AWGN Parameters setting for OFDM system using Simulink

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Alaa Mourad
Alaa Mourad 2016-2-22
回答： Matheus Fortunato Alves 2023-12-1
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 !

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回答（2 个）

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.
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!

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