Uniform Power Spectral Density Research Articles

Joint Assignment of Power, Routing, and Spectrum in Static Flexible-Grid Networks

This paper proposes a novel network planning strategy to jointly allocate physical layer resources together with the routing and spectrum assignment in transparent nonlinear flexible-grid optical networks with static traffic demands. The physical layer resources, such as power spectral density, modulation format, and carrier frequency, are optimized for each connection. By linearizing the Gaussian noise model, both an optimal formulation and a low complexity decomposition heuristic are proposed. Our methods minimize the spectrum usage of networks, while satisfying requirements on the throughput and quality of transmission. Compared with existing schemes that allocate a uniform power spectral density to all connections, our proposed methods relax this constraint and, thus, utilize network resources more efficiently. Numerical results show that by optimizing the power spectral density per connection, the spectrum usage can be reduced by around ${\text{20}}\%$ over uniform power spectral density schemes.

Vibration protection of laptop hard disk drives in harsh environmental conditions

Ultra-portability and compact design of laptop computers have made them more vulnerable to harsh environments. Hard disk drives (HDDs) in particular, are critical components in laptop computers whose read/write performance is severely affected by excessive vibrations. Here we take a system-level approach to design an optimal vibration isolator so as to minimize the transmitted vibration to the HDD while the laptop chassis is confined within an allowable vibration travel. The laptop is modeled as a 3-dof lumped-parameter system and the base excitation is assumed Gaussian random vibration with zero mean and uniform power spectral density over the frequency range [0–2000] Hz. The problem is cast as a constrained optimization problem with two decision variables, namely isolation frequency and damping. A combination of analytical and numerical approaches is utilized to solve the constrained optimization problem. It is shown that the optimized isolation system could reduce the transmitted root-mean-square acceleration to the HDD by a factor of over four compared to a rigidly-mounted laptop. Furthermore, the methodology presented here is not case-specific and could be applied to the isolation system design of a wide range of systems.

Utilizing arbitrary waveform generators to produce noise with imposed spectral characteristics

<p>The reliability and performance of many systems mostly depend of their noise rejection capability. The behavior of systems that are prone to noise is therefore investigated since the early production stage, as well as routinely during periodical maintenance actions. Actually, there are very few noise sources available on the market, the majority of which is capable of generating only noise characterized by a uniform power spectral density in a limited bandwidth; generators capable of producing colored noise are instead very rare. In theory, arbitrary waveform generators could be deployed and suitably programmed to serve as noise sources. But, the technicians charged of test and measurement assignments will barely find application notes that support them in stepping from theory to practice.</p><p>This work presents tutorial notes related to the simulation of colored noise, and proposes an analog generator that exploits an arbitrary waveform generator as noise source. The proposed generator is capable of producing noise signals characterized by arbitrary power spectral densities.</p>

Tunable sharp and highly selective microwave-photonic band-pass filters based on stimulated Brillouin scattering

Stimulated Brillouin scattering (SBS) in optical fibers has long been used in frequency-selective optical signal processing, including in the realization of microwave-photonic (MWP) filters. In this work, we report a significant enhancement in the selectivity of SBS-based MWP filters. Filters having a single passband of 250 MHz–1 GHz bandwidth are demonstrated, with selectivity of up to 44 dB. The selectivity of the filters is better than that of the corresponding previous arrangements by about 15 dB. The shape factor of the filters, defined as the ratio between their −20 dB bandwidth and their −3 dB bandwidth, is between 1.35 and 1.5. The central transmission frequency, bandwidth, and spectral shape of the passband are all independently adjusted. Performance enhancement is based on two advances, compared with previous demonstrations of tunable SBS-based MWP filters: (a) the polarization attributes of SBS in standard, weakly birefringent fibers are used to discriminate between in-band and out-of-band components and (b) a sharp and uniform power spectral density of the SBS pump waves is synthesized through external modulation of an optical carrier by broadband, frequency-swept waveforms. The signal-to-noise ratio of filtered radio-frequency waveforms and the linear dynamic range of the filters are estimated analytically and quantified experimentally. Lastly, a figure of merit for the performance of the filters is proposed and discussed. The filters are applicable to radio-over-fiber transmission systems.

Response of a nonrotating rotor blade to lateral turbulence Part II: Experiment

In Part I of this work, a theoretical simulation study of rotor blade response to turbulence in forward flight is presented. For verification of this theoretical computational method, a new experimental method based on a special gust field generated by a rotating slotted cylinder with an airfoil (RSC/airfoil) in a wind tunnel is developed to simulate the aerodynamic environment of a rotating rotor blade in forward flight. This gust generator can produce a single harmonic gust wave and also turbulence with uniform power spectral density over a certain frequency band in the lateral and longitudinal directions. In this article, quantitative comparisons are also made with theoretical results for both random and nonrandom parametric excitation. The quantitative agreement between theory and experiment indicates that this experimental method is useful.

250 MHz/GHz Scintillation Parameters in the Equatorial, Polar, and Auroral Environments

Ionospheric scintillation effects encountered in the equatorial anomaly crest, polar cap, and auroral regions have been contrasted to provide information for the design and evaluation of the performance of multifrequency satellite communication links in these regions. The equatorial anomaly region is identified as the most disturbed irregularity environment where the amplitude and phase structures of 250 MHz and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</tex> -band scintillations are primarily dictated by the strength of scattering rather than ionospheric motion. In the anomaly region, the spectra of intense amplitude scintillations at these frequencies are characterized by uniform power spectral density from the lowest frequency (10 MHz) to 4 Hz at 257 MHz and to 1 Hz at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</tex> -band (1541 MHz) and steep rolloff at higher fluctuation frequencies with power law indexes of -5 to -7. Such structures are compatible with intensity decorrelation times of 0.1 and 0.3 s at 257 and 1541 MHz, respectively. The phase spectra at 244 MHz are described by power law variation of psd with frequency with typical spectral indexes of -2.4. The strong scattering at VHF induces extreme phase rates of 200° in 0.1 s. The 90th percentile values of rms phase deviation at 244 MHz with 100 s detrend are found to be 16 rad in the early evening hours, whereas amplitude scintillation can cover the entire dynamic range of 30 dB not only in the 250 MHz band but at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</tex> -band as well. In the polar cap, the 50th and 90th percentile values of rms phase deviation at 250 MHz for 82 s detrend are 3 and 12 rad, respectively, with comparable values being obtained in the auroral oval. The corresponding values for the S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> index of scintillation are 0.5 and 0.8 in the polar cap, which are slightly higher than those recorded in the auroral oval. The power law index of phase scintillation at high latitudes is in the vicinity of -2.3, which is not a result of very strong turbulence as in the equatorial region but is considered to be a consequence of shallow irregularity spectral indexes. The phase rates at auroral locations are an order of magnitude smaller than in the equatorial region and attain values of 100° in 0.5 s. The extreme variability of ionospheric motion in the auroral oval sensitively controls the structure of scintillations. The long-term morphology (period 1979-1984) of intensity scintillations at 250 MHz in the polar cap shows that, in addition to the absence of diurnal variation of scintillations, and the presence of an annual variation with a pronounced minimum during local summer, there exists a marked solar control of scintillation activity such that it abruptly decreases when the solar activity falls below a threshold level.

Comments on "A uniform power spectral density jamming signal"

Comments on "A uniform power spectral density jamming signal"

A uniform power spectral density jamming signal

In this work a technique is described for generating a jamming signal with a continuous uniform-power-spectral density band-limited over any desired frequency band. Experimental results demonstrating the technique are presented.

Random Signal Method of Nonlinear Amplitude Distortion Measurement

The degree and orders of nonlinearity of a system can be determined by the use of a random test signal. A Gaussian-distributed random signal with a uniform power spectral density except for a narrow spectral notch is used as an input test signal. The power within the notch at the system output is a measure of the degree of system nonlinearity. Relative variations of the output power within the notch with input loading identify the orders of nonlinearity.

Sampling Technique for Generating Gaussian Noise

A sampling technique for generating Gaussian noise having a uniform power spectral density from approximately 0.1 cps to 5 kc is described. In principle one could extend the uniform power spectral density property at both ends of the spectrum. The only nonlinear circuit required to implement the technique is a simple high level sampling circuit. Random noise is periodically sampled in order to generate a pulse train having short pulse durations and statistically independent pulse amplitudes. The random pulse train is then applied to a low pass filter in order to produce a Gaussianly distributed output as is predicted by the central limit theorem of probability. The technique is also useful for studying periodic overlapping impulse noise.