Optimal control and allocation of resource in wireless systems

Abstract

In this thesis, soft handoff initiation mechanism in code division multiple access (CDMA) networks and resource allocation in multiuser orthogonal frequency division multiplexing (OFDM) systems using partial channel state information (CSI) feedback are studied. Due to diversity that leads to advantages in terms of reverse link capacity and signal quality, soft handoff is usually used in CDMA systems. Soft handoff initiation mechanism makes the decision to start a soft handoff as mobile moves from one cell to another. We present an analytical model for the soft handoff initiation mechanism and study its behavior. We investigate the effects of commonly used soft handoff initiation parameters, namely, hysteresis margin, signal averaging coe±cient and the length of drop timer, in terms of number of performance measures. These performance measures accounts for signaling overhead, signal quality and forward link resource usage. Our analysis shows good agreement with simulation data and can be used to extract an optimal set of parameters depending on the required performance. In the second part of our thesis, we deal with the problem of resource allocation in multiuser OFDM. In general, the capacity of multiuser OFDM systems can be maximized by allocating resources (subcarrier and power) to the user with the highest instantaneous channel gain. This assumes complete CSI at the transmitter, which is achieved by every user reporting its CSI for all subcarriers to the transmitter via feedback channel. In practice, due to limited capacity of the feedback channel, the completeness of CSI may be severely damaged especially with a large number of users transmitting a large amount of feedback information. In order to reduce the amount of feedback information while preserving the maximal capacity, quality based CSI feedback (QCF) is proposed. The system capacity is derived with QCF and compared with that of full CSI feedback. The results show that QCF successfully reduces the a...