Signal not enough for my phone works consistently

My phone( T-Mobile Samsung Galaxy SII ) always losing connection maybe because I am living at the edge of the signal coverage. Battery get eaten very fast because of weak signal strength. It is still manage to last over one day with my mpj extended battery though, I have to reboot frequently just to get connected. How can I boost the signal enough for it to work consistently? Please help and thank you millions in advanced.
 
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