201 research outputs found
Digital Filters for Instantaneous Frequency Estimation
This technical note is on digital filters for the high-fidelity estimation of
a sinusoidal signal's frequency in the presence of additive noise. The complex
noise is assumed to be white (i.e. uncorrelated) however it need not be
Gaussian. The complex signal is assumed to be of (approximately) constant
magnitude and (approximately) polynomial phase such as the chirps emitted by
bats, whale songs, pulse-compression radars, and frequency-modulated (FM)
radios, over sufficiently short timescales. Such digital signals may be found
at the end of a sequence of analogue heterodyning (i.e. mixing and low-pass
filtering), down to a bandwidth that is matched to an analogue-to-digital
converter (ADC), followed by digital heterodyning and sample rate reduction
(optional) to match the clock frequency of the processor. The spacing of the
discrete frequency bins (in cycles per sample) produced by the Fast Fourier
Transform (FFT) is equal to the reciprocal of the window length (in samples).
However, a long FFT (for fine frequency resolution) has a high complexity and a
long latency, which may be prohibitive in embedded closed-loop systems, and
unnecessary when the channel only contains a single sinusoid. In such cases,
and for signals of constant frequency, the conventional approach involves the
(weighted) average of instantaneous phase differences. General, naive, optimal,
and pragmatic (recursive), filtering solutions are discussed and analysed here
using Monte-Carlo (MC) simulations.Comment: Added arXiv ID to header and fixed a few typo
Physically Informed Subtraction of a String's Resonances from Monophonic, Discretely Attacked Tones : a Phase Vocoder Approach
A method for the subtraction of a string's oscillations from monophonic,
plucked- or hit-string tones is presented. The remainder of the subtraction
is the response of the instrument's body to the excitation, and potentially
other sources, such as faint vibrations of other strings, background
noises or recording artifacts. In some respects, this method is similar to a
stochastic-deterministic decomposition based on Sinusoidal Modeling Synthesis
[MQ86, IS87]. However, our method targets string partials expressly,
according to a physical model of the string's vibrations described in this thesis.
Also, the method sits on a Phase Vocoder scheme. This approach has
the essential advantage that the subtraction of the partials can take place
\instantly", on a frame-by-frame basis, avoiding the necessity of tracking the
partials and therefore availing of the possibility of a real-time implementation.
The subtraction takes place in the frequency domain, and a method
is presented whereby the computational cost of this process can be reduced
through the reduction of a partial's frequency-domain data to its main lobe.
In each frame of the Phase Vocoder, the string is encoded as a set of partials,
completely described by four constants of frequency, phase, magnitude
and exponential decay. These parameters are obtained with a novel method,
the Complex Exponential Phase Magnitude Evolution (CSPME), which is
a generalisation of the CSPE [SG06] to signals with exponential envelopes
and which surpasses the nite resolution of the Discrete Fourier Transform.
The encoding obtained is an intuitive representation of the string, suitable
to musical processing
Spectral and correlation analysis with applications to middle-atmosphere radars
The correlation and spectral analysis methods for uniformly sampled stationary random signals, estimation of their spectral moments, and problems arising due to nonstationary are reviewed. Some of these methods are already in routine use in atmospheric radar experiments. Other methods based on the maximum entropy principle and time series models have been used in analyzing data, but are just beginning to receive attention in the analysis of radar signals. These methods are also briefly discussed
A zero placement algorithm for synthesis of flat top beam pattern with low sidelobe level
Flat top beam pattern synthesis is increasingly important for beamformer in high mobility scenarios due to the rapid change of Direction of Arrival (DOA). A Zero Placement for Flat Top (ZPFT) beam pattern synthesis algorithm is presented in this paper. It works in Z domain directly and breaks down the total response into two portions. The first portion satisfies the beamwidth requirement with low Sidelobe Level (SLL) which is realized through algorithms like Dolph-Chebyshev algorithm. The second portion is then used to create a broadening effect. The location of the broadening zeros are derived using principles result from the broadening effect analysis of two quadratic functions. Compared to conventional Finite Impulse Response (FIR) method or iterative methods, the proposed method identifies the zeros of the array factor directly and computes the weight without iteration. Since it works in the spatial angle domain directly, the steering of the mainlobe beam could be implemented through a simple angle shift. Numerical simulation confirms the effectiveness of the algorithm. ZPFT can achieve 22dB lower SLL while maintaining the same main beam performance as compared with FIR method for an Uniform Linear Array (ULA) with 7 elements. It can achieve the same optimal performance as the iteration based global optimisation techniques like Semi-Definite Relaxation (SDR) with about 380 times less computing time in an Intel Core i7 Windows platform. ZPFT can steer the main beam easily in real time. All these make it an ideal candidate for high mobility applications where the DOA changes rapidly
Adaptive beamforming and switching in smart antenna systems
The ever increasing requirement for providing large bandwidth and seamless data access to commuters has prompted new challenges to wireless solution providers. The communication channel characteristics between mobile clients and base station change rapidly with the increasing traveling speed of vehicles. Smart antenna systems with adaptive beamforming and switching technology is the key component to tackle the challenges.
As a spatial filter, beamformer has long been widely used in wireless communication, radar, acoustics, medical imaging systems to enhance the received signal from a particular looking direction while suppressing noise and interference from other directions. The adaptive beamforming algorithm provides the capability to track the varying nature of the communication channel characteristics. However, the conventional adaptive beamformer assumes that the Direction of Arrival (DOA) of the signal of interest changes slowly, although the interference direction could be changed dynamically. The proliferation of High Speed Rail (HSR) and seamless wireless communication between infrastructure ( roadside, trackside equipment) and the vehicles (train, car, boat etc.) brings a unique challenge for adaptive beamforming due to its rapid change of DOA. For a HSR train with 250km/h, the DOA change speed can be up to 4⁰ per millisecond. To address these unique challenges, faster algorithms to calculate the beamforming weight based on the rapid-changing DOA are needed.
In this dissertation, two strategies are adopted to address the challenges. The first one is to improve the weight calculation speed. The second strategy is to improve the speed of DOA estimation for the impinging signal by leveraging on the predefined constrained route for the transportation market. Based on these concepts, various algorithms in beampattern generation and adaptive weight control are evaluated and investigated in this thesis. The well known Generalized Sidelobe Cancellation (GSC) architecture is adopted in this dissertation. But it faces serious signal cancellation problem when the estimated DOA deviates from the actual DOA which is severe in high mobility scenarios as in the transportation market. Algorithms to improve various parts of the GSC are proposed in this dissertation. Firstly, a Cyclic Variable Step Size (CVSS) algorithm for adjusting the Least Mean Square (LMS) step size with simplicity for implementation is proposed and evaluated. Secondly, a Kalman filter based solution to fuse different sensor information for a faster estimation and tracking of the DOA is investigated and proposed. Thirdly, to address the DOA mismatch issue caused by the rapid DOA change, a fast blocking matrix generation algorithm named Simplifized Zero Placement Algorithm (SZPA) is proposed to mitigate the signal cancellation in GSC. Fourthly, to make the beam pattern robust against DOA mismatch, a fast algorithm for the generation of at beam pattern named Zero Placement Flat Top (ZPFT) for the fixed beamforming path in GSC is proposed. Finally, to evaluate the effectiveness and performance of the beamforming algorithms, wireless channel simulation is needed. One of the challenging aspects for wireless simulation is the coupling between Probability Density Function (PDF) and Power Spectral Density (PSD) for a random variable. In this regard, a simplified solution to simulate Non Gaussian wireless channel is proposed, proved and evaluated for the effectiveness of the algorithm.
With the above optimizations, the controlled simulation shows that the at top beampattern can be generated 380 times faster than iterative optimization method and blocking matrix can be generated 9 times faster than normal SVD method while the same overall optimum state performance can be achieved
Performance Improvement of Wide-Area-Monitoring-System (WAMS) and Applications Development
Wide area monitoring system (WAMS), as an application of situation awareness, provides essential information for power system monitoring, planning, operation, and control. To fully utilize WAMS in smart grid, it is important to investigate and improve its performance, and develop advanced applications based on the data from WAMS. In this dissertation, the work on improving the WAMS performance and developing advanced applications are introduced.To improve the performance of WAMS, the work includes investigation of the impacts of measurement error and the requirements of system based on WAMS, and the solutions. PMU is one of the main sensors for WAMS. The phasor and frequency estimation algorithms implemented highly influence the performance of PMUs, and therefore the WAMS. The algorithms of PMUs are reviewed in Chapter 2. To understand how the errors impact WAMS application, different applications are investigated in Chapter 3, and their requirements of accuracy are given. In chapter 4, the error model of PMUs are developed, regarding different parameters of input signals and PMU operation conditions. The factors influence of accuracy of PMUs are analyzed in Chapter 5, including both internal and external error sources. Specifically, the impacts of increase renewables are analyzed. Based on the analysis above, a novel PMU is developed in Chapter 6, including algorithm and realization. This PMU is able to provide high accurate and fast responding measurements during both steady and dynamic state. It is potential to improve the performance of WAMS. To improve the interoperability, the C37.118.2 based data communication protocol is curtailed and realized for single-phase distribution-level PMUs, which are presented in Chapter 7.WAMS-based applications are developed and introduced in Chapter 8-10. The first application is to use the spatial and temporal characterization of power system frequency for data authentication, location estimation and the detection of cyber-attack. The second application is to detect the GPS attack on the synchronized time interval. The third application is to detect the geomagnetically induced currents (GIC) resulted from GMD and EMP-E3. These applications, benefited from the novel PMU proposed in Chapter 6, can be used to enhance the security and robust of power system
Radar Technology
In this book âRadar Technologyâ, the chapters are divided into four main topic areas: Topic area 1: âRadar Systemsâ consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: âRadar Applicationsâ shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: âRadar Functional Chain and Signal Processingâ describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: âRadar Subsystems and Componentsâ consists of design technology of radar subsystem components like antenna design or waveform design
Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
Observations of the high-redshift Universe with the 21 cm hyperfine line of
neutral hydrogen promise to open an entirely new window onto the early phases
of cosmic structure formation. Here we review the physics of the 21 cm
transition, focusing on processes relevant at high redshifts, and describe the
insights to be gained from such observations. These include measuring the
matter power spectrum at z~50, observing the formation of the cosmic web and
the first luminous sources, and mapping the reionization of the intergalactic
medium. The epoch of reionization is of particular interest, because large HII
regions will seed substantial fluctuations in the 21 cm background. We also
discuss the experimental challenges involved in detecting this signal, with an
emphasis on the Galactic and extragalactic foregrounds. These increase rapidly
toward low frequencies and are especially severe for the highest redshift
applications. Assuming that these difficulties can be overcome, the redshifted
21 cm line will offer unique insight into the high-redshift Universe,
complementing other probes but providing the only direct, three-dimensional
view of structure formation from z~200 to z~6.Comment: extended review accepted by Physics Reports, 207 pages, 44 figures
(some low resolution); version with high resolution figures available at
http://pantheon.yale.edu/~srf28/21cm/index.htm; minor changes to match
published versio
- âŠ