Basic BPSK digital communication system with AWGN in Simulink | applied electronics engineering

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Basic BPSK digital communication system with AWGN in Simulink

By Applied Electronics - Wednesday, March 8, 2017 No Comments
In this 10th simulink tutorial of Modeling digital communication systems using Simulink we show how to create basic BPSK digital communication system in Simulink and how to add AWGN channel and observe the basic errors introduced by the channel.

We start by building a model of basic BPSK system. We will show how to create BPSK signal using random integer generator and BPSK modulator. We will also have BPSK demodulator and add To Workspace blocks to view the generated data in matlab workspace.

In the next tutorial we will show how to observe the real and imaginary signals of the modulated and demodulated signal. The real signal of the BPSK modulated signal is the actual signal with 1 and -1 antipodal signal. Then in the tutorial after that you will learn how to measure the Bit Error Rate(BER) of the BPSK system.

The explanation of basic creation of simulink model, adding blocks and changing parameters and configuration simulation run time will not be explained in this tutorial because these were covered in the earlier tutorials. See Modeling digital communication systems using Simulink to learn how to set up simulink model, blocks, parameters and run time. Also the To Workspace blocks will not be explained here. This is explained in great details in How to export simulink data to matlab workspace tutorial. 

Basic BPSK Digital Communication System


The BPSK modulation scheme in the presence of AWGN is shown below.


The blocks include a Random Integer source, a BPSK modulator, a BPSK demodulator and several To Workspace blocks used to transfer data to the MATLAB Workspace.

The Random Integer source block is shown in the figure below. In the menu, binary numbers are selected with M=2 and the initial random seed=37.1 This is a sample-based computation where individual samples are issued in 1 s intervals. The outputs of this block are random double precision numbers that are either 0 or 1.


The BPSK modulator menu is shown in below.


Click on the Constellation button. You can see that zero phase angle is selected. A corresponding phase offset occurs in the BPSK demodulator. If the phase offsets angles between the modulator and demodulator do not agree, then errors will be made. Implementation considerations may force such a disagreement and the degradation experienced can then be determined.


Click on the data tab reveals and you will see that the output is double precision. The output sequence of the BPSK modulator consists of complex-valued double precision numbers with real values equal to +1 or −1.


The BPSK demodulator properties ss shown below where hard decisions are made at the demodulator output and the phase angle is again selected to be zero.



The data type tab view shown in below and it indicates that the output is also double precision, which is inherited from the preceding block.



The following table shows the first six values produced by each block based on a 5 s simulation time. The values are displayed in the work space by selecting the tab with the corresponding label in the simulation. Note that with no additional noise the BPSK input and BPSK demodulator output produce the same sequence.


BPSK Digital Communication System with AWGN


Now we will add the AWGN channel to the above basic BPSK Digital Communication System. The figure below displays a modified simulation model where an AWGN block is introduced between the modulator and demodulator and a scope is included to compare input and output data sequences. The routing symbols labeled S are connectors for the data, used to avoid cluttering the model, with an extra line.


The parameter selection for the AWGN block is shown below. Here the initial seed is set to 67, the number of bits/symbol is set to 1, the symbol period is set to 1s and the signal power is 1W. The Eb/No is selected to be 100 dB to demonstrate that the AWGN block introduces no errors with this large Eb/No value. 



The simulation time is extended to 100 s allowing the input and output sequences to be observed in the scope display as shown in the figure below. The sequences in the figure are random and agree symbol by symbol due to the high Eb/No and are represented as double precision, real values that are either zero or one.



To observe the effect of more noise in the channel, the Eb/No value is changed in the AWGN block to value −10 dB. The following figure shows the observed numerous errors in the demodulated BSPK signal.



In the next tutorial we show how to read real and imaginary signal of the modulated and demodulated signal.

Following are other examples of BPSK modulation system analysis in simulink but are not related to the modeling digital communication systems in simulink tutorial series.

- BPSK Simulink Model without communication toolbox
- BPSK in Simulink

Also for learning more about digital modulation and demodulation see the following books:

- Digital Modulation Techniques pdf Fuqin Xiong free download
- Communication System by Simon Haykin

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