Ultra-wideband Radio Signals Research Articles

Focusing Gain Model of Time-Reversed Signals in Dense Multipath Channels

The time reversal (TR) technique consists of transmitting in the channel a signal filtered by the time-reversed channel impulse response. To assess the performance of a TR system using impulse radio ultrawideband signals, one interesting parameter is the focusing gain defined as the ratio of the maxima in the time waveforms of the received signal with and without the time-reversal operation. We propose a heuristic approach to get an approximate analytical expression for the distribution function of this gain, as a function of the channel delay spread normalized to the pulse width and assuming a dense multipath environment. Predicted results are compared to experimental values obtained in reverberating chambers.

On Optimal Front-End Filter for Single-User Detection in IR-UWB Systems

We consider a K user Gaussian multiple access system with impulse radio ultra-wideband signaling. The receiver is assumed to treat the Multi-Access Interference (MAI) as additive noise and does not enjoy multiuser detection. It is well known that for such a system the MAI is neither Gaussian nor white. Although, the non-Gaussianity of the MAI has been extensively studied, little attention has been directed to the non-whiteness of it. In this paper, we show that by employing a new front-end filter at the receiver, the non-whiteness of the MAI can be exploited to improve the performance of the single-user detector. We use the signal-to-interference-plus-noise ratio (SINR) as a merit to evaluate the performance improvement brought to the system. The SINR improvement depends on the interference level as well as pulse waveform. The bit error rate of the system is also simulated and compared with that of conventional matched filter receiver.

Provision of IR-UWB wireless and baseband wired services over a WDM-PON

A simple scheme to simultaneously generate an on-off keying or bi-phase modulation (BPM) impulse radio ultra wideband (IR-UWB) signal and a baseband wired signal in the optical domain using a dual-drive modulator is proposed and demonstrated. Although the two signals have spectral overlap in the optical spectrum, they are located at different frequency bands when converted to electrical signals at a photodetector (PD), which can be well separated by an electrical filter. An experiment is carried out. Eye diagrams, electrical spectra and BER measurements show that the co-channel interference between the UWB and the wired signals is small for a single-channel 36-km fiber link to provide 1.25-Gb/s UWB wireless and 1.25-Gb/s baseband wired services. The inter-channel interference is also small and negligible when the link is operated together with two other 1.25 Gb/s baseband wired links, which demonstrates that a conventional WDM-PON can be upgraded to provide additional UWB services without affecting the existing services by modifying the modulators in the center office and inserting UWB antennas in the optical network units.

3D positioning scheme exploiting nano-scale IR-UWB orthogonal pulses

In these days, the development of positioning technology for realizing ubiquitous environments has become one of the most important issues. The Global Positioning System (GPS) is a well-known positioning scheme, but it is not suitable for positioning in in-door/building environments because it is difficult to maintain line-of-sight condition between satellites and a GPS receiver. To such problem, various positioning methods such as RFID, WLAN, ZigBee, and Bluetooth have been developed for indoor positioning scheme. However, the majority of positioning schemes are focused on the two-dimension positioning even though three-dimension (3D) positioning information is more useful especially in indoor applications, such as smart space, U-health service, context aware service, etc. In this paper, a 3D positioning system based on mutually orthogonal nano-scale impulse radio ultra-wideband (IR-UWB) signals and cross array antenna is proposed. The proposed scheme uses nano-scale IR-UWB signals providing fine time resolution and high-resolution multiple signal specification algorithm for the time-of-arrival and the angle-of-arrival estimation. The performance is evaluated over various IEEE 802.15.4a channel models, and simulation results show the effectiveness of proposed scheme.

Distribution of Double-Sideband OFDM-UWB Radio Signals in Dispersion Compensated Long-Reach PONs

The performance of orthogonal frequency division multiplexing ultra wideband radio signals distribution in dispersion compensated (DC) long-reach passive optical networks (LR-PONs) is assessed numerically for conventional chirpless Mach-Zehnder (MZ) and chirped linearized (L) electro-optic modulators (EOMs). The optimum modulation index and the minimum required optical signal-to-noise ratio are evaluated for optical network units (ONUs) at different distances from the optical line termination (OLT). The degradation due to first-order polarization mode dispersion (PMD), fiber nonlinearity, phase noise due to the Kerr effect, and the phase noise due to finite laser linewidth is assessed as well. It is shown that the use of dispersion compensation in LR-PONs employing the MZ-EOM is a powerful solution to mitigate the dispersion-induced power fading. It is also shown that, contrarily to the L-EOM case, the same optimum voltage level at the EOM input is required by DC LR-PONs employing the MZ modulator, independently of the ONUs distances. In addition, an optical signal-to-noise ratio penalty not exceeding 0.5 dB due to first order PMD effect is obtained for a PMD parameter below 0.5 ps·km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/2</sup> and for a fiber nonlinearity corresponding to a nonlinear phase shift not exceeding 11 mrad. This conclusion holds for pre (at the OLT) and post (at the remote node) compensation schemes. The performance degradation induced by the laser phase noise is also negligible in DC LR-PONs for typical laser linewidths due to the reduced phase-to-intensity noise conversion.

Performance Comparison of OFDM-UWB Radio Signals Distribution in Long-Reach PONs Using Mach-Zehnder and Linearized Modulators

The performance of orthogonal frequency division multiplexing ultra wideband (UWB) radio signals distribution in long-reach passive optical networks (LR-PONs) using conventional chirp-less Mach Zehnder (MZ) and linearized (L) Y-fed directional couplers electro-optic modulators (EOMs) is compared. Particularly, the optimum modulation index and the corresponding minimum optical signal-to-noise ratio (OSNR) required to achieve a bit error probability of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> are evaluated through numerical simulation for systems operating with single and three UWB sub-bands and different standard single-mode fiber (SSMF) distances indicated for LR-PONs. Both modulators are characterized experimentally and theoretical model parameters are adjusted to correctly describe the power and chirp characteristics of the electro-optic conversion in the simulation process. It is shown that the optimum modulation index and the tolerance to modulation index variations, considering either single or multi band UWB operation, is approximately two times higher for systems employing L-EOM than MZ-EOM. Additionally, with MZ-EOM, the required OSNR may increase considerably when the fiber length increases due to the power fading induced by fiber chromatic dispersion, achieving a penalty of almost 3 dB for systems with 100 km of SSMF and single UWB sub-band operation. Instead, with L-EOM, the required OSNR penalty (when compared with the back-to-back case) is lower for fiber lengths up to 100 km than it is for systems employing the MZ-EOM modulator due to the combined effect of the chirp generated by the modulator and the chromatic dispersion.

Robust Weighted Non-Coherent Receiver for Impulse Radio UWB PPM Signals

This letter proposes an energy detection based robust weight estimation scheme for pulse-position modulated (PPM) impulse radio ultra-wideband (IR-UWB) signals using weighted non-coherent receiver (WNCR). Conventional data-aided WNCR (DA-WNCR) scheme estimates the weighting coefficients, or channel state information (CSI), using a large number of training symbols over time-varying channels. In contrast, the proposed Robust WNCR (R-WNCR) scheme is non-data-aided (NDA), adaptive and robust to channel variations. The proposed R-WNCR estimates the weighting coefficients adaptively based on the received stochastic data, and the weight estimation process is refined using a decision directed approach.

Integration of Optically Generated Impulse Radio UWB Signals Into Baseband WDM-PON

We propose a compact integration system to simultaneously provide wireline and wireless [baseband and ultra-wideband (UWB)] services to end-users in a wavelength-division-multiplexed-passive optical network (WDM-PON). A 1-Gb/s UWB signal is optically generated and shares the same wavelength with the baseband signal. Error-free performance was achieved after 23-km single-mode-fiber (SMF) transmission for both signals and additional 0.4-m wireless transmission for the UWB signal. The low complexity and high spectrum efficiency of this system makes it attractive for deployment of in wireline/wireless converged gigabit optical access networks.

Distribution of photonically generated 5 Gbits/s impulse radio ultrawideband signals over fiber

We propose an approach to generate ultrawideband (UWB) pulses with tunable high-speed modulation based on pulse compression. Flexible generation of up to a record 5 Gbits/s on-off keying impulse radio UWB signals are successfully demonstrated as well. We also investigate 5 Gbits/s on-off keying bit-error-rate (BER) performance after 40 km single mode fiber transmission by employing a digital signal processing receiver, and the BER below forward error correction limit is achieved.

Distribution of IR-UWB Signals With PAM Modulation in Long-Reach FTTH Networks

Fiber-to-the-home (FTTH) networks have been proposed as a means to extend the application of ultrawideband (UWB) radio signals in future wireless personal area networks to the delivery of high-definition content. In this paper, we analyze, using numerical simulation, the feasibility of the distribution of impulse-radio UWB signals with pulse amplitude modulation in long-reach FTTH networks. The simulation results show a severe performance degradation of the transmitted signals in FTTH networks, both in terms of the channel error probability and in terms of the temporal and spectral distortion factors. This degradation is mainly due to the effect of the fiber group velocity dispersion.

TOA Estimation with the IEEE 802.15.4a Standard

This paper discusses a ranging algorithm appropriate for impulse radio ultra-wideband signals compliant with the IEEE 802.15.4a standard. Three steps are indicated to locate the so-called ranging marker in the received signal. The first is to find the highest peaks in the channel responses to the transmitted pulses. The second consists in measuring the distance of each peak to the starting time of the response. The last one involves the identification of the first symbol of the physical-layer header. Algorithms to accomplish all these tasks are indicated. They are implemented in digital form and are in keeping with a non-coherent receiver structure. The achievable accuracy depends on the sampling rate. For example, at SNR = 20 dB and with a rate of 1 GHz the ranging errors are on the order of 20 cm.

3.125 Gb/s Impulse Radio Ultra-Wideband Photonic Generation and Distribution Over a 50 km Fiber With Wireless Transmission

A 3.125 Gb/s photonic impulse radio ultra-wideband signal is created using the incoherent optical field summation resulting from the cross gain modulation of an uncooled distributed feedback laser injected with an external cavity laser. After 50 km of fiber and wireless transmission over 2.9-3.3-m, successful detection using a digital signal processing receiver is achieved.

Semi-analytical approach for performance evaluation of direct-detection OFDM optical communication systems

A semi-analytical method to evaluate the bit error ratio (BER) in direct-detection (DD) optical fibre transmission systems employing orthogonal frequency division multiplexing (OFDM) and optically pre-amplified receivers is proposed. The method considers a Gaussian approach for the signal at the equalizer output and allows evaluating accurately the BER of each OFDM subcarrier for the receiver structure considered and for practical optical and electrical filters shapes, being a powerful tool to perform the optimization of these systems. The results obtained by the proposed method have shown excellent agreement with Monte Carlo estimates for DD-OFDM ultra-wideband radio signals and for two different DD-OFDM signals proposed for long-haul systems.

Detection of an ultra-wideband quasi radio signal against background random noise

We perform synthesis and analysis of the maximum-likelihood detector of an ultra-wideband quasi radio signal whose duration may amount to several periods or even a fraction of a period of harmonic oscillation with unknown amplitude and phase. Characteristics of the classical quadrature detector on receipt of the ultra-wideband quasi radio signal are found. Applicability conditions of the model of a narrow-band radio signal for solving the detection problem to specified accuracy are formulated.

Up-Conversion of Triple-Band OFDM UWB Signals by a Multimode VCSEL

We present novel experimental results for the all-optical up-conversion of the triple-band orthogonal frequency-division-multiplexing ultra-wideband radio signals from lower frequency band group 1 up to higher frequency band groups 2 or 3 based on the vertical-cavity surface-emitting laser optical second- and third-order nonlinearities. Low conversion losses and error vector magnitude values, respectively, for low bias currents have been demonstrated.

A Low-Power Baseband ASIC for an Energy-Collection IR-UWB Receiver

This paper reports on the realization and the characterization of an application-specific integrated circuit (ASIC) intended for the processing of impulse radio ultra-wideband (IR-UWB) baseband signals. The incoming baseband signals result from the direct down-conversion of IR-UWB radio-frequency pulses, which are modulated by a binary frequency-shift keying (BFSK) scheme. The realized mixed-signal integrated circuit features an analog demodulation based on the quadricorrelation method, a non-coherent pulse detector using an integrate-and-dump operation and a bit-level synchronization digital circuit. An novel acquisition algorithm intended for low duty-cycled IR-UWB signals enabling a signal-to-noise ratio (SNR) estimate is proposed. The baseband ASIC is able to demodulate, acquire and decode BFSK IR-UWB signals. It requires 13 mW of supply power during the initial acquisition and 6.5 mW during the signal tracking phase at a pulse repetition rate (PRR) of 5 MHz. The circuit is fabricated in a 0.18-mum CMOS technology.

Wavelet-based spectral shaping of UWB radio signal for multisystem coexistence

Although Ultra Wide Band (UWB) wireless systems supposed to coexist with other spectrally overlapping (narrowband) wireless systems, mutual interference degrades the performance of both systems. In this paper we investigate two techniques for reducing this mutual interference which do not require modification of the narrowband system. We propose to shape the spectrum of the Transmitted Reference (TR)-UWB signal using wavelet based multi-resolution technique to avoid its interference to other wireless systems. The reverse (narrowband) interference is alleviated using a notch filter at UWB receiver that could have much smaller bandwidth in this Gaussian pulse-shaped multi-resolution environment. TR simulations under AWGN and multipath channel conditions show that up to 55 dB reduction of UWB RF energy is possible at the interfering IEEE 802.11a band using the wavelet spectral shaping technique. The challenge is not to exceed the specified pulse duration while shaping the spectrum. The proposed technique does not reduce the throughput of the UWB system. It is general in the sense, it can be used for the better coexistence of any narrowband wireless system with UWB system.

Coexistence Between Ultra-Wideband Radio and Narrow-Band Wireless LAN Communication Systems—Part I: Modeling and Measurement of UWB Radio Signals in Frequency and Time

The correct modeling and measurement of ultra-wideband (UWB) radio signal are a critical issue to evaluate the electromagnetic (EM) emission of any communication system based on this technology. In this paper (Part I), UWB radio communication systems based on impulse radio (IR) and multiband orthogonal frequency division multiplex (MB-OFDM) technologies are characterized by simulations and experiments in both frequency and time domains. The EM characteristics of UWB radio are measured by different methods (conducted and radiative) and in different environments (anechoic and reverberation chambers).

Analysis Techniques for the Power Spectral Density Estimation of Convolutionally Coded Impulse Radio UWB Signals Subject to Attenuation and Timing Jitter

A method for the spectral analysis of convolutionally coded Markov-driven impulse radio (IR)-based ultrawideband (UWB) systems is introduced. Example applications in UWB systems include the study of pulse position modulation (PPM), pulse-amplitude modulation (PAM), biorthogonal modulation, and pulse-shape modulation combined with periodic (e.g., pseudorandom)/random time-hopping (TH), as well as periodic/random direct-sequence (DS) multiplication. The effects of random jitter and pulse attenuation are considered in this analysis. The final result allows simple examination of the power spectral density (PSD) of such signals. This result clearly delimitates the relative contributions of parameters that allow enhanced design of UWB systems. Application examples are presented for a new convolutional encoder, providing a spectral-line-free PSD for quaternary biorthogonal (PAM/PPM) modulation IR UWB systems.

480-Mbps, Bi-Directional, Ultra-Wideband Radio-Over-Fiber Transmission Using a 1308/1564-nm Reflective Electro-Absorption Transducer and Commercially Available VCSELs

We describe 480 Mbps, bi-directional ultra-wideband (UWB) radio signal transmission over 1 km of single-mode optical fiber. Key components are a highly linear, reflective electro absorption transducer (EAT) and commercially available 1308-nm and 1564-nm VCSELs with 4.8-GHz bandwidth. Detailed EAT and 1308-nm VCSEL distortion analyses and measurements are presented highlighting the low intermodulation and harmonic distortion necessary for typical -18-dB wireless channel error vector magnitudes (EVMs). Direct VCSEL modulation with Wimedia supported band group 1 (3.1-4.8 GHz) MB-OFDM UWB signals was modelled with VPItransmissionMaker, suggesting a minimum EVM of -18.733 dB at 0.4502 OMI. This was confirmed by 480 Mbps upstream and downstream EVM measurements over fiber of -21.4 dB or better. Fully functional, half-duplex, bi-directional data transfer was achieved with interlocked RF switches.