| Most practical wireline and wireless transmission channels suffer from impairments such as dispersion, attenuation, crosstalk, and noise. Despite these impairments, the demand for high-speed transmission over these channels has been growing over the years. The ultimate goal is to reliably transmit and receive the highest data rate possible. This can be accomplished by optimizing every component of the communication system. In this dissertation, we focus on the optimization of the transmission bandwidth of multicarrier systems.; Multicarrier systems partition the entire channel into several subchannels that are mutually orthogonal and over which multiple streams of data can be sent without intersymbol interference. The two most common realizations are Orthogonal Frequency Division Multiplexing (OFDM) and Discrete Multi-Tone Modulation (DMT). They differ in the way they distribute energy and bits to the various subchannels: OFDM assigns equal energy and the same number of bits to all subchannels, while DMT tailors the energy and bit distributions to the channel and thus can achieve capacity on a given channel. They both require knowledge of the channel at the receiver for decoding; however, DMT also requires a priori knowledge of the channel at the transmitter.; An overview of multicarrier modulation is first presented, and various schemes to allocate energy and bits, i.e. loading algorithms, are discussed. The system performance gains obtainable from optimizing the bandwidth of multicarrier systems are then computed, both for fixed-margin and fixed-rate systems. Next, the effect of imperfect knowledge of the channel at the receiver and at the transmitter is analyzed. This leads to mismatch errors which degrade the performance of our system, especially for time-varying applications. The degradation in performance is quantified and related to system design parameters. Finally, the system performance gains obtained from optimizing the bandwidth of single-input-single-output systems are extended to multiple-input-multiple-output systems.; This leads to guidelines on when to optimize the bandwidth of multicarrier systems: wireline and slowly-varying wireless systems should be optimized, while multiple-input-multiple-output systems should not. |
