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

We consider the effect of mobility on a wideband direct sequence spread spectrum (DSSS) communication system, and study a scale-lag Rake receiver capable of leveraging the diversity that results from mobility. A wideband signal has a large bandwidth-to-center frequency ratio, such that the typical narrowband Doppler spread assump-tions do not apply to mobile channels. Instead, we assume a more general temporal scaling phenomenon, i.e., a dilation of the transmitted signal’s time support. Based on a uniform ring of scatterers model, we determine that the wideband scattering function, which quantifies the average scale spreading, has a “bathtub-shaped” scale profile. We investigate, through frame-theoretic tools, the translation- and dilation-spacing parameters of a scale-lag Rake basis, and compare the performances of a scale-lag Rake and a Doppler-lag Rake, each capable of leveraging the diversity that results from mobility. When the translation spacing of the Rake functions is equal to the minimum resolvable lag, there is no significant performance difference between the receivers. For wider spacings, the receiver is more reliant on dilation diversity; hence, the scale-lag Rake receiver performs relatively better. Such analysis applies, for example, to ultra-wideband (UWB) radio frequency channels and underwater wideband acoustic channels. We study the correlation structure of the scale-lag Rake fingers and show that the normalized scale spread parameter relates directly to the time-variability of the ii channel. We discover that much of the channel energy is concentrated in few eigenmodes and hence propose principal components combining for a reduced-complexity solution. Finally, we perform physical experiments in the air-acoustic channel to demonstrate the applicability of the wideband channel model.

The UWB (Ultra Wideband) technology has drawn phenomenal interest in industry as well as academia. Ultra Wide Band impulse radios are microwave systems that communicate using baseband pulses of very short duration. UWB systems transmit information data over a wide frequency spectrum with low power consumption and high speed for local area wireless network applications. Unlike the traditional digital communication method based on a carrier wave, UWB is pulse based. Pulse Generation, modulation, and multiple access are time domain dependent functions. This paper presents the development of analytical model for UWB system. A theoretical reference for UWB system performances is designed in non-ideal channels. In this mathematical models for biphase, pulse–position and hybrid modulation are developed. The detection rules are formulated for detecting signals in AWGN channels. The performance of UWB system is described with the help of BER. The BER of a UWB system depends on the modulation scheme and detection method it uses. It is observed that for optimum performance modulation parameter selection is important.

Abstract—For ultra-wideband (UWB) impulse radios, noncoherent energy detectors are motivated for their simple circuitry and effective capture of multipath energy. A major performancedegrading factor in energy detection is the noise floor, which is aggravated for low-duty-cycle UWB signals with a large timebandwidth product. In this paper, weighted energy detection (WED) techniques are developed for effective noise suppression. The received signal is processed by a set of parallel integrators, each corresponding to a different integration time-window within a symbol period. The outputs of these integrators are weighted and linearly combined to generate decision statistics, while the weights are determined by the signal power collected from the corresponding integrators to improve the effective signal to noise ratio. The WED principle is applied to all phases of receiver processing, including signal detection, timing synchronization and data demodulation. For each phase, the optimal linear detector parameters, including decision thresholds and weighting coefficients, are derived analytically. Simulations show that the proposed noncoherent WED receiver enhances the bit-error-rate performance compared to conventional energy detectors. Index Terms—Ultra-wideband (UWB), weighted energy detection, channel estimation, synchronization, decision direction. I.