1. Field of the Invention
The present invention relates generally to an apparatus and method for power control in a mobile communication system, and more particularly, to an apparatus and method for flexibly changing a fixed target Signal-to-Interference Ratio (SIR), a fixed target SIR step, and a time to perform a transmission (TX) power control request, in order to prevent a receiver apparatus from performing an excessive TX power control request in the event of a sudden reception (RX) channel environment change.
2. Description of the Related Art
In a mobile communication system, when an output power of a Mobile Station (MS) is high, this often causes interference with an adjacent MS. The adjacent MS detects a noise of the interference, and increases its output power in order to increase an SIR (or a Signal-to-Noise Ratio (SNR)). Consequently, the mobile communication system maintains the same output power level of adjacent MSs to control the data TX power of a transmitter.
Directly controlling the TX power of a mobile communication system as described above is referred to as an inner loop power control, and setting the range of the inner loop power control is referred to as an outer loop power control.
The above-described TX power control method is applicable to a Base Station (BS) controlling the output power of an MS, and to an MS controlling the output power of a BS.
In Wideband Code Division Multiple Access (CDMA), for TX power control, a receiver apparatus uses a BLock Error Rate (BLER) satisfying a Quality of Service (QoS). This ensures that data of an RX transport block is received at a certain level. The receiver apparatus measures the BLER of the current channel, determines whether to control the TX power of a transmitter, and requests the transmitter apparatus to increase/decrease its TX power accordingly.
The receiver apparatus uses the SIR of an RX channel to detect a channel BLER. More specifically, the receiver apparatus measures the SIR of an RX channel and sets a target SIR satisfying a desired BLER of the receiver apparatus.
Thereafter, if the SIR of the current RX channel is smaller than the target SIR, the receiver apparatus transmits a Transmission Power Control (TPC) Up request to the transmitter apparatus. However, if the SIR of the current RX channel is greater than the target SIR, the receiver apparatus transmits a TPC Down request to the transmitter apparatus, thereby adjusting the BLER of a RX Dedicated Channel (DCH).
The receiver apparatus may detect the occurrence or nonoccurrence of a transport block error at every Transmission Time Interval (TTI) to set the target SIR.
For example, after detecting the occurrence of a transport block error, the receiver apparatus adds an SIR Step Up size to the current target SIR to set the next target SIR (Next_Target_SIR=Current_Target_SIR+SIR_Step_Up). After detecting the nonoccurrence of a transport block error, the receiver apparatus subtracts an SIR Step Down size from the current target SIR to set the next target SIR (Next_Target_SIR=Current_Target_SIR−SIR_Step_Down). Herein, the SIR Step Down size is the product of the SIR Step Up size and the BLER (SIR_Step_Down=SIR_Step_Up×BLER).
As described above, the target SIR is not fixed, but varies depending on the channel environment. However, in the event of a sudden channel environment change, a sudden Additive White Gaussian Noise (AWGN) decrease, a sudden channel fading change, or a BS output power decrease or increase, a receiver apparatus will request an excessive output power of a transmitter apparatus in order to satisfy the BLER.