This installment of Networking is the first in a two-part series on two different “tiny area networks,” or TANs, used in healthcare: near-field communication (NFC), covered in this article, and body area networks, covered in part two.
Most sources describe a TAN as a local area network with only two or three nodes. My use of the term is more related to the compact physical area the network covers. Common examples are Bluetooth or radio-frequency identification (RFID). An even smaller TAN than these two technologies is near-field communication, or NFC, with a typical wireless range of 4 cm, or 1.5 inches. This article will cover the basic functionality of NFC, where it’s used, and what its impact might be on healthcare technology.
Using NFC
In general, an NFC reader generates a magnetic field to excite and power an NFC tag via inductive coupling. The power is usually so low that it will only work within a 4-cm range.
NFC is used most often in a variety of consumer applications, including payment systems.1,2 With an NFC tag placed in a credit card, you can tap your card on an NFC reader at checkout to pay for your items. (The credit card information may also be placed in many smartphones.) There is also little to no network setup or initializing per se, making the whole process that much speedier. Your purchase limit or bank information is preloaded, so there’s no need to connect with the bank at checkout, further speeding up the process.
NFC is used in a number of healthcare applications as well. In some facilities, clinicians can tap their ID badge on a bedside chart containing a NFC reader to automatically log their visit and update the patient’s EHR. NFC-enabled patient monitoring devices already on the market include pedometers, body composition monitors, blood pressure monitors, blood glucose monitors, basal thermometers, walking intensity monitors, and pulse oximeters.3
Background
NFC is not really a new technology. It was approved as an ISO/IEC standard in 2003. In 2004, Nokia, Sony, and Royal Philips Electronics started a cooperative alliance called the NFC Forum. Since then, more than 160 other companies and organizations, including giants like Samsung, Microsoft, and Motorola, have joined. NFC has been used in many smartphones since about 2007.2,4 Although Apple has been slow to adopt NFC, the new iPhone6 will include something called Apple Pay, which appears to be NFC enabled.5
NFC is partly based on the RFID definitions (called far field communication), as noted in the ISO/IEC14443 standard,6 especially in defining communication protocols and signal interfaces. The biggest differences between RFID and NFC are that NFC has two-way communication and uses considerably less power than RF systems.1 NFC is specifically standardized in ISO/IEC 18092,7 as well as ECMA standard 340, which is fully aligned with ISO/IEC18092.8
Communication Structure
The NFC reader is also called the proximity reader or, officially, the proximity coupling device (PCD). The NFC tag is also known as the proximity card or, officially, the proximity integrated circuit card (PICC).9
The PCD initiates the communication session by generating a magnetic field oscillating at 13.56 MHz near the tag (about 1.5 inches away). Think of the transfer of energy as an air-core transformer with the primary winding in the reader and the secondary winding in the tag. Both coil circuits that make up the winding are tuned to 13.56 MHz. When the reader sends current through its primary winding, a magnetic flux is generated and an induced voltage is sensed on the secondary winding in the tag. As the secondary winding resonates with the sensed energy, it is rectified to provide DC power to the tag’s electronics.9
After the initial carrier signal powers the tag, the reader (which always talks first), via half-duplex communication, generates a digital message by modulating the amplitude on the primary coil at 106 Kbits per second. The reader uses a transmission method called delayed encoding, or Miller encoding. The method guarantees a binary transition with every other bit, so that the receiver can adjust its data clock on a continuing basis. A binary 0 does not cause an amplitude transition unless immediately followed by another 0, which causes a transition to happen at the first half of the next bit time frame. A binary 1 is represented by a transition in the middle of the bit period. The bit stream then modulates the carrier using 100% amplitude shift keying (ASK).3,10
ASK Modulation
ASK modulates the amplitude of the carrier wave tuned to 13.56 MHz, which is in the unlicensed ISM band. The simplest form of ASK acts like a switch. For a binary value of 1, the carrier is typically transmitted at full strength, or at 100% for a bit duration of T seconds, based on the data rate. To send a binary 0, the carrier is either turned off (0% for the bit duration) or at 10% of maximum amplitude. The 100%/0% method is called on-off keying, and is what the reader uses to modulates its data. The tag responds using a 10% ASK.4
Amplitude levels can also be used to represent more than one bit, increasing the data-transmission rates overall. For example, a four-level amplitude scheme would allow two bits to be transmitted at once. Level 1 could represent a binary value of 00 using 25% of the available amplitude; level 2, 01 at 50%; level 3, 10 at 75%; and level 4, 11 at 100%. An eight-level system could represent three bits at each level, and so on. However, as the number of levels increases, so does the need for a high signal-to-noise ratio, while maintaining very close proximity.
The maximum data rate for an NFC system is typically quoted to be 424 Kbits per second. The system will use either 212 Kbits per second or 106 Kbits per second as environmental electromagnetic noise levels increase.
The Tag Responds
The PICC (NFC tag) responds (again half-duplex) to the reader by changing the impedance of its winding resonant circuit. The reader senses the changing impedance on its side of the transformer and detects the information being sent. In this process, called load modulation, the tag uses Manchester encoding and a 10% ASK. Just by loading the field more or less, information is transferred.10
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Types of NFC Tags
The NFC Standard defines four types of tags. All tags are preconfigured to be read and rewrite capable or read-only. They can also be configured as write-protected.
NFC Forum Type 1 Tag. Based on ISO/IEC 14443A. Available memory: 96 bytes up to 2 KBytes. Communication speed for this tag is 106 Kbits per second.
NFC Forum Type 2 Tag. Based on ISO/IEC 14443A. Available memory: 48 bytes up to 2 KBytes. Communication speed for this tag is also 106 Kbits per second.
NFC Forum Type 3 Tag. Based on the Japanese Industrial Standard (JIS) X 6319-4, also called FeliCa. Available memory varies; the theoretical maximum is 1 MByte. Communication speed for this tag is 212 Kbits per second.
NFC Forum Type 4 Tag. This tag is fully compatible with the ISO/IEC 14443 (types A and B) standard series. Available memory varies up to 32 Kbytes. Communication speed for this tag can vary from 106 to 212 or 424 Kbits per second.
Adapted from Poole, I. (2014, September 14). NFC Tags and Tag Types. Radio-Electronics.com. [/reference]
Applying the NDEF Protocol
Now that we’ve explored modulating a nonpropagating, quasi-static magnetic field between the devices (say that three times fast!), let’s look into the data that is transferred. The NFC data exchange format (NDEF) protocol specifies a message encapsulation format (called a record) to exchange information in an NFC network. NDEF is called a lightweight binary message format, and can be used to encapsulate one or several application-defined payloads of any type and size into a single message. In other words, NDEF messages are made of one or more NDEF records. There can be several separate records in a NDEF message.11
Each record has a header field and payload field. Within the header, the record lists an NFC record type definition (RTD) identifier, data length information, and the type of tag in use (see sidebar).
NFC RTD Technical Specification
The format for standard record types is specified by the NFC Forum application definitions. The RTDs are based on the NDEF data format. The RTD specification also shows how to define record formats for new applications.
The application data can be just about any type of information defined by the NFC Forum, including the following RTDs:
- URI type (uniform resource identification that includes URLs, telephone numbers, and SMS and email addresses);
- Text type (any alphanumeric characters or plain text words and phrases);
- Smart poster type (for example, text and a URL from a movie poster to get more information about a movie);
- Business card (for exchanging vCards);
- Signatures; and
- Handover parameters (specifies Bluetooth and Bluetooth address or Wi-Fi information including PIN, SSID, and WEP Key).12
NFC Forum Connection Handover Technical Specification
Higher-level wireless communication methods are often set up via NFC, as indicated in the RTD list above. The connection handover combines the simple provisioning of NFC (establishing communication in 100 msec) with higher-speed communication methods like Wi-Fi or Bluetooth. The RTD indicates the preferred communication method to the reader. If a match is found, the connection can switch to the selected carrier. Via this specification, the other higher-bandwidth standards also can provide the information needed for the connection provisioning to be in the NDEF messages.12
Summary
One of the coolest NFC-based innovations in healthcare is the MiniME device from a company named Veryday (formerly Ergonomidesign). Announced in 2010, MiniME (not to be confused with the little dude in the Austin Powers movies) connects various biosensors to track physiological data using NFC. It measures ECG, blood pressure, heart rate, pulse oximetry, body temperature, blood glucose, cholesterol, hemoglobin, and prothrombin time.13 I expect use of NFC for devices like this to grow as the NFC market expands and NFC become cheaper and more widely available. As an example of this expansion, Frost & Sullivan expects NFC-style payment methods to reach $111.2B by next year.14 Add to this the news that a lab prototype NFC connection has achieved data rates of 6.78 Mbits per second from tag to reader.10
Given these trends, it seems that we’ll be seeing a lot more of NFC!
Jeff Kabachinski is the director of technical development for Aramark Healthcare Technologies in Charlotte, NC. For more information, contact [email protected].
References
1. Newton H. Newton’s Telecom Dictionary. New York: Flatiron Publishing; 2011.
2. Kessler S. (2010, May 6). NFC technology: 6 ways it could change our daily lives. Available at: Mashable.com. Accessed September 16, 2014.
3. Near field communication in health care. (2014, August 24). Available at: NFCNearFieldCommunication.org. Accessed September 16, 2014.
4. Near field communications. (2014, August 8). Available at: Wikipedia. Accessed September 16, 2014.
5. Your wallet without the wallet. (2014, September 12). Available at: Apple.com. Accessed September 16, 2014.
6. ISO/IEC 14443: Identification Cards—Contactless Integrated Circuit Cards—Proximity Cards. Available at: Wikipedia. Accessed September 16, 2014.
7. ISO/IEC 18092: Information Technology—Telecommunications and Information Exchange Between Systems—Near Field Communication—Interface and Protocol (NFCIP-1). Available at: TechStreet.com. Accessed September 16, 2014.
8. ECMA 340: Near Field Communication Interface and Protocol (NFCIP-1). Available at: ECMA International . Accessed September 16, 2014.
9. Philips Semiconductors. mifare® (14443A) . 13.56 MHz RFID Proximity Antennas. Koninklijke, Netherlands; November 2002.
10. Patauner C, Witshnig H, Rinner D, Maier A, Merlin E, Leitgeb E. High speed RFID/NFC at the frequency of 13.56 MHz. Gratkorn, Austria: NXP Semiconductors; 2007. Available at: Eurasip.org. Accessed September 16, 2014.
11. Nokia. (2014, September 9). Understanding NFC data exchange format (NDEF) messages. Available at: Nokia Developer Wiki. Accessed September 16, 2014.
12. NFC forum technical specifications. (2014, August 23). Available at: NFC Forum. Accessed September 16, 2014.
13. MiniME device is the future of healthcare, says Ergonomidesign. (2010, November 23). Available at: Product Design and Innovation. Accessed September 16, 2014.
14. HCL Technologies. (2013). Near field communication in medical devices. Available at: HCLTech.com. Accessed September 16, 2014.
