Adaptive low-complexity MB-OFDM for ultra-wideband wireless communication

Ultra-wideband (UWB) is seen as the foundation of future pervasive, wireless personal area networks (WPANs). The ability to provide tremendous capacity without the expense of multiple antennas or the power of narrowband transmissions makes it ideal for low-cost high-speed wireless communications. The realization of WPANs that encompass these UWB properties, however, hinges on solutions to the following key challenges. The high data rates demanded of multimedia WPANs mean that spectral resources must be used efficiently. This requires an UWB device to be able to accurately estimate channel conditions. Unfortunately, current signal processing algorithms cannot be applied directly without prohibitively increasing receiver complexity given the tremendous bandwidth of UWB systems. The result is that first-generation UWB receivers are using simple zero-forcing (ZF) approaches that work poorly in short impulsive channels. Accordingly, this thesis proposes several low-complexity channel estimation techniques that perform comparably to optimal minimum mean square error (MMSE) estimation. UWB WPANs must be reliable even when channels are highly frequency-selective or suffer from interference. With cost constraints limiting the current ECMA-368 UWB standard to low-complexity block-spreading and convolutional codes, this the¬sis adopts a holistic approach that exploits the interactions between diversity techniques to reduce packet error rates and improve error recovery. Furthermore, this thesis proposes and investigates the following novel heuristics for mitigating inter-ference: adaptive sizing the overlap-add window so as to balance recovery of delayed signal energy with noise; adaptive changing the time-frequency interleaving pattern to avoid interfering signals; and adapting the degree of companding to minimize both nonlinear distortions from clipping and noise. The contributions of this thesis grant significant performance and reliability im-provements whilst minimizing incremental complexity and maintaining backwards compatibility with existing UWB devices. Furthermore, specific recommendations to revise the ECMA-368 standard are justified through theoretical analyses and Monte Carlo simulations.