Wireless Communication

The protocol is based on a wireless interface. There are always two parties to the communication;

hence the protocol is also known as peer-to-peer communication protocol. The protocol establishes

wireless network connections between network appliances and consumer electronics devices.

The interfaces operate in the unregulated RF band of 13.56 MHz. This means that no restrictions are

applied and no licenses are required for the use of NFC devices in this RF band. Of course, each

country imposes certain limitations on the electromagnetic emissions in this RF band. The limitations

mean that in practice the distance at which the devices can connect to each other is restricted and

this distance may vary from country to country. Generally speaking, we consider the operating

distances of 020 cm.

As is often the case with the devices sharing a single RF band, the communication is half-duplex.

The devices implement the "listen before talk" policy - any device must first listen on the carrier and

start transmitting a signal only if no other device can be detected transmitting.

NFC protocol distinguishes between the Initiator and the Target of the communication. Any device

may be either an Initiator or a Target. The Initiator, as follows from the name, is the device that

initiates and controls the exchange of data. The Target is the device that answers the request from

the Initiator.

NFC protocol also distinguishes between two modes of operation: Active mode and Passive mode.

All devices support both communication modes. The distinction is as follows:

In the Active mode of communication both devices generate their own RF field to carry the

data.

In the Passive mode of communication only one device generates the RF field while the

other device uses load modulation to transfer the data. The protocol specifies that the

Initiator is the device responsible to generate the RF field.

The application sets the initial communication speed at 106, 212 or 424 kbit/s. Subsequently the

application and/or the communication environment may require speed adaptation, which can be

done during communication.

NFCIP-1 uses different modulation and bit encoding schemes depending on the speed. While

establishing the communication, the Initiator starts the communication in a particular mode at a

particular speed. The Target determines the current speed and the associated low-level protocol

automatically and answers accordingly.

The communication is terminated either on the command from the application or when devices move

out of range.

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4

Unique features

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

centimetres. 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

1

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