Please, any ideas about for FFT with 6 bits OFDM receiver.

Hello!

I have been implementing OFDM with fixed-point FFT. I have 16 bits at Tx output for DAC, but I have only 6 bits ADC for Rx. As you can see below

At Tx.....Outout from FPGA 16 bits then connected to DAC .........

At Rx....ADC with 6bits input to FPGA for FFT processing.

Therefore, the problem is how to process and calculate FFT at Rx because the number of bits is not equal at both Tx(16 bits) and Rx(6 bits).

Please, any ideas about for FFT with 6 bits at Rx.


Thanks so much

Re: Please, any ideas about for FFT with 6 bits OFDM receive

Hi..

The problem is not clear. Are you asking how can we have FFT at TX side is generating output of 16 bits and IFFT at RX which can take input of 6 bit ? Or how to code FFT/IFFT which can take 6 bit input and generate 16 bit output ?

Re: Please, any ideas about for FFT with 6 bits OFDM receive

Thanks so much...

The problem is how to process with 6 bits input for Rx.

At Tx, I use fixed-point which is 4 bits integer and 12 bits factional (16,12).Then I pass the 16 bits to DAC and send it out.

At Rx, I have 6 bits ADC, so the problem is how to define integer and factional of the 6 bits for FFT processing.

Thanks you so much again....

Re: Please, any ideas about for FFT with 6 bits OFDM receive

I don't see the problem..you can use the normalized form of data and so if you have 6 bit at RX you have at output of your FFT you have 6 bit + log2(NFFT) where NFFT is the number of points of your FFT (1024, 2048...).
This is "the integer part" but there's no difference between them because probably you have an ADC front end with input range between -1V and 1V and so these 6 bits are totally fractional part...6 bit is only a dinamic range!!
Also if you drive a DAC the integer and fractional part is defined only by the voltage output range as I sayed in previous example!
In signal processing is useful to take this approach also because you have an increasing of datawidth and so first of all choose the internal precision of your FFT (i suggest for example 16 bit or 32 what you want) and of your phase tap (16 bit for example...) and after design your FFT circuit.
It depends on what are you specifications in terms of Signal-to-Noise ratio.
Let me know if someone is not clear!

Enjoy your design!

Alex

Re: Please, any ideas about for FFT with 6 bits OFDM receive

Thanks so much Mr.Alex....

I think, it would be better to post a picture about the problem.

And how accuracy with 6 bits ADC if we put it in factional, please?

If you have any ducuments, please tell me.

Again thanks very much.

Bon!