Problem description
We have embedded devices periodically sending us data. We want to be alerted as early as possible when a device stops sending data.
A very simple approach is to take the time difference of the last few times a device sent data and calculate the average. When we know a device sends data roughly every 15 minutes, we can easily trigger an alarm if no data arrived for that time.
The above approach assumes devices send data with the same period always. However, that is unfortunately not true for all. We have found devices which never send data during the night. Or devices which stop sending every afternoon, presumably because their GSM internet connection becomes disturbed. Continue reading “Predicting periodic events with FFT”