Loop SNR Research Articles

Error performance analysis of optical communication over Lognormal-Rician turbulence channel using Gram-Charlier Series

Abstract In this paper, the symbol-error rate (SER) performance of a coherent free-space optical (FSO) communication system in lognormal-Rician turbulence channel is analyzed using the generalized Gram-Charlier (GCC) series. We proposed the differential evolution (DE) algorithm to solve the parameters in GCC efficiently. It is shown that highly accurate closed-form SER expressions are obtained for M-ary phase-shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) schemes with maximum ratio combining (MRC) technique. The asymptotic error rate analysis is presented to reveal the performance behavior in the high signal-to-noise (SNR) regime. The effects of imperfect phase noise compensation on the error rate performance are also studied, and it is found that the impact of phase compensation error can be small enough with loop SNR ρ c more than seven.

New high-frequency radio observations of the Cygnus Loop supernova remnant with the Italian radio telescopes

ABSTRACT Supernova remnants (SNRs) represent a powerful laboratory to study the cosmic ray acceleration processes at shocks, and their relation to the properties of the circumstellar medium. With the aim of studying the high-frequency radio emission and investigating the energy distribution of accelerated electrons and the magnetic field conditions, we performed single-dish observations of the large and complex Cygnus Loop SNR from 7.0–24.8 GHz with the Medicina and Sardinia Radio Telescopes, focusing on the northern filament (NGC 6992) and the southern shell. Both regions show a spectrum well fitted by a power-law function (S ∝ ν−α), with spectral index α = 0.45 ± 0.05 for NGC 6992 and α = 0.49 ± 0.01 for the southern shell and without any indication of a spectral break. The spectra are significantly flatter than the whole Cygnus Loop spectrum (α = 0.54 ± 0.01), suggesting a departure from the plain shock acceleration mechanisms, which for NGC 6992 could be related to the ongoing transition towards a radiative shock. We model the integrated spectrum of the whole SNR considering the evolution of the maximum energy and magnetic field amplification. Through the radio spectral parameters, we infer a magnetic field at the shock of 10 μG. This value is compatible with purely adiabatic compression of the interstellar magnetic field, suggesting that the amplification process is currently inefficient.

Error Probability of $ M$-Phase Signaling With Phase Noise Over Fading Channels

This correspondence focuses on the analysis of average symbol error rate (ASER) of $M$ -ary phase-shift keying (MPSK) over $\boldsymbol {\kappa }$ - $\boldsymbol {\mu }$ , $ \boldsymbol {\eta }$ - $ \boldsymbol {\mu }$ , and $\boldsymbol {\alpha }$ - $\boldsymbol {\mu }$ fading channels subject to imperfect carrier phase recovery. The random phase noise is considered to be Tikhonov (or von Mises) distributed. Specifically, exact expressions for the ASER i) under non-fading scenario, ii) under $\boldsymbol {\kappa }$ - $\boldsymbol {\mu }$ , iii) $ \boldsymbol {\eta }$ - $ \boldsymbol {\mu }$ , and iv) $\boldsymbol {\alpha }$ - $\boldsymbol {\mu }$ fading channels, as well as v) their corresponding asymptotic behavior for high signal-to-noise ratio, (SNR) values are analytically obtained and evaluated. The derived expressions support arbitrary values of the fading parameters, namely $\boldsymbol {\alpha }$ , $ \boldsymbol {\kappa }$ , $\boldsymbol {\eta }$ and $ \boldsymbol {\mu }$ , and they are validated by reducing them to particular cases, for which results are available in the literature, and by means of simulations. Several important conclusions concerning the system performance as a function of the channel parameters and loop SNR are drawn.

Observation of the Monoceros Loop SNR region with the HEGRA system of IACTs

The array of 5 imaging atmospheric y Cerenkov telescopes (IACTs) deployed at La Palma (Canary Islands), and operated by the HEGRA (High Energy Gamma Ray Astronomy) collaboration, was used for observations of the Monoceros Loop SNR region for a total of about 120 hrs and 20 hrs in ON-source and OFF-source mode, respectively. The giant molecular cloud Rosette Nebula appears in the sky region, close to the south-east part of the SNR rim. Using the HEGRA system of IACTs of rather large field of view (4.3 degree in diameter), we have mapped the extended sky region of 3 ◦ × 3 ◦ associated with the Monoceros SNR/Rosette Nebula, which is centered towards the hard spectrum X-ray point source SAX J0635+533. The EGRET unidentified source of diffuse γ-ray emission (3EG J0634+0521) observed in the energy range between 100 MeV-10 GeV, was effectively in the field of view of our present observations. Also, the GeV source GeV J0633+0645 was within the available field of view. The performance of the IACTs array reveals an energy threshold of 500 GeV and an angular resolution of 0.1 ◦ for γ-rays. In what follows, we present the result of the data analysis and its physical interpretation.

Molecular hydrogen gas at high-velocity associated with the Monoceros Loop SNR

We present Far Ultraviolet Spectroscopic Explorer ($\it FUSE$) observations of molecular hydrogen (H 2 ) gas observed at a high-velocity of $V_{\rm LSR} = +66$ km s -1 towards the star HD 47240 which lies just behind the Monoceros Loop Supernova Remnant at a distance of ~1800 pc. These absorption features have been detected in six lines of the $J = 3$ rotational level, with an equivalent molecular hydrogen column density of log $N({\rm H}_{2}) = 14.10, \pm\,0.12$ cm -2 . The observed data are best fit with a single excitation temperature, T ex , of ~1000 K, which when comparised to temperatures generally found for low J -levels is unusually high for interstellar H 2 . The molecular fraction in this HV cloud has a very low value of log $f = -4.5\pm0.25$, which is similar to that found for HV clouds in the galactic halo.

Far Ultraviolet Spectroscopic Explorer observations of high-velocity gas associated with the Monoceros Loop SNR

We present Far Ultraviolet Spectroscopic Explorer ($\it FUSE$) observations of high-velocity gas ( V LSR = +65 km s -1 ) seen towards the star HD 47240 which lies just behind the Monoceros Loop Supernova Remnant at a distance of ~1800 pc. This high-velocity absorption feature is detected in the far ultraviolet lines of O I, Ar I, N I, C I, Fe II and P II, in addition to being detected at visible wavelengths in Na I and Ca II and at near ultraviolet wavelengths in Mg II, Mg I, S II, O I, Si II, C II*, Al II and Fe II. High-velocity interstellar gas has not been detected in the high-ionization (high-temperature) species of O VI, C IV and Si IV. Gas phase abundances relative to that of sulphur for this high velocity feature have been derived. The refractory elements of Fe, Si and Al are all less depleted than that normally found for cold disk gas in the interstellar medium, with a pattern of relative abundance more similar to that of warm interstellar disk gas. However, the elements of N, O, and Ar show an opposite pattern of relative depletion in which their apparent elemental deficiency may be attributed to ionization effects, as also found for high-velocity gas associated with the Vela SNR by Jenkins et al. ([CITE]). The lack of detection of high-ionization gas at high velocity suggests that the Monoceros Loop remnant is more evolved than other remnants such as the Vela SNR or Cygnus Loop, and that an age of 30 000-150 000 years seems appropriate.

Approximate mean cycle slip time of synchroniser with triangular type phase detector

An approximate closed formula for the mean cycle slip time of a synchroniser with triangular type phase detector is derived. The worst case error of the derived formula is within 10% for the loop SNR α < 12. Numerical results obtained are compared to those for the multiplier phase detector at the same loop SNR.

Multiple symbol partially coherent detection of MPSK

The authors show that by using the known (or estimated) value of carrier tracking loop SNR in the decision metric, it is possible to improve the error probability performance of a partially coherent MPSK system relative to that corresponding to the commonly used ideal coherent decision rule. Using a maximum-likelihood approach, an optimum decision metric is derived and shown to take the form of a weighted sum of the ideal coherent decision metric (i.e., correlation) and the noncoherent decision metric which is optimum for differential detection of MPSK. The performance of a receiver based on this optimum decision rule is derived and shown to provide continued improvement with increasing length of observation interval (data symbol sequence length). Unfortunately increasing the observation length does not eliminate the error floor associated with the finite loop SNR. Nevertheless, in the limit of infinite observation length, the average error probability performance approaches the algebraic sum of the error floor and the performance of ideal coherent detection, i.e., at any error probability above the error floor, there is no degradation due to the partial coherence. While the above is strictly speaking only true in the limit of infinite observation length, it is shown that one can virtually achieve this limiting behavior with practical size observation lengths. Furthermore, the performance is quite insensitive to mismatch between the estimate of loop SNR (e.g., obtained from measurement) fed to the decision metric relative and its true value.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On the effects of phase jitter on QPSK lock detection

The performance of a QPSK (quadrature phase-shift keying) lock detector is described, taking into account the degradation due to carrier phase jitter. Such an analysis is necessary for accurate performance prediction purposes in scenarios where both the loop SNR is low and the estimation period is short. The derived formulas are applicable to several QPSK loops and are verified using computer simulations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A sheet description of the emission from middle-aged supernova remnants

view Abstract Citations (106) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Sheet Description of the Emission from Middle-aged Supernova Remnants Hester, J. Jeff Abstract The hypothesis that sheetlike shock fronts propagating into large clouds immersed in a fairly uniform intercloud medium can provide a consistent picture accounting for essentially all the observational data for the Cygnus Loop SNR is considered. Filaments are interpreted as line-of-sight projections of portions of the sheet. Variations in the projection of the shock velocity along the line of sight lead naturally to 'turbulent' velocities consistent with observation. An analog model of a large, distorted, bumpy shock front is presented and shown to produce the observed morphology of the remnant's prominent optical filaments. Comparison with the observed morphology supports the idea that regions of optical emission lie on the local outer boundary of the shell and have not been engulfed by the blast wave. Bright X-ray emission arises when the blast wave encounters a preshock medium with an intermediate density higher than average for the adiabatic portion of the remnant, but still lower than that required for the shock to become radiative. Publication: The Astrophysical Journal Pub Date: March 1987 DOI: 10.1086/165049 Bibcode: 1987ApJ...314..187H Keywords: Nebulae; Sheets; Shock Fronts; Supernova Remnants; Astronomical Models; Interstellar Matter; X Ray Sources; Astrophysics; NEBULAE: INDIVIDUAL NAME: CYGNUS LOOP; NEBULAE: INDIVIDUAL ALPHANUMERIC: IC 443; NEBULAE: SUPERNOVA REMNANTS; SHOCK WAVES full text sources ADS | data products SIMBAD (2)

The Cygnus loop - A detailed comparison of X-ray and optical emission

A comparison at a resolution of 17 arcsec is presented between optical emission from forbidden O III and forbidden S II and the thermal X-ray emission for a field on the southeast edge of the Cygnus Loop SNR. The relationship between optical and X-ray emission in the field is described, generalizing to the Loop as a whole when possible. Several possible explanations for the presence of bright X-ray emission in the vicinity of optical emission are presented and evaluated based on the data. These mechanisms involve evaporation, gradual variations and gradients in the density of the preshock intercloud medium, and additional compression of material which has already been heated to X-ray temperatures by the adiabatic blast wave. The additional compression could result from rapid deceleration of the blast wave itself or from reshocking by reflected or bow shocks around dense clouds. Implications of the observations for models of SNR evolution and the interstellar medium are discussed.

Digital analysis of narrow-band imagery of the Cygnus Loop

Calibrated surface brightness and spectral line ratio maps which involve emission from six different ionic species are derived from the digital analysis of narrow passband direct imagery of a field in the southeast part of the Cygnus Loop SNR, and the spatial structure is categorized on the basis of the presence or absence of features in images isolating different emission lines. While features present in all emission lines are found to have spectral behavior consistent with steady flow shock model calculations for a range of v(s), the features present only in such 'hot' lines as the O III forbidden line 5007 A are found to account for relative intensities of that line greater than can be matched by steady flow model calculations.

The spectrum of 3C 58

Digital spectra of three faint knots in the SNR 3C 58 have been obtained in the wavelength range lambdalambda4700--7300 with the intensified Reticon spectrometer at the 1.3 m telescope of McGraw-Hill Observatory. Emission lines of (S II), (N II), H..cap alpha.., and (O III) were detected with radial velocities less than 100 km s/sup -1/. Although 3C 58 resembles the Crab Nebula in its radio properties and is thought to be the remnant of the supernova observed in A.D. 1181, the relative line intensities and radial velocities reported here more nearly resemble those of the Cygnus Loop and Kepler's SNR.

The Effects of Bandpass Limiters on n-Phase Tracking Systems

The combination of a bandpass limiter and an nthpower tracking loop is considered. It is shown that the performance of the combination does not depend on the form of the nonlinear function used to create the nthharmonic signal as long as some energy in that zone is produced. Furthermore, the order in which the limiter and n power nonlinearity occur is unimportant so that the results apply equally well to the n -phase Costas type of implementations of the nthpower loops. Closed form expressions for the signal suppression factors are obtained, and it is shown that the coherent and noncoherent SNR's out of the nthpower-limiter combination can be expressed in terms of two of these suppression factors. This latter point enables one to estimate the loop SNR of an nthpower-limited phase locked loop by simply calculating the suppression factors for nthand ( (2n)^{th} ) power loops. Finally, n thpower phase locked loops without limiters are compared with similar loops with limiters where it is shown that the presence of the limiter can actually enhance the output SNR at moderate to large values of input SNR.

Simplified Formula for Mean Cycle-Slip Time of Phase-Locked Loops With Steady-State Phase Error

Previous work has shown that the mean time from lock to a slipped cycle of a phase-locked loop is given by a certain double integral. Accurate numerical evaluation of this formula for the second-order loop has proved extremely vexing because the difference between exponentially large quantities is involved. This article simplifies the general formula to avert this problem, provides a useful approximation to a needed conditional expectation, and produces an asymptotic formula for the mean slip time that is moderately accurate even at low loop SNR (less than 7 dB) and small steady-state phase errors (less than 0.3 rad). The approximations extend to higher order loops, as well.