A mobile phone network consists of base stations and multiple mobiles. The base station transmits control messages and voice traffic to the mobiles on the 1.23-MHz bandwidth forward link. The mobiles send control messages and voice traffic to the base station on the separate 1.23-MHz reverse link. While, both the forward and reverse links require power control, the main need for power control arises in the reverse link. The reverse link requires power control primarily to solve the near-far problem.
All handsets transmit on the same frequency channel at the same time but with different codes.
Therefore, one handset s signal may interfere with the others. A mobile s received signal quality at the base station is inversely proportional to the power of the interference from other mobiles. The near-far problem arises when two mobiles transmit at the same power but at different distances from the base station. Due to different propagation losses, the transmissions can arrive with very different received powers. The mobile near the base station, which has a high received signal power, greatly interferes with the distant mobile, which may not be detected.