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MindMap Gallery Analog system modulation

Analog system modulation

This is a mind map about analog system modulation. The main contents include: anti-noise performance of linear modulation systems, modulation methods, functions and purposes, and definitions.

Edited at 2024-10-28 23:46:26

Isabelmia

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Analog system modulation

Isabelmia

Recent works View more works>>

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Outline

Chapter 5 - Digitization of Analog Signals
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Chapter 9-10 Content Synchronization and Best Reception
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stochastic process
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Chapter 6 - Digital Baseband Transmission Systems
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Chapter 4 - Analog Modulation
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Principles of Communication, 7th Edition Chapter 10 Source Coding Mind Map
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Analog system modulation

definition

Modulation is a process definition of converting a signal form into a form suitable for transmission in a channel.

baseband modulation

carrier modulation

Function and purpose

Improve emission efficiency

Improve channel utilization

Improve system anti-interference ability

Modulation method

Linear modulation (amplitude modulation)

Common amplitude modulation

AM, double sideband, single sideband, vestigial sideband

Amplitude Modulation (AM)

Spectrum

Carrier component, upper sideband, lower sideband

bandwidth

Twice the bandwidth of the baseband signal

total power

Carrier power

Does not carry information

sideband power

related to modulated signals

Modulation efficiency

The maximum value is 1/3

advantage

System structure is simple and low price

application

radio broadcast

double sideband modulation

Modulation efficiency

100%

Bandwidth is twice the bandwidth of the baseband signal

The envelope of the DSB signal is no longer consistent with the change pattern of the modulated signal, and simple envelope detection cannot be used to recover the modulated signal.

Using coherent demodulation, also known as synchronous detection

advantage

Saves carrier power

single sideband modulation

It is formed by filtering out one sideband of the double sideband signal.

Generation method

filter method

First generate a double-sideband signal, and then pass it through a sideband filter to filter out unwanted edges. bring

difficulty

Making sideband filters

The smaller the normalized value of the transition band relative to the carrier frequency, the more difficult it is to implement the sideband filter.

phase shift method

Using a phase shift network, the carrier and modulated signals are appropriately phase shifted so that one of the sidebands is canceled out during the synthesis process.

difficulty

Fabrication of Broadband Phase Shift Network

Using coherent demodulation, also known as synchronous detection

advantage

Save transmit power

The bandwidth is equal to the baseband signal bandwidth

vestigial sideband modulation

demodulation

coherent demodulation

Implemented by multiplying the carrier with the multiplication method

Suitable for demodulation of all linearly modulated signals

Incoherent demodulation (envelope detection)

composition

Half-wave or full-wave rectifiers and low-pass filters

Advantages

Simple, no need for carrier synchronization

For modulated signals that suppress the carrier, the insertion carrier envelope detection method can be used

Requirements: The amplitude of the inserted carrier wave should be much larger than the amplitude of the signal. It is also required that the inserted carrier wave and the modulated carrier wave have the same frequency and phase.

Nonlinear modulation (angle modulation)

Common angle modulation

Frequency modulation (FM), phase modulation (PM)

The difference between angle modulation and amplitude modulation is that the spectrum of the modulated signal is no longer a linear shift of the original modulated signal, but a nonlinear transformation of the spectrum, which will produce new frequency components that are different from the spectrum shift, so it is also called nonlinear modulation.

phase modulation

Refers to the linear change of the instantaneous phase with the modulation signal.

Frequency modulation

Refers to the instantaneous frequency offset that changes proportionally with the modulation signal

The relationship between FM and PM

If the modulated signal is first differentiated and then frequency modulated, the phase modulated wave will be obtained. This method is called indirect phase modulation.

If the modulated signal is first integrated and then phase modulated, the result is an FM wave. This method is called indirect FM.

Noise immunity performance of linear modulation systems

The system gain of the DSB modulation system is 2, that is to say, the demodulator of the DSB signal improves the signal-to-noise ratio by a factor of 1

The system gain of the SSB modulation system is 1, but the anti-noise performance of SSB is the same as that of DSB, and the transmission bandwidth of SSB is only 1/2 of DSB

The anti-noise performance of VSB is approximately the same as that of the SSB modulation system.

AM anti-noise

Large signal-to-noise ratio situation

Small signal-to-noise ratio situation