I. Field
The present disclosure relates generally to communication, and more specifically to techniques for controlling transmit power in wireless communication.
II. Background
In a wireless multiple-access communication system, a base station may communicate with multiple terminals (e.g., cellular phones) on the downlink and uplink. The downlink (or forward link) refers to the communication link from the base stations to the terminals, and the uplink (or reverse link) refers to the communication link from the terminals to the base stations.
To reduce interference and improve system capacity, power control may be used for the downlink and uplink. Downlink power control may entail adjusting the transmit power of a downlink transmission to each terminal to achieve a target received signal quality at the terminal. Received signal quality may be quantified by signal-to-interference-plus-noise ratio (SINR), signal-to-noise ratio (SNR), energy-per-symbol-to-total-noise ratio (Es/Nt), or some other measure. For clarity, SINR is used for received signal quality in much of the description below. Similarly, uplink power control may entail adjusting the transmit power of an uplink transmission from each terminal to achieve a target SINR at the base station. For each link, the target SINR may be adjusted to achieve the desired level of performance, which may be quantified by a target frame error rate (FER) or some other performance metric.
The transmit power adjustment for a given link may be achieved by estimating a received SINR at a receiver, comparing the received SINR against the target SINR, generating a transmit power control (TPC) command based on the comparison result, and sending the TPC command to a transmitter. The transmitter then adjusts the transmit power either up or down based on the received TPC command. The accuracy of the transmit power adjustment is dependent on the reliability of the received TPC command.
A communication system may impose certain constraints on how TPC commands may be sent, as described below. These constraints may adversely impact the reliability of the received TPC commands. There is therefore a need in the art for techniques to achieve reliable power control in such a communication system.