i am also facing the similar issues . It gets diconnected very frequently .
you can try this the below step once .
1) go to wifi -> click on the options icon close to your local wifi network
2) click on forget this netwok
3) try connecting again .
I am facing the issue on iphone 4s . Many suggest that this because of the wifi chip getting overheated .
May you can try disabling the wifi for one day and use it the next day .
I too was having this wifi issue for last one month . Since i did not renew my warranty , i did not approach apple store . I went to some local iphone repair shops and they told the issue is with the mother board and they cannot fix it .
I was frustrated . 2 days back , my iphone battery drained by itself . After charging it for a while , I tested if the wifi is working or not .
I found it is working fine . I was using face time calls . After some 20 mins of face time call , my phone got very much heated and there came default alert from the iphone , asking me to wait till the iphone cools itself .