OFDMA capacity analysis and wireless broadcast-unicast hybrid network design.

摘要

Motivated by the increasing popularity of OFDMA, this thesis first studies the capacity optimality of OFDMA as a multicarrier multiple-access scheme. We address the relationship between OFDMA and the optimal multicarrier multiple-access solution. More specifically, we are interested in answering the following questions: (i) Is OFDMA capacity optimal? If not, (ii) what are the conditions under which OFDMA is optimal, and what are the probabilities of these conditions? (iii) in the case OFDMA is suboptimal, what is the performance gap between OFDMA and the optimal multicarrier multiple access solution? and (iv) Under the framework of OFDMA, how to allocate power and subcarriers to maximize the sum capacity? Within a generic discrete multicarrier framework, we provide answers to above questions for both SISO and MIMO channels.;The second part of this thesis is the design of broadcast and unicast hybrid network. Wireless infrastructures can be conveniently categorized into two types: those that provide point-to-point unicast connectivity (e.g., cellular) and others that are broadcast in nature (such as TV and radio) and are inherently point-to-multipoint. We introduce a transmission scheme for multicarrier hybrid system that supports both broadcasting and unicasting on a single-frequency platform. In particular, we present a dirty-paper coding (DPC) based overlay architecture to enable interference free reception of unicast signals. The fundamental limits of hybrid communications are investigated, along with power allocation algorithms that approach the hybrid capacity. Our results show that OFDMA for unicast offers the best hybrid performance and considerable gains over orthogonal multiplexing (e.g., TDM/FDM) can be achieved through interference-free overlay. In addition, we describe approaches to further improve the spectral efficiency and the broadcast coverage through multi-cell cooperation.