When you change the bit rate and the number of subcarriers, you need to change the bit rate in the BER Test Set to reflect this. Look at the examples in the technical background of the OFDM Modulations. The bit sequence generators (e.g. BER Test Set) need to take the Bit rate value of Global bit rate * number of sub carriers / maximum possible subcarriers. This will correctly “fill” exactly all of the carriers with bits before the OFDM Modulation creates the OFDM symbol and transmits it.
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