Infrared

1. Infrared
• Two different basic transmission technologies can be used to set up
WLANs.
 Transmission of infra-red light (e.g., at 900 nm wavelength),
 Radio transmission in the GHz range (e.g., 2.4 GHz in the license-free
ISM band).
• Both technologies can be used to set up ad-hoc connections for work
groups, to connect, e.g., a desk-top with a printer without a wire, or to
support mobility within a small area.
Infra red
• This technology uses diffuse light reflected at walls, furniture etc. or
directed light if a line-of-sight (LOS) exists between sender and receiver.
Senders can be simple light emitting diodes (LEDs) or laser diodes.
Photodiodes act as receivers.
Radio Waves
• Typically using the license free ISM band at 2.4 GHz. e.g., GSM at 900,
1,800, and 1,900 MHz, DECT at 1,880 MHz etc.

2. Infrared
Infrared transmission Radio transmission
uses IR diodes, diffuse light, multiple
reflections (walls, furniture etc.)
typically using the license free ISM
band at 2.4 GHz
Advantages  Simple
 Extremely cheap
 Licenses are not needed
 Electrical devices do not interfere
 Cover large areas.
 Can penetrate walls, furniture’s.
 Does not need a LOS.
 Higher transmission rates.
Disadvantages interference by sunlight, heat sources
etc.
many things shield or absorb IR light
low bandwidth
 Shielding is not so simple.
 Can interfere with other senders.
 Limited ranges of license-free
bands.
Example IrDA (Infrared Data Association)
interface available everywhere
Mobile cellular phones