beamwidth (1 degree or less). That may or may not be a problem depending on the application. One thing that directionality does do is further improve the security.

Except for range, all the other factors seem very favorable. Solving the range problem will really give us that new unexpected wireless technology to deploy when we really have some fast data to transmit.

What are the applications?
High-speed data is the obvious conduit and there are few things that need to go that fast. One possibility is to use 60 GHz as a fiber replacement. Think of a 60-GHz back-haul link that can deliver 5 Gb/s, maybe more. A 1-Gbit or 10-Gbit wireless Ethernet link comes to mind. I wonder if 60 GHz is the next target for Wi-Fi 802.11? There could be a group looking into that right now. There is a high speed working group for the IEEE 802.15.3c standard which falls in the wireless personal area network (PAN) area. Several companies (e.g. Proxim's GigaLink) already make commercial 60 GHz back haul systems that can transmit at rates to 1.25 Gb/s at a distance of a mile or so with a parabolic dish in good weather.

Video is about the only other high-speed data need out there right now. And we still have not completely solved the problem of transmitting video around the home wirelessly. Sure we can transmit video via wireless like 802.11a/g/n or ultra wideband (UWB) but it has to be compressed first. That takes away some of the fine detail in a true HD video production, but few can tell the difference unless you have a really big screen. And range and reliability are still issues. It would be great to be able to transmit uncompressed 1080p, the highest resolution HDTV format. That translates into a data rate of about 3.8 Gb/s. That is with the 1080 x 1920 pixel format with 24-bit color and the fastest frame rate of 60 frames per second plus audio. A 60-GHz wireless link would be a welcomed addition in high-end home entertainment systems assuming the range is good enough.

About the only other application is radar. Millimeter wave radars have been used for years in military aircraft and otherwise to get the high resolution needed to see greater detail. But they are expensive. Some auto manufacturers like Mercedes have a 77-GHz radar used in its sophisticated cruise control and automatic braking system. So a 60-GHz radar would be fairly easy, but what would you do with it? How about an anti-insect radar that guides a laser beam and shoots pesky flies and mosquitos out of the sky? That’d be some upgrade for your fly-swatter. And not a bad consumer product idea. You’ll just have to be careful, as they said in the Christmas Story movie, “You’ll shoot your eye out.”

Who's Doing What?
I spoke with John LeMoncheck, CEO of SiBeam, a relatively new wireless semiconductor company. They recently announced their 60-GHz chipset that complies with the new WirelessHD standard for video transmission. There will be more on WirelessHD later, but consider their chipset for the moment, made up of an RF transceiver and a network processor. The system uses OFDM with BPSK in a 2.5-GHz channel to achieve a data rate to 4 Gb/s that is fully adequate for transmitting uncompressed 1080p HD video and audio. The chips implement AES-128 encryption. The network processor chip allows the creation of wireless video area networks (WVAN) or wireless personal area networks (WPANs) with a Coordinator node and multiple Station nodes. Stations join and disconnect from the network automatically and can share data. The chipset is targeted at home entertainment equipment like HDTV sets, DVD players, DVRs, set top boxes, A/V receivers, projectors and other equipment in a consumer installation. The chips can also be used in PCs, laptops, digital cameras, and other devices that need a fast connection.

Besides doing all this in CMOS, the real innovation by SiBeam is their advanced antenna technology. They use a steered beam system that adjusts to changing conditions. On both the transmitter and receiver chips is a 6- by 6-inch patch array with high gain and steerability. This eliminates the need for a precise LOS link, something difficult in most situations. The transmit/receive beams "find" one another to optimize the link. If the link is blocked from LOS, the antennas find an alternate path. For example, the transmitter may actually find a reflecting surface to get the signal to the receive antenna. This automatic beam-finding is the key to making this short range technology work reliably.

SiBeam won the award for "Best of Innovations" in the enabling technologies category at the recent International Consumer Electronics Show in Las Vegas. It is really cool wireless technology that we will be seeing more of. Click here to see more wireless technology from the show.

The SiBeam chipset implements the WirelessHD standard. WirelessHD is an industry consortium dedicated to creating the next universal interoperable specification for a multi gigabit wireless high definition digital interface for consumer electronics and computer products. John Marashal of the WirelessHD organization said that the members of the organization are Intel, LG Electronics, Matsushita (Panasonic), NEC, Samsung, SiBeam, Sony and Toshiba. No doubt there will be others. This initiative has resulted in the creation of the WirelessHD 1.0 specification that fully defines a standard for consumer electronics. WirelessHD has chosen Digital Transmission Content Protection (DTCP) scheme to keep videos from being stolen or copied as they are transmitted. WirelessHD will test and certify products to their standard. First testing is likely to begin later in 2008 with the first products to be available in late 2008 or early 2009.

Another recent announcement is the creation of a 60-GHz transceiver on a single 130 nm CMOS chip by National ICT Australia Limited (NICTA), a national research institute funded by Australia's Information and Communications Technology (ICT) Research Centre of Excellence. It is capable of transmitting video at a rate to 5 Gb/s with a range to 10 meters. Look for some possible commercialization of that.

At the IEEE's International Solid State Circuit Conference in San Francisco last month, IMEC introduced a prototype of its 60-GHz multiple-antenna receiver. It too can achieve a data rate of many Gb/s up to 10 meters. The initial device features two separate antenna and signal paths at its input. A forthcoming version will implement four antennas and will ultimately lead to fully steerable phase arrays. IMEC is also beginning the design or a 60-GHz power amplifier. IMEC is an independent research center in nanoelectronics based in Belgium.

IBM has been working on 60 GHz hardware since 2003. Their initial funding was from NASA and DARPA. They too have developed a low-cost transceiver for use in back haul systems, HDTV distribution via HDMI or IEEE 1394, and for wireless Ethernet and USB 2.0 transmission. IBM has investigated other millimeter wave applications like vehicular radar in the 76- to 77-GHz bands and penetrating imagers in the 94-GHz band. Look for commercial products in the future.

There is a lot of other 60 GHz work going on. Toshiba has developed some 60-GHz chips. Work at NASA's Jet Propulsion Lab has produced HEMT power amplifiers that can generate 50- to 300-mW per 0.6 to 1.2 mm of gate periphery of the transistors on chip in either gallium-arsenide (GaAs) or indium phosphide (InP).

I have probably missed others but this gives you some idea about how well along the millimeter wave action is. Keep watching as you will begin to see 60 GHz products in the near future. We have such a richness and variety of wireless technologies now it is hard to know where to use them all. What a great problem to have.

TAGS: Intel
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