Infrared Data Association
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 phones, laptops, cameras, printers, 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:
- SIR: 9.6–115.2 kbit/s, asynchronous, RZI, UART-like, 3/16 pulse
- MIR: 0.576–1.152 Mbit/s, RZI, 1/4 pulse, HDLC bit stuffing
- FIR: 4 Mbit/s, 4PPM
- VFIR: 16 Mbit/s, NRZ, HHH(1,13)
- UFIR: 96 Mbit/s, NRZI, 8b/10b
- GigaIR: 512 Mbit/s – 1Gbit/s, NRZI, 2-ASK, 4-ASK, 8b/10b
- 5/10GigaIR: seems to be a new IrPHY coming soon
Further characteristics are:
- 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
- Wavelength: 850–900 nm
The frame size depends on the data rate mostly and varies between 64 byte and 64 kbyte. 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 Mbyte 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 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 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.
The mandatory IrLAP (Infrared Link Access Protocol) is the second layer of the IrDA specifications. It lies on top of the IrPHY layer and below the IrLMP layer. It represents the Data Link Layer of the OSI model. The most important specifications are:
- Access control
- Discovery of potential communication partners
- Establishing of a reliable bidirectional connection
- Distribution of the Primary/Secondary device roles
- Negotiation of QoS Parameters
On the IrLAP layer the communicating devices are divided into a Primary Device and one or more Secondary Devices. The Primary Device controls the Secondary Devices. Only if the Primary Device requests a Secondary Device to send is it allowed to do so.
The mandatory IrLMP (Infrared Link Management Protocol) is the third layer of the IrDA specifications. It can be broken down into two parts. First, the LM-MUX (Link Management Multiplexer) which lies on top of the IrLAP layer. Its most important achievements are:
- Provides multiple logical channels
- Allows change of Primary/Secondary devices
Second, the LM-IAS (Link Management Information Access Service), which provides a list, where service providers can register their services so other devices can access these services via querying the LM-IAS.
The optional Tiny TP (Tiny Transport Protocol) lies on top of the IrLMP layer. It provides:
- Transportation of large messages by SAR (Segmentation and Reassembly)
- Flow control by giving credits to every logical channel
The optional OBEX (Object Exchange) provides the exchange of arbitrary data objects (e.g., vCard, vCalendar or even applications) between infrared devices. It lies on top of the Tiny TP protocol, so Tiny TP is mandatory for OBEX to work.
The optional IrLAN (Infrared Local Area Network) provides the possibility to connect an infrared device to a local area network. There are three possible methods:
- Access Point
- Peer to Peer
As IrLAN lies on top of the Tiny TP protocol, the Tiny TP protocol must be implemented for IrLAN to work.
IrSimple achieves at least 4 to 10 times faster data transmission speeds by improving the efficiency of the infrared IrDA protocol. A 500 KB normal picture from a cell phone can be transferred within 1 second.
One of the primary targets of IrSimpleShot (IrSS) is to allow the millions of IrDA-enabled camera phones to wirelessly transfer pictures to printers, printer kiosks and flat panel TVs.
IrDA was popular on PDAs, laptops and some desktops during the late 90s through the early 2000s. However, it has been displaced by other wireless technologies such as WiFi and Bluetooth, favored because they don't need a direct line of sight, and can therefore support hardware such as mice and keyboards. It is still used in some environments where interference makes radio-based wireless technologies unusable.
IrDA popularity has been making a comeback with its highly efficient IrSimple protocols by providing sub 1 second transfers of pictures between cell phones, printers, and display devices. IrDA hardware is still less expensive and doesn't share the same security problems encountered with wireless technologies such as Bluetooth. For example, some Pentax DSLRs (K-x, K-r) have incorporated IrSimple for image transfer and gaming.
- IrDA Principles and Protocols; Knutson and Brown; MCL Press; 214 pages; 2004; ISBN 978-0975389201.
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