mobiles
...800Mhz band. The digital processing uses phase modulation that results in only a very small and essentially random changes in the amplitude of the carrier wave. The phase modulation consists on two electromagnetic waves, which have the same frequency but may be out of phase. Meaning that one wave is displaced from the other so that, when one has its maximum positive value the other has its minimum negative value. When the wave is phase modulated, each digit transmitted introduces a phase charge in the carrier wave and the change produced by a one is different from the one produced by a zero. In this system, each user requires a frequency channel of 200kHz; therefore there is a maximum of 174 channels within the 35MHz bandwidth of the 900MHz and 374 channels of the 1800MHz band. The channels are distributed across the cells in order for them to not cause interference with each other. The maximum power that the GSM mobile phones are permitted to transmit by regulation are 2W in the 900MHz band and 1W in the 1800MHz band. Another type of technology used is the CDMA (Code Division Multiple Access), 'a digital cellular technology that uses spread-spectrum techni...