Abstract—Attractive features of time-hopping spread-spectrum multiple-access systems employing impulse signal technology are outlined, and emerging design issues are described. Performance of such communications systems in terms of achievable transmission rate and multiple-access capability are estimated for both analog and digital data modulation formats under ideal multiple-access channel conditions. Index Terms—Impulse radio, ultra-wide bandwidth. I. INTRODUCTION TO IMPULSE RADIO SYSTEMS THE TERM wideband, as applied to communication systems, can have different meanings. In conventional systems, “wideband ” implies a large modulation bandwidth and thus a high data transmission rate. In this paper, a spread-spectrum

Abstract—An ultra-wide bandwidth (UWB) signal propagation experiment is performed in a typical modern laboratory/office building. The bandwidth of the signal used in this experiment is in excess of 1 GHz, which results in a differential path delay resolution of less than a nanosecond, without special processing. Based on the experimental results, a characterization of the propagation channel from a communications theoretic view point is described, and its implications for the design of a UWB radio receiver are presented. Robustness of the UWB signal to multipath fading is quantified through histograms and cumulative distributions. The all Rake (ARake) receiver and maximum-energy-capture selective Rake (SRake) receiver are introduced. The ARake receiver serves as the best case (bench mark) for Rake receiver design and lower bounds the performance degradation caused by multipath. Multipath components of measured waveforms are detected using a maximum-likelihood detector. Energy capture as a function of the number of single-path signal correlators used in UWB SRake receiver provides a complexity versus performance tradeoff. Bit-error-probability performance of a UWB SRake receiver, based on measured channels, is given as a function of signal-to-noise ratio and the number of correlators implemented in the receiver. Index Terms—All Rake receiver (ARake), bit-error probability (BEP), energy capture, propagation channel, selective Rake (SRake) receiver, spread-spectrum, ultra-wide bandwidth (UWB). I.

10 0 C/A-code spectrum A multitude of applications would benefit from precise indoor navigation. Anywhere from automating storage in warehouses to tracking firemen in hazardous environments would make such an endeavor worthwhile. Some server-based GPS systems, like SnapTrack, already claim some navigation capabilities indoors. However, such systems are in general accurate to within a few tens of meters. Furthermore, pseudolites have been deployed for indoor use. Although some experimental setups show decent navigation performance, there is a question of whether GPS has a “good enough ” signal structure for such applications in the first place. Spread spectrum pseudoranging is susceptible to multipath that is less than one chip width away from a direct path ray. In the case of GPS C/A-code, the chip length is about 300 m. Obviously, most indoor signal reflection delays would be significantly shorter than that distance. Ultra-WideBand (UWB) technology is built around transmitting short discrete pulses instead of continuously modulating a code onto a carrier signal. Such pulses typically last only 1-2 ns, and one can distinguish pulses that are more than 1-2 ft apart. Thus, making UWB systems robust to multipath delays of more than one pulse width. We measured the impulse response of the RF channel at the Stanford University LAAS Laboratory. This paper quantifies that multipath channel in terms of average delay and delay spread. We found several cases where multipath components were stronger in magnitude than the direct signal. Whereas such an environment would bias pseudorange measurements of GPS C/A-code, a properly designed UWB system could resolve most multipath and accuracy would degrade more gracefully than for GPS.

In this thesis we give an accurate and general model that can be used to predict short-range/time UWB reflection. This reflection occurs when the source and the receiver are near a single reflecting boundary. Our approach uses an image-based method based on Laplace-transform formulation of the Sommerfeld half-space problem. The boundary between two mediums is replaced by a point source of given strength and location. The component amplitude of the image is chosen such that transverse electric and magnetic fields are continuous across the boundary. The complete field formulation is based on a simple branch-integral consisted in the reflection coefficient. Since the analysis is done in