Power control in the uplink of LTE consists of an open-loop and a closed-loop power control.
The open-loop mechanism establishes a baseline for the desired transmit power: the MS determines the downlink path loss from a pilot with known transmit power, and from that computes the necessary uplink power (including necessary margins in the process).
A power control signal that is transmitted in the PDCCH then “fine-tunes” the transmit power.
One-bit power control signals request the power to be changed by ±1 dB; 2-bit signals select from the set [−1, 0, 1, 3] dB.
No downlink power control is specified, though a BS can adjust the power at will (since such adjustments do not contradict the standard). While the mechanisms of power control are somewhat similar to that of WCDMA, their importance and motivation are very different.
For WCDMA, power control is essential for proper functioning of the data transmission. In LTE (just like in GSM), power control is just used for increasing battery lifetime, and reduction of intercell interference.