AWR2944: Question on 2DFFT output from HWA in DDMA demo

Chris Meng

Mastermind 36485 points

Part Number: AWR2944

Hi,

I thought below is the 2DFFT output with FFT shift by 4TX & 2 empty band DDMA.

Then what's the data format on memory which is output from HWA after 2DFFT? Is it without fft shift like below?

Thanks,

Chris

8 months ago

0 Samhitha Bobba 8 months ago

TI__Genius 9780 points

Hi Chris,

You can refer to the following diagram to understand the format of Doppler FFT samples stored on the memory.

For more information, you can refer to mmwave_mcuplus_sdk_<ver>/mmwave_mcuplus_sdk_04_<ver>/ti/datapath/dpu/dopplerprocDDMA/docs/doxygen/html/index.html

Regards,

Samhitha

0 Chris Meng 8 months ago in reply to Samhitha Bobba

TI__Mastermind 36485 points

Samhitha,

The 2DFFT data on above picture you shared is not as our expected. We though there should be half band at beginning. Did the HWA do some shift when output the 2DFFT result to memory?

Thanks,

Chris

0 Samhitha Bobba 8 months ago in reply to Chris Meng

TI__Genius 9780 points

Hi Chris,

Data format depends on the phase shift per each Tx antenna. Can you check the phase shift that you configured?

Regards,

Samhitha

0 Chris Meng 8 months ago in reply to Samhitha Bobba

TI__Mastermind 36485 points

Samhitha Bobba said:
Data format depends on the phase shift per each Tx antenna. Can you check the phase shift that you configured?

This is the config. How the 2DFFT output from HWA on memory?

What’s the output of HWA FFT looks like? Does it like FFT in matlab or fftshift in matlab? I want to know if there is shift after FFT by HWA or not. I didn't find fftshift info in TRM HWA FFT section.

Thanks,

Chris

0 Samhitha Bobba 8 months ago in reply to Chris Meng

TI__Genius 9780 points

Hi Chris,

Chris Meng said:
What’s the output of HWA FFT looks like? Does it like FFT in matlab or fftshift in matlab?

HWA does not perform FFT shift. And when the 2D FFT output is transferred from HWA memory bank to L2, the format will be like the one that I shared previously.

Regards,

Samhitha

0 Gmsy Bryant 8 months ago in reply to Samhitha Bobba

Expert 1650 points

Hi Samhitha:

I have a follow-up question based on what you and chris discussed.

we use 4 Txs and 2 empty band,and we use 768 chirps,so each band has 128 points.The phase of each transmitting antenna is shown in the figure below:

After 2D-FFT,which of the following X-coordinate arrangements is correct(A or B,why?)?We are very confused about this.

0 Samhitha Bobba 8 months ago in reply to Gmsy Bryant

TI__Genius 9780 points

Hi Gmsy,

It should be like A. I will recheck and let you know in a day or two.

Regards,

Samhitha

0 Gmsy Bryant 8 months ago in reply to Samhitha Bobba

Expert 1650 points

Hi Samhitha,

Thank you very much and look forward to your answer.

Regards,

Bryant

0 Samhitha Bobba 8 months ago in reply to Gmsy Bryant

TI__Genius 9780 points

Hi Gmsy,

As per my understanding, band A will not be split into two halves. Look at the subplot 2 (Doppler FFT) in the following screenshot.

4 peaks corresponding to zero doppler are visible. And the band is not split into two halves.

Regards,

Samhitha

0 Gmsy Bryant 8 months ago in reply to Samhitha Bobba

Expert 1650 points

Hi Samhitha,

if we config the phase of TX1 is a negative phase,will there be the phenomenon of B diagram I mentioned above.

Regards,

Bryant

0 Samhitha Bobba 8 months ago in reply to Gmsy Bryant

TI__Genius 9780 points

Hi Gmsy,

I will check and get back to you by Monday. May I know the reason why you want to achieve half bands? Can you also specify phase of other tx antennas?

Regards,

Samhitha

0 Gmsy Bryant 8 months ago in reply to Samhitha Bobba

Expert 1650 points

Hi Samhitha,

The phase of the transmitting antenna is -pi/6 pi/6 3pi/6 5pi/6.Asking this question is purely theoretical,at the same time, we have doubts about the HTML information provided by TI.As shown in the following picture:

Access path file:///C:/ti/mmwave_mcuplus_sdk_04_02_00_03/ti/datapath/dpc/objectdetection/objdethwaDDMA/docs/doxygen/html/index.html.

Regards,

Bryant

0 Samhitha Bobba 8 months ago in reply to Gmsy Bryant

TI__Genius 9780 points

Hi Bryant,

Gmsy Bryant said:
The phase of the transmitting antenna is -pi/6 pi/6 3pi/6 5pi/6.

Thank you for the confirmation. I will let you know on Monday.

Regards,

Samhitha

0 Samhitha Bobba 8 months ago in reply to Samhitha Bobba

TI__Genius 9780 points

Hi Bryant,

Gmsy Bryant said:
The phase of the transmitting antenna is -pi/6 pi/6 3pi/6 5pi/6.

For the above-mentioned phase shift, the band is split into two halves. You can observe it in the following plot.

Regards,

Samhitha

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AWR2944: Question on 2DFFT output from HWA in DDMA demo