rf modulation tecniques
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Gemini Communication Ltd.Gemini Communication Ltd.
Innovation & LeadershipInnovation & Leadership
Basics of RF TechnologyRef. 1020005100
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RF Modulation Techniques
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TransmitterA transmitter transmit radio signalA transmitter usually has a power supply, an oscillator,
a modulator, and amplifiers
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Transmitter
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ReceiverA receiver is a device that receives aradio signal from an antenna and
decodes the signal for use
Generally, receiver refers to a
demodulator, a preamplifier, and a
power amplifier
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Receiver
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ModulationModulation is the process of varying some characteristics of a carriersignal, in accordance with the instantaneous value of the information
signal
The three parameters of a sinusoid signal are its amplitude, its phase
and its frequency
Any of them can be varied in accordance with an information signal to
obtain the modulated signal
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Analog ModulationTechniques
Amplitude Modulation (AM)
Single Sideband Modulation (SSB)
Vestigial Sideband Modulation (VSB)
Frequency Modulation (FM)
Phase Modulation (PM)
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Amplitude ModulationAmplitude of a carrier wave is varied
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Frequency Modulation
Frequency of a carrier wave is varied
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Phase Modulation
Phase of a carrier wave is varied
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Pulse ModulationThese are hybrid of digital and analogue techniquesPulse Code Modulation (PCM)
Pulse Amplitude Modulation (PAM)
Pulse Width Modulation (PWM)
Pulse Position Modulation (PPM)
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Pulse Code ModulationA digital representation of an analog signal
The signal is sampled regularly at uniform intervals
Then quantized to a series of symbols in a binary code
Several PCM streams may be multiplexed into a larger aggregate datastream
This is called Time Division Multiplexing (TDM)
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Pulse Amplitude ModulationPAM involves the modulation of amplitude of the carrier pulses
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Pulse Width Modulation
PWM involves the modulation of duty cycle of the carrier pulses
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Pulse Position ModulationPPM involves the modulation of position of the carrier pulses
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Digital Modulation Techniques
Amplitude Shift Keying (ASK)
Phase Shift Keying (PSK)
Frequency Shift Keying (FSK)
Minimum Shift Keying (MSK)
Quadrature Amplitude Modulation (QAM)
Continuous Phase Modulation (CPM)
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Amplitude Shift KeyingASK conveys data by changing the amplitude of a carrier wave
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Phase Shift Keying
PSK conveys data by changing the phase of a carrier wave
Binary Phase Shift Keying (BPSK)
Quadrature Phase Shift Keying (QPSK)
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Frequency Shift KeyingFSK conveys data by changing the frequency of a carrier wave
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Minimum Shift KeyingMSK is encoded with bits alternating between quaternary components
Instead of square pulses, MSK encodes each bit as a half sinusoid
a) Binary Sequenceb) sI(t)c) sQ(t)d) sI(t) cos(2fct)
e) sQ(t) sin(2
fct)f) Modulated Signal s(t)
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Quadrature Amplitude ModulationQAM conveys data by changing the amplitudes of two carrier waves out
of phase with each other by 90
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Channel Access MethodsTo share a communications channel between multiple usersFrequency Division Multiple Access (FDMA)
Time Division Multiple Access (TDMA)
Code Division Multiple Access (CDMA)
Spread Spectrum Multiple Access (SSMA)
Direct Sequence Spread Spectrum (DS SS)
Frequency Hopping Spread Spectrum (FH SS)
Carrier Sense Multiple Access
Orthogonal Frequency Division Multiplexing (OFDM)
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Frequency Division Multiple AccessDifferent users use different frequency to transmit simultaneously
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Time Division Multiple AccessDifferent users use different time slots to transmit
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Code Division Multiple Access
Different users use different codes to transmit simultaneously
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Spread SpectrumHere, the information is deliberately spread over a wide band of
frequencies
Employs direct sequence or frequency hopping, which can be used for
multiple access
Decreases the potential interference to other receivers while achieving
privacy
The receiver correlates the received signals to retrieve the originalinformation signal
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Direct Sequence Spread SpectrumUtilizes a digital code sequence (PN Sequences)
This code has a chip rate much higher than the information signal bit
rateEach information bit is transmitted as a pseudorandom sequence of
chips
To recover the original data, the same PN Sequence is multiplied to the
received signal
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Frequency Hopping Spread SpectrumA method of transmitting signals by rapidly switching a carrier among
many frequency channels
This uses a pseudorandom sequence known to both transmitter andreceiver
Highly resistant to noise and interference
Difficult to intercept
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Carrier Sense Multiple AccessA transmitter verifies the absence of other traffic before transmitting on ashared physical medium
Carrier Sense Multiple Access with Collision DetectionCarrier Sense Multiple Access with Collision Avoidance
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DuplexDuplex means two way
A simplex channel is a one way channel
A half duplex channel carries information in both directions, but not at
the same timeA full duplex channel carries information in both directionssimultaneously
Time division duplex (TDD)Frequency division duplex (FDD)
Orthogonal Frequency Division
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Orthogonal Frequency DivisionMultiplexing
An OFDM carrier signal is the sum of a number of orthogonal sub-
carriers
The base-band data on each sub-carrier is independently modulated
This composite base-band signal is typically used to modulate a main
RF carrier
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OFDM
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OFDM
Orthogonal Frequency Division
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O t ogo a eque cy s oMultiplexing
As the frequencies are closely spaced, each one has room for a
Narrowband signal
This results in a signal with high resistance to interference
OFDM is used in conjunction with channel coding (error correction
technique)
COFDM signals show good resistance to multi-path fading
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