Pulsed ultra-wideband: Transmission, detection, and performance.

摘要

Ultra-wideband (UWB) communication has emerged as a very promising technology for short-range wireless applications, including high-speed multimedia transmissions and sensor networks. UWB system designs involve many different aspects covering analog and digital processing, channel estimation and modeling, and modulation and demodulation. Although UWB still faces many challenges, significant progress has been made to commercialize UWB systems. This thesis focus on schemes to improve the performance and to lower the complexity of the UWB physical layer.;We first propose a frequency-hopped multi-band UWB system structure for higher throughput with better inter-symbol interference (ISI) immunity. This system is analyzed and compared to a single-band system. Pulse overlapping causes inter-pulse interference and may limit the system performance, especially in dense multipath environments. We then build a mathematical model with pulse overlapping considered and investigate the optimum linear RAKE receiver structure in such situation. The analysis is further is extended to systems that employ a prerake diversity combining scheme, in more realistic channel environments. The prerake scheme shifts RAKE receivers' related signal processing needs to the transmitter side and helps combat narrow-band interference.;To lower complexity, we develop a decision-directed autocorrelation (DDA) receiver, which offers more effective multipath energy capture at a lower complexity than the conventional RAKE receiver structures. Compared with transmit-reference receivers, the proposed DDA methods can considerably lower the noise level in the self-derived template waveform by operating in an adaptive decision-directed mode, thus improving the overall detection performance. There is little loss in energy efficiency since no reference pilots are required during adaptation.;Finally, we propose a hybrid modulation method that enables a heterogeneous network structure where users can flexibly choose a coherent RAKE receiver or a transmit-reference receiver structure. While neither type of receiver sacrifices performance loss by enabling the heterogeneous structure, the coherent RAKE receivers enjoy great performance advantages when further combined with forward error correction and iterative decoding methods.;Throughout the thesis, theoretical performance analysis is always presented along with corroborating simulations.