Novel adaptive power and rate control in third generation wideband CDMA mobile systems

This Dissertation proposes novel adaptive power control and rate change schemes and investigates the performance of a Wideband Code Division Multiple Access (W-CDMA) system in conjunction with these adaptive techniques. In these schemes, the transmit power and rate are adapted to the variations of the fading channel using adaptive thresholds based on the probability distribution function (pdf) of the predicted mobile channel power values.;We define a policy similar to the traditional power control technique with thresholds with the exception that in our Adaptive Transmitter Power Control (TPC) and Adaptive Seamless Rate Change (SRC) the thresholds are set based on several regions of operation. These regions are defined by means of the probability distribution function (pdf) of the total average channel power. The pdf is initially constructed based on the history of the predicted channel power values derived from the long-range prediction algorithm. These regions can be defined such that the system operates at a constant average Eb/N0 dictated by the policy.;In a 1-user model with one channel path, the pdf of the channel power would be an exponential or chi-square function with 2 degrees of freedom. However, in a W-CDMA system, normally the rake receiver has several fingers. That is, at the receiver, the system either estimates or predicts the channel coefficients at each rake finger and performs maximal ratio combining by multiplying each finger with its conjugate or chooses the ones with the highest energy and performs maximal ratio combining on the selected fingers.;In a two-user system where the multi-access interference is modeled as the Standard Gaussian Approximation (SGA), the system performance and error probability of our W-CDMA system becomes similar to the one for our one-user system. Consequently, in a single user detector system, when all users adopt a similar policy for their adaptive power and rate control, the average total Multi-Access Interference (MAI) will be reduced. The resulting channel capacity of the system in this case will be increased and the system may operate in a lower transmit power level.;We evaluate the performance of these schemes using a detailed block diagram simulation of a W-CDMA system. All major components of the system are modeled and simulated, including an accurate model for realistic mobile channels. We present simulation results to verify that the proposed novel schemes are superior to the traditional approach of transmitter power control and rate change. Furthermore, our simulation results show that our proposed techniques reduce the effect of Multi Access Interference in a multi-user system.