Analysis of a hybrid series parallel resonant bridge converter

The steady-state operation of a hybrid series parallel resonant bridge is analyzed. Two expressions are derived for the power output as a function of capacitor ratio, switching frequency, and conversion ratio. One power output expression is for conversion ratios less than or equal to one, and the other expression is for conversion ratios greater or equal to one and less than or equal to two. The optimum conversion ratio for maximum power transfer is also derived     

Simple formula giving spectrum-narrowing ratio of semiconductor-laser output obtained by optical feedback

The letter presents a theory of the spectrum-narrowing effect of semiconductor lasers by optical feedback. A simple formula for the 3 dB spectral width is derived as a function of the intensity and phase of the returning beam and the round-trip time of the feedback circuit. The spectrum-narrowing ratio of a GaAlAs laser with a small amount of optical feedback was measured as a function of the optical feedback power ratio. The derived formula and experiment show very good agreement.     

A bound on the multiple scattered power from a plasma medium

A measure of the validity of the first Born approximation for scattering from an inhomogeneous plasma is obtained. This measure is derived using the inequalities appropriate to quadratically summable functions and bounded operators. A simple upper bound for the ratio of multiple scattered power to first Born power is derived as a function ofB, the sufficiency condition for the convergence of the series.     

Performance of polarization diversity in correlated nakagami-m fading channels

This paper analyzes the performance of systems with dual-polarized antennas in correlated Nakagami-m fading channels as a function of envelope correlation and cross-polarization discrimination by means of the characteristic function of the instantaneous post-maximal ratio combining (MRC) signal-to-noise ratio (SNR). Systems of interest include systems with receive polarization diversity and systems with transmit and receive polarization diversity employing Alamouti space-time code. The expressions for the average symbol error probability as a function of SNR assuming no power control, and the expressions for the average required transmit power to achieve the constant desired post-MRC SNR assuming perfect fast power control, are derived. Finally, a comparison between analytical and simulation results is used to validate the analysis.     

过采样OFDM信号峰均功率比统计特性分析

对连续正交频分复用信号所构成的随机过程进行分析,得到任意时刻之间信号相关性的解析表达式,并将其推广到任意过采样率情况下进行了讨论。随着过采样率增加,采样点之间相关性迅速上升,新增加采样点对信号峰值平均功率比的影响下降。分析和仿真结果表明,在过采样率为Nyquist采样率的2倍时,采样点之间可以近似满足相互独立同分布的关系,并得到此时信号峰值平均功率比概率分布的理论表达式。     

Co-channel interference in cellular radio systems using frequency hopping code division multiple access (FH-CDMA)

The expected interference power in a digital cellular radio system using frequency hopping code division multiple access is investigated. The up-link only is considered. Using both analytical and numerical methods, a probability density function for this power is derived. This function is used to predict the hop erasure probability of a system, as a function of the tolerable signal to interference ratio and of the system load.Mr. Al-Etaibi is sponsored by Saudi Telecom     

连续混沌调频雷达信号分析

该文给出了连续混沌调频信号(CCFMS)的数学表达式,理论推导了CCFMS的自相关函数和均方根带宽。结果表明CCFMS自相关函数的旁瓣抑制性能优异;其均方根带宽与调频指数、混沌信号的均方根成正比。仿真计算了典型混沌产生的CCFMS性能,进一步证明了CCFMS具有较高的时间峰值旁瓣比、平坦的功率谱形状、近似图钉型的模糊函数和与正弦发射信号相同的峰均功率比。分析了CCFMS雷达的抗噪声干扰性能,与线性调频信号雷达相比,信干比改善因子提高约5.5 dB。     

Capacity analysis of M-SC receivers over TWDP fading channels

An expression for the probability distribution function (PDF) of the signal-to-noise ratio of a selection combining receiver in two-wave with diffuse power fading channel is derived. Using this PDF expression, the capacity for the different adaptive transmission techniques employing selection combining (SC) are obtained. The study presents the effects of the ratio of total dominant signal power to the scattered signal power on the system capacity. The change in the capacity of the system with the diversity order for a SC receiver in the fading channel is also presented.     

Beam efficiency limitations of large antennas

The beam efficiency of an antenna may be defined as the ratio of the power radiated within the main beam to the total power radiated. The beam efficiency is derived for ideal rectangular and circular apertures, as a function of the edge-to-center amplitude ratio. Random phase errors are assumed to exist across the aperture. Various types of feeds for parabolic reflectors are also considered in relation to the fraction of power which the feed directs into the paraboloid. A primary limitation on the beam efficiency of a paraboloid is shown to be produced by the surface roughness.     

Optimization in scaling fiber-coupled laser-diode end-pumped lasersto higher power: influence of thermal effect

The optimum mode-to-pump ratio in scaling fiber-coupled laser-diode end-pumped lasers to higher power has been investigated by including the thermal effect into the space-dependent rate equation analysis. The optical path difference (OPD) distribution has been derived as a function of the pump-beam quality, focus position of pumping light, and pump radius at the focal plane under the assumption that the end faces of the crystal are thermally insulated. The diffraction losses arising from thermally induced spherical aberration have been estimated by the Strehl intensity ratio. The present results for the optimum mode-to-pump ratio are markedly different from previous analyses in which thermal effects are neglected. Here, the optimum mode-to-pump ratio is a decreasing function of input pump power, and is less than unity in the case of a slightly high pump power. The practical example of a Nd:YAG laser pumped by a 13-W fiber-coupled laser diode is considered to confirm our physical analysis     

Average block error probability in the reverse link of a packetDS/CDMA system under Rayleigh fading channel conditions

Analytic expressions have been derived for the probability density functions of the total signal-to-interference ratio when considering mixed-type interference sources in the reverse link of a DS/CDMA packet radio system with Rayleigh fading. Four different scenarios were studied, and the corresponding expressions are presented for each situation. The users are divided into two groups: those that apply a closed-loop power control and those that only use an open-loop power control. By making use of these expressions, the mean block error probability is derived as a function of the number of total interfering users in each group     

非对称信道下协作通信系统中断概率的研究

首先建立了非对称信道下协作系统的数学模型,考虑了源节点到目的节点的直通链路,利用特征函数法推导出协作系统的平均中断概率公式,通过仿真验证了该中断概率公式的精确性,理论和仿真都表明协作系统的中断概率和中继节点的个数、位置分布以及协作系统的功率分配因子有着密切关系,并且考虑源到目的节点的直通链路相对于不考虑直通链路的情况具有更高的性能增益;然后又在此公式基础卜就协作系统中继节点的位置分布对最优功率分配因子的影响进行了仿真分析,并指出协作系统的最优功率分配因子受制于中继节点的位置分布情况.     

幂函数分布的振幅型光瞳滤波器

为了提高衍射远场显微成像的分辨率,采用一种振幅透过率随半径呈幂函数分布的光瞳滤波器进行了理论分析和数值模拟。通过在光路中加入幂函数分布的振幅型光瞳滤波器,利用标量衍射理论推导出夫琅禾费衍射分布的计算公式;通过MATLAB软件给出衍射图样,对比衍射分布的主瓣宽度。结果表明,当幂次数为3时,模拟仿真的衍射分布斯特雷尔比为0.16,最大旁瓣强度比为0.1,分辨参量为0.76,分辨率提高倍数为1.3;随着振幅透过率幂次数的增加,主瓣宽度依次减小;同时也伴随着主瓣强度降低和旁瓣强度增大的缺点。这一研究对于远场光学显微镜实现超分辨成像是有帮助的。     

Performance Analysis of Rayleigh Fading Channel in the Presence of Co-channel Interference with Multiple Interferers Under Different Adaptation Policies

In this paper, an approach to performance analysis on signal-to-interference ratio operating over Rayleigh fading channels experiencing an arbitrary number of multiple, Rayleigh co-channel interferers is presented. We have presented a general analysis of selection combining, where each branch experiences an arbitrary number of multiple equal power co-channel interference. Useful closed-form expressions are derived for the probability density function and cumulative distribution function at the output of the combiner. Also, outage analysis is performed in order to show the effects of interferers and diversity order. Capacity per unit bandwidth expressions are derived for selection diversity scheme under different adaptation policies.     

Space telemetry degradation due to Manchester data asymmetryinduced carrier tracking phase error

The author analyzes the deleterious effects that the Manchester (or Bi-φ) data asymmetry has on the performance of phase-modulated residual carrier communication systems. Expressions for the power spectral density of an asymmetric Manchester data stream, the interference-to-carrier signal power ratio (I/C), and the error probability performance are derived. Since data asymmetry can cause undesired spectral components at the carrier frequency, the I/C ratio is given as a function of both the data asymmetry and the telemetry modulation index. Further, the data asymmetry and asymmetry-induced carrier tracking loop and the system bit-error rate to various parameters of the models are presented     

Distribution of SIR and performance of DS-CDMA systems inlognormally shadowed Rician channels

New closed form expressions for the probability density function and the cumulative distribution function of the ratio of L_S Rician signals to L_I Rician interferers, so-called signal-to-interference (SIR) power ratio, are derived. These SIR distributions are then used to evaluate the error probability and capture probability of direct sequence code division multiple access systems operating in Rician faded channels with lognormal shadowing. The influence of various system parameters such as the Rice K factor, shadowing spread, number of interferers, and spread spectrum processing gain on the system performance are analyzed and discussed     

On the channel capacity for constant envelope signals witheffective bandwidth constraint

The problem of the optimization of the information rate with an assigned cost function is addressed. In the case of a constant envelope channel with a prescribed effective bandwidth as a cost function, an expression of the channel capacity is derived in the presence of Gaussian noise for large values of signal-to-noise ratio. The analysis of the optimum source statistics has also shown that the source signal is Gaussian, and therefore its autocorrelation function and power spectral density have been determined in terms of the required channel capacity     

基于能效最优准则的双跳中继网络功率分配算法

针对单天线多跳系统中的资源分配策略进行了研究,重点研究了基于能效最优的功率分配算法。所提算法以系统能效最大化为设计目标,以满足指定的系统服务质量(QoS, quality of service)为约束条件,建立了以源节点和中继节点发射功率为设计变量的数学优化模型。通过大信噪比区间近似等效,将原始的非凸优化问题转化为凸优化问题。再利用拉格朗日对偶函数凸优化算法,并借助于Lambert 函数,最终得到一种功率分配方案的闭合形式解,避免了采用交替迭代方法来求解最优化问题。相比传统以系统频谱效率最大化为目标的算法,所提算法能更好地提升系统整体能效,同时降低了功率分配算法的复杂度。     

存在同信道干扰和多用户分集的多蜂窝系统性能分析

考虑存在来自其他蜂窝的不同功率同信道干扰的多用户上行链路,分析了基站采用多用户调度和最大比合并接收时的系统性能.在期望信号和干扰信号分别为Nakgami-m和Rayleigh时,运用基于概率密度函数的性能分析法推导了系统中断概率和平均误符号率(ASER)的闭合表达式.仿真结论显示,系统中断概率和ASER的解析曲线与数值仿真结果一致,系统性能随着天线数和用户数的增大而提升,多天线和多用户分集增益明显,干扰功率有较大差异时系统中断概率性能有所下降.     

Improved energy detector for random signals in gaussian noise

New and improved energy detector for random signals in Gaussian noise is proposed by replacing the squaring operation of the signal amplitude in the conventional energy detector with an arbitrary positive power operation. Numerical results show that the best power operation depends on the probability of false alarm, the probability of detection, the average signal-to-noise ratio or the sample size. By choosing the optimum power operation according to different system settings, new energy detectors with better detection performances can be derived. These results give useful guidance on how to improve the performances of current wireless systems using the energy detector. It also confirms that the conventional energy detector based on the generalized likelihood ratio test using the generalized likelihood function is not optimum in terms of the detection performance.