Analysis of the performance of multiuser MIMO systems with user scheduling over Nakagami-m fading channels

A performance analysis of user scheduling schemes for multiuser MIMO systems exploiting the multiuser and antenna diversities over Nakagami-$m$ fading channels is presented. We consider different scheduling schemes including absolute SNR-based scheduling, and normalized SNR-based scheduling schemes for both heterogeneous and homogeneous wireless networks. We derive closed-form expressions for the average spectral efficiency, average bit error rate (BER), and outage probability of the system under study for each scheduling scheme. Using the results obtained from the closed-form analytical expressions, we compare the presented schemes and show their significant advantages.     

Performance analysis of wavelength/spatial coding system with fixed in-phase code matrices in OCDMA network

This paper proposes a wavelength/spatial (W/S) coding system with fixed in-phase code (FIPC) matrix in the optical code-division multiple-access (OCDMA) network. A scheme is presented to form the FIPC matrix which is applied to construct the W/S OCDMA network. The encoder/decoder in the W/S OCDMA network is fully able to eliminate the multiple-access-interference (MAI) at the balanced photo-detectors (PD), according to fixed in-phase cross correlation. The phase-induced intensity noise (PIIN) related to the power square is markedly suppressed in the receiver by spreading the received power into each PD while the net signal power is kept the same. Simulation results show that the W/S OCDMA network based on the FIPC matrices cannot only completely remove the MAI but effectively suppress the PIIN to upgrade the network performance.     

Performance gain of displacement receiver with optimized prior probability

We numerically study the performance of the displacement based quantum receiver for the discrimination of weak 3- and 4-phase-shift keyed (PSK) coherent state signals. We show that due to the nontrivial asymmetry of the receiver structure, optimization of the prior probability increases the mutual information and achieves sub-shot-noise limit discrimination. Moreover, we estimate the cutoff rate for a 4-PSK signal and confirm that the prior probability optimization shortens the code length for a given decoding error criterion. Such consideration for the asymmetric channel matrix is essential in a study of the compassable quantum receiver.     

Performance analysis of LDPC codes on OOK terahertz wireless channels

Atmospheric absorption, scattering, and scintillation are the major causes to deteriorate the transmission quality of terahertz(THz) wireless communications. An error control coding scheme based on low density parity check(LDPC) codes with soft decision decoding algorithm is proposed to improve the bit-error-rate(BER) performance of an on-off keying(OOK) modulated THz signal through atmospheric channel. The THz wave propagation characteristics and channel model in atmosphere is set up. Numerical simulations validate the great performance of LDPC codes against the atmospheric fading and demonstrate the huge potential in future ultra-high speed beyond Gbps THz communications.     

Performance analysis of dense wavelength division multiplexing secure communications with multiple chaotic optical channels

The performance of dense wavelength division multiplexing secure communications with multiple chaotic optical channels is numerically analyzed in this paper. Taking the multiplexing of three chaotic optical channels as an example, we investigate the effects of second-order dispersion coefficient and nonlinear coefficient of fiber, channel spacing, message amplitude and bit rates on chaotic synchronization and multiplexing communications. Chaotic synchronization quality and Q-factor of the recovered message decrease with the increasing fiber length. A 1.25 Gbits/s non-return-to-zero (NRZ) sequence can be securely transmitted up to 60 km under the influence of the other two chaotic optical channels. Compared with the fiber dispersion, the cross-phase modulation is the primary factor which deteriorates the quality of communications. The results also show that the quality of communications is unlimited to the channel spacing as long as chaotic synchronization can be maintained. In addition, the effect of the amplitude of encrypted message on Q-factor and the confidentiality is demonstrated.     

Performance analysis of space-shift keying over negative-exponential and log-normal FSO channels

The average bit-error rate(ABER) performance of free-space optical(FSO) communication links is investigated for space-shift keying(SSK) over log-normal and negative-exponential atmospheric turbulence channels. SSK is compared with repetition codes and a single-input single-output system using multiple pulse amplitude modulations. Simulation results show that the signal-to-noise ratio gain of SSK largely increases with greater spectral efficiencies and/or higher turbulence effects. A tight bound for ABER is derived based on an exact moment generation function(MGF) for negative-exponential channel and an approximate MGF for log-normal channel.Finally, extensive Monte Carlo simulations are run to validate the analytical analysis.     

Performance analysis of wireless powered sensor network with opportunistic scheduling over generalized κ−μ shadowed fading channels

This paper investigates the performance of a multi-node wireless powered sensor network (WPSN) with an opportunistic scheduling scheme over $\kappa -\mu$ shadowed fading channels. The system assumes that all the sensor nodes (SNs) are energy constrained and harvest energy from a hybrid access point (HAP) in the downlink. In contrast, the node with the best end-to-end instantaneous signal-to-noise ratio (SNR) is scheduled for information transmission to HAP in the uplink. For the underlying system model, approximate closed-form analytical expressions is developed with the help of the moment matching method, which is then used to evaluate the system performances such as outage probability, effective throughput, and average bit error rate (BER). In addition, we also perform an asymptotic analysis by assuming that the system operates at a high SNR region, which gives us valuable insights about the diversity order and coding gain. The accuracy of the analysis is further confirmed with Monte-Carlo simulations, which validate the correctness of the theoretical analysis.     

Brillouin gain analysis for fibers with different refractive indices

We studied an anomalous result in the measured stimulated Brillouin scattering threshold for single-mode optical fibers with different refractive index profiles and effective areas. It was found that, in addition to the optical effective area, the refractive-index-dependent interaction between the optical and the acoustic fields must be considered in order to account for the differences in the stimulated Brillouin scattering threshold between fiber types. A detailed analytical formalism describing the acousto-optic interaction was derived to accommodate the influence of the index profile design on Brillouin scattering.     

Performance characteristics of an energy selective electron refrigerator with double resonances

This paper establishes the energy selective electron (ESE) engine with double resonances as a refrigerator in one dimensional (1D) system. It consists of two infinitely large electron reservoirs with different temperatures and chemical potentials, and they are perfectly thermally insulated from each other and interaction only via a double `idealized energy filter' whose widths are all finite. Taking advantage of the density of state and Fermi distribution in the 1D system, the heat flux into each reservoir may then be calculated. Moreover, the coefficient of performance may be derived from the expressions for the heat flux into the hot and cold reservoirs. The performance characteristic curves are plotted by numerical analysis. The influences of the resonances widths, the energy position of resonance and the space of two resonances on performance of the ESE refrigerator are discussed. The results obtained here have theoretical significance for the understanding of thermodynamic performance of the micro--nano devices.     

Accuracy of the equivalent circuit model using a fixed beamimpedance for klystron gain cavities

Most small-signal calculations of the modulation in a klystron's gain cavity use an equivalent circuit which includes a fixed beam impedance. Comparing this calculation to the gain calculated self-consistently, we note there are appreciable errors in both the calculated amplitude and phase of the cavity's modulation. These errors may lead to large accumulated errors in determining either the tube's small-signal or large-signal gain. Both techniques are used in a comparison with an existing S-band klystron     

风场探测干涉仪中基准光程差的选择原理

为了确定风场成像干涉仪（Wind Imaging Interferometer,WINDII）中存在的基准光程差的值,首先从风场探测机理出发,分析了影响基准光程差的因素.针对WINDII分别从调制度、相位及相近谱线同相的要求三个方面加以剖析,依次获得了它们与基准光程差之间的定量关系.综合考虑三个条件的要求,最终得出了基准光程差的选择原理.并用此理论对几种不同的风场成像干涉仪的基准光程差值进行了验证.     

Continuous-variable quantum teleportation of even and odd coherent states through varied gain channels

This paper has investigated quantum teleportation of even and odd coherent states in terms of the EPR entanglement states for continuous variables. It discusses the relationship between the fidelity and the entanglement of EPR states, which is characterized by the degree of squeezing and the gain of classical channels. It shows that the quality of teleporting quantum states also depends on the characteristics of the states themselves. The properties of teleporting even and odd coherent states at different intensities are investigated. The difference of teleporting two such kinds of quantum states are analysed based on the quantum distance function.     

Three dimensional gain analysis of free electron laser with focusing permanent magnet wiggler

A three dimensional simulation software system developed to estimate a free electron laser (FEL) gain has been applied to FEL using a standard plane polarized wiggler and an alternately shifted magnet wiggler. It is seen for the latter wiggler that a large filling factor could be selected and each maximum gain corresponding to each orbit of electron beam concentrates at a certain frequency region of FEL radiation. It is, therefore, implied that a proper shift between the adjacent magnets in the wiggler produces the improvement of the FEL gain.     

Dispersion properties of coupled waveguides with loss and gain: a full-vectorial analysis

Waveguide structures with a balance of loss and gain have been frequently discussed in the photonic community not only as photonic analogues of quantum-mechanical systems with parity-time (PT) symmetry (breaking), but also as components with potentially interesting technical applications. In this contribution, properties of mutually coupled photonic waveguides with loss and gain are numerically analyzed using our proprietary full-vectorial Fourier modal method. Beside the classical case of a directional coupler with a balance of loss and gain, more general waveguide coupler structures exhibiting the behaviour analogous to PT-symmetry breaking, potentially applicable for photonic switching, are analyzed, too. For applications, simultaneous mutually balanced change of both loss and gain is evidently impractical. For a directional coupler structure with loss in one channel and gain in the other channel it is shown by rigorous numerical modelling that the behaviour analogous to PT-symmetry breaking can be realized by varying gain (or loss) only. Finally, it is confirmed by rigorous numerical modelling that the exceptional point does exist also in a very high-contrast asymmetric structure of a plasmonic directional coupler with strongly localized gain in one channel.     

考虑钕玻璃放大器增益特性的光谱色散匀滑系统性能研究

采用数值方法研究了钕玻璃放大器的增益特性对高功率激光系统中光谱色散匀滑单元性能的影响.分析结果表明,入射光中心波长与放大器增益曲线中心波长不一致时,焦斑强度分布会受到一定的影响,且该影响随放大倍数增大趋于明显,而两个波长一致时,强度分布变化较小.靶面焦斑整体的辐照均匀性则主要取决于经过相位调制后的激光束的带宽,放大器的增益特性对其空间功率谱及均匀性无明显的影响.所得结论为光谱色散匀滑单元在激光系统中的实际应用提供了重要的理论参考.     

Stability analysis of fixed points via chaos control

This paper reviews recent advances in the application of chaos control techniques to the stability analysis of two-dimensional dynamical systems. We demonstrate how the system's response to one or multiple feedback controllers can be utilized to calculate the characteristic multipliers associated with an unstable periodic orbit. The experimental results, obtained for a single and two coupled diode resonators, agree well with the presented theory. (c) 1997 American Institute of Physics.     

Physical principles and methodology for investigating the frequency selective properties of randomly inhomogeneous channels with discrete opaque inhomogeneities

The characteristic features of experimental and theoretical investigations of the pass band in channels having discrete mutually screening inhomogeneities are analyzed. A comparison is made of methods and methodologies for measuring the delay spectra and the angular energy spectra of a multibeam field at a point of observation in such channels and in channels having continuously distributed “transparent” inhomogeneities. It is shown that when estimating the pass band in the former, the delay spectrum must be analyzed in a moving system of coordinates whose origin is coincident with the time of arrival of the first “beam.” A corresponding theoretical analysis is performed for the case when the “beam” arrival times form a nonsteady-state Poisson stream. State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 95–101, June, 1996.     

Theoretical analysis of gain characteristics of Dy-doped fiber amplifiers

The rate equations and power evolution equations of Dy³⁺-doped fiber amplifiers (DDFA) are proposed, and numerically analyzed. Based on the numerical analysis, several major characteristics of the fiber amplifier are calculated and compared with those of Pr³⁺-doped fiber amplifier (PDFA). The results show that DDFA can achieve better efficiency and wider gain bandwidth than PDFA.     

A moment method for analysis the gain spectrum in fiber Raman amplifier with broadband pumps

The governing equations of optical fiber Raman amplifier with broadband pumps in the steady state are systems of uncountable nonlinear ordinary differential equations (NODE). In this paper, the Moment method is used to reduce the uncountable system of NODE to a system of finite number of NODE. This system of equations is solved numerically. The results are compared with that of the full numerical method. It was shown that the Moment method is a precise and efficient technique for analysis of optical fiber Raman amplifier with broadband pumps.