【Fundamentals】Digital Signal Modulation and Demodulation in MATLAB: Implementing ASK, FSK, and PSK Modulations

# 1. Fundamental Concepts of Digital Signal Modulation in MATLAB

Digital signal modulation is a technique that encodes digital information into an analog carrier signal. In MATLAB, we can utilize a variety of functions and tools to implement digital signal modulation. This section will introduce the concepts, basic principles, and commonly used functions of digital signal modulation in MATLAB.

# 2. Amplitude Shift Keying (ASK) Modulation and Demodulation

### 2.1 ASK Modulation Principles

Amplitude Shift Keying (ASK) is a form of digital modulation that represents digital information by varying the amplitude of a carrier signal. The ASK modulator converts a binary data stream into a series of carrier signals with different amplitudes.

The principle of ASK modulation is illustrated in the following diagram:

graph LR
subgraph ASK Modulator
     A[Data Stream] --> B[Modulator] --> C[ASK Signal]
end
subgraph ASK Demodulator
     D[ASK Signal] --> E[Demodulator] --> F[Data Stream]
end

The ASK modulator receives a binary data stream and converts it into a series of carrier signals with varying amplitudes. The amplitude of the carrier signal is determined by the logical value of the binary data. For example, a logic "0" can be represented by a low-amplitude carrier, while a logic "1" can be represented by a high-amplitude carrier.

### 2.2 ASK Demodulation Principles

The ASK demodulator receives an ASK signal and converts it back into a binary data stream. The ASK demodulator typically uses an envelope detector to measure the amplitude of the carrier signal. The envelope detector outputs a signal that is proportional to the amplitude of the carrier signal.

The principle of ASK demodulation is illustrated in the following diagram:

graph LR
subgraph ASK Modulator
     A[Data Stream] --> B[Modulator] --> C[ASK Signal]
end
subgraph ASK Demodulator
     D[ASK Signal] --> E[Envelope Detector] --> F[Amplitude Signal] --> G[Comparator] --> H[Data Stream]
end

The ASK demodulator receives an ASK signal and uses an envelope detector to measure its amplitude. The envelope detector outputs a signal that is proportional to the amplitude of the carrier signal. Then, the comparator compares the amplitude signal with a threshold to determine the logical value of the binary data.

### 2.3 ASK Modulation and Demodulation Implementation in MATLAB

The following MATLAB code implements ASK modulation and demodulation:

% ASK Modulation
data = [***];
carrier_frequency = 1000;
sampling_frequency = 10000;
t = 0:1/sampling_frequency:length(data)/sampling_frequency;
carrier_signal = sin(2*pi*carrier_frequency*t);
modulated_signal = carrier_signal .* data;

% ASK Demodulation
demodulated_signal = abs(hilbert(modulated_signal));
threshold = mean(demodulated_signal);
demodulated_data = demodulated_signal > threshold;

% Plotting the waveforms
figure;
subplot(3,1,1);
plot(t, data, 'b-o');
xlabel('Time (s)');
ylabel('Data');
title('Original Data');
subplot(3,1,2);
plot(t, carrier_signal, 'r-');
xlabel('Time (s)');
ylabel('Carrier Signal');
title('Carrier Signal');
subplot(3,1,3);
plot(t, modulated_signal, 'g-');
xlabel('Time (s)');
ylabel('Modulated Signal');
title('Modulated Signal');

**Code Logic Analysis:**

* `ASK Modulation` section:
* Generates a binary data stream.
* Generates a carrier signal.
* Performs ASK modulation using element-wise