Ultra-wide bandwidth spread-spectrum techniques for wireless multiple-access communications

A revolutionary development (http://commsci.usc.edu/ulab/ulab.html) in wireless communications is on the horizon. It involves the use of extremely large transmission bandwidths (in excess of one GHz, a factor of over one hundred times the bandwidth of currently available wideband systems for the same applications) and spread-spectrum techniques to reduce power consumption, cost, complexity, and multipath problems in a variety of communication environments. This ultra-wide bandwidth (UWB) time-hopping spread-spectrum (TH-SS) impulse radio communication technique has both commercial and military applications, such as high-speed wireless LANs, fully mobile fade-free (and relatively shadow-free) wireless full-motion video communications, and platoon-level covert communications. This dissertation presents the experimental results and theoretical development of this novel baseband carrierless UWB impulse radio.; The UWB impulse radio and the associated receiver processing are described using a modulation format that can be supported by current technology. Multiple-access performance of such communication systems is estimated for both analog and digital data modulation formats under ideal channel conditions.; General expressions for the power spectral density (PSD) of a variety of TH-SS signaling schemes in the presence of arbitrary timing jitter are derived using stochastic theory. A flexible model for general TH-SS signals is proposed and a unified spectral analysis of this generalized TH-SS signal is carried out using a systematic and tractable technique.; The UWB signal propagation experiment is reported, to characterize the UWB signal propagation channel. The experimental results show that a typical response to a subnanosecond pulse may last a few hundred nanoseconds. This illustrates one of the attractive features of impulse radio signaling: relatively dense multipath that causes fading in more narrowband signals is resolved into separately observable received signal components. These can be processed in a Rake diversity-combining multiple-correlator receiver for improved performance. The low-power payoff results from the fact that very little fading margin is required for this system to operate reliably. Robustness of the UWB signal to fades is quantified, and the measured results confirm that the UWB signal suffers minimal fading.; A communication theoretic approach to statistical characterization of the propagation channel is presented. Several concepts such as the Infinite Rake (IRake) receiver, the selective Rake (SRake) receiver, and energy capture are introduced; and their implication to the design and performance of wireless communications systems is described. These results play significant role in the context of system design for robust and high rate communications in the presence of multipath.