Novel Adaptive Power and Rate Control in Third Generation Wideband CDMA Mobile Systems

Ali Soheil Sadri: Novel Adaptive Power and Rate Control in Third Generation Wideband CDMA Mobile Systems, under the direction of Dr. Winser Alexander. This Dissertation proposes novel adaptive power control and rate change schemes and investigates the performance of a Wideband Code Division Multiple Access (WCDMA) 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 except that the thresholds are set based on several regions of operation in our Adaptive Transmitter Power Control (TPC) and Adaptive Seamless Rate Change (SRC) schemes. 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 ratio of energy per bit over noise power. 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 WCDMA 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. We model and simulate all major components of the system including an accurate model for realistic mobile channels. We present simulation results to verify that the proposed novel schemes are superior to the traditional approaches for 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. Novel Adaptive Power and Rate Control in Third Generation Wideband CDMA Mobile Systems By: ALI SOHEIL SADRI A Dissertation Submitted to the Graduate Faculty of the North Carolina State University in Partial Fulfillment of the Requirement for the Degree of Doctoral of Philosophy Department of Electrical and Computer Engineering Raleigh, North Carolina April 27, 2000 Approved by: ________________________________________ Dr. Winser Alexander, Chairman ______________________________________ ____________________________________ Dr. Brian Hughes, Member Dr. Ernest Stitzinger, Member ________________________________________ Dr. Andy Rindos, Member