“…Nonwearable sensors are widely applied, such as load cells, force sensors, air cushions, pressure pads, water-filled vinyl tubes [7], smartphones [31], [63], Shimmer sensors [10], Doppler radar signals [64], [65] also with sound signals [65], [66], pressure sensors [16], [17], [17], [20]- [22], [67], and radio signals [68]. Air cushions under the bed collect data such as respiration rate, heart rate, and body movement to estimate sleep stages.…”