Table 1 The meanings of symbols
From: Critical data points retrieving method for big sensory data in wireless sensor networks
Symbols | Meanings |
|---|---|
δ | The relative error of the approximate critical point |
N | The number of sensor nodes in a given WSN |
V={1,2,..N} | The set of sensors |
i | The ID of a sensor node |
S i | The real physical world curve at node i’s location |
S i (t) | The sensed value of sensor node i at time t |
S i (k)(t) | The k-order derivative of S i at time t. |
\(\widehat {S_{i}}^{(k)}(t)\) | The estimation of the k-order derivative of S i at time t. |
X 1 | The extremum point set returned by our algorithm. |
X 2 | The inflection point set returned by our algorithm. |
t s | The start time of an observation period |
t f | The final time of an observation period |
t c | The current data sampling time slot |
f max | The maximum sampling frequency |
t ′ | The step-size increment |
α | The decrease factor |