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Mathe Forum Schule und Studenten
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The Infrared Data Association (IrDA) is an industry-driven interest group that was founded in 1993 by around 50 companies. IrDA provides specifications for a complete set of protocols for wireless infrared communications, and the name "IrDA" also refers to that set of protocols. The main reason for using IrDA had been wireless data transfer over the “last one meter” using point-and-shoot principles. Thus, it has been implemented in portable devices such as mobile telephones, laptops, cameras, printers, and medical devices. Main characteristics of this kind of wireless optical communication is physically secure data transfer, line-of-sight (LOS) and very low bit error rate (BER) that makes it very efficient.

The mandatory IrPHY (Infrared Physical Layer Specification) is the physical layer of the IrDA specifications. It comprises optical link definitions, modulation, coding, cyclic redundancy check (CRC) and the framer. Different data rates use different modulation/coding schemes:

Further characteristics are:

The frame size depends on the data rate mostly and varies between 64 B and 64 kB. Additionally, bigger blocks of data can be transferred by sending multiple frames consecutively. This can be adjusted with a parameter called "window size" (1–127). Finally, data blocks up to 8 MB can be sent at once. Combined with a low bit error rate of generally <10−9, that communication could be very efficient compared to other wireless solutions.

IrDA transceivers communicate with infrared pulses (samples) in a cone that extends at least 15 degrees half angle off center. The IrDA physical specifications require the lower and upper limits of irradiance such that a signal is visible up to one meter away, but a receiver is not overwhelmed with brightness when a device comes close. In practice, there are some devices on the market that do not reach one meter, while other devices may reach up to several meters. There are also devices that do not tolerate extreme closeness. The typical sweet spot for IrDA communications is from 5 to 60 cm (2.0 to 23.6 in) away from a transceiver, in the center of the cone. IrDA data communications operate in half-duplex mode because while transmitting, a device’s receiver is blinded by the light of its own transmitter, and thus full-duplex communication is not feasible. The two devices that communicate simulate full-duplex communication by quickly turning the link around. The primary device controls the timing of the link, but both sides are bound to certain hard constraints and are encouraged to turn the link around as fast as possible.

 

  • Range:
    • standard: 1 m;
    • low-power to low-power: 0.2 m;
    • standard to low-power: 0.3 m.
    • The 10 GigaIR also define new usage models that supports higher link distances up to several meters.
  • Angle: minimum cone ±15°
  • Speed: 2.4 kbit/s to 1 Gbit/s
  • Modulation: baseband, no carrier
  • Infrared window (part of the device body transparent to infrared light beam)
  • Wavelength: 850–900 nm
  • standard: 1 m;
  • low-power to low-power: 0.2 m;
  • standard to low-power: 0.3 m.
  • The 10 GigaIR also define new usage models that supports higher link distances up to several meters.
  • Access control
  • Discovery of potential communication partners
  • Establishing of a reliable bidirectional connection
  • Distribution of the primary/secondary device roles
  • Negotiation of QoS parameters
  • Provides multiple logical channels
  • Allows change of primary/secondary devices
  • Transportation of large messages by SAR (Segmentation and Reassembly)
  • Flow control by giving credits to every logical channel
  • IrDA Principles and Protocols; Knutson and Brown; MCL Press; 214 pages; 2004; .

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Wikipedia

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