AWR6843AOP: AWR6843AOP Child Presence detection cfg adjustment

Hi, Vincent:

In case 1), we have total chirping time 159.4ms.  When we concatenate 4 frames, the total obeservation window is 159.4+200*3 = 759.4ms. 

profileCfg 0 60.00 2789 11 41 0 0 97.00 1 64 2200 0 0 36
profileCfg 1 60.00 20 11 41 0 0 97.00 1 64 2200 0 0 36
chirpCfg 0 0 0 0 0 0 0 1
chirpCfg 1 1 0 1 0 0 0 2
chirpCfg 2 2 0 1 0 0 0 4
frameCfg 0 2 54 0 200 1 0

In case 2), we have total chirping time 9.88ms.  When we concatenate 4 frames, the total obeservation window is 9.88+200*3 = 609.88ms. 

profileCfg 0 60.00 20 11 41 0 0 97.00 1 64 2200 0 0 36
chirpCfg 0 0 0 0 0 0 0 1
chirpCfg 1 1 0 0 0 0 0 2
chirpCfg 2 2 0 0 0 0 0 4
frameCfg 0 2 54 0 200 1 0

So, the observation window between these two configuration has some differences. So, case 1) will slightly better sensitivity.  

In terms of FCC regulations.  Case 1) highest duty cycle is only 4% for every 33ms.  Case 2) the active chirping time is slightly over 7.5ms.  You will need to further reduce the number of loops to make it within 7.5ms. 

Let me know if you have any questions.

Best,

Zigang

Hi Zigang,

Thanks for your reply.
But I couldn't calculate the 159.4ms for case 1, I calculated the total time to be 143.2ms
Here's how I calculated it :
---------------------------------
Idle time : 2789(us)
Ramp End time : 41(us)
Num Loop : 54 
Compliance Chirp time : ((2489+41)/1000)*1*54 = 136.62(ms)
---------------------------------
Idle time : 20(us)
Ramp end time : 41(us)
Num Loop : 54 
Compliance Chirp time : ((20+41)/1000)*2*54 = 6.588(ms)
---------------------------------
Total Compliance Chirp time : 136.62 + 6.588 = 143.2(ms)
Duty cycle : 143.2/200 = 0.716 = 71.6%
Can you tell me which step is wrong in calculation?

Besides, I don't quite understand what you're talking about.
1. "When we concatenate 4 frames, the total observation window is 159.4+200*3 = 759.4ms."
Why we need to concatenate 4 frames?

BR,
Vincent

Hi Zigang,

Can we use the RF duty cycle of mmWave estimator as a basis?
The calculation above is based on this software.


BR,
Vincent

HI, Vincent:

In the following calculation, you use 2489 instead of 2789.

Idle time : 2789(us)
Ramp End time : 41(us)
Num Loop : 54 
Compliance Chirp time : ((2489+41)/1000)*1*54 = 136.62(ms)

Inside the CPD demo, the previous four frames are processed together to improve sensitivity.  Check the highlighted users guide below:

Best,

Zigang

HI, Vincent:

I am not sure sensing estimator supports multiple profile settings and it does not calculate the worse duty cycle in 33ms. 

Best,

Zigang 

Hi Zigang,

I'll recalculate the 4% for every 33ms you mentioned.
The following is my operation logic.
I am not sure if it is similar to your idea.
---------------------
1. Calculate Total Compliance Chirp time
((2789+41)/1000*1*54)+((20+41)/1000*2*54 ) = 159.408(ms)
2. Calculate Total Idle time
((2789)/1000*1*54) + ((20)/1000*2*54) = 152.766(ms)
3. Calculate signal transmission time
159.408- 152.766 = 6.634ms
Duty cycle = 6.634/159.408= 0.0416= 4.16%
---------------------
As you mentioned, case 2 will slightly over 7.5ms.
But the transmission time after my calculation is only 6.64ms
Duty cycle = 6.64/9.882 = 0.672 = 67.2%
Is there any error or misunderstanding in my calculation method?

BR,
Vincent

Hi Vincent,

Please give Zigang another day to follow up.

Thanks,

Clinton

Hi, Vincent:

The duty cycle in general should be the total active chirping time divided by total frame time. 

The general duty cycle is 41*3*54/1000/200 = 3.32%

But for FCC, things are more complicated. 

Note: For FCC regulations, any non-chirp (no output) time < 2ms contributes toward the duty cycle calculation. Max burst duty cycle is also calculated based on any 33ms period during operation, even if the frame period is greater than 33ms. This manifests as an on-time or active time limit for the chirping portion of frame.

The duration of one set of three chirps: (2789+41)+(20+41)*2 = 2952us.  For 33ms, there can be maximum 12 sets of three chirps. 

Based on the above FCC regulations, 2789us is longer than the 2ms, can be exclude from chirping calculation.  The maximum burst duty cycle is  ((41+20)*2 + 41) * 12 / 1000 / 33 = 5.93%.

Let me know if it makes sense to you.

Best,

Zigang

Hi Zigang,

I saw in the content from "">docs.fcc.gov/.../FCC-23-35A1.pdf" that the FCC requirement is "Off time requirement: off times (>=2ms) must sum to at least Xms per 33ms interval".

It requires that >=2ms must be added in 33ms, which is different from the <2ms you mentioned.

I also don't quite understand why the 20ms idle time is calculated in the duty cycle in "((41+20)*2 + 41) * 12 / 1000 / 33 = 5.93%."

Could you please provide further guidance on this?

BR,
Vincent

Hi, Vincent:

My understanding is that any idle time less than 2ms has to be part of the active time.  Only the idle time >=2 ms can be treated as off-time.  That is why I added 20us idle time into the duty cycle calculation, but exclude the 2789us. 

Best,

Zigang