A cell phone is really a low-power radio
transmitter and receiver.When switched on,it sends out radio signals that are detected
by nearby cellular
transmitter-
receivers.Each of these sends and receives by radio ovwer a local area or "cell".several receivers may send their identity signals back to the phone.the phone then selects the most suitable receiver and establishes connection through it to the network.the size of a cell varies but it is usually a few miles across.Cities where more people are packed together have small cells,because each cell can cope with only a limited number of calls.Tall buildings or hills might also disrupt signals and cause dead spots.