Default S2 poor wifi signals

Hello all..

Got this phone as my secondary phone 3 days ago from a local vendor.. about 8 months used.. the problem is that the wifi reception is worst in this phone.. where my s4 gets 3 dots the s2 refuses to even maintain a single dot.. even on that single dot the internet doesnt work until and unless i move close to the router.. any way to boost wifi signals on the phone.. any modem which can help.. please respond nicely.. thanks

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IPhone 3g > IPhone 3gs > IPhone 4 > Samsung Galaxy S2 > Samsung Galaxy S3 > Htc one X, Samsung Galaxy S4 & Samsung Galaxy Note II