Resource allocation techniques for improved performance of multiuser systems

by Oh, Changyoon.

iii The increasing demand for wireless services necessitates efficient sharing of radio resources. The premise of this thesis is that the performance of multiuser wireless systems can be significantly improved by efficient resource allocation. This thesis investigates scheduling and power allocation problems for several types of wireless communication systems each employing CDMA as the multiple access mechanism. Scheduling refers to the process of selecting the subset of users to transmit using the available resources. The resources considered are sectored antennas, orthogonal codes, and time slots. This thesis investigates three distinct scheduling paradigms. The first one is appropriate for real-time CDMA services with constant QoS requirement, whereas the last two are appropriate for delay tolerant CDMA services. This thesis first considers spatial scheduling and power allocation for a CDMA system employing directional antennas. Spatial scheduling, in this context, refers to scheduling users to sectors served by the directional antennas. The joint optimization problem of cell sectorization, transmit power control, and receiver filter design is studied for both uplink and downlink. Specifically, we determine the optimum sector beam width, such that the total transmit power is minimized, while each user satisfies the minimum signal to interference ratio (SIR) at receivers capable of employing linear multiuser detection. Near optimum solutions with reduced complexity are also sought. This thesis next investigates the multiuser scheduling and power allocation problem for interference limited multiuser systems. Scheduling, in this context, refers to iv scheduling a subset of users to allocate the downlink bandwidth so as to maximize the throughput. The aim is to characterize the optimum base station transmission strategy and to find the corresponding power allocation. We model the interference level by the aid of the orthogonality factor, and find the optimum policy for a range of the orthogonality factor values. Lastly, this thesis considers the temporal scheduling and power allocation problem for delay constrained CDMA services, i.e., scheduling users to time slots. The motivation is to design an energy-efficient transmission strategy, while each user satisfies a short term throughput fairness requirement. We provide the optimum scheduling policy which minimizes the total transmit power.