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NFC-Near Field Communication

Device A

Device B

Description

Communication Mode

Active

Active

RF field generated by both devices

Active mode

Active

Passive

RF field generated by device A only

Passive mode

Passive

Active

RF field generated by device B only

Passive mode

An NFC reader is always an active device and is capable of bidirectional information transfer with another NFC device. An NFC reader can be in one of two forms: internal and external. An internal NFC reader can be integrated to an NFC enabled mobile phone, so that when the NFC mobile is touched to an NFC tag, it can read/write data from/to the tag. Thus the interaction between an NFC mobile (with embedded NFC reader) and an NFC tag is, respectively, the interaction between active and passive devices.

 

In the case of the interaction between two NFC mobiles, a link-level communication is created between them. An NFC reader embedded in an NFC mobile is always active and generating its own RF field, unless the NFC mobile is in standby or airplane mode. An external NFC reader is generally used for reading data from an NFC mobile. The most common example of an external NFC reader is a contactless POS terminal which can perform contactless NFC enabled payments when an NFC device is touched to the NFC reader.

NFC readers

An NFC tag is actually a passive RFID tag. Currently only a small amount of data can be stored on an NFC tag. In order to power an NFC tag, the user touches an active device such as an NFC mobile or an NFC reader to it. As the active device creates an RF signal, the energy is consumed by the NFC tag so that it boots up immediately and data are transferred back, since the pre-loaded algorithm is designed to do so.

By being a passive device, an NFC tag can communicate with only an active NFC device (NFC mobile or NFC reader); two tags cannot communicate with each other because no power source exists in NFC tags to enable the communication. NFC tags can be used in applications that require small capability such as smart posters. NFC tags may contain any type of data, but the size limitation cannot be exceeded. NFC Forum as a standardization body has defined four NFC tag types (Type 1, Type 2, Type 3, and Type 4).

NFC tags

NFC enabled mobile phones are also referred to as NFC mobiles. Currently, integration of NFC technology in NFC mobiles creates a big opportunity to show the ease of use and for acceptance of NFC ecosystem. Many NFC mobile models are already available in the market. Mobile phones enable secure storage of data and hence are able to behave like secure smart cards. By using this feature, NFC enables the use of NFC enabled applications that require secure implementation such as payment, ticketing, loyalty applications, and access control.

NFC enabled mobile phones

The Table shows the possible combinations of initiator/target roles with respect to active/passive roles for a device. An active device can act as both an initiator and a target. However, a passive device cannot be an initiator.

NFC occurs between two NFC devices. These devices can play an initiator or a target role as well as being an active or a passive device. The Table  shows the possible interaction styles between NFC devices which are NFC enabled mobile phones, NFC tags, and NFC readers:

Polling device (initiator) and listening device (target) configuration

In addition, there are two different roles that a device can play in NFC which can be illustrated as a “request and reply” concept as shown in Figure 3.1. The initiator sends a request message to a target and the target replies by sending a message back to the initiator. In this case the role of the initiator is to start the communication. The role of the target is to respond to the requests coming from the initiator.

NFC occurs between two NFC devices in a close proximity range (within a few centimeters). These two NFC devices can operate in several modes. NFC modes are distinguished based on whether each device has an embedded power source, so that they can generate their own RF, or one retrieves the power from the RF field generated by the other. In terms of power, if a device generates its own RF field, it is called an active device; otherwise, it is called a passive device.

 

Alternatively devices can be classified based on an algorithmic point of view; if a device actively leads in a communication session such as by asking for a credit card number, or by passing some information to the partner based on some intelligent decisions, it is assumed to be an active device. However, if it replies to the interrogator, it is assumed to be a passive device. In essence, both points of view (classification of devices based on their internal power source or the algorithm used) mostly match. When a device has an embedded power source, it naturally initiates and leads communication. On the other hand, if it does not have any embedded power source, it can only respond to the active device.

 

Similarly, operation modes defined in NFC protocol are also classified as active and passive communication modes. In active communication mode, both devices generate their own RF field to exchange data (see Table). In passive communication mode, only one device generates an RF field, while the other uses load modulation to transfer data.

Introduction to NFC