I’ve always wondered why mobile phone reception varies as you walk around. Stand in one place and you’ve got 5 bars, move to the right a step or two and you don’t. Reading Wireless Communications by Molisch provided the answer in the first 20 pages. Simply put, your signal is broken up between several pieces that come to your phone from different paths (multipath) and therefore at slightly different times (out of phase). At your phone they arrive to add together or subtract from each other. If they add together you have strong reception and if the subtract from each other you have weak reception.
Since the actual length of the signal is about 1m, when the multipath signals arrive at 1/2 the wavelength away from you (0.5m or about 1.5 ft) you can experience a vastly different signal strength better or worse.
In this picture, BS (base station) broadcasts signal meant for the phone. The signal reflects off buildings, gets scattered through trees and defracts through other buildings. The signals in this case are coming from different directions and are of different lengths. Your phone has to add them together to make one big signal but the slight delay on some of the signals from others forces the total signal received to be less than what was transmitted.
Now you have the answer.
P.S. Could this be improved now? Practically speaking, no, since improvements would require much more processing power which will enlarge the phone handset and require a bigger battery. In the future the answer is maybe. Research continues all the time on this problem so it is likely that multipath signal noise will be reduced further. No garentees however it is likely.