Adaptive step-size power control scheme in WCDMA

In the wideband code division multiple access (WCDMA) system, fast transmit power control (TPC) should overcome the pathloss caused by fast multipath fading. However, the conventional fixed step size transmit power control (FS-TPC) does not compensate the fading well due to the complexity of fast fading in Rayleigh channel. We proposed and evaluate a single-bit adaptive step-size transmit power control (AS-TPC) scheme which can be applied in WCDMA. The new scheme divides the power control process into Markov states according to the received TPC command in history. On the basis of analysis of the step-size of the channel fading, it chooses step-size according to the largest probability density of step-size of the multipath Rayleigh fading channel with respect to the period of the transmit power control. Each TPC step size is corresponding to a channel Markov states. Considering the power circuits minimum resolving is about 0.5 dB, we can decide the step size set. The relationship between the Markov state and the TPC step-size is made out by computer simulation. The transmitter decides increasing or decreasing the transmit power according to the received TPC command. However, the changing quantity is chosen according to the current TPC command and the historical TPC commands.