Rf Modulation Tecniques

8/3/2019 Rf Modulation Tecniques

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www.gcl.in Gemini Communication Company Confidential Ver 1.0

Gemini Communication Ltd.Gemini Communication Ltd.

Innovation & LeadershipInnovation & Leadership

Basics of RF TechnologyRef. 1020005100


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Data as on June,06 2

Ver 01www.gcl.in Gemini Communication Company Confidential Ver 1.0

RF Modulation Techniques


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Data as on June,06 3

Ver 01www.gcl.in Gemini Communication Company Confidential Ver 1.0

TransmitterA transmitter transmit radio signalA transmitter usually has a power supply, an oscillator,

a modulator, and amplifiers


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Data as on June,06 4Ver 01


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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Thank YouContact : [email protected]

Rf Modulation Tecniques

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