Transmit optimization for multicarrier and multiple-input multiple-output wireless communications.

摘要

To meet growing demand for wireless access to voice, data and multimedia services, current wireless communication technologies need further improvement in spectral efficiency. Many enabling technologies have been proposed, including multicarrier modulation, multiple-input multiple-output (MIMO) and link adaptation. This thesis investigates link adaptation, particularly transmit optimization in multicarrier and MIMO wireless communications.; In the first part of this thesis, we propose a new bandwidth efficient Orthogonal Frequency Division Multiplexing (OFDM) scheme with adaptive zero-padding (AZP-OFDM) for wireless transmission. A new system design criterion based on the channel matrix condition is studied and applied to the design of an AZP-OFDM system. It has been shown that AZP-OFDM offers a more flexible tradeoff between performance, bandwidth efficiency and complexity.; The second part of this thesis investigates power allocation for OFDM. We propose new minimum bit error rate (MBER) and approximate MBER (AMBER) subcarrier power allocation algorithms for cyclic prefix (CP)-OFDM. It is shown both analytically and by simulation that the proposed CP-OFDM with MBER and AMBER power allocation schemes are superior to CP-OFDM without power allocation as well as zero-forcing (ZF)-equalized single-carrier with CP. BER performance analysis of power allocation with imperfect channel state information is conducted.; Precoding for MIMO spatial multiplexing generally requires high feedback overhead and/or high complexity processing. In the third part of this thesis, simultaneous reduction in complexity and overhead is proposed by imposing a diagonal structural constraint to precoding, i.e., power allocation. MBER is employed as the optimization criterion. It has been shown that interference cancellation and detection ordering with MBER power allocation offer superior performance over previously proposed MBER precoding with ZF equalization as well as over MMSE precoding/decoding. Performance under noisy channels and power feedback is analyzed.; In the fourth part of this thesis, transmit optimization for two-input multiple-output (TIMO) spatial multiplexing systems is investigated. Approximate MBER transmit power allocation for a variety of receiver structures is investigated. An approximate MBER transmit beamforming scheme is proposed, which eliminates error floors in ill-conditioned TIMO channels.