Essay Preview: Wireless Communication
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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
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
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.
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
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