Me and my friend's galaxy 5 has a weak Wi-Fi signal. Even in a few meters from access point, it has 2 lines of antenna.
Is there any solution for increasing signal?
Sometimes there may be interference from other electronic / microwave equipment.
In your router / access point's settings change the channel and see if there's any improvement.
Also, don't be taken in so much by the bars displayed. Very often, I see only 2 bars, but in the WiFi settings, I see the signal strength displayed as EXCELLENT.
The other usual rules apply - place your router as high as you can. Place it away from other cordless phones or electronic devices that can generate interference.