For those who are tracking this issue.. We have some interesting updates with respect to the interference from IMX412 camera. As it has been previously documented, the IMX412 camera(s) on Starling 2 and Starling 2 Max are causing interference as soon as the streaming is enabled (there are clients to the streams that camera server offers for those cameras).
IMX412 camera has several internal clocks, which are generated from the 24 Mhz base frequency that is fed from Voxl2 to all cameras. These clocks are configured during the camera initialization phase - the settings are contained within the imx412 sensormodule files.
We were able to perform some parameter sweeps - specifically varying only the output MIPI bitrate, while keeping all other settings the same (gain, exposure, fps).
The test was set up as follows:
generate imx412 sensormodule drivers for desired frequency range (1200-2100)
all tests use the same camera resolution 3840x2160 at 45FPS
higher fps = more interference
tried to have a relatively large frequency range while keeping the fps high (low mipi rates cannot support high fps), so 45fps was a good compromise
repeat for each frequency
copy appropriate sensormodules (for specific frequency) into /usr/lib/camera/
log baseline satellite signal strengths for all satellites 10 seconds -- this allows the experiment to not depend on any initial SNR captures at the beginning of the test, since SNR can change relatively quickly due to the environmental factors
start voxl-camera-server and voxl-inspect-cam hires_front_misp_color hires_down_misp_color and wait for 3 seconds
collect satellite SNRs for 10 seconds while the cameras are streaming
stop voxl-camera-server
wait for 3 seconds and repeat the loop for the next frequency
After data has been collected, analyze the logs and generate plots.
The tests were done outdoors using Starling 2 Max with original GPS receiver + V3 GPS mast and 75mm FR4 (with copper) circular plate under the receiver. Full Sun light and exposure was set to 0.1ms, gain to 100 (1.0x). During testing it was discovered that the most interference was present when the image was darker than normal (under-exposed) -- probably related to specifics of the MIPI packets that are causing the interference.
Note that the default IMX412 MIPI bitrate was set to the maximum that the camera officially supports, which is 2100Mbps.
As the plots show, there are several peaks where the satellite SNRs drop by 10-15dB, as initially noted in the overall system testing. Additionally, 2100Mbps is one of the worst frequencies to use, based on this data.
As a result of testing, the following frequencies were identified as causing significant interference with GPS L1 band:
1212Mhz
1260Mhz
1572-1578 Mhz (L1 band!!)
1800Mhz
2100Mhz
We will be releasing updated IMX412 drivers very shortly to avoid using 2100Mhz frequency.
There results below show 3 tests:
1200-2100 Mhz sweep with steps of 30Mhz
1200-2100 Mhz sweep with steps of 6Mhz
1760-2200 Mhz sweep with steps of 8Mhz (focusing on the upper range, slightly different PLL configuration)
1200-2100 Mhz sweep with steps of 30Mhz
imx412_pll_sweep_1200_2100_30_3840x2160_45fps_heatmap.png
1200-2100 Mhz sweep with steps of 6Mhz
imx412_pll_sweep_1200_2100_6_3840x2160_45fps_heatmap.png
imx412_pll_sweep_1200_2100_6_3840x2160_45fps_median.png
1760-2200 Mhz sweep with steps of 8Mhz
imx412_pll_sweep_1760_2200_8_3840x2160_45fps_heatmap.png
imx412_pll_sweep_1760_2200_8_3840x2160_45fps_median.png
