Investigation of co-channel interference, channel dispersion, and multi-user diversity in MIMO-based cellular systems
Creators: name: Pupala, Rahul N.
Publisher: name: No Publisher Supplied
Year: 2008

description: In recent years, Multiple-Input/Multiple-Output (MIMO) systems employing multiple antennas at both ends of the wireless link have been shown to deliver high spectral efficiencies with reasonable constellation sizes. A MIMO link is a special case of a Multi-Element Antenna (MEA) link, wherein one or both ends use a multi-element array. Recently proposed 4G cellular systems are being evaluated that combine MIMO with Orthogonal Frequency Division Multiplexing (MIMO-OFDM) for use at the radio layer, while WiMAX 802.16e is considering MIMO with Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) for use on the downlink. Multi-User Diversity (MuD) has also been shown to have important consequences in the ever-increasing demand for higher spectral efficiency. A detailed study of MIMO, MIMO-OFDM, and MuD is of utmost importance to understand how to maximize the performance gains that can be realized from these promising technologies.This thesis is broadly divisible into three parts. Part I investigates aspects of co-channel interference (CCI) as they relate to MIMO channels. First, the throughputs attainable by interference-limited cellular systems that employ MEA links are computed. The emphasis in this study is on the system-level perspective. That is, determining the distribution of performance over a coverage area, e.g., the cumulative distributive function (CDF) of throughput (TP) over the randomness of user location and shadow fading, as well as and taking into account the CCI produced by co-channel links in other cells. Using a general-purpose simulation platform developed in this work, throughput statistics are obtained over several channel conditions and system-level design choices. In this study, particular interest is in understanding the gains that accrue as a result of using excess receive antennas, and the effects of limiting the constellation sizes to present-day implementations. Using the simulation platform, an evaluation of alternative Transmit Diversity, and Spatial Multiplexing systems has been carried out. The study incorporates costs/overhead incurred by using a finite alphabet, limited channel coding, and imperfect channel estimation. Next, a noise-like model for co-channel interference is postulated in the context of MIMO/MEA channels. The validity of the noise-like model is demonstrated. The model is then used to derive an analytical solution for throughput in CCI-limited MIMO systems. The analysis is shown to be accurate and to permit extensive investigation without the need for lengthy simulations.In Part II, the effects of both frequency selectivity and correlation among transmit-receive antenna path gains on a single-carrier MIMO link are addressed. Degradations in system-level throughput statistics are evident when these distortions are assumed to be present in addition to CCI. This study includes the frequency-selective MIMO link when it uses non-dispersive cancellation of cross-stream interference at the receiver. We extend this analysis to MIMO-OFDM, and include the impact of dispersive effects which is the often ignored in such systems. In Part III, the benefit of adding MuD to the MEA link is quantified. The three important schedulers considered in the MuD implementation are: Maximal Throughput (MAX), Proportional Fair (PF), and Equal Grade of Service (EGoS). Again, performance evaluation is at the system-level, and over several important system design parameters, in particular, excess receive antennas and finite constellation sizes. The main interest is to determine the tradeoff involved in the number of receive antennas on the mobile device versus the number of users needed in order to obtain a particular throughput. Studying the many tradeoffs discussed above will enable design engineers to make well-founded decisions in crafting link techniques; and will aid system engineers in estimating attainable throughputs for particular designs. The results presented will be to the benefit of operators and customers alike as MIMO, MIMO-OFDM, and MuD technologies are put into service in support of new applications.