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Infrared (IR) Communication

Infrared (IR) Communication. Microwaves. Visible. X-Rays. Gamma Rays. Radio (RF). Infrared (IR). Ultraviolet. Freq. (Hz). 10 9. 10 12. 10 14. 10 15. 10 17. 10 20. $. FCC. Light Spectrum.

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Infrared (IR) Communication

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  1. Infrared (IR) Communication

  2. Microwaves Visible X-Rays Gamma Rays Radio (RF) Infrared(IR) Ultraviolet Freq. (Hz) 109 1012 1014 1015 1017 1020 $ FCC Light Spectrum • Implementation costs rise significantly around 1-10 GHz. (But one important exception is IR at around 500 THz ; very inexpensive.) • Signals above 100 GHz cannot penetrate walls • Most signals below 300 GHz are regulated by the FCC Introduction

  3. How do you Transmit with IR • No conductor • Signal spreads from origin • Signal strength decreases with distance • Can’t use amplitude • Too much noise from other IR sources (lights, people, etc.) • Can’t use sign (no +/-) • Solution: Modulation • Send pulses of light to represent binary information Introduction

  4. Modulation Schemes • SIR - Serial Infrared • 2400bps to 115,200bps • SIR modem is simple and low-cost • SDLC-based MIR • 576Kbps and 1.152Mbps • guarantees a minimal occurrence rate of light pulses • FIR - Fast Infrared • 4Mbps • power usage constant (always the same) Introduction

  5. SIR - Serial Infrared Modulation • 1.6us (or 3/16 bit interval) pulse of light for each ‘0’ in a standard asynchronous data stream • Inverse of serial RS-232 where signal is held high, then pulled down for zeros • Stream consists of a start bit, N data bits, and 1 stop bit (serial packet) Introduction

  6. SDLC-based MIR • A data stream ‘0’ is coded for by the presence of an optical pulse 1/4 of the bit interval in duration (217ns for 1.152Mbps) • The SDLC protocol, with its zero-insertion bit-stuffing approach, guarantees a minimal occurrence rate of zeroes (and therefore light pulses) in the data stream • This also ensures synchronization between a transmitter and receiver can be maintained throughout a packet Introduction

  7. FIR - Fast Infrared • More Ethernet-like in its framing • a packet is made up of a preamble, start of frame delimiter (SFD) and a data payload. • Utilizes 1:4 Pulse Position Modulation (PPM) • each pair of bits in the data stream are represented by a pulse of light emitted in one of 4 available slot positions which comprise a 4PPM symbol • PPM always requires a pulse for each slot, so power usage is independent of the data Introduction

  8. IR Communication Protocols • To use IR hardware easily, we build up layers of protocol that get us farther away from the implementation each step. • Common Protocols: • Serial IR • IrDA Introduction

  9. Differences between Waves and Wire • Distance/$$$ • Wave transmissions are much more expensive than wire • Speed • Wire is a very simple and highly controllable medium which allows for much higher transfer rates • Limitations • IR: • Line of Sight - IR can not travel through opaque objects, so transceivers must be able to see each other. For many commercial products they must be within 15º of each other. • Signal Power - even though we can not see IR, making the signal too strong can easily blind us • RF: • FCC Regulation • Interference with objects and other RF waves Introduction

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