Near field communication (NFC) has recently popped up in the news. The technology is most closely associated with mobiles phones—Google has added support for NFC in Android, and Samsung has NFC hardware in its Nexus S handset, while Apple is rumored to be adding NFC support to future iPhones. NFC is an evolution of the simple RFID technology employed in "contactless" payment systems such as MasterCard PayPass and Visa payWave. It's also similar to (and compatible with) the FeliCa system used widely in Asia for mobile payments and ticketing systems.

In this article, we'll tell you what NFC is, how it works, and how it can be used.

RFID and FeliCa: NFC precursors

NFC is an evolution of the original specifications used to create RFID tags and contactless payment systems. ISO/IEC 14443 defines specifications for identification cards, contactless integrated circuit cards, and proximity cards, which for the purposes of discussion here we'll call "tags." The spec also describes two primary methods of data transmission over the 13.56MHz frequency band—Type A and Type B—using a standard connection protocol between an active "reader" device and a typically "passive" tag.

Type A communication uses Miller bit coding with a 100 percent amplitude modulation. Here, the signal varies between nearly zero amplitude and full amplitude to signal low and high values. Miller, or delay encoding, works by varying the time between signal transitions depending the sequence of bits compared to a clock signal. It also transmits data at 106kBps.

Type B uses variations of Manchester encoding along with a 10 percent modulation. Here a 90 percent signal is "low" while a 100 percent signal is "high." Manchester encoding only looks at the signal transition at the middle of a clock period, so the transition from low to high is considered a "0" while a transition from high to low is considered a "1."

When two devices are brought within a range of about 4cm (the spec does allow for maximum distances of up to 20cm, though 4cm or less is common), a reader device's RF signal will cause a current to flow through the antenna built in to a RFID tag or smart card, activating its circuit. In this near RF field, the antennas of the two devices act as coils of a transformer with the distance between the two acting as an air core. Changes in signal transmitted by the reader result in changes in power flow in the tag, and changes in power flow of the tag—accomplished via load modulation—result in changes in signal detected by the reader. Data is transmitted back and forth using the various coding schemes described above.

Once current starts flowing, the reader will poll the tag to find out what communication method it uses. Communication is half-duplex, meaning that communication only happens in one direction at a time, so the protocol defines specific methods for two devices to ask for data and respond correctly. In effect, the reader will ask the tag to agree to a communication speed and method, and begin setting up a link once the signaling method is agreed upon.

After a link is established, the reader will tell the tag what kind of applications it supports and request data or commands. The tag will respond with any data or commands that correspond to the request. To give an example, a credit card reader that works with Visa's oft-advertised "payWave" system will ask the tag embedded in a Visa credit card for the card number and expiration date. The card, if it is designed to respond to that request, will transmit the information back to the reader.

The system is application-agnostic, so it's possible to develop applications that use the communication standard and data format in ways that the NFC Forum hasn't foreseen.

Once the requested data is transmitted, the tag or reader might request additional data or commands. As long as the reader and tag are in close proximity, these data exchanges can occur. Once data has been exchanged according to either the reader's or tag's design, the connection can be terminated. Alternately, moving the two devices away from each other will also break the connection. In our payWave example, once the reader has the requested credit card information, it will break its connection with the card and begin a transaction authorization.

This type of RFID technology is employed in the MIFARE-based cards that are widely used for transit systems and secure building access, biometric passports, and contactless payment systems like payWave and Mastercard's PayPass.

Sony developed a similar platform for contactless payments called FeliCa, widely used in Asia. FeliCa-based cards are used for transit systems and security access, as well as contactless payment systems. Incorporation of FeliCa technology in mobile phones in Japan led to the system becoming a de facto mobile payment standard there, with customers able to pay for parking, train fare, vending machine items, and more using a FeliCa-equipped handset.

FeliCa uses a slightly different variation of Manchester coding than Type B RFID communication, but similar communication protocols are employed. Data can be transmitted at higher speeds using the FeliCa variation, either 212kBps or 424kBps. FeliCa has been accepted as a standard in Japan, dubbed JIS X 6319-4.

Evolution, not revolution

The NFC standard grew out of work by Sony and Philips (which at the time owned MIFARE) to make their standards interoperable while extending the general capabilities of the set-up-free two-way communication offered by those standards. The basic NFC communication operation became an accepted ISO standard (ISO/IEC 18092) in 2003, and later an ECMA standard (ECMA-340) as well.

In 2004, Sony, NXP Semiconductors (a spin-off of Philips that manufactures MIFARE chips), and Nokia created the NFC Forum. This consortium, whose members include handset makers, mobile carriers, credit card companies, and chipmakers, works to define standards on top of the existing ISO/IEC 18092 spec to ensure compatibility across devices and NFC implementations.

The NFC standard incorporates previous communication and linking protocols from both RFID Type A and B and FeliCa. It also defines four tag types and four different modes of operation.

In addition, the NFC Forum has defined a standard data format and a number of common operations to facilitate certain applications, such as transferring credit card information, or extracting URLs or other information from "smart posters." However, the system is application-agnostic, so it's possible to develop applications that use the communication standard and data format in ways that the NFC Forum hasn't foreseen. The standards are there to help facilitate interoperability, particularly among similar applications like mobile payment or transit ticketing systems.