I've a Samsung Galaxy Ace but my Wifi is always not in range.
Google Helps state:
Use WiFi driver re-installation Code
*#*#526#*#*...Reinstall the firmware for Wifi. Try it on other Routers as well this is a common problem with Androids. as i see (seen in lot of forums people discussing Wifi problem of Androids) My cousin bought the same Handset and he is having same problem. If it doesn't help show it to your vendor from where you have brought it
How do I use the WiFi driver re-installation Code