Figure 3.

Schematic of the fuzzy pattern recognition algorithm: (a) nine RPs in a grid area and the interval of the RPs is 2 m; (b) $l_t=l_{t - 1}$ when the RSSI has no variation or a similar variation in four directions; (c) $l_t=l_{pn}$ when the RSSI variation trend follows the trajectory from ${\mathrm{P}}_0$ to ${\mathrm{P}}_{\mathrm{n}}$; (d) $l_t=l_{pn}$ when the RSSI has a similar variation trend in the north and east, we assume the RSSI variations follow the trajectory from ${\mathrm{P}}_0$ to ${\mathrm{P}}_{\text{ne}}$; (e) $l_t=l_{t - 1}$ when the RSSI has a similar variation in the east and west; (f) $l_t=l_{pn}$ when the RSSI has a similar variation in the east, west and north, we assume the RSSI variations follow the trajectory from ${\mathrm{P}}_0$ to ${\mathrm{P}}_{\mathrm{n}}$.