After NodeB receives a signal from the UE, it estimates the signal-to-interference ratio (SIR) of this signal at the receiver end. Then, NodeB compares the signal-to-interference ratio with the preset target signal-to-interference ratio (SIRtarget). If the received signal-to-interference ratio is smaller than target signal-to-interference ratio, NodeB will inform the UE through the downlink dedicated control channel to increase the transmitting power; on the contrary, if the received signal-to-noise ratio is greater than target signal-to-interference ratio, NodeB will inform the UE through downlink dedicated control channel to decrease transmitting power. The whole control process is equivalent to a negative feedback process, which can make the signal-to-interference ratio of the received signal fluctuate near the target signal-to-interference ratio.The fast power control process of the downlink channel is the same with that of the uplink channel, but the start points are different. Power control of the uplink channel is mainly to overcome the near-far effect. A downlink channel does not have the problem of near-far effect, and downlink channel power control is to overcome Rayleigh fading and the interferences of adjacent cells.