  Sleep monitoring provides valuable insights into the general health of an
individual and helps in the diagnostic of sleep-derived illnesses.
Polysomnography, is considered the gold standard for such task. However, it is
very unwieldy and therefore not suitable for long-term analysis. Here, we
present a non-intrusive wearable system that, by using photoplethysmography, it
can estimate beat-to-beat intervals, pulse rate, and breathing rate reliably
during the night. The performance of the proposed approach was evaluated
empirically in the Department of Psychology at the University of Fribourg. Each
participant was wearing two smart-bracelets from Ava as well as a complete
polysomnographic setup as reference. The resulting mean absolute errors are
17.4 ms (MAPE 1.8%) for the beat-to-beat intervals, 0.13 beats-per-minute (MAPE
0.20%) for the pulse rate, and 0.9 breaths-per-minute (MAPE 6.7%) for the
breath rate.
