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EEEE2044 Coursework 2

Digital Modulation

The aim of the coursework is to evaluate BER for a range of popular digital modulation techniques.

The coursework has a total of four tasks:

- Task 1 is familiarisation with the Matlab Simulink programme and the parameters of the simulation. For this part a manual on how to build a simple communication channel is added in this document.

- Task 2 is evaluation of the BER for QPSK, 8PSK, 16PSK, 64PSK, 4QAM, 8QAM, 16QAM and 64QAM modulation techniques in the presence of the additive white Gaussian noise.

For a given modulation scheme, the BER analysis is done by changing the signal to noise ratio (parameter Eb/No) in the communication block that has additive white noise (AWGH block). Please note that the simulation parameters will need to be adjusted for each modulation technique.

- Task 3 will consider a practical transmission system where additive white noise, time delay and frequency offset are added as a consequence of a more realistic communication system. The effect of the low pass filter on signal spectrum is also included. In this task you will plot BER for QPSK and compare that results from the one obtained in Task 2 and comment on the results.

Guidance on how to build a communication link in Simulink is given in the Appendix.

A report of results should be in the provided document and should not be longer than 4 pages. The penalty for exceeding the length is 5% per page.

The marking scheme is given in Table 1.

 

Table 1. Rubric marking scheme

 

Appendix: BUILDING A QPSK COMMUNICATION CHANNEL IN SIMULINK

This manual will help you define a very simple communication channel with additive white noise. The only parameters that you will need to change is to use different modulation and demodulation boxes and obtain BER analysis for each type of modulation. Parameters in boxes need to be defined accordingly.

Open the Matlab programme.

Click on Simulink on the top bar:

 

 

Click on Blank Model:

 

Click on Library Browser. This Library has all the components that can be used to build a communication system.

 

 

 

 

 

 

 

 

 

 

This is the circuit you want to build:

 

 

Start:

Select Communication Toolbox, double click on Comms Sources -> Random Data Sources -and then drag Random Integer Generator into the workspace. This is representing a random source signal.

 

 

 

Click on Communication Toolbox->Modulation->Utility Blocks and drag Integer to Bit Converter into the workspace.

 

Click on Communication Toolbox->Modulation->Digital Baseband.

Double click on Digital Baseband ->  PM and drag into the workspace QPSK modulator and QPSK demodulator block.

 

 

Click on Communication Toolbox->Channels->AWGN channel and drag the AWGN channel block into the workspace. AWGN block adds Gaussian white noise to the signal. 

 

 

 

 

Click on Communication Toolbox->Comm Sinks and drag Error Rate Calculation into the workspace

 

In Error rate Calculation set the Output data to Port:

 

Click on Simulink->Sinks and drag the Display box into the workspace. Display box will show the reading for the BER.

 

 

Use the arrows at the input/output ports of each block to connect them as shown below. Use the Tx arrow of the Error Calculation block to connect it to transmitter. The completed system now looks like:

 

 

 

Save your model:

 

 

 

Now check that you have set all the parameters correctly for the QPSK modulation.

Random Integer generator has Set size=1; Sample time =0.1 and samples per frame =1; These parameters are fixed for different modulations.

 

 

Integer to bit converter: Number of bits per integer=1

 

 

For QPSK modulator: input type is integer; phase offset is pi/4; For different type of M-ary modulation the phase offset will be different.

 

AWGN block: Mode: Signal to noise ratio; Number of bits per symbol = 2; Input signal power =1 W; Symbol period=0.1s (to compare it to bit error rate rather than symbol error rate); Different modulation will have different number of bits per symbol but the symbol period is kept fixed at 0.1s.

 

 

For QPSK demodulator: input type is integer; phase offset is pi/4; For different type of M-ary modulations the phase offset will be different.

 

 

 

Now click on Run and  observe E Eb/N=5dB and observe and record error rate calculation in the display box.

 

Change Eb/N in the AWGN block and repeat to get a waterfall plot for QPSK.

 

Please note the parameter “Stop time” is set to 1000 sec. You should investigate the impact of this parameter as part of the coursework in the Task 1. In order to obtain accurate results you need to consider a signal of adequate duration and the duration of the signal is controlled by the parameter “Stop time”.

 

 

 

Please note for M-QAM modulations select Rectangular QAM Modulator (and Demodulator) and select “Average Power” for normalisation method. Below are parameters for 4QAM:

 

 

Manual for Task 3 only:

Open Matlab and click on Simulink. Click on Examples -> Communication Toolbox and then open QPSK Transmitter and Receiver.