Infrared (IR) CommunicationInfrared (IR) Communication

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Light SpectrumLight Spectrum

Implementation costs rise significantly around 1-10 GHz. Implementation costs rise significantly around 1-10 GHz. (But one important exception is (But one important exception is IRIR at around 500 THz ; at around 500 THz ; very inexpensive.)very inexpensive.)

Signals above 100 GHz cannot penetrate wallsSignals above 100 GHz cannot penetrate walls Most signals below 300 GHz are regulated by the FCCMost signals below 300 GHz are regulated by the FCC

Radio (RF)Microwaves

Infrared (IR)Visible

UltravioletX-Rays Gamma

Rays

FCC$109 1012 1014 1015 1017 1020

Freq.(Hz)

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How do you Transmit with IRHow do you Transmit with IR

No conductorNo conductor– Signal spreads from originSignal spreads from origin– Signal strength decreases with distanceSignal strength decreases with distance

Can’t use amplitudeCan’t use amplitude– Too much noise from other IR sources (lights, people, etc.)Too much noise from other IR sources (lights, people, etc.)

Can’t use sign (no +/-)Can’t use sign (no +/-)

Solution: ModulationSolution: Modulation– Send pulses of light to represent binary informationSend pulses of light to represent binary information

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Modulation SchemesModulation Schemes

SIR - Serial InfraredSIR - Serial Infrared– 2400bps to 115,200bps2400bps to 115,200bps– SIR modem is simple and low-costSIR modem is simple and low-cost

SDLC-based MIRSDLC-based MIR– 576Kbps and 1.152Mbps576Kbps and 1.152Mbps– guarantees a minimal occurrence rate of light pulsesguarantees a minimal occurrence rate of light pulses

FIR - Fast InfraredFIR - Fast Infrared– 4Mbps4Mbps– power usage constant (always the same)power usage constant (always the same)

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SIR - Serial Infrared ModulationSIR - Serial Infrared Modulation

1.6us (or 3/16 bit interval) pulse of light for 1.6us (or 3/16 bit interval) pulse of light for each ‘0’ in a standard asynchronous data each ‘0’ in a standard asynchronous data stream stream – Inverse of serial RS-232 where signal is held high, then Inverse of serial RS-232 where signal is held high, then

pulled down for zerospulled down for zeros

Stream consists of a start bit, N data bits, and Stream consists of a start bit, N data bits, and 1 stop bit (serial packet)1 stop bit (serial packet)

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SDLC-based MIRSDLC-based MIR

A data stream ‘0’ is coded for by the presence A data stream ‘0’ is coded for by the presence of an optical pulse 1/4 of the bit interval in of an optical pulse 1/4 of the bit interval in duration (217ns for 1.152Mbps) duration (217ns for 1.152Mbps)

The SDLC protocol, with its zero-insertion bit-The SDLC protocol, with its zero-insertion bit-stuffing approach, guarantees a minimal stuffing approach, guarantees a minimal occurrence rate of zeroes (and therefore light occurrence rate of zeroes (and therefore light pulses) in the data stream pulses) in the data stream

This also ensures This also ensures synchronization between synchronization between a transmitter and a transmitter and receiver can be receiver can be maintained throughout a maintained throughout a packetpacket

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FIR - Fast InfraredFIR - Fast Infrared

More Ethernet-like in its framing More Ethernet-like in its framing – a packet is made up of a preamble, start of frame delimiter a packet is made up of a preamble, start of frame delimiter

(SFD) and a data payload. (SFD) and a data payload.

Utilizes 1:4 Pulse Position Modulation (PPM) Utilizes 1:4 Pulse Position Modulation (PPM) – each pair of bits in the data stream are represented by a each pair of bits in the data stream are represented by a

pulse of light emitted in one of 4 available slot positions pulse of light emitted in one of 4 available slot positions which comprise a 4PPM symbolwhich comprise a 4PPM symbol

PPM always requires a PPM always requires a pulse for each slot, so pulse for each slot, so power usage is power usage is independent of the dataindependent of the data

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IR Communication ProtocolsIR Communication Protocols

To use IR hardware easily, we build up layers To use IR hardware easily, we build up layers of protocol that get us farther away from the of protocol that get us farther away from the implementation each step. implementation each step.

Common Protocols:Common Protocols:– Serial IRSerial IR– IrDAIrDA

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Differences between Waves and WireDifferences between Waves and Wire

Distance/$$$Distance/$$$– Wave transmissions are much more expensive than wireWave transmissions are much more expensive than wire

SpeedSpeed– Wire is a very simple and highly controllable medium which Wire is a very simple and highly controllable medium which

allows for much higher transfer ratesallows for much higher transfer rates

LimitationsLimitations– IR:IR:

• Line of Sight - IR can not travel through opaque objects, so transceivers must 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 be able to see each other. For many commercial products they must be within 15º of each other.15º of each other.

• Signal Power - even though we can not see IR, making the signal too strong Signal Power - even though we can not see IR, making the signal too strong can easily blind us can easily blind us

– RF:RF:• FCC RegulationFCC Regulation• Interference with objects and other RF wavesInterference with objects and other RF waves