1,489 research outputs found
Optimal Waveforms Design for Ultra-Wideband Impulse Radio Sensors
Ultra-wideband impulse radio (UWB-IR) sensors should comply entirely with the regulatory spectral limits for elegant coexistence. Under this premise, it is desirable for UWB pulses to improve frequency utilization to guarantee the transmission reliability. Meanwhile, orthogonal waveform division multiple-access (WDMA) is significant to mitigate mutual interferences in UWB sensor networks. Motivated by the considerations, we suggest in this paper a low complexity pulse forming technique, and its efficient implementation on DSP is investigated. The UWB pulse is derived preliminarily with the objective of minimizing the mean square error (MSE) between designed power spectrum density (PSD) and the emission mask. Subsequently, this pulse is iteratively modified until its PSD completely conforms to spectral constraints. The orthogonal restriction is then analyzed and different algorithms have been presented. Simulation demonstrates that our technique can produce UWB waveforms with frequency utilization far surpassing the other existing signals under arbitrary spectral mask conditions. Compared to other orthogonality design schemes, the designed pulses can maintain mutual orthogonality without any penalty on frequency utilization, and hence, are much superior in a WDMA network, especially with synchronization deviations
UWB Signal Generation and Modulation Based on Photonic Approaches
Demands for efficient and reliable wireless communications between computers, mobile phones, and other portable electronic devices in short distances are increasing very fast. Ultra-wideband impulse radio is one of the promising techniques, which has gained much research interests in recent years. It covers a wide scope of applications in short-reach wireless communications. Conventionally, the low-bandwidth electronics can process the UWB signals very well. More recently, microwave photonics has enabled a new paradigm for developing UWB techniques in photonic domain. The photonic approaches offer much higher bandwidth and seamless compatibility with optical fiber networks, which allow for scaling the UWB technology to more advanced application scenarios. This chapter is included because photonic approaches have become a unique and effective technique in microwave signal processing. We do not attempt to offer a comprehensive review of UWB photonics, but rather to introduce the typical photonic solutions for UWB signal generation, modulation, transmission, down conversion, and so on
Performance of Bit Error Rate and Power Spectral Density of Ultra Wideband with Time Hopping Sequences.
This thesis focuses on several modulation methods for an ultra wideband (UWB) signal. These methods are pulse position modulation (PPM), binary phase shift keying (BPSK), on/off key shifting (OOK), and pulse amplitude modulation (PAM). In addition, time hopping is considered for these modulation schemes, where the capacity per time frame of time hopping PPM is studied using different spreading ratios. This thesis proves that with the addition of time hopping to all types of modulated UWB signals, the performance of power spectral density improves in all aspects, despite the increase of data per time frame. Note that despite the increase of data per frame, the bit error rate remains the same as standard non-time hopping UWB modulated signals
Comparison of Bit Error Rate and Power Spectral Density on the Ultra Wideband Impulse Radio Systems
Ultra-Wideband (UWB) is defined as a wireless transmission scheme that occupies a bandwidth of more than 25% of its center frequency. UWB Impulse Radio (UWB-IR) is a popular implementation of the UWB technology. In UWB-IR, information is encoded in baseband without any carrier modulation. Pulse shaping and baseband modulation scheme are two of the determinants on the performance of the UWB-IR.
In this thesis, both temporal and spectral characteristics of the UWB-IR are examined because all radio signals exist in both the time and frequency domains. Firstly, the bit error rate (BER) performance of the UWB-IR is investigated via simulation using three modulation schemes: Pulse position modulation (PPM), on-off shift keying (OOK), and binary phase shift keying (BPSK). The results are verified for three different pulse shaping named Gaussian first derivative, Gaussian second derivative, and return-to-zero (RZ) Manchester. Secondly, the effects of the UWB-IR parameters on the power spectral density (PSD) are investigated because PSD provides information on how the power is distributed over the radio frequency (RF) spectrum and determines the interference of UWB-IR and the existing systems to each other in the spectrum. The investigated UWB-IR parameters include pulse duration, pulse repetition rate, modulation scheme, and pseudorandom codes
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Ultra-wideband systems exploiting orthonormal waveforms
textElectrical and Computer Engineerin
Waveform-independent frame-timing acquisition for UWB signals
In this paper, the problem of frame-level symbol
timing acquisition for UWB signals is addressed. The main goal
is the derivation of a frame-level timing estimator which does not
require any prior knowledge of neither the transmitted symbols
nor the received template waveform. The independence with
respect to the received waveform is of special interest in UWB
communication systems, where a fast and accurate estimation of
the end-to-end channel response is a challenging and computationally
demanding task. The proposed estimator is derived under the
unconditional maximum likelihood criterion, and because of the
low power of UWB signals, the low-SNR assumption is adopted. As
a result, an optimal frame-level timing estimator is derived which
outperforms existing acquisition methods in low-SNR scenarios.Peer Reviewe
Study and miniaturisation of antennas for ultra wideband communication systems
PhDWireless communications have been growing with an astonishing rate over the past
few years and wireless terminals for future applications are required to provide
diverse services. This rising demand prompts the needs for antennas able to cover
multiple bandwidths or an ultrawide bandwidth for various systems.
Since the release by the Federal Communications Commission (FCC) of a bandwidth
of 7.5 GHz (from 3.1 GHz to 10.6 GHz) for ultra wideband (UWB) wireless
communications, UWB has been rapidly evolving as a potential wireless technology
and UWB antennas have consequently drawn more and more attention from both
academia and industries worldwide.
Unlike traditional narrow band antennas, design and analysis of UWB antennas are
facing more challenges and difficulties. A competent UWB antenna should be
capable of operating over an ultra wide bandwidth as assigned by the FCC. At the
same time, a small and compact antenna size is highly desired, due to the integration
requirement of entire UWB systems. Another key requirement of UWB antennas is
the good time domain behaviour, i.e. a good impulse response with minimal
distortion.
This thesis focuses on UWB antenna miniaturisation and analysis. Studies have been
undertaken to cover the aspects of UWB fundamentals and antenna theory. Extensive
investigations are also conducted on three different types of miniaturised UWB
antennas.
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The first type of miniaturised UWB antenna studied in this thesis is the loaded
orthogonal half disc monopole antenna. An inductive load is introduced to broaden
the impedance bandwidth as well as the pattern bandwidth, in other words, an
equivalent size reduction is realised.
The second type of miniaturised UWB antenna is the printed half disc monopole
antenna. By simply halving the original antenna and tuning the width of the coplanar
ground plane, a significant more than 50% size reduction is achieved.
The third type of miniaturised UWB antenna is the printed quasi-self-complementary
antenna. By exploiting a quasi-self-complementary structure and a built-in matching
section, a small and compact antenna dimension is achieved.
The performances and characteristics of the three types of miniaturised UWB
antennas are studied both numerically and experimentally and the design parameters
for achieving optimal operation of the antennas are also analysed extensively in order
to understand the antenna operations.
Also, time domain performance of the Coplanar Waveguide (CPW)-fed disc
monopole antenna is examined in this thesis to demonstrate the importance of time
domain study on UWB antennas.
Over the past few years of my PhD study, I feel honoured and lucky to work with
some of the most prestigious researchers in the Department of Electronic
Engineering, Queen Mary, University of London. I would like to show my most
cordial gratitude to those who have been helping me during the past few years. There
would be no any progress without their generous and sincere support.
First of all, I would like to thank my supervisors Professor Clive Parini and Professor
Xiaodong Chen, for their kind supervision and encouragement. I am impressed by
their notable academic background and profound understanding of the subjects,
which have proved to be immense benefits to me. It has been my great pleasure and
honour to be under their supervision and work with them.
Second of all, I would like to thank Mr John Dupuy for his help in the fabrication
and measurement of antennas I have designed during my PhD study. Also, a special
acknowledgement goes to all of the staff for all the assistance throughout my
graduate program
Simple pre-distortion schemes for improving the power efficiency of SOA-based IR-UWB over fiber systems
International audienceIn this paper, we investigate the usage of SOA for reach extension of an impulse radio over fiber system. Operating in the saturated regime translates into strong nonlinearities and spectral distortions, which drops the power efficiency of the propagated pulses. After studying the SOA response versus operating conditions, we have enhanced the system performance by applying simple analog pre-distortion schemes for various derivatives of the Gaussian pulse and their combination. A novel pulse shape has also been designed by linearly combining three basic Gaussian pulses, offering a very good spectral efficiency (>55%) for a high power (0 dBm) at the amplifier input. Furthermore, the potential of our technique has been examined considering a 1.5 Gbps-OOK and 0.75 Gbps-PPM modulation schemes. Pre-distortion proved an advantage for a large extension of optical link (150 Km), with an inline amplification via SOA at 40 Km
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