Factors affecting cellphone signals

spill

I am currently studying an International Baccalaureate Physics course, and I am currently in my first year of study (i.e. I'm 16). As part of this, I am doing a presentation on cellphones; not my decision, but to get to the point:

If anyone could refer me to some information detailing which factors affect cellphone signal strength, it would be much appreciated. Obviously, I know what they are, but finding detailed scientific information about, say, how important they are relative to one another is proving exceedingly difficult. I have contacted a number of network providers only to recieve apologetic letters saying they cannot go into detail due to the risk of revealing their secrets. Any help would be great, and an equation of some kind would be fantastic. Many thanks

PS. I accidentally placed this thread in 'general physics' first,and now I'm not allowed to delete it (not authorised) despite the fact that I'm logged in. Any help?