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Home Forums SYSTEM 32QAM and 64QAM OFDM with 512 ifft? # 32QAM and 64QAM OFDM with 512 ifft?

Dear all,

I am going to use matlab component to implement 32QAM or 64QAM real ofdm with 512 ifft. its output is electrical and real (using Hermitian symmetry before ifft). how to implement it? as we know the sequence length should be power of 2 bits. when I use 32QAM and 64QAM, the bits per symbol are 5 and 6 respectively. how can the output signal and time have same samples? for instance, bit rate= 10Gbps, sequence length= 65536, sample per bit=32, then the total number of samples=2097152,time window=6.5536e-6,sample rate=320e9.

so the matlab component ofdm should have 2097152 samples also.

### Responses (2):

• #17333 zsliu
Participant

Dear all,

I am going to use matlab component to implement 32QAM or 64QAM real ofdm with 512 ifft. its output is electrical and real (using Hermitian symmetry before ifft). how to implement it? as we know the sequence length should be power of 2 bits. when I use 32QAM and 64QAM, the bits per symbol are 5 and 6 respectively. how can the output signal and time have same samples? for instance, bit rate= 10Gbps, sequence length= 65536, sample per bit=32, then the total number of samples=2097152,time window=6.5536e-6,sample rate=320e9.

so the matlab component ofdm should have 2097152 samples also.

• #22164 alistu
Participant

Hi Zsliu,

In order for the output signal and time to have the same number of samples, you should first calculate the number of symbols exiting your OFDM block, using the total number of samples and the bits per symbol related to the coding scheme you are using. Then you have to calculate time samples by using symbol rate. I hope you have got your answer.

Cheers,
Ali

• #22178 Ravil
Participant

Hi Zsliu,

It looks like you are on a right track with the answer to your question. As you said, the number of symbols will be defined by the number of bits (length of bit sequence) and the number of bits per symbol (depends on your modulation scheme). However, I am not exactly sure what do you mean by “output signal and time have same samples”. Are you relating this question to the clocking scheme or you are planning to adjust the sampling rate?