Modulation and demodulation simulation of BFSK based on MATLAB
It's a dream 2021-06-04 10:47:47

Write it at the front

This is 【Matlab】BASK The simulation of modulation and demodulation of The second part of , Considering the reading experience , So I'm going to open another article to share BFSK The simulation of modulation and demodulation of .

Indexes

  • Write it at the front
  • One 、BFSK Modulation of
    • 1.1 Different frequency carrier generation
    • 1.2 Signal combination
    • 1.3 Waveform Preview
    • 1.4 Parameter setting ( Reference resources )
  • Two 、BFSK Demodulation of
    • 2.1 Model structures,
    • 2.2 Waveform Preview
    • 2.3 Parameter setting ( Reference resources )
  • 3、 ... and 、 common problem
  • At the end

One 、BFSK Modulation of

One FSK The signal can be seen as two different carriers BASK Superposition of signals ,BFSK The spectrum of the signal can be seen as \(f_1\) and \(f_2\) Two BASK The combination of spectrum .

Frequency shift keying is the use of carrier frequency to transmit digital signals , stay BFSK in , The carrier frequency varies with the binary baseband signal \(f_1\) and \(f_2\) Between two frequency points , Frequency shift keying (FSK) uses the frequency shift of carrier to transmit digital information . So the expression is :

\[e_{BFSK}(t)= \begin{cases} A\cos{(\omega_1t+\phi_n)}\\ A\cos{(\omega_2t+\theta_n)}\\ \end{cases} \]

BFSK There are two kinds of modulation modes of the , They are analog frequency modulation and keying . This article uses keying , adopt Simulink Conduct simulation . The schematic diagram of the keying method is shown in the figure below :

Let's use Matlab/Simulink Implement the model step by step .

1.1 Different frequency carrier generation

according to BFSK Signal expression , We need to prepare two different frequency carriers . In order to generate different frequency carrier , We will BASK In modulation model Signal Geneator Replace with Sine Wave. in addition , In order to reflect 01 Characteristics of signal , 需要使曼彻斯特码的其 in One 通道经过非门 NOT, And then through the multiplier .

Above picture , adopt Product 0b The generated signal represents binary 0 Carrier of , adopt Product 1b The generated signal represents binary 1 Carrier of .Scope The waveforms of are shown in the figure below :

1.2 Signal combination

Observe 1.1 Oscillogram in , We can easily draw a conclusion :BFSK The modulation signal is generated by the 0 code BFSK Modulation signal and 1 code BFSK Sum of modulated signals . So we let two different frequency carriers pass through Sum You can get the complete BFSK Modulation signal .
For model visibility , I will 0 code BFSK Modulation signal and 1 code BFSK The modulation signal is packaged .

1.3 Waveform Preview

Use Scope modular , We can observe the waveform of the signal in each stage . Put the Manchester code and BFSK The modulated signal is connected to the oscilloscope , We can see the figure below :

1.4 Parameter setting ( Reference resources )

We can adjust the parameters of each module to control BFSK Shape of modulated signal , The reference parameters of each module are given below :

Module name Parameters Set the value
Pulse Generator Period (secs) 1
Pulse Width (% of period) 50
Sine Wave 0b Frequency (rad/sec) 12*pi
Sine Wave 1b Frequency (rad/sec) 24*pi

notes : Module parameters not listed are processed by default .


Two 、BFSK Modulation of

BFSK There are two ways to demodulate , They are coherent demodulation and incoherent demodulation . Coherent demodulation is used in this paper , adopt Simulink Conduct simulation . The schematic diagram of coherent demodulation is shown in the figure below :

graph LR Input["BFSK Signal input "] BandpassFilter0b[" Bandpass filter 0b"] BandpassFilter1b[" Bandpass filter 1b"] Product1[" Multiplier "] Product2[" Multiplier "] LowpassFilter1[" low pass filter "] LowpassFilter2[" low pass filter "] SamplingDecimator[" Sampling decimator "] SamplingPulse[" Sampling pulse "] Cosine0b["Cosine Wave 0b"] Cosine1b["Cosine Wave 1b"] Output["BFSK Demodulation signal output "] Input --> BandpassFilter0b --> Product1 --> LowpassFilter1 --> SamplingDecimator --> Output Input --> BandpassFilter1b --> Product2 --> LowpassFilter2 --> SamplingDecimator SamplingPulse --> SamplingDecimator Cosine0b --> Product1 Cosine1b --> Product2

Let's use Matlab/Simulink Implement the model step by step .

2.1 Model structures,

stay Simulink in , We can use Analog Filter Design To replace band-pass filter and low-pass filter , use Sine Wave Output same frequency demodulation carrier , use GreaterThanOrEqual Instead of sampling decider and sampling pulse . The specific model is as follows :

2.2 Waveform Preview

Use Scope modular , We can observe the waveform of the signal in each stage . Manchester code 、BFSK Modulation signal and BFSK The demodulated signal is connected to the oscilloscope , We can see the figure below :

2.3 Parameter setting ( Reference resources )

The reference parameters of each module are given below :

Module name Custom name Parameters Set the value
Analog Filter Design Bandpass Filter 0b Filter type Bandpass
Lower passband edge frequency (rad/s) 12*pi-20
Upper passband edge frequency (rad/s) 12*pi+20
Bandpass Filter 1b Filter type Bandpass
Lower passband edge frequency (rad/s) 24*pi-20
Upper passband edge frequency (rad/s) 24*pi+20
Lowpass Filter 0b Passband edge frequency (rad/s) 10*pi
Lowpass Filter 1b Passband edge frequency (rad/s) 23*pi
Sine Wave Sine Wave Frequency (rad/sec) 12*pi
Sine Wave1 Frequency (rad/sec) 24*pi
GreaterThanOrEqual GreaterThanOrEqual Relational operator <

notes : Module parameters not listed are processed by default .


3、 ... and 、 common problem

Q: Sine wave distortion is encountered during simulation ( Including amplitude and shape ), What to do with ?
A: If sine wave distortion is encountered in the simulation process ( Including amplitude and shape ), Can be in Simulink Right click the blank space of the project , choice Model Configuration Parameters, After entering the page , On the tab Solver -> Solver details The following parameters are set in :

Parameters Set the value
Max step size 1e-5
Relative tolerance 1e-5

.


At the end

It's been a busy few weeks , It took a day to finish this article , But I had to finish it by Thursday Orz
I hope this essay and sister essay can help you ~

Please bring the original link to reprint ,thank
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