Sensors of Smart Devices in the Internet of Everything (IoE) Era: Big Opportunities and Massive Doubts

Table 1

Time-domain features.

Feature	Citation	Definition
Mean	[18, 74, 75, 92, 95, 180–184]	The summation of data points divided by their number
Std deviation	[18, 58, 74, 75, 180, 183, 184]	It is the square root of variance
Average deviation	[18, 58, 74, 180, 183]	The average separation of data points from their mean or average value
Skewness	[18, 180, 183]	Measures the asymmetry from the mean value. It utilizes the mean and the variance
Kurtosis	[18, 180, 183]	Estimates the frequency of extreme values. It utilizes the mean value in its formula
RMS amplitude	[18, 180, 183, 184]	It is leveraged to calculate the power of a signal. It utilizes the maximum value of a set
Lowest value	[18, 180, 182–184]	The maximum data point
Highest value	[18, 180, 182–184]	The minimum data point
ZCR	[18, 183]	Zero crossing rate is a counter of how many times the data points cross the zero value
Nonnegative count	[18, 183]	Total number of positive data points in a set
Average absolute difference	[75, 185]	The average of the total differences between all data points in a set
Time between peaks	[75, 184, 185]	The number of points between two high peaks or low peaks
Binned distribution	[75]	The processes of grouping data points into smaller number of points or “bins”