wifi internet frequenct disconection or hard connection

I got the high speed internet two weeks ago but  it is often hard to connect to the wifi with my smart phone or when connected the connection drops lot of times a day .I can see the lights on the moden flashing when the disconnection happens.I checked out nearby routers and shifted my router channel to 11.It seems not working.So far what I can do is to switch the power off and then on，it sometimes works or waite for a while and the connection may return.It never happens to the wifi connection of my phone at other venues for example in Starbucks.I use Netgear 3000 witi wireless router.And the tricky thing is the wifi sometimes works well！