Page 2: Enter the cognitive radio >>

Editor's note: There's nothing more contentious in the smart grid communications space than the debate over wireless technologies. RF vs. cellular. Public vs. private. Licensed vs. free. It would be easier to get peace in the Middle East than to get smart grid experts to agree on a single "best" approach. So when Brian Andrew got in touch to describe his version of "best," I asked him to submit a guest post. I offer it to you as one point of view in the long-standing and ongoing dialog. I hope you will use the Comment form at the bottom to weigh in (politely!) with your opinions pro and con. -- Jesse Berst

 

 

By Brian Andrew

 

Can utilities use free spectrum to get a private, secure, encrypted, high-reliability, 30-mile wireless network with no interference and no towers?

 

I say yes. Allow me to explain.

 

The most common solutions for smart grid/SCADA wireless data communications are 900 MHz and Wi-Fi at 2.4 GHz.  But these systems have limitations and concerns over distance, interference, tall tower heights and ever-growing foliage. For instance, the rules set by the FCC for 900 MHz and Wi-Fi at 2.4 GHz introduce interference issues. What's more, the physics of these frequencies limits their range and penetration.

 

To escape those issues, some companies have purchased or licensed spectrum.  But even in those cases there are usually not enough channels available to provide the throughput and/or number of links needed.

The benefits lower frequencies

There are lower frequencies designated for industrial use that don't require you to purchase or lease spectrum. For instance, the 217-220 MHz frequency is FCC approved for industrial use in a shared environment. The 200 MHz frequency range is excellent for providing distance and low-height deployment.

 

The drawbacks -- the sharing rules require that radios not interfere with existing users and the channels are narrow at only 12.5 kHz each. Fortunately, a technology solution now exists that eliminates interference. With it, you can use the 217-220 MHz narrow band channels to deliver a private digital network.

 

We should first review why the 200 MHz frequency range is so beneficial. The lower the frequency, the longer the wavelength, the better it travels through buildings, trees or long distances. For instance, TV channels 7-13 operate in the 174 to 216 MHz frequency range and a single central TV tower can cover as far as 80-100 miles.

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Talk Back to the Author

Current Comments (3)

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RE:Free Spectrum

Free Spectrum appears to be used quite loosely. A portion of the spectra (as mentioned) is already shared and in public use. Google for US Amateur Radio bads and look at the 1.25 meter band (Above 219MHz). Spectra that is becoming available after moving to digital TV -- isn't uniformly free. Small rural areas still often use analog TV repeaters that may sit in the same band as the author proposes to use. If there are spectra available - it would be auctioned off - much like what was done for cellphones. Finally any spectra that is used must be coordinated with ITU and the spectrum users in neighboring countries.

Dennis Heidner - 05/18/2012 - 11:24

Free tends to come with caveats

Whilst most of what the article puts forwards is true, it sidesteps the main problem, which is the old issue that “if you build roads, the cars will come to fill them”. Today the 220 MHz band is deliciously free of traffic. However, it contains the constraints which could make it self defeating. As Brian says, the advantage of this frequency is that it has long range. The corollary is that the throughput is low. If we try to connect every meter (and possibly every HAN component) on this band, then it runs the risk of becoming very congested. Here the range can become an Achilles’ heel, as each radio listening to find a free frequency will hear every other smart grid component in a radius of several tens of miles. If that happens, then the network becomes gridlocked and grinds to a halt. Which means your latency goes out of the window and any hopes of using it for demand response disappear. Whilst all of that listening will be draining the batteries in every gas meter. It’s the same problem that the proponents of 169MHz are starting to see. It may be fine for a daily meter reading in suburban or rural areas, but it runs out of throughput as soon as you move into denser locations, or try to move more data across the network. Sadly, most magic RF wands turn out to be more fiction than fact.

Nick Hunn - 05/21/2012 - 01:32

no

No, it can't. Lack of throughput, latency increased for other users, and of course backlash from those who rightfully want to use free spectrum for genuine mobile devices, will prevent deployment of this kind of network, and rightfully so. Keep AC-wired devices communicating by wire (powerline and fibre on poles).

Craig Hubley - 09/13/2012 - 08:02

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