AWGN Parameters setting for OFDM system using Simulink

I am simulating a WLAN systems based on OFDM using simulink. I want to draw the BER curves via the SNR, I have some problems regarding the settings of the AWGN Channel simulink block. when I choose the EbNo mode, how should i choose the follwoing parameters:

 *Number of Bits*: It should depend on the moudlation and coding scheme, for example 8QAM and 1/2 code, it should be set to 6, is it right?
 *Sympol peroid*: is it meant the symbol period after the modulator and before the OFDM?

on the other hand, why I don't need these paremeters in case of SNR mode? Thanks for your help !

Answer 1

[Muhammad Yousaf Khan]

Have you found the solution for this problem... Moreover, I have implemented an OFDM system. It is working fine when the channel is transparent but it gives a huge error when you I add AWGN channel to the model. Can you please help.

[Abdelwahab Afifi]

Have you get the answer?

Answer 2

[Matheus Fortunato Alves]

Hi all,

Don't know if you've solved your question or not. But in order to reduce BER when using AWGN Channel Block and OFDM Baseband Modulator / Demodulador Block, you should change the parameter:

Input signal power, referenced to 1 ohm (watts):

to 1/N_FFT

For example, consider this simple wireless communication system using digital modulation for symbol mapping (BPSK, QPSK, etc.) and OFDM for modulation.

I configured input (Random Integer) to transmit 1000 data samples. Please note that Set Size parameter is equal to 2 as I'm using BPSK, so please adjust accordingly.

On OFDM channel, FFT length is equal to Num Samples + Num Guard Bands (see https://www.mathworks.com/help/comm/ref/ofdmmodulatorbaseband.html)

Finally, on AWGN channel, you should adjust input power per symbom. And as on OFDM modulation block we have 1000 + 11 symbols, input power = 1 / 1011

Remember to change OFDM Demodulation to sync with OFDM Modulator

From first figure, you can see that for Es/No = 6 dB, BER is around 1e-3, which is a suitable result for most realistic wireless systems without FEC or Error Correction.

When power is doubled (i.e., 9 dB on AWGN), BER is almost 10e-6

Hope it helps!