Mobile phones have been the craze of the entire world, for being the latest mode of communication.
Mobile phones are part of huge wireless/mobile communication systems
To send and share data quickly
The various technologies that are in use in the mobile phones are Bluetooth, IR, and WIFI. etc.
Near Field Communication (NFC) is a promising contact less technology integrated into these cellular phones.
WPAN is used in this technology
This paper deals with the concept, the implementation and the security of NFC and NFC enabled devices.

Near Field Communication (NFC) is a standards-based, short-range wireless connectivity technology
NFC operates in the standard 13.56MHz frequency band over a distance of up to around 20 centimeters
Currently it offers data transfer rates of 1Mbit/s and higher rates are expected in the future
For two devices to communicate using NFC one device must have an NFC reader/writer and one must have an NFC tag,
For two devices to communicate using NFC one device must have an NFC reader/writer and one must have an NFC tag . The tag is essentially an integrated circuit containing data , connected to an antenna that can be read and written by the reader,

Two active devices communicate with each other , Each device has to generate its own RF field, if it ants to send data , the RF field is alternately generated by one of the two devices.

In this mode the communication takes place between an active and a passive device , the passive device has no battery and uses the RF field generated by the active device.

Coding and modulation

The distinction between active and passive devices specifies the way data is transmitted. Passive devices encode data always with Manchester coding and a 10%ASK1.
The Manchester coding using a modulation ratio of 10% if the data rate is greater than106 kbps.

The Manchester coding depends on two possible transitions at the midpoint of period. A low-to-high transition expresses a 0 bit, whereas a high-to-low transition stands for a 1 bit.

This line code is characterized by pauses occurring in the carrier at different positions of a period. Depending on the information to be transmitted, bits are coded as shown in Figure
While a 1 is always encoded in the same way, coding a 0 is determined on the basis of the preceded bit.

In the case of an active configuration in which the RF field is alternately generated, the roles of initiator and target are strictly assigned by the one who starts the communication.
By default all devices are NFC targets, and only act as NFC initiator device if it is required by the application
In the case of two passive devices communication is possible

NFC is a short-range wireless technology.
NFC provides unique advantages over other available wireless technologies.
The design includes a near-field transmitter and receiver to send data from one computer to another, Not restricted to 1-to-1 communication
Maximum transfer bit rate of 1MB/s .No special software is required, Operation at a frequency of 13.5 MHz .

The VCO produces a frequency-modulated signal at the transmitter and Phase lock loop demodulates the signal at the receiver.
At the Transmitter the hardware used are PC interface (MAX232A),
Voltage-Controlled Oscillator (POS+25), Power Amplifier (LM6181), Loop Antenna and at the Receiver, Loop Antenna, Amplifier (LM6181), Phase Lock Loop (NE564), and PC interface (MAX232A) are the hardwares .

Initial applications for NFC technology fall into three categories:
Peer-to-peer, where NFC is used to enable communication between two devices
Payment & Ticketing, where NFC will build on the emerging smart ticketing and electronic payment infrastructures
Service initiation, where NFC is used to perform service discovery or to ‘unlock’ another service (such as opening another communication link for data transfer).

Near Field Communication is an efficient technology for communications with short ranges,
A significant advantage of this technique is the compatibility with existing RFID infrastructures,
NFC by itself cannot provide protection against eavesdropping or data modifications.
In other words, if NFC systems work under these conditions, there is a good chance they will work with our handheld devices in our everyday life.