SINR analysis and power control for downlink W-CDMA and multiuser OFDM systems

Three issues in downlink W-CDMA systems and multiuser OFDM systems are addressed in the research of this thesis.;In the first part, the SINR performance of the concatenated OVSF and truncated PN code is analyzed, and its application to W-CDMA systems is studied. Previous work along this direction focused on the performance analysis of the concatenated OVSF and full-period PN code. For the full-period PN code, the spread symbols of interfering users satisfy the ideal characteristics of randomness so that the analysis can be greatly simplified. When the truncated PN code is used to replace the full-period PN code, the randomness property does not exist any more, and some modifications have to be made to have a correct representation of SINR. In this research, we perform a thorough SINR analysis for the concatenated OVSF and truncated PN code. Furthermore, we show the correlation between OVSF codes when the same truncated PN code is used. Simulation results are given to demonstrate the correctness of our analysis.;In the second part, two power control schemes for multimedia transmission in downlink W-CDMA systems with QoS provision are presented. The first power control scheme is symbol-based. It adjusts the transmission power level based on the information of received symbols at the mobile end. When the QoS requirement for a symbol is indulged or cannot be satisfied, the transmission power will be reduced or increased, respectively. This power control scheme can provide better QoS for audio/speech service. The second power control is packet-based. It aims at reducing the time required for a packet to get through the channel so that it is suitable for time-critical service. Simulation results show that these two schemes can provide QoS for wireless multimedia service in W-CDMA systems.;In the third part, a new scheme to control the transmission power, allocate subcarriers, and choose modulation schemes for each mobile terminal in a multiuser OFDM system is proposed. It makes OFDM systems more flexible and robust to the channel variation along time. We solve the problem in two stages. In the first stage, the minimum signal-to-noise ratio (SNR) of subchannels is maximized under some constraints so that the system performance is maintained at an acceptable level. Based on results of the first stage, we choose modulation schemes for subchannels of each mobile terminal to maximize the total transmission rate and meet the performance requirement of each mobile terminal in the second stage. Simulations are conducted under a different total number of mobile terminals and different SER (symbol error rate) requirements, and it is shown that the proposed scheme has excellent performance among several competitive schemes.