Data length error in OFDM Simulink

Greetings Community members,

I am trying to simulate an OFDM modulated Communicaion system, where I used very basic blocksets such as 16-QAM, Integer Generator, OFDM modulator. I have also used all the required Demodulators and their parameters are same as those of its corresponding modulators. Now after this, when I'm evaluating the error rate, I'm getting an error that the length of Tx. and Rx. is not same. But I'm not able to figure out why?

Please Do help me if anyone knowws the answer. Thank you.

[Swetha Polemoni]

Hi

Can you share the simulink model(.slx?)

[rajmouli jujjavarapu]

Thank you for showing your interest in solving my question.

I have shared the file, I would also like to mention that I have added the buffers hoping that it would solve the issue but still there is a problem.

Answer 1

[vidyesh]

Hello Rajmouli,

I understand you're encountering an error when calculating the error rate, stemming from a mismatch in the lengths of Tx (transmit) and Rx (receive) vectors.

The output length from the OFDM Modulator is determined by the ‘FFT length’ plus the ‘Cyclic Prefix length’. In your case, the output length is 80 (64 + 16). Additionally, 'Number of guard bands' property is set to [6; 5], which means there are a total of 11 guard bands (6 + 5).

Upon demodulation, the OFDM Demodulator will remove both the prefix and the guard bands. This will yield an output length of (80 - 16 - 11), which equals 53.

To align with this, you should configure the 'Samples per Frame' property of the Random Integer Generator block to 53. If you need to simulate a larger number of samples, consider either decreasing the 'Sample Time' or increasing the 'Stop Time'. This way, you'll simulate more time steps, each with 53 samples.

Note that in this case, we have not considered the DC null and that with this configuration, the model can be run without buffers.

For further guidance, you may refer to the 'Digital Video Broadcasting – Terrestrial' example, which employs both the OFDM Modulator and OFDM Demodulator blocks. This example can serve as a useful point of reference:

https://www.mathworks.com/help/comm/ug/digital-video-broadcasting-terrestrial.html

Hope this helps.