Information Theoretic Aspects of Multiuser Multicarrier Systems

This thesis deals with multiuser multicarrier communications over unknown time and frequency selective fading channels. Since there is a growing demand for capacity, especially in mobile communications, wireless multiuser communications experiences increasing interest in recent year. The wireless channel in general is a time and frequency selective fading channel. In that case, orthogonal frequency division multiplexing (OFDM) promises robust high-rate transmissions. In general, no channel state information (CSI) is available at transmitter and receiver. This corresponds to noncoherent transmissions. This thesis investigates noncoherent OFDM based multiuser systems, such as Multi-CarrierCDMA (MC-CDMA) and orthogonal frequency division multiple access (OFDMA), transmitting over a time and frequency selective fading channel. The focus is on the uplink case where multiple users transmit to one receiver. An information theoretic analysis is performed with emphasis on sum system capacity and sum information rate calculation. Since in most cases no exact analytic results can be obtained, bounding techniques are applied. First OFDM, OFDMA, and MC-CDMA are described. Then the wireless channel is discussed in terms of descriptions, statistics, and parameters, and an appropriate input-output relation will be introduced. Furthermore, an overview of known results is given. Then, upper and lower bounds on sum system capacity for MC-CDMA and OFDMA are derived. These theoretical results are supported by numerical evaluations and extensive simulation results involving different propagation scenarios.