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Near Field Communication

This type of wireless system is unique in the wireless spectrum as it can offer zero power consumption for an application. It also offers short distance, and low data-rate similar to BLE and Zigbee.

NRC can be used with BlueTooth and BLE for pairing of devices.

A device can be either passive which is a tag/card that stores information that can be read by a reader device. An active device can be a reader and can also be a writer (write to a tag or does this mean act like a tag and write/send tag data to another reader?).

Radio Frequency Identification (RFID)

Is a wireless system comprised of two components, a tag and a tag reader. A reader is a device that has an antenna that emits radio waves and receives signals back from the tag.

Tags use radio waves to communicate their identity to nearby readers. A tag can be passive meaning that it is powered by the reader and does not have a battery (if it has a battery it is called an active tag).

Coupling mode

This is the method used to link the RFID tag and the reader to one another. This is needed so that the reader can recognize and retrieve information from the tag. There are two main types of coupling which are inductive and radiactive coupling.

Inductive coupling

Also called magnetic coupling and is generally used by low and high frequency systems (LF and HF).

--------| = Magnetic field

------------------
\\\||||||||||////
\\\||||||||||///       
|--+---------+------------|   +----------+
|--| Reader  |------------|   |   Tag    |
|--+---------+------------|   +----------+
 //|||||||||||\\
///|||||||||||\\\
-----------------

The reader creates a magnetic field which when it comes in range of the tag, that is the reader or the tag needs to move closer to each other than shown above as they are currently out of range. When they are in range the reader will send electricity through the conductive antenna. This allows the tag to be powered and allow for data stored on in the tag to be read. This transfer of power is one things that limits the distance of this technology. And it is also the reason that that tag does not require and battery.

LF has a range of up to 1 m. HF has a proximity range of up to 10 cm and a visinity range of up to 1m.

Radiactive coupling

This is usually used for Ultra High Frequency (UHF) and sometimes called backscatter coupling (kinda like radar). In this case the reader will radiate electromagnetic waves and any nearby tag can reflect back the information stored in the tag. Notice that the reader does not power the tag in this case so it will need to have its own power source.

Proximity cards

Are also known as Passive 125kHz cards and have a limited range and must be held close to the reader (but does not have to touch/swipe). The are often used for hotel room keys. These operate in the 125 kHz (LF) range.

Visinity cards

Are known as active cards as they have a battery that powers them and can have a range of up to two meters. The key for my car has this and if the key is close to the car the doors can be opened. These operate in the 13.56 MHz (LF) range.

Communication

As mentioned above the reader creates a magnetic field which alternates which can power the tag. This is called the carrier frequency and the reader can modulate this frequency to send information to the tag. The tag also modulates this magnetic field to provide the answer to the reader. This is done by passing current in a loop.

Carrier frequency 13.56 MHz Reader to tag: Amplitude Shift Modulation (ASK) Tag to reader: Load modulation (ASK) TODO: explain this

ISO 14443

  • 13.56 MHz carrier wave.
  • Magnetic coupling between reader and tag.
  • Passive
  • Proximity cards
  • Short Range
  • Communication speeds up to 106 kbits/s

Reader to tag:

                  Type A            Type B
Bit encoding      Modified Miller   NRZ (No Return to Zero)
Data modulation   100% ASK          10% ASK

Tag to reader:

                  Type A            Type B
Bit encoding      Manchester        NRZ
Data modulation   Load modulation   Load modulation

See rf.md for explaination of bit encodings mentioned above.

ISO 15693

  • 13.56 MHz carrier wave.
  • Magnetic coupling between reader and tag.
  • Passive
  • Vicinity cardsd
  • Long range
  • Communication speeds up to 26 kbits/s

NFC Forum Standards

This build upon exising ISO standards 14443, 15693, and 18092 which standardize things like physical interface, frames, anti-collision, and adds new features like a technical specification of protocols, data exchange format, tag types, record types and more.