Infrared Data Association

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The Infrared Data Association (IrDA) defines physical specifications communications protocol standards for the short-range exchange of data over infrared light, for uses such as personal area networks (PANs).

For the devices to communicate via IrDA they must have a direct line of sight similar to a TV remote control.

Contents

Specifications

IrPHY

The mandatory IrPHY (Infrared Physical Layer Specification) is the first (lowest) layer of the IrDA specifications. The most important specifications are:

  • Range: standard: 1 m; low power to low power: 0.2 m; standard to low power: 0.3 m
  • Angle: minimum cone ±15°
  • Speed: 2.4 kbit/s to 1 Gbit/s
  • Modulation: baseband, no carrier
  • Infrared window
  • Wavelength: 875 ± 30 nm[1]

IrDA transceivers communicate with infrared pulses (samples) in a cone that extends minimum 15 degrees half angle off center. The IrDA physical specifications require that a minimum irradiance be maintained so that a signal is visible up to a meter away. Similarly, the specifications require that a maximum irradiance not be exceeded so that 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 24 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.

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