how to improve mobile reception quality

Am a college student staying at hostel. in my hostel i have to go to the top floor to make and recieve calls. and in my room i dont get any signal. is it possible to make a circuit to recieve the signal in the room itself.

am using a nokio 2100 and my mobile carrier is airtel(india) working at 1800MHz band


help me in this regard

There is no easy way to do this. Ideally you would need a bi-directional amplifier coupled to your phone and of course this is not practical.
This next idea is maybe not practical either but....if you have access to some point in your building where you can get phone reception and your room is not too far from that point you could try this. Get a high gain antenna, place it where you can get phone reception, point it at your nearest base station, run low loss coaxial cable from here into your room. Then connect another antenna to the coaxial cable end in your room. This is a very simple passive repeater. Factors that will help it work will be keeping the cable run as short as possible, using as low a loss cable as possible, use as high a gain antenna as possible.
I realize that this is pretty crazy but hey.......could just work if you can set it up.

Pssive repeaters are rarely used. I have seen one for TV broadcasting . He can get better result if will directly apply mobile RF connector (hope it is there for car kit connection) to cable in room . But that case it will be wireline )).

You can hook a directional antenna to your phone and use it in the room, but it will be fairly large (0.5 meter or so).

Using a passive receiver can improve it.
Use two antennas connected by a cable.
put one outside and the other one inside.

I did't understand the statement above.

What are the problems associated with using passive repeater in a situation like the one quoted. Is it not the suitable solution ? Is it not a cost-efective solution ? What are the limitations of using it ?

is it possible to construct a booster like circuit (the one used for TV) for the mobile frequency

change the anttena or matching problems
to check the circuits

I dont want to say this. But try changing your phone. If the reception in your area is crappy there is not much you can do about it. I am sure your room must have a window, try using the phone near the window, hope that helps. best of luck
Abhishek