To confirm wifi Signal level:
at linino console;-
/usr/bin/pretty-wifi-info.lua
where give you wifi info
Current WiFi configuration
SSID: TP-LINK_2.4GHz
Mode: Client
Signal: 100%
Encryption method: WPA PSK (CCMP)
Interface name: wlan0
Active for: 28 minutes
IP address: 192.168.0.103/255.255.255.0
MAC address: 90:A2:DA:F0:06:76
RX/TX: 914/268 KBs
or you could use Arduino IDE, at Example->Bridge->WiFiStatus upload Sketch then open serial monitor to view.