Ultra-wideband Pulse Shaping Research Articles

Spectrally Efficient UWB Pulse Shaping Based on Polynomially Weighted Gaussian Pulses With Maximally Flat Amplitude Spectra

This letter presents a new class of symmetric waveforms that is suitable for spectrally efficient ultra-wideband (UWB) pulse shaping. The waveforms are based on polynomially weighted Gaussian, where polynomials are constructed by imposing maximum flatness at the peak of the pulse’s amplitude spectrum. To perform pulse shaping, frequency shift and bandwidth scaling are applied. The proposed approach is illustrated with the design of UWB pulses that fill the FCC masks and provide high spectral efficiency. Compared to other Gaussian-based UWB waveforms, the proposed pulses have significantly higher spectral efficiency and slightly lower energy concentration.

A Novel heuristic time-domain diffraction model for UWB diffraction by lossy wedges and buildings

Diffraction is a vital propagation mechanism to predict the signal strength and to study the cell coverage in different kinds of scenarios. In this paper, a new heuristic based time-domain (TD) diffraction model is proposed for diffraction of ultra wideband (UWB) signals by lossy obstacles like wedges and buildings. The TD model is derived by using the heuristic frequency-domain (FD) diffraction coefficient that can estimate the radiowave propagation in urban scenarios. The analysis of slope diffraction is also considered to account for double diffraction or grazing incidence where amplitude diffracted field is negligible. Two dimensional (2-D) uniform theory of diffraction (UTD) approach is used for analyzing both soft and hard polarizations. The TD results are compared with the numerical inverse fast Fourier transform (IFFT) of the corresponding FD results with very good agreement between them. The TD solution is also validated by comparison with the IFFT of the Maliuzhinets’ coefficient that can be adopted as reference. Building materials with different electromagnetic properties are considered. To analyze the distortion to the input pulse, the UWB channel impulse response is also investigated. Different excitation pulse types have been employed to confirm the general behavior of the proposed TD solution. Finally the TD and IFFT-FD solutions are compared in the context of their computational time. The TD results can contribute to analyze the UWB pulse shape distortion by diffraction under frequency selective channel.

Interference Mitigation Techniques Using UWB Pulse Shaping

Wireless Body Area Network (WBAN) is an evolving area in the field of wireless communication, remote health monitoring and telemedicine. Ultra wideband (UWB) is a preferred candidate for WBAN as it provides very high data rate at minimal power consumption. Since UWB-BAN is affected by interference from existing wireless personal and local area networks, interference mitigation has become an important research issue in WBANs. This paper investigates the impact of UWB pulse shaping techniques on interference mitigation in WBAN. Through simulations, performance of different UWB pulse shaping techniques is compared in terms of their interference mitigation capability.

Analysis of power spectral density of ultra wideband waveforms for pulse shape modulation

Choice of ultra wideband (UWB) pulse shapes has become an interesting challenge such that the spectral limits of the frequency band approved by the Federal Communications Commission (FCC) can be utilised efficiently. In this paper, we compare the efficiency of various UWB pulse shapes based upon their power spectral density (PSD) and autocorrelation functions (ACF). We propose a set of prolate spheroidal wave functions (PSWF) for a typical M-ary pulse shape modulation (PSM) scheme. In the process, we show closed form expressions for the ACF of PSWF-based UWB pulse shapes of different orders.

Photonic multi-shape UWB pulse generation using a semiconductor optical amplifier-based nonlinear optical loop mirror

We propose and demonstrate a scheme to implement photonic multi-shape ultra-wideband (UWB) signal generation using a semiconductor optical amplifier (SOA) based nonlinear optical loop mirror (NOLM). By employing the cross phase modulation (XPM) effect, cross gain modulation (XGM), or both, multi-shape UWB waveforms are generated including monocycle, doublet, triplet, and quadruplet pulses. Both the shapes and polarities of the generated pulses are flexible to adjust, which may be very useful in UWB pulse shape modulation and pulse polarity modulation.

Reconfigurable ultra-wideband waveform generation with simple photonic devices

We propose and experimentally demonstrate a low cost, low power consumption technique for ultra-wideband pulse shaping. Our approach is based on thermal apodization of two identical linearly chirped fiber Bragg gratings (LCFBG) placed in both arms of a balanced photodetector. Resistive heating elements with low electrical power consumption are used to tune the LCFBG spectral responses. Using a standard gain switched distributed feedback laser as a pulsed optical source and a simple energy detector receiver, we measured a bit error rate of 1.5×10−4 at a data rate of 1 Gb/s after RF transmission over a 1-m link.

Ultra-wideband pulse shaping: bypassing the inherent limitations of the Gaussian monocycle

UWB impulse radio transmissions are power limited as they must respect a frequency mask with low total permitted power and severe isolation requirements for the GPS band. Shaping of the short UWB impulse maximizes transmit power subject to these constraints. We have previously published results for intricate pulse shaping in the optical domain that achieves record levels of power transmission. The most successful pulse shaping techniques in the electrical domain have been achieved with derivatives of the Gaussian pulse shape. The Gaussian monocycle is a low performance choice in terms of transmit power, but nonetheless the subject of intense research activity. In this paper we compare and contrast these UWB pulses, and quantitatively compare their performance in realistic systems (specific RF and antenna hardware). There is the perception that failings in the pulse shape (especially for the monocycle) can be compensated by simple highpass filter and the bandpass nature of the UWB antenna. We fabricate and characterize two UWB antenna designs available in the literature, as well as one commercial antenna. We use our optical pulse shaping device to experimentally investigate the three different pulse shapes and measure their transmitted power spectral density with each of the UWB antennas. We find that the monocycle is significantly less powerful than the others. The fine pulse shaping available in optical processing provides 1.7 to 2.9 dB gain over the electrical processing methods, depending on the antenna used.

Ultra-Wideband Pulse Shaping Using Lossy and Dispersive Nonuniform Transmission Lines

This paper presents the first known synthesis method for the design of nonuniform transmission lines (NUTLs) for ultra-wideband (UWB) pulse shaping, which can account for, and partially compensate for, the loss and dispersion present in real transmission lines. Without this compensation, cumulatively increasing distortion occurs in UWB pulse trains generated using NUTLs. The synthesis method novelly combines techniques from both the microwave and digital design domains: first, the transfer function of the transmission line is modeled as a cascade of minimum-phase and all-pass networks in the Z-domain; next, this model is used in a modified layer-peeling algorithm that automatically partially corrects for line nonidealities. Two possible implementations are presented: one taking advantage of noncausal filtering and the other with filtering implemented in the frequency domain. The effectiveness of the method is confirmed with both simulations and measurements of an UWB pulse shaper, which generates the first known sequence of modified Hermite polynomial pulses with successful compensation for loss and dispersion in an NUTL up to 15 GHz. The presented example shows that the synthesis method reduced the error between NUTL models and measurements by an average of 55%.

Simulation analysis of a photonic ultrawideband pulse generator by using a dual-parallel Mach–Zehnder modulator

This study analyzes a photonic ultrawideband pulse generator by using a dual-parallel Mach-Zehnder modulator. A simple configuration capable of generating two popular types of ultrawideband pulse shape, Gaussian monocycle and doublet, is proposed. The generated ultrawideband pulses have very high quality, and the exact waveform is tunable with respect to parameter settings. By changing the time delay between two-path driving pulses applied to the upper and lower sub-Mach-Zehnder modulator of the dual-parallel Mach-Zehnder modulator, the generated ultrawideband pulses can be switched from Gaussian monocycle to doublet. The proposal is first analyzed and then validated by simulations. Results of the study demonstrate that it can offer a realistic solution to photonic ultrawideband pulse generation.

Application of Nonuniform Transmission Lines to Ultra Wideband Pulse Shaping

The work presented in this letter demonstrates that nonuniform transmission lines (NUTLs) can be used for pulse shaping applications in ultra wideband pulsed systems and presents an approach to their design for this application. The pulsed waveforms generated are modified Hermite polynomials and encoded pulse trains thereof and are characterised by a broad bandwidth ranging from near DC to over 10 GHz and relatively long temporal duration in the region of nanoseconds. These pulses are more mathematically complex and at least three times higher bandwidth than previously has been reported in the literature. It is also believed to be the first time that modified Hermite polynomial pulses have been generated in practice. The NUTL design approach is verified by test structures fabricated on FR4 circuit board. The results demonstrate that NUTLs, which are completely passive structures, allow generation of complex pulse shapes in applications requiring fast, transient waveforms.

Optimal waveform design for ultra-wideband communication based on Gaussian derivatives

Ultra-wideband (UWB) radios have attracted great interest for their potential application in short-range high-data-rate wireless communications. High received signal to noise ratio and compliance with the Federal Communications Commissions (FCC) spectral mask call for judicious design of UWB pulse shapers. In this paper, even and odd order derivatives of Gaussian pulse are used respectively as base waveforms to produce two synthesized pulses. Our method can realize high efficiency of spectral utilization in terms of normalized effective signal power (NESP). The waveform design problem can be converted into linear programming problem, which can be efficiently solved. The waveform based on even order derivatives is orthogonal to the one based on odd order derivatives.

All-Optical 500-Mb/s UWB Transceiver:An Experimental Demonstration

We propose and demonstrate experimentally, for the first time, a prototype for all-optical ultra-wideband (UWB) transceiver at 500 Mb/s. We report 1) UWB pulse optimization that takes into account the transmitter RF front end and the U.S. federal communications commission (FCC) spectral mask, 2) a new approximate match filter receiver using optical signal processing, and 3) modulation at 500 Mb/s. Our previous optimization of UWB pulse shapes was based only on the FCC spectral mask, without taking into account the frequency response of the RF components (amplifier and antenna) in the UWB transmitter. Here, we modify our pulse optimization technique to ensure that the equivalent isotropic radiated power (EIRP) from the transmitter meets FCC specifications. For the RF hardware used, we achieve 63.6% efficiency over the FCC mask, which yields an 11.6- and a 5.9-dB improvement over Gaussian monocycle and doublet pulses, respectively. We also introduce simple optical signal processing at the receiver that allows the incoming RF signal to be matched against a square pulse whose duration is adapted to the channel. The exact matched filter would require a new optimized pulse that would include not only hardware frequency response but channel effects that vary with antenna placement as well. The proposed approximation allows a simple variation of the pulse duration: an increase to account for pulse expansion in the channel but an upper limit to combat multipath effects. Finally, we demonstrate the optimized pulse and approximate match filter receiver at 500 M/s. We attain a 10-6bit error rate at a 65-cm separation line of sight (LOS) link with simple on-off keying and no forward error correction.

Adaptive Arbitrary Pulse Shaper

A simple, yet effective, ultra wideband pulse shaping circuit architecture is presented. The circuit enables generation of an arbitrary pulse based on in-time superposition of the excitation waveform. The proposed system addresses problems associated with spectrum management, pulse reception and equalization. The pulse shaper was implemented in planar microstrip technology to provide a fully variable waveform.

Wavelet-based ultra wideband pulse generator circuits

Aiming to generate ultra wideband (UWB) pulses based on wavelet packets, four different circuits are proposed. It has been shown that the wavelet packets are quasi-orthogonal and have almost identical time duration, and therefore appear to be valuable candidates for UWB pulse shape modulation systems. However, as with any technology, circuitry is an important challenge to solve before a theoretical application can live up to its full potential. The four proposed circuits are based on different interpretations of the equation defining the wavelet packets and their performance is investigated by computer simulation. The research also illustrates the characteristics and the consequent implementation advantages or issues afferent to each circuit.

Ultra-Wideband Waveform Generator Based on Optical Pulse-Shaping and FBG Tuning

We propose and demonstrate experimentally a prototype for ultra-wideband (UWB) waveform generator based on optical pulse shaping. The time-domain pulse shape is written in the frequency domain, and a single-mode fiber performs frequency-to-time conversion. A U.S. Federal Communications Commission (FCC)-compliant power efficient pulse shape is inscribed in the frequency domain by a fiber Bragg grating (FBG) with an excellent match between optimized and measured pulses. Two other popular UWB pulse shapes (Gaussian monocycle and doublet pulses) are achieved by proper tuning of two FBG-based variable optical filters. A balanced photodetector removes an unwanted rectangular pulse superimposed on the desired waveform, assuring compliance at low frequency.

Generalized time domain multipath channel and its application in ultra-wideband (UWB) wireless optimal receiver - part III: system performance analysis

This paper deals with the time domain characteristics of UWB multipath channel while considering UWB pulse shape distortion and its impact on system performance as well as optimal receiver design. It appears that no deterministic and analytical channel model in the time domain has ever appeared in the literature, to our best knowledge. A generalized channel model and some related exact solutions for some specific geometric configurations are discussed, based on the pulse propagation mechanisms of reflection and diffraction. In addition, a system performance framework integrated with the close-form channel model expressions is also provided, corresponding to the optimal receiver structure and the concrete geometric configurations of a UWB channel. This work is very important in the design of the optimal UWB systems

On the Use of Wavelet Packets in Ultra Wideband Pulse Shape Modulation Systems

This paper proposes wavelet packets for use in ultra wideband communications. The pulse shapes that are generated are quasi orthogonal and have almost identical time duration. After normalization, an M-ary signaling set can be constructed allowing higher data rate. Finally, the performance of such a system when multipath propagation occurs is investigated by computer simulations. In order to combat multipath fading, a Rake receiver using coherent channel estimation is designed. This channel estimation is carried out using adaptive algorithms such as least-mean square (LMS), normalized least-mean square (NLMS), or recursive least square (RLS) algorithms which adapt the received signal given a reference signal.

The Effect of NBI on UWB Time-Hopping Systems

This letter presents an analysis of the effect of narrowband interference (NBI) on ultrawideband (UWB) time-hopping (TH) systems in the presence of multipath fading using both analytical derivations and simulations. Our analysis demonstrates that NBI may be an issue in some instances. In addition, we suggest three NBI suppression schemes for combating NBI in UWB TH systems. Single-link performance of these schemes in conjunction with a Rake-type receiver structure is estimated for both the ideal all-Rake receiver and the simpler partial-Rake receiver in an indoor environment. Two UWB pulse shapes that meet the Federal Communications Commission rules for UWB communications are considered in the investigation.

Designing optimal pulse-shapers for ultra-wideband radios

Ultra-wideband (UWB) technology is gaining increasing interest for its potential application to short-range indoor wireless communications. Utilizing ultra-short pulses, UWB baseband transmissions enable rich multipath diversity, and can be demodulated with low complexity receivers. Compliance with the FCC spectral mask, and interference avoidance to, and from, co-existing narrow-band services, calls for judicious design of UWB pulse shapers. This paper introduces pulse shaper designs for UWB radios, which optimally utilize the bandwidth and power allowed by the FCC spectral mask. The resulting baseband UWB systems can be either single-band, or, multi-band. More important, the novel pulse shapers can support dynamic avoidance of narrow-band interference, as well as efficient implementation of fast frequency hopping, without invoking analog carriers.