Semester

Summer

Date of Graduation

2009

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Daryl Reynolds.

Abstract

It is well known that multiple antenna wireless communication systems improve the capacity and reliability of wireless communication systems by leveraging spatial diversity. In many wireless applications where it is impractical to implement multiple antennas at the transceivers, cooperation between wireless users wherein single antenna terminals share their resources has been proposed as a viable option to achieve spatial diversity.;The main goal of this research is to characterize the performance bounds for the multiuser, multirelay cooperative communication systems using information theoretic tools and use it to provide guidance in the design of practical systems. The protocols developed in this work either lead to improved performance or make the system design more practical. To this end, we first consider a two-phase user cooperation scheme where users have been allocated orthogonal channels for transmission. We develop a strategy that jointly performs relay selection and power allocation in a decode-and-forward (DF) multiuser cooperative uplink while minimizing the total uplink power such that each user satisfies its data rate. Results indicate that significant cooperation gains could be obtained using a space-time coded cooperative diversity over the wide range of target rates and total number of users when using the proposed joint relay selection and power minimization algorithm. We also propose a two-phase multiuser DF cooperation protocol that operates in an asynchronous CDMA uplink while relaxing the inter-user orthogonality constraint. The protocol developed here leads to fully distributed cooperation where no inter-user coordination is required and greatly simplifies the medium-access control protocol design. We evaluate the information-outage probability performance of the proposed scheme in an underloaded, fully-loaded and overloaded CDMA uplink. Finally, we propose a DF multistage cooperation protocol wherein the transmission between source and destination takes place in T ≥ 2 equal duration and orthogonal time phases. In the first time phase, the source broadcasts its message which is received by all potential relays. During subsequent time phases, the relays that have successfully decoded the message using information from all previous transmitting relays, transmit a space-time code for the source's message. The non-decoding relays keep accumulating information and transmit in the later stages when they are able to decode the message. The process repeats for T cooperation time phases. We develop an exact analytical expression for the outage probability of multistage cooperation and use it to analyze near-optimal relay locations and the number of cooperation stages needed for the best performance.

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