MODULATION
Table of Contents
READ ME
If you want to know more about this project and its handling run this file and refer to the following link:
init;
disp(get_link('-> read me first','README'));
INTRO
Modulation techniques are very important to transmit information. They all have in common, that one parameter of a radiofrequent carrier
is modified by an information signal 
of a lower frequency. The spectra of modulated signals contain new frequencies around the carrier frequency. Since information is being shifted from the baseband to higher frequencies it can be transmitted over an RF channel.
is modified by an information signal of a lower frequency. The spectra of modulated signals contain new frequencies around the carrier frequency. Since information is being shifted from the baseband to higher frequencies it can be transmitted over an RF channel. The information 
can modulate the amplitude 
or the phase
of a sinusoidal carrier: 
can modulate the amplitude or the phase of a sinusoidal carrier: If the signal modifies the carrier´s amplitude we talk about Amplitude Modulation (AM). If it modifies the phase it is called angle modulation subdivided into Phase Modulation (PM) and Frequency Modulation (FM).
The information can be available in analog or digital form and the carrier can be sinusoidal or pulse shaped. So there are four possible groups of modulation methods. This lesson is about sinusoidal carriers.
SINUSOIDIAL CARRIER AND ANALOG INFORMATION
Amplitude Modulation (AM)
Amplitude Modulation can be created by modifying the amplitude of a radiofrequent carrier 
according to an information signal of a lower frequency. The amplitude of the information signal has to be within the range from 0 to 
. This avoids phase shifts also referred to as overmodulation. The depth of an AM modulated signal is described by the modulation index 
.
according to an information signal of a lower frequency. The amplitude of the information signal has to be within the range from 0 to . This avoids phase shifts also referred to as overmodulation. The depth of an AM modulated signal is described by the modulation index .Amplitude Modulation can be obtained by modifying the amplitude of a radiofrequent carrier. Since AM-signals can be created and demodulated quite easily it has been used from the beginning of radio engineering. AM does not need much bandwith, but the power efficiency is low and the Signal to Noise Ration (SNR) is small.
disp(get_link('-> more about AM','MOD_AM'));
Phase Modulation (PM)
Phase Modulation can be obtained by modifying the phase of a radiofrequent carrier. The SNR is 5 dB less compared to FM with the same modulation index. This is one reason, why analog FM is preferred.
disp(get_link('-> more about PM','MOD_PM'));
Frequency Modulation (FM)
Frequency Modulation can be obtained by modifying the frequency of a radiofrequent carrier. FM has the highest SNR compared to AM and PM. The bandwith requirement is comparable to PM and can be calculated with Carson´s formula: 
If the frequency deviation of a carrier is constant and the information signal contains more frequency components, the higher frequencies are modulated with less depth, since the modulation index is inversely proportional to it: 
.
. Therefore a boost of higher frequency components called preemphase is done at times. The inverse transformation is applied at the receiver.
disp(get_link('-> more about FM','MOD_FM'));
SINUSOIDIAL CARRIER AND DIGITAL INFORMATION
If digital information is transmitted by a sinusoidal carrier we talk about shift-keying. The way data is coded can be shown either in a time dependent or in a constellation diagram. The function plot_SK is used to illustrate shift-keying. A tutorial about it can be found via the link below:
disp(get_link('-> Tutorial_plot_SK','MOD_SK_NOTE1'));
Amplitude Shift Keying (ASK)
A shift of the carrier´s amplitude caused by a digital information signal is called amplitude shift-keying (ASK).
disp(get_link('-> more about ASK','MOD_ASK'));
Phase Shift Keying (PSK)
A shift of the carrier´s phase caused by a digital information signal is called phase shift-keying (PSK).
disp(get_link('-> more about PSK','MOD_PSK'));
Frequency Shift Keying (FSK)
A shift of the carrier´s frequency caused by a digital information signal is called frequency shift-keying (FSK).
disp(get_link('-> more about FSK','MOD_FSK'));
SOFTWARE DEFINED RADIO (SDR)
Software Defined Radio refers to radio systems where most of the signal processing is done by means of software. Except a small hardware frontend including antenna, RF-amplifier, Anti-alias filter and highspeed ADC- and DACs the rest of the signal chain to recover the information (demodulation, synchronisation, decoding) is done on a DSP-platform or a computer.
disp(get_link('-> more about SDR','MOD_SDR'));