. 2017 Jun 29;17(7):1527. doi: 10.3390/s17071527

Table 1.

Symbols.

Symbol	Description
$R_{S}$	Sensing radius of a sensor node.
$R_{C}$	Communication radius of a sensor node.
$E_{T}$	Consumed energy of sending per unit data.
$E_{R}$	Consumed energy of receiving per unit data.
d	The size of data collected by a sensor node.
$O R_{i, j}$	Overlapping rate of sensing area of two nodes $v_{i}$ and $v_{j}$ .
$O R_{T}$	Threshold of overlapping rate of sensing area.
$G A_{i}$	Gathering area with $v_{i}$ as the gathering node.
$G N$	Gathering node, which aggregates the data collected in a gathering area.
$C G_{i}$	Candidate gathering node set of $v_{i}$ .
$C P_{i}$	Candidate parent node set of $v_{i}$ , including all the upper-level nodes that couldcommunicate with $v_{i}$ directly.
$N_{i}$	Neighbor node set of $v_{i}$ , which consists of the nodes at the same level that couldcommunicate with $v_{i}$ directly.
$L_{i}$	Level of $v_{i}$ , and $L_{i} \in N^{+}$ .
$d_{i}^{T}$	The total amount of data transferred from $v_{i}$ .
$d_{i}^{R}$	The total amount of data received by $v_{i}$ .
$E_{G N_{i}}$	The energy consumed for delivering aggregated data from the gathering node $v_{i}$ .
$E_{G A_{i}}$	The total energy cost of the nodes in the gathering area $G A_{i}$ .
$E_{i}^{k}$	The total energy cost of transmitting data of node $v_{k}$ to the sink via another node $v_{i}$ .
$F N_{n}$	Free nodes at the level n.