Effects Of Phase Errors Research Articles

Beam quality factor for coherently combined fiber laser beams

The beam quality factor for a coherently combined beam is studied in detail. A theoretical analysis and a numerical calculation are given to illustrate that the M 2 factor is not a proper means for evaluating the beam quality of a coherently combined beam. The beam propagation factor is introduced to evaluate the beam quality. The effect of phase error on the beam quality is also studied. Results indicate that the beam quality of a coherently combined beam depends mainly on the fill factor of the laser array and not on the number of lasers. It is also revealed that the allowed phase error does not change with the number of lasers in order to ensure the energy encircled in a certain bucket.

Effect of Carrier Frequency Offset on Cooperative Alamouti STC OFDM Systems

In this paper, the effect of carrier frequency offset on a network where multiple independent devices cooperate to form virtual multiple input multiple output networks is analyzed. The common phase error and inter-carrier interference effect on Cooperative Alamouti space-time code orthogonal frequency division multiplexing system due to carrier frequency offset is investigated.

Wavefront estimation for adaptive optics systems on ground‐based telescopes

Here M(x, y) is the telescope’s pupil indicator function, i.e. is 1 inside the pupil and 0 otherwise, and the function φ(x, y) denotes the phase error, or simply the phase, and is determined by the deviation from planarity of the incoming wavefronts of light at the point (x, y). In Figure 1, we plot (2) in the diffraction limited case, i.e. when φ = 0, and with a nonzero φ generated by a physically realistic model. Note the negative effect of nonzero phase error on the right-hand side PSF. The job of the AO system is to remove the phase error from incoming wavefronts by introducing a counter wavefront φDM via, e.g., a deformable mirror (see Beckers [2]). Assuming the PSF has the form (2), the phase corrected PSF will have the form

Performance Analysis of a New ICI-Self-Cancellation-Scheme in OFDM Systems

In orthogonal frequency division multiplexing communication systems, the system performance may be degraded by the effect of inter-carrier interference. In this paper, a new scheme is proposed to cancel the effect of ICI. The system performances are evaluated based on carrier-to-interference ratio and bit error rate. The simulation results show that the effect of phase error with the proposed scheme is lighter than that with Zhao's scheme. Hence, the BER performance of proposed scheme is better than that of Zhao's scheme even in a large frequency offset.

Effects of Fourier-plane amplitude and phase errors on image reconstruction I Small amplitude errors

The effects of Fourier-plane, or spectral, amplitude and phase errors on reconstructed images are studied in terms of the expected mean square error in the image. The relationship between the variance of amplitude and phase errors and the expected mean square error is derived for small amplitude errors and arbitrarily large phase errors. This allows "equivalent" amplitude and phase errors to be defined. The effects of large amplitude errors are discussed in general terms. Simulations are used to verify these relationships, and the effects of spectral amplitude and phase errors on reconstructed images are compared.

Effects Influencing Focusing in Synthetic Aperture Vector Flow Imaging

Previously, a synthetic aperture vector velocity estimation method was proposed. Data are beamformed at different directions through a point, where the velocity is estimated. The flow direction is estimated by a search for the direction where the normalized cross-correlation peaks and the velocity magnitude along this direction are found. In this paper, different effects that influence the focusing in this method are investigated. These include the effect of phase errors in the emitted spherical waves, motion effects, and the effect of various interpolation methods in beam-forming. A model based on amplitude drop and phase error for spherical waves created using the virtual source concept is derived. This model can be used to determine the opening angle of a virtual source. Simulations for different virtual source placements are made, and it is recommended that the virtual sources be placed behind the aperture when shallow structures are imaged, and when deeper-lying structures are imaged the virtual sources be placed in front of the aperture. Synthetic aperture methods involve summation of data from numerous emissions. Motion between these emissions results in incoherence and affects resolution, contrast, and the signal-to-noise ratio. The effects of motion on the synthetic aperture vector velocity estimation method are investigated, and it is shown that for both axial and lateral motion, the contrast and signal-to-noise ratio can be seriously affected. A compensation method using the previous vector velocity estimate, when new data are beamformed, is implemented and tested. It is shown from a number of flow phantom experiments that a significant improvement with respect to bias and standard deviation of the velocity estimates can be obtained by using this compensation. Increased performance is gained at the expense of computation time. Different interpolation methods can be used for beam-forming the data. In this paper, the velocity estimation performance using various more complex interpolation schemes are compared to that using linear interpolation. No significant difference in the performance of the method is seen when other interpolation methods are used.

Coherent and incoherent combining of fiber array with hexagonal ring distribution

Beam combining of fiber array with hexagonal ring distribution is studied in detail. The theoretical analysis and numerical calculation results are given to illustrate the propagation properties of the resulting beam through free space. A comparison between the coherent and the incoherent case shows that high peak irradiance and good beam quality for coherent combining can be obtained in the far field. The effect of phase errors and the beam quality M 2 factor are also studied. Results indicate that the element numbers should be increased to achieve high power and the space between adjacent elements should be reduced to maintain good beam quality, which is basically the same for both coherent and incoherent beam combining.

The effects of phase errors on optical SSB system performance

The authors present a system performance analysis of an optical single sideband system (OSSB) when phase errors occur in the modulating signal driving the dual-arm Mach–Zehnder modulator (MZM). The performance is evaluated in terms of the optical sideband suppression, received subcarrier power, frequency response, and power-penalty measurements. Experiments were carried out and a mathematical model of the OSSB system, incorporating the phase error, was developed. Both the theoretical and experimental results show that, although optical sideband suppression reduces with phase errors, the received subcarrier power can increase as high as 3 dB for positive phase errors. However, for transmission over longer fiber, the frequency response of the OSSB system is not only dependent on the phase error, but also on the phase shift due to chromatic dispersion (CD). The power penalty was found to be dependent on the frequency response of the OSSB system. At any frequency-response null point, the power-penalty slope is reversed as the received subcarrier power is reduced. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1574–1578, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21724

Effects of carrier phase error on EGC receivers in correlated Nakagami-m fading

The effects of incoherently combining on dual-branch equal-gain combining (EGC) receivers in the presence of correlated, but not necessarily identical, Nakagami-m fading and additive white Gaussian noise are studied. Novel closed-form expressions for the moments of the output signal-to-noise ratio (SNR) are derived. Based on these expressions, the average output SNR and the amount of fading are obtained in closed-form. Moreover, the outage and the average bit error probability for binary and quadrature phase-shift keying are also studied using the moments-based approach. Numerical and computer simulation results clearly depict the effect of the carrier phase error, correlation coefficient, and fading severity on the EGC performance. An interesting finding is that higher values of the correlation coefficient results to lower irreducible error floors.

Effects of carrier phase error on EGC receivers in correlated Nakagami-m fading

The effects of incoherently combining on dual-branch equal-gain combining (EGC) receivers in the presence of correlated, but not necessarily identical, Nakagami-m fading and additive white Gaussian noise are studied. Novel closed-form expressions for the moments of the output signal-to-noise ratio (SNR) are derived. Based on these expressions, the average output SNR and the amount of fading are obtained in closed-form. Moreover, the outage and the average bit error probability for binary and quadrature phase-shift keying are also studied using the moments-based approach. Numerical and computer simulation results clearly depict the effect of the carrier phase error, correlation coefficient, and fading severity on the EGC performance. An interesting finding is that higher values of the correlation coefficient results to lower irreducible error floors.

Analysis Method of Errors (Motion and Atmospheric) in Synthetic Aperture Radar (SAR) Images

Abstract. A method to allow the analysis of the effects of motion and atmospheric errors in SAR images is here presented. The objective of the method is to allow the visualization of the effects of motion errors and atmospheric artefacts on the processed (focused) SAR image. The method is intended to allow the analysis of the interaction of motion and atmospheric errors with the adopted SAR processing procedure and motion compensation algorithms. In this article the analysis method has been applied and tested to a C-Band E-SAR (DLR airborne SAR system) data set where we see that the effects of linear and non-linear phase errors observed are in agreement with the theory.

A novel adaptive algorithm of CPE correction for OFDM systems

On the basis of the analysis of the effect of PHase Noise (PHN) and Common Phase Error (CPE) on Orthogonal Frequency Division Multiplexing (OFDM) systems, a cost function is constructed. By the cost function and the idea of Least-Mean-Square (LMS) adaptive algorithm, the adaptive algorithm for the correction of CPE is presented. The simulations have been performed to investigate the performance for tracking PHN and estimating CPE, the results show that the algorithm performs soundly.

Intensity imbalance in phase shift masks and correction by multiple exposures

In this paper, the issue of intensity imbalance in an alternating phase shift mask has been studied for hole patterns with pitches 300 nm and below. A method of processing is developed, which would nullify the effects of phase errors that cause focus dependent difference in the sizes of holes belonging to opposite phases. This method uses two exposures with opposite foci. Using this method, the effect of the focus on the difference in the size of holes from opposite phases could be totally eliminated. It also changes the nature of the focus curve, bringing a significant improvement in the depth of focus without affecting exposure latitude and mask error enhancement factor. The method works quite effectively for all the via pitches, however, some constant size difference existed across focus, that is easily correctable by biasing one phase with respect to the other. It was also found that this technique could bring remarkable immunity against the lens aberrations such as defocus and astigmatism.

Study of behavior of digital modulations for beam steerable reflectarray antennas

This paper investigates the bit error rate (BER) performance of digital modulations in a system with a scanning reflectarray antenna. A reflectarray causes intersymbol interference (ISI) in a digitally modulated signal, its phase shifters' phase errors cause signal distortion, and its phase shifters' phase transient causes beam pattern degradation during direction switching. In this paper, composite signal models of the reflectarray are established for both static and transient states. Due to different feed-to-element distances and the element-to-observation distances, different delays exist in signal components. These delays cause ISI whose effect is analyzed and evaluated. Effects of phase shifters' phase errors and phase transient during beam switching are also analyzed and evaluated. Numerical calculations and simulations are performed. The analytical and simulation results for an example reflectarray at f/sub c/=26.5 GHz and bit rate of 1.325 Gbps show that the BER degradation due to ISI is proportional to the symbol rate and the loss ranges from about 1 dB to around 2 dB in E/sub b//N/sub o/, depending on original E/sub b//N/sub o/, for BPSK, QPSK, 8PSK, and 16QAM. The phase error effect is negligible for lower order modulations and is unacceptable for higher order modulations such as 64QAM and 256QAM. The degradation due to phase transient effect is about 2 dB for BPSK and QPSK.

Process method to suppress the effect of phase errors in alternating phase shift masks

We have developed a process method to suppress the effect of phase errors in alternating phase shift masks. Our method uses double exposure at reversed focus offsets to nullify the intensity imbalance caused by the phase errors. We have evaluated our technique using 120nm half-pitch line space patterns and found it very successful with remarkable improvement in usable depth of focus without loosing exposure latitude. We also observed that our technique could bring immunity against the lens aberrations such as defocus and astigmatism.

Effect of amplitude tapering and frequency-dependent phase errors on radiation characteristics of radial waveguide fed non-resonant array antenna

A high-gain low sidelobe level array antenna that is fed by a radial waveguide and designed to operate over a frequency range is considered. Assuming azimuthally symmetric excitation, the radiation pattern of the circular array is approximated by the space factor for the equivalent circular aperture and a simple and efficient tool is introduced for analysis of the array radiation pattern. The effect of the tapering, for both paraboloidal and bell-shaped aperture amplitude distributions, and the consequences of the phase errors, caused by the variation with frequency of the electrical lengths in the radial waveguide feed structure, on the gain and sidelobe level are studied in detail. Results obtained based on the proposed analysis are validated with respect to experimental data available in the literature. They are applicable to designs of arrays as well as aperture antennas.

Error models for long-distance Qubit teleportation

A recent proposal for realizing long-distance, high-fidelity qubit teleportation is reviewed. This quantum communication architecture relies on an ultrabright source of polarization-entangled photons plus a pair of trapped-atom quantum memories, and it is compatible with long-distance transmission over standard telecommunication fiber. Models are developed for assessing the effects of amplitude, phase, and frequency errors in the entanglement source, as well as fiber loss and imperfect polarization restoration, on the throughput and fidelity of the system.

Measurement of underwater sound intensity and determination of source bearing angle

Measurements of the underwater acoustic pressure and pressure gradient can be used to calculate the components of the acoustic intensity vector. The intensity vector points in the direction of net power flow and can therefore be used to find the direction or bearing angle to an acoustic source. Use of intensity measurements for determination of bearing is of interest because high-angular resolution can be achieved using a relatively small array with physical dimensions less than 1/4 of the wavelength. The usefulness of this technique was investigated in a series of experiments on the Scotian Shelf in 70 m of water. The intensity sensor is an array of six hydrophones arranged as three orthogonal dipoles. The hydrophone spacing is 11.4 cm with a frequency range of 500–4000 Hz. For signal-to-noise ratios greater than 10 dB, bearing angles to a source were determined with a standard deviation of less than 0.1 deg. However, offsets of several degrees from the correct bearing angle were often present. The offset error is believed to be due to acoustical scatter from supporting structures. The effect of noise, gain error, and phase error on intensity measurements is discussed.

Phase error effect on contrast measurement in Schwider-Hariharan phase-shifting algorithm

Abstract Exact relationship due to linear phase error in contrast measurement in phase shifting interferometry using Schwider-Hariharan method has been obtained. Starting with five irradiance distributions, basic relationships for the contrast have been described.

Analysis of equal-gain diversity with partially coherent fading signals

An analytical technique based on Gram-Charlier series expansion is presented for the computation of the error probability of equal-gain combiner (EGC) with partially coherent fading signals. Imperfect carrier recovery is attributed to the random noise present in the carrier recovery loops. The resulting noisy phase references are assumed to satisfy Tikhonov distribution. The fades on the diversity branches are assumed to be slowly varying and statistically independent with Rayleigh-distributed envelopes. The error-rate performance of coherent and differentially coherent phase-shift keying (PSK) systems are compared and the phase precision requirement for a reliable coherent detection is computed. Detection loss caused by carrier phase errors is computed for several signal-to-noise ratio (SNR) reliability and bit error probability levels. It is demonstrated that the effect of carrier phase errors on the mean SNR is negligible compared to their effect on deep fades or small bit error probabilities. It is also shown that the carrier phase precision requirement can be reduced through signal combination.