Graduation date: 2007
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.