EEEE2044 Coursework 2, Digital Modulation
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Task 1: Change the parameter “Stop time” until you see that convergence of the BER value is achieved. Do this for at least 3 digital modulation techniques, namely QPSK, 16PSK and 16QAM. Once you have shown convergence you will need to use the appropriate value for the “stop Time” for the rest of the coursework.
In Fig.1 plot the BER w.r.t. stop time for QPSK, 16PSK, 16QAM and comment on the results.
Fig.1. Convergence of BER results for QPSK, 16PSK and 16QAM modulations
Comment:
The random integer input of all modulations are set to be 4, and Eb/No for all are set to be 10dB, with 2 of the number of bits per simple for QPSK, 4 for both 16QAM and 16PSK.
The convergence of BER results for three different types of modulations are as shown in Fig.1. The BER curve for QPSK converges rapidly, achieving stability at approximately 4000-5000 seconds. This quick convergence aligns with theoretical expectations, as QPSK’s low-order modulation reduces susceptibility to noise and inter-symbol interference, enabling faster error rate stabilization. The final BER value is <0.1, indicating robust performance in moderate noise environments. 16PSK converges slower, requiring >4000 seconds to stabilize, which reflects the higher sensitivity of 16PSK to phase noise and synchronization errors due to its 16 distinct phase states. The final BER plateaus at approximately 0.5, which is notably higher than QPSK, highlighting the trade-off between spectral efficiency and error resilience. The BER for 16QAM is small at initial, which can be described as stable at initial. This is because of the input data size that doesn’t match with modulation (16QAM and 16PSK). The module might deem all the bits are wrong, but the logic limits the BER of 16QAM to be 10-5.
Overall, the stop time that allows modulations to achieve BER convergence is set to be 5000s in following tasks.
Task 2: In Fig.2 plot the BER for QPSK, 16PSK, 16QAM, 64PSK, 64QAM and 256QAM . The graph for each modulation is obtained by changing Eb/N ratio in AWGN block and reading the value in display block. The BER axis should be on a log scale.
Fig.2. Comparison of BER for QPSK, 16PSK, 16QAM, 64PSK, 64QAM and 256QAM
Comment on the results: (are the results logical and expected from what you have learned and how do they compare with other results (theoretical or other sources). Comments not to exceed this page.
Task 3. Compare your results from the Task 2 with theoretical values and discuss. For this task only consider QPSK, 16PSK, 16QAM, 64PSK, 64QAM and 256QAM
Fig.3. Comparison of BER for QPSK, 16PSK, 16QAM, 64PSK, 64QAM and 256QAM.
Comment on the results:
Task 4 Tasks 1-2 have explored ideal coms channel with additive white noise. In reality communication channels are more damaging to the signal and can cause frequency shift of the carrier and time delay of received signals. These effects are incorporated in this Simulink example. Please familiarise with the example and then conduct BER analysis for the case of QPSK modulated signal.
In Fig.4 compares obtained result with the BER results for the QPSK modulated signal from the Task 2. Comment on the result.
Fig.4. Comparison of BER results
Comment on the results: