Angular alignment monitoring using structured illumination from an LED array

A 16x16 light-emitting diode (LED) array has been used to monitor the angular alignment between the array and a remote single photon avalanche diode (SPAD) detector. For this purpose, a lens was used to project the LED array such that each LED element corresponded to a 1.8 degree x 1.8 degree solid angle. The SPAD was placed in the projection cone at a distance of approximately 2.5 m. The LEDs were modulated using on-off-keying at 2 kb/s super-imposed with a 25 MHz, 25% duty cycle square wave. Data were sent using 38 bit long frames, where the first 6 bits were a fixed sequence “001101”, used for clock synchronisation, and the remaining 32 bits were the payload. The payload bits were chosen such that each individual LED transmitted a unique digital fingerprint. The SPAD receiver could then identify the received fingerprint and thus determine which solid angle (with respect to the LED array) it was located in. The angular alignment was then deliberately changed to demonstrate live tracking of the alignment.
This dataset contains the live tracking result as well as a record of the phase difference between transmitter and receiver clocks that demonstrates the clock synchronisation using the preamble of the data frames.

clock_phase.txt:
First column: frame number
Second column: phase difference between transmitter and receiver clocks in degrees

row_count.txt:
First column: time in seconds
Columns 2-17: These correspond to rows 1-16 of the LED array. For each 0.25 seconds time bin starting at the time specified in the first column of this file, the numbers in these columns indicate how often the recorded position was in the corresponding LED row.

column_count.txt:
First column: time in seconds
Columns 2-17: These correspond to columns 1-16 of the LED array. For each 0.25 seconds time bin starting at the time specified in the first column of this file, the numbers in these columns indicate how often the recorded position was in the corresponding LED column.