NFC在近距无线技术中如何超过Bluetooth(英)

While Bluetooth is an excellent technology for short-range data communication, shortcomings in its transport layer protocol can make the initial set-up of links between devices cumbersome for the user.

Simply associating a Bluetooth headset to a cellular phone can take up to 30 seconds (worst case) and even re-connecting previously recognized nodes often requires some manual intervention.

Fortunately, Near Field Communication (NFC) technology can be used in conjunction with Bluetooth to simplify the process of adding nodes to a user’s normal personal area network, or establishing temporary links to public resources such as cash machines, photo printers, or point-of-sale terminals.

Using NFC to do the initial "handshake" between Bluetooth nodes eliminates the need for user intervention and enables almost instantaneous pairing of devices. Its separate operating frequency and complimentary applications (see Table 1) make it easy for NFC to co-exist with Bluetooth in the same product, allowing it to simplify the discovery and negotiation phases of a Bluetooth transaction.

Table 1 – A quick comparison between NFC and Bluetooth

There are three main features that make NFC different and complementary to any other wireless network technology.

1. Shorter distance: NFC has been deliberately designed with an extremely short (10cm) operating range to prevent accidental or unauthorized activation of the link.
2. Intuitive linking procedure: NFC’s linking procedure was developed to work the way ordinary consumers do, instead of the way engineers or programmers think. Much like today’s smart cards, initiating a transaction with an NFC-enabled PDA or cell phone is accomplished by simply holding it in close proximity to the device you wish to connect to.
3. Ability to communication with un-powered RFID products: NFC works in the conventional way between self-powered devices and also supports communication to passive devices such as contactless smart cards or RF transponders.

NFC basics
NFC was originally designed for "no-touch" data transfers across very short distances (10cm or less) using the 13.56 MHz RFID band. It is an open standard, defined by ISO 18092 and ECMA 340 and is backward-compatible with the global standard for RFID per ISO 1443.

Its low cost, high reliability and global compatibility has made it the technology of choice for applications such as RFID, electronic payment, and "no swipe" smart cards. These same characteristics also allow NFC to serve as a secondary channel to automatically perform the authentication and initial parameter exchange required to establish a Bluetooth link.

Whereas a normal "pairing" operation between Bluetooth devices usually takes five or six seconds (and up to 30 seconds in congested environments), NFC’s streamlined single-link protocol completes the same task in 100-200 milliseconds.

This efficiency is in good part due to the fact that NFC is a relatively simple protocol initially developed for a handful of straightforward, point-to-point applications, an approach which contrasts sharply to Bluetooth’s more complex series of usage models.

Using a subset of standard RFID technology and a typical output power of between 1 to 2 dBm, NFC can support ultra-short data links with transfer rates of 106 Kbits/s, 212 Kbits/s, and 424 Kbits/s in both its active and a passive operational modes (see figure 1). NFC’s "active mode" requires both devices to support full duplex data exchanges while "active/passive" operation only requires a single active transmitter which can be used to energize its passive counterpart.

The passive element’s receiver is only required to acknowledge its presence when polled, confirm availability to enter communication, and acknowledge receipt of data. NFC’s active mode on the other hand, requires both nodes to be engaged and negotiate the exchange. While most applications require that both NFC nodes be active, the "active/passive" mode will be useful for communicating with un-powered devices, like contactless cards.

Fig. 1a - NFC Active Mode Operation

Figure 1b - NFC Passive Mode Operation

An NFC transaction always follows a straightforward sequence of Discovery, Authentication, Negotiation, Transfer, and Acknowledgment. NFC’s link layer includes a secure authentication procedure and anti-collision mechanisms that preclude a third party from hacking the link by playing "man in the middle."

In addition, its short (10 cm) range limits access to potential "black hat" hackers. For sensitive applications such as secure payment exchanges, AES and triple DES encryption can be added at higher layer using the same techniques employed by standard smart card technologies. NFC’s negotiation phase establishes parameters which define the upcoming transaction such as link speed, device ID, application, transfer size, and action requested.

At this point, the NFC link can either perform a simple data transaction of its own, or be used to establish a connection to a Bluetooth-based peer-to-peer or host/client link between devices. The latter involves negotiating Bluetooth node addresses for both ends and using Bluetooth’s higher-layer protocols to handle link termination. These parameters are passed between the Bluetooth and NFC devices using either serial link, typically either an I²C, or SPI interface, and a simple exchange protocol.

This ability to handle lower-layer tasks automatically enables the NFC protocol to greatly improve the user experience of many consumer applications. The illustration below (see Figure 2) compares the interactions required by the user to establish a link between two cellular handsets or PDAs in order to play a game or exchange photos. Similar mechanisms have also been developed for Wi-Fi and Wireless USB users to enjoy the same level of speed and convenience when making connections to their networks.

Figure 2 – NFC’s transparent handoff to Bluetooth simplifies establishing a link for multiplayer gaming between handheld devices

NFC in the real world

Since NFC compliments Bluetooth’s longer range and higher data rates, devices equipped with both technologies enjoy greater flexibility and offer a much better user experience. A simplified way of looking at the synergies between the two technologies is to imagine that Bluetooth is a versatile "cable" that can be used to enable exchanges between any two electronic devices while NFC serves as a universal "connector" that makes the process quick and easy.

But rather than simply list the dozens of applications where NFC is expected to find a ready market, we’ll explore a few scenarios that show how simplifying Bluetooth’s linking process can help make today’s applications easier and more fun to use. We’ll also look at how NFC will enable new applications that unleash the power of handheld devices and may even give rise to entirely new classes of products.

Hands-free connections
NFC will gain early market acceptance by simplifying the process of linking Bluetooth-equipped cell phones with headsets and hands-free systems. A headset or speaker unit need only contain a contactless RFID card to enable pairing with a cell phone simply by touching the two devices together. In this scenario, the phone reads the card to determine both the offered functionality of the headset and the Bluetooth set-up parameters.

Desktop/Handheld synchronization
Smart phone users will also enjoy the benefits of NFC-enabled Bluetooth when they synchronize their contact lists, calendars, and other vital data with their PCs. Synchronization of your phone or PDA is now as simple as holding the device close to your PC and answering a couple of questions from a menu on your handheld’s screen.

Gaming
NFC will also find many applications in the world of electronic games by enabling local networked game play in ad-hoc environments such as students gathering at lunch or commuters on their way to and from work. When used in conjunction with Bluetooth, NFC overcomes many of problems currently associated with establishing a connection that have slowed its acceptance.

Unlike connecting Bluetooth headsets to cell phones where a link is usually configured only once, ad-hoc gaming requires a gamer to establish a new link every time they hook up with a player. The three-to-five-minute procedure that was acceptable for a one-time set-up of a phone and headset quickly becomes a time-consuming hassle if a user has to repeat it several times a day.

This process can get even more complicated in crowded public spaces where many Bluetooth devices may be visible at any one time—a situation which makes it difficult to determine which device is the one you want to attach to.

NFC provides the solution to this problem, allowing connections to be made seamlessly, intuitively and instantly. Whether you’ve got a dedicated gaming device such as a Game Boy or PS2, or you’re using the games embedded in your cell phone or PDA, NFC makes setting up a multiplayer connection a simple "touch-and-go" operation. The two gamers only need to touch their devices and allow the NFC software on the devices to handle the discovery, inquiry, authentication and encryption set-up required to establish a Bluetooth link.

Image printing
The rise of digital photography has created an explosive demand for instant prints, both from home printers and the photo kiosks that are finding their way into nearly every drugstore, discount outlet, and convenience store. NFC-enabled Bluetooth links can provide a simpler alternative to the USB cables CDs, and memory cards that are currently used to move images between cameras and printers.

Printing the images on your phone or camera at a commercial photo kiosk would simply involve placing your device in a designated area on top of the machine, enabling image sharing from your handheld’s menu, and printing in the normal manner. In the home and office, printers with NFC-enabled Bluetooth capabilities will make printing directly from any similarly equipped camera a seamless process. During the two-to-three years it will take for the technology to become commonplace, USB-based adapter "dongles" can enable older computers and printers to talk to Bluetooth-equipped handhelds.

Image sharing
The same technology will also help ’liberate’ images from the cramped confines of the tiny screens in PDAs and smartphones. It’s not too hard to imagine friends swapping photos between handhelds in the same way that they ’beam’ business cards to each other today. This ability to fluidly move images will also enable computers, televisions, and flat panel screens to become temporary displays for pictures.

Image transfer capabilities can be inexpensively embedded in a DVD player, home theater unit, or perhaps even in the video display itself. Simply touching your handheld device to an NFC-enabled Bluetooth appliance will initiate a link and bring a menu up on the portable unit’s screen that allows you to select, transfer and display an image. And much like computers, aftermarket Bluetooth adapters will enable earlier-generation video products to accept a user’s photos from any Bluetooth-enabled source.

The feasibility of image sharing has already been proven in a technical demonstration conducted by Philips. In this proof-of-concept test, a separate user-level application is used to initiate transfer the picture. In subsequent commercial implementations, the NFC software will be integrated into the unit’s software to minimize user interaction.

NFC today and tomorrow
NFC is already gaining wide acceptance with the technology already complimenting Bluetooth capabilities in cell phones, PDAs, and other high-volume consumer devices. We can expect to see Bluetooth-equipped devices that support NFC on the market during 2006. NFC-enabled POS terminals cash machines are already deployed in different regions and touch-and-go photo print kiosk are slated to hit the market in early 2007.

During these early days, NFC will find its way into products as a stand-alone chip. Initial target cost for the types of applications described above is under $1 for high production volumes that are driven by widespread acceptance.

Within two–to-three years, it is expected that most NFC devices will become functional cores within larger integrated solutions, making it more of a design feature than a cost addition. This widespread acceptance of NFC as an enabling technology for wireless protocols will help create a new generation of wireless products that interoperate seamlessly and exchange voice, video, and e-cash with equal ease.

For further information
NFC is an open standard, governed by the NFC Forum whose charter is to guarantee interoperability between applications. Its activities include development of benchmarks, test certification standards, and supporting "plugfest" events. For more information, visit: More information is available at www.nfcforum.org.

The web site SmartCardBasics.com More information is available at www.smartcardbasics.com/standards.html provides a good overview of smartcard standards and technologies.

About the author
Taoufik Ghanname is a marketing manager for contactless and embedded security at Philips Semiconductors, and is responsible for near field communication (NFC) business Ghanname holds a Master in Electronics & Telecommunications from Institut National Polytechnique de Grenoble (INPG-ENSERG).