Near Field Communication
Published on Mar 02, 2016
NFC Near Field Communication is one of the latest wireless communication technologies. As a short-range wireless connectivity technology, NFC offers safe - yet simple and intuitive - communication between electronic devices. Users of NFC-enabled devices can simply point or touch their devices to other NFC-enabled elements in the environment to communicate with them, making application and data usage easy and convenient.
With NFC technology, communication occurs when an NFC-compatible device is brought within a few centimeters of another NFC device or an NFC tag. The big advantage of the short transmission range is that it inhibits eavesdropping on NFC-enabled transactions. NFC technology opens up exciting new usage scenarios for mobile devices.
Near Field And Far Field
he terms "far field" and "near field" describe the fields around an antenna or, more generally, any electromagnetic-radiation source .The names imply that two regions with a boundary between them exist around an antenna. Actually, as many as three regions and two boundaries exist. These boundaries are not fixed in space. Instead, the boundaries move closer to or farther from an antenna, depending on both the radiation frequency and the amount of error an application can tolerate. To talk about these quantities, we need a way to describe these regions and boundaries.
Like ISO 14443 , NFC communicates via magnetic field induction , where two loop antennas are located within each other's near field , effectively forming an air-core transformer . It operates within the globally available and unlicensed radio frequency ISM band of 13.56 MHz , with a bandwidth of almost 2 MHz.
Working distance with compact standard antennas: up to 20 cm .
Supported data rates: 106, 212, or 424 kbit/s .
There are two modes:
Passive Communication Mode: The Initiator device provides a carrier field and the target device answers by modulating existing field. In this mode, the Target device may draw its operating power from the Initiator-provided electromagnetic field, thus making the Target device a transponder.
STANDARDS AND COMPATIBILITY
Near Field Communication is an open platform technology, developed by Philips and Sony. NFC, described by NFCIP-1 (Near Field Communication Interface and Protocol 1), is standardized in ISO 18092, ECMA 340 as well as in ETSI TS 102 190. These standards specify the basic capabilities, such as the transfer speeds, the bit encoding schemes, modulation, the frame architecture, and the transport protocol. Furthermore, the active and passive NFC modes are described and the conditions that are required to prevent collisions during initialization.
NFC devices not only implement NFCIP-1, but also NFCIP-2, which is defined in ISO 21481 , ECMA 352 and ETSI TS 102 312. NFCIP-2 allows for selecting one of three operating modes:
• NFC data transfer (NFCIP-1),
• proximity coupling device (PCD), defined in ISO 14443 , and
• vicinity coupling device (VCD), defined in ISO 15693 .
NFC devices have to provide these three functions in order to be compatible with the main international standards for smartcard interoperability, ISO 14443 (proximity cards, e.g. Philip’s Mifare ), ISO 15693 (vicinity cards) and to Sonys FeliCa contactless smart card system. Hence, as a combination of smartcard and contactless interconnection technologies, NFC is compatible with today’s field proven RFID-technology. That means, it is providing compatibility with the millions of contactless smartcards and scanners that already exist worldwide.
NFC operates in the standard, globally available 13.56MHz frequency band. Possible supported data transfer rates are 106, 212 and 424 kbps and there is potential for higher data rates. The technology has been designed for communications up to a distance of 20 cm, but typically it is used within less than 10 cm. This short range is not a disadvantage, since it aggravates eavesdropping.
COMMUNICATION MODES: ACTIVE AND PASSIVE
The NFC interface can operate in two different modes: active and passive. An active device generates its own radio frequency (RF) field, whereas a device in passive mode has to use inductive coupling to transmit data. For battery-powered devices, like mobile phones, it is better to act in passive mode. In contrast to the active mode, no internal power source is required. In passive mode, a device can be powered by the RF field of an active NFC device and transfers data using load modulation. Hence, the protocol allows for card emulation, e.g., used for ticketing applications, even when the mobile phone is turned off. This yields to two possible cases, which are described in Table . The communication between two active devices case is called active communication mode, whereas the communication between an active and a passive device is called passive communication mode.
In general, at most two devices communicate with each other at the same time. However in passive mode the initiator is able to communicate with multiple targets. This is realized by a time slot method, which is used to perform a Single Device Detection (SDD). The maximal number of time slots is limited to 16. A target responds in a random chosen time slot that may lead to collision with the response of another target. In order to reduce the collisions, a target may ignore a polling request set out by the initiator. If the initiator receives no response, it has to send the polling request again.
What makes the communication between the devices so easy is that the NFC protocol provides some features not found in other general-purpose protocols.
First of all, it is a very short-range protocol. It supports communication at distances measured in centimeters . The devices have to be literally almost touched to establish the link between them. This has two important consequences:
(1) The devices can rely on the protocol to be inherently secured since the devices must be placed very close to each other. It is easy to control whether the two devices communicate by simply placing them next to each other or keeping them apart.
(2) The procedure of establishing the protocol is inherently familiar to people: you want something to communicate – touch it. This allows for the establishment of the network connection between the devices be completely automated and happen in a transparent manner. The whole process feels then like if devices recognize each other by touch and connect to each other once touched.
Another important feature of this protocol is the support for the passive mode of communication. This is very important for the battery-powered devices since they have to place conservation of the energy as the first priority. The protocol allows such a device, like a mobile phone, to operate in a power-saving mode – the passive mode of NFC communication. This mode does not require both devices to generate the RF field and allows the complete communication to be powered from one side only. Of course, the device itself will still need to be powered internally but it does not have to “waste” the battery on powering the RF communication interface.
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