Wireless Systems Design

Near Field Communications Brings New Meaning To Short-Range Wireless

The neat thing about wireless communications is that there is something for everyone. There’s a technology, protocol, or standard for any wireless need or application. And just when you think we have it all pretty much covered, a new technology comes along to provide one more option.

One of the newer options is near-field communications (NFC). It appears to fill that gap in the range spectrum from zero to 20 cm. I’m not sure I realized there was such a gap, and maybe you didn’t either. Yet there appears to be a good rationale for this ultra-short-range radio. Here’s a quick update on this technology in case it fits something you’re working on.

The term “near field,” of course, derives from the near field of a radio wave. As a wireless person, you already know that a radio wave is made up of both electric and magnetic fields. At a distance of about 10 wavelengths or more of the operating frequency, the radio wave behaves in accordance with Maxwell’s equations where the two fields exchange energy and reinforce one another in transit. This is called the far field.

Inside those 10 wavelengths is the near field, where what you see is individual electric and magnetic fields. The electric field isn’t too useful, but the magnetic field can be used for short-range communications. Think of NFC as a transformer with a very low coefficient of coupling because of a large distance between primary (transmitter) and secondary (receiver) windings. The main problem with near-field magnetics is that the signal strength drops off at a rate of about 1/d6, where d is the distance or range. Far-field RF drops off at a 1/d2 rate. There’s no wonder near field is such a short-range technology.

NFC isn’t new. When I was much younger, I built a near-field paging device. It used an audio power amplifier and microphone and a large coil of wire attached to the speaker terminals. I wrapped the wire around the perimeter of the ceiling in a room. This was the primary winding. Then I made a receiver with a coil of wire for a secondary connected to a high-gain IC audio amplifier. The output was an earphone. It worked pretty well.

Aura Communications Technologies (www.auracomm.com) has had a near-field magnetic chip set for several years now. The company sells it as a wireless headset link. Most wireless headsets use Bluetooth, but the NFC headsets are an option on some phones. It’s also useful in other short-range situations, such as networking in cars.

Now, Philips and Sony have come together to give us the most recent version of NFC. It is an actual standard. ECMA International adopted it as a standard first (NFCIP-1 or ECMA-340). The ECMA then submitted it to the ISO/IEC, and it is standardized there also as ISO/IEC 18092. Given a fully blessed standard, semiconductor companies can begin making compatible and interoperable chips.

This standard is similar to and compatible with the same NFC technology used in smartcards, which include an internal chip that lets you pay by passing the card over a point-of-sale terminal reader. The technology also is similar to radio frequency identification (RFID).

The standard specifies an operating frequency of 13.56 MHz, which is the international no-license band and one of the industrial/scientific/medical (ISM) band Part 15/18 frequencies in the U.S. The transfer data rate is 106, 212, or 424 kbits/s. The speed depends upon the range, which is up to a maximum of 20 cm or about 8 in. In most cases, the actual range will be only a few inches or no more than 10 cm.

The standard also specifies several operational modes. In the active mode, both parties have powered transceivers. Either may initiate a half-duplex transmission with a “listen before transmit” protocol. One of the devices is the initiator, and the other becomes the target.

In the passive mode, the target is a passive device like an RFID tag. The tag gets its operational power from the field transmitted by the initiator. It then transmits data back to the initiator by modulating the magnetic field (backscatter modulation, a kind of AM).

As for applications using this ultra-short-range technology, Sony and Philips mostly talk about automatic payment tools like smartcards. But instead of using a smartcard, the NFC transceiver is built into your cell phone. To buy something, you just tap your cell phone on the reader or pass it within an inch or so, and zap, your credit card account is automatically billed (see “Near-Field Communications Sees Large-Scale Trial Run,” Wireless Systems Design Update, Jan. 10, 2006). You could use it to buy theater tickets or even to pay for plane or train tickets or hotel reservations.

Another use is automatic gated entry. Passing your cell phone near the reader can let you into a building, parking lot, or other controlled area. Maybe we will even come up with an NFC “business card” so we can exchange “cards” by just “toasting” one another with our cell phones.

Another proposed use is to initiate setup for other forms of wireless. Some short-range wireless modes like Wi-Fi or Bluetooth require the two parties desiring a peer-to-peer link to first exchange info to set up the correct protocol. This sometimes is called pairing. Placing your cell phone, laptop, or other device next to the connecting device allows all this protocol setup to be exchanged automatically. After that, the two devices then automatically begin talking in the new wireless mode faster and at a longer distance.

I suspect that designers will come up with all sorts of nifty applications using laptops, PDAs, printers, and cameras, as well as cell phones. And there’s no doubt that some applications will surprise us—like the automatic wireless toilet flusher, which has to be the most widespread use of infrared (IR) wireless these days. IR wireless has been around for years, but it was never that successful. Even though its range is at least several feet, it requires a direct line-of-sight path, which is difficult to achieve in some cases. NFC doesn’t have that problem.

I like NFC. It may catch on, whereas smartcards have not. American Express, Visa, Mastercard, and other companies offer smartcards, but few of us have them. And the reader terminals aren’t that prevalent. You still have to swipe your mag-stripe card through a reader to charge something. Potentially, all you have to do is pass your cell phone over the reader, and you’re charged. Most of the countries of the world are beginning to use smartcard or RFID technology for passports. The U.S. will start using them this year.

Anyway, it has taken me a while to get used to such short-range wireless. I thought a Bluetooth headset was a really stupid idea. Why replace a 3-ft cable with a complex digital radio? Give me a break. But as in many short-range wireless applications, it makes sense if the price is right and it provides some measure of convenience or comfort. NFC will undoubtedly provide that. And, NFC will be just one more RF device to go into the cell phone besides Bluetooth, Wi-Fi (for VoWi-Fi), or GPS. Can Ultra-Wideband or ZigBee be far behind?

For more info on NFC, go to the NFC industry’s consortium, called the NFC Forum, at www.nfc-forum.org. Philips and Sony formed this organization along with Nokia last year, and it already has about 50 members. ECMA also has a good white paper on the topic at www.ecma-international.org.

An Interesting Wireless Web Site And Blog

I highly recommend this site. Lots of stuff in there to think about. —LF


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