I watched Dan's demonstration of the 4-chip AWR1243 for improved angular resolution. It looks like a wonderful solution. I am designing a very similar 4-chip cascaded solution with tweaks for our application.
I have also read swra554 on MIMO several times, but I am still confused.
Using BPM and simultaneous transmission, you need 9 orthogonal codes. What coding scheme are you using (how many chirps)? The entire sequence needs to be completed before the signals can be unfolded with auto-correlators. What CPU power does it take to separate those out? Are you doing this in real-time?
If TDM is used, doesn't that decrease your maximum velocity by a factor of 9? The max velocity is based on the inter-chirp time difference and phase shift. If successive chirps are sent from different antennas, the phase shift is also increased/decreased. One would only be able to compare every ninth chirp. Are those being compensated somehow? Wouldn't you need the phase shift caused by the separate TX antennas, which would then require you to first determine the angle?
Likewise, how does one improve the angular resolution with transmits from different chirps. The angle is computed by comparing the received phase from the different virtual antennas at the same time. Chirp-to-chirp, there is a combined effect of the velocity and the angle change. You can discern the difference between RX antennas for each TX, but can you discern between the same RX in different chirps without first knowing the velocity?
There are hopefully straightforward methods that I am just not seeing. Please help me to understand.
