卫星量子通信的光子偏振误差影响与补偿研究

针对采用偏振编码的卫星量子通信中的偏振保持问题,研究了大气散射和卫星与地面站间相对运动对量子偏振态相位和对准的具体影响。仿真分析了量子偏振态相位延迟和对准误差对系统量子误码率影响,提出了一种新的BB84协议与半波片旋转相结合的偏振补偿方案。该方案通过对准提前量补偿的加入弥补原有补偿方案补偿过程中不能进行通信的缺陷,可基本实现零角度偏振误差,保证卫星量子通信的安全可靠性,且因该方案仅需在原有系统上添加一个半波片,易于实现。     

超混沌复系统的自适应广义组合复同步及参数辨识

该文针对含未知参数的异结构超混沌复系统,基于自适应控制及Lyapunov稳定性理论,提出一种新的自适应广义组合复同步方法 (GCCS)。首先给出广义组合复同步的定义,将驱动-响应系统的同步问题转化为误差系统零解的稳定性问题;然后从理论上设计了非线性反馈同步控制器及参数辨识更新律,并引入误差反馈增益,以控制同步的收敛速度;最后以超混沌复Lorenz系统、超混沌复Chen系统、超混沌复L系统的广义组合复同步与参数估计为例,从数值仿真角度验证了所提方法的正确性和有效性。     

Spectrally encapsulated OFDM: Vectorized structure with minimal complexity

To efficiently use frequency resources, the next 6th generation mobile communication technology must solve the problem of out-of-band emission (OoBE) of cyclic prefix (CP) orthogonal frequency division multiplexing (OFDM), which is not solved in 5th generation technology. This study describes a new zero insertion technique to replace an existing filtering scheme to solve this internal problem in OFDM signals. In the development of the proposed scheme, a precoder with a two-dimensional structure is first designed by generating a two-dimensional mapper and using the specialty of each matrix. A spectral shaping technique based on zero insertion instead of a long filter is proposed, so it can be applied not only to long OFDM symbols, but also very short ones. The proposed method shows that the transmitted signal is completely blocked at the bandwidth boundaries of signals according to the current standards, and it is confirmed that the proposed scheme is ideal with respect to bit error rate (BER) performance because its BER is the same as that of CP-OFDM. In addition, the proposed scheme can transformed into a real time structure through vectorizing process with minimal complexity.     

Time-spreading wavelength-hopping optical CDMA system using EWO and TCM

In this paper, time-spreading wavelength-hopping optical CDMA system using trellis coded modulation scheme is investigated. The carrier hopping prime code and its shifted version are employed as signature sequences. Since the carrier hopping prime code is a symmetric code, the out of phase autocorrelation is zero. Applying the orthogonality of the signature sequences, the ternary transmission mechanism can be achieved. The proposed coding scheme is simple in both transmitter and receiver. As the multiple access interference and beat noise are the major deterioration of system performance, using coding scheme is an effective way to reduce the error floor. The numerical results reveal that the proposed coding scheme can significantly improve the system performance.     

Digital repetitive learning controller for three-phase CVCF PWMinverter

In this paper, a plug-in digital repetitive leaning control scheme is proposed for three-phase constant-voltage constant-frequency (CVCF) pulsewidth modulation inverters to achieve high-quality sinusoidal output voltages. In the proposed control scheme, the repetitive controller (RC) is plugged into the stable one-sampling-ahead-preview-controlled three-phase CVCF inverter system using only two voltage sensors. The RC is designed to eliminate periodic disturbance and/or track periodic reference signal with zero tracking error, The design theory of plug-in repetitive learning controller is described systematically and the stability analysis or overall system is discussed. The merits of the controlled systems include features of minimized total harmonic distortion, robustness to parameter uncertainties, fast response, and fewer sensors. Simulation and experimental results are provided to illustrate the effectiveness of the proposed scheme     

Alamouti code based on block repetition in FBMC/OQAM systems

In this paper, we address the Alamouti code in Filter-Bank Multicarrier with Offset Quadrature Amplitude Modulation (FBMC/OQAM) and propose a novel block-wise Alamouti code, in which a repeated block is designed to eliminate the imaginary interference among FBMC/OQAM symbols. The proposed approach exhibits a higher spectral efficiency than the conventional block-wise Alamouti scheme, as only one column of zero symbols is used as a guard interval instead of two. Furthermore, compared to the conventional scheme, the bit error ratio is improved in the proposed block-wise Alamouti, as the assumption on channel invariance at two adjacent subcarriers is not required. Simulation results indicate that, with a significantly reduced overhead, the proposed Alamouti scheme achieves better performance over the conventional block-wise Alamouti scheme.     

频率选择性信道下高速数据传输中的单载波频域均衡技术

本文利用空时联合检测的方法，提出了在频率选择性信道下多天线发送的单载波频域均衡方案，它可以提供和一个发送天线多个接收天线单载波系统相同的分集增益，和单载波时域均衡相比具有低的复杂度。分析了信道估计误差对系统的影响，类似于基于迫零算法的线性均衡器的情形，在低信噪比下，信道估计误差对系统影响很大，给出了一种简单的克服方法。在不增加发射功率的情况下，使用信道编码可以进一步改善系统的性能。本方案的系统性能在6径典型城市信道模型下进行了评估，仿真的结果证明了本方案的有效性。     

MIMO OFDM排序判决反馈检测方法

一般多天线系统的判决反馈检测方法中,是顺序检测每用户天线端接收信号,其缺点是若从前面若干幅接收天线检测出的信号误差较大,则会降低后续天线端检测性能.为解决该问题,本文提出一种排序判决反馈检测方法,其思想先对待检测的用户天线支路排序,利用计算预测误差获得的待检测天线支路对应信道逆阵向量是已检测天线支路对应信道逆阵向量的线性组合特征,应用正交变换求解获得用户天线支路的检测顺序,使当前待检测用户天线端的迫零向量与已检测用户天线支路的迫零向量正交,这样可使由已检测用户天线支路带来的判决反馈误差最小,进而提高了检测性能.     

Progressive image transmission by transform coefficient residualerror quantization

A progressive image transmission scheme based on iterative transform coding structure is proposed for application in interactive image communication over low-bandwidth channels. The scheme not only provides progressive transmission, but also guarantees lossless reproduction combined with a degree of compression. The image to be transmitted undergoes an orthogonal transform, and the transform coefficients are quantized (scalar or vector) before transmission. The novelty is that the residual error array due to quantization is iteratively fedback and requantized (scalar or vector); the coded residual error information is progressively transmitted and utilized in reconstructing the successive approximations. It is shown that the average reconstruction error variance converges to zero as the number of iterative stages approaches infinity. In practice, lossless reproduction can be achieved with a small number of iterations by using an entropy coder on the final residual-error image. Computer simulation results demonstrate the effectiveness of the technique     

Mobile speed estimation based on average fade slope duration

Based on the zero crossing rate of the slope (first derivative) of the underlying fading process, a mobile speed-estimation scheme, constructed by counting the average number of sampling steps in a positive-going (and/or negative-going) fade envelope slope, is proposed. The proposed speed-estimation approach requires neither knowledge of the average fade power nor a variable temporal observation window. The computational complexity and the required memory storage are negligibly small. Simulation results show that the proposed speed estimator yields good estimation accuracy, with relatively small estimation error.     

Three New Unconditionally-Stable FDTD Methods With High-Order Accuracy

Three novel finite-difference time-domain (FDTD) methods based on the split-step (SS) scheme with high-order accuracy are presented, which are proven to be unconditionally stable. In the first novel method, symmetric operator and uniform splitting are adopted simultaneously to split the matrix derived from the classical Maxwell's equations into six sub-matrices. Accordingly, the time step is divided into six sub-steps. The second and third proposed methods are obtained by adjusting the sequence of the sub-matrices deduced in the first method, so all the novel methods presented in the paper have similar formulations, of which the numerical dispersion errors and the anisotropic errors are lower than the alternating direction implicit finite-difference time-domain (ADI-FDTD) method, the initial SS-FDTD method and the modified SS-FDTD method based on the Strang-splitting scheme. Specifically, for the second method, corresponding to a certain cell per wavelength (CPW), there is a Courant number value making the numerical anisotropic error to be zero, while in the third novel method, corresponding to a certain Courant number value, there exists a CPW making the numerical anisotropic error to be zero. In order to demonstrate the high-order accuracy and efficiency of the proposed methods, numerical results are presented.     

A new 2-D systolic digital filter architecture without global broadcast

In this paper, we propose two-dimensional (2-D) systolic-array infinite-impulse response (IIR) and finite-impulse response (FIR) digital filter architectures without global broadcast, by the hybrid of a modified reordering scheme and a new systolic transformation. This architecture has local broadcast, lower-quantization error, and zero latency without sacrificing the number of multipliers, as well as delay elements under the satisfactory critical period. Furthermore, we extend this new architecture to a useful 2-D systolic cascade-form architecture and provide the comprehensive error analysis for the proposed architectures.     

Adaptive Iterative Learning Control for a Class of Uncertain Nonlinear Systems with Second-Order Sliding Mode Technique

This paper addresses the problem of robust adaptive iterative learning control for a chain of uncertain integral nonlinear systems, whose aim is to stabilize the tracking error of the system and improve convergence speed in the presence of uncertainties. In response to unknown bounded disturbances, a continuous second-order sliding mode adaptive iterative learning control scheme is proposed, in which an integral term is to attenuate the effects of the disturbances and achieve fast convergence performance. By designing a suitable controller and composite energy function, it is proved that the tracking error along iterative learning horizon will converge to a small neighborhood of zero. Numerical examples are provided to validate the efficacy of the proposed method.     

A turbo-coded hybrid ARQ for low earth orbit microsatellite communications

A proposed turbo-coded hybrid ARQ designed for improving the throughput of UoSAT/SSTL LEO microsatellite downlink communications is presented. The flexibility and robust error correcting capability of turbo codes are incorporated adaptively into the existing ARQ protocol. The proposed scheme optimizes the increment of coding parity and schedules the decoding iterations to take place during intervals between microsatellite passes. Simulations show a remarkable improvement over the existing protocol, giving more than 84% gross throughput or 69% net throughput at channel bit error rate of 5×10⁻³, whereas with the current protocol the throughput would be close to zero. Copyright © 1999 John Wiley & Sons, Ltd.     

A space vector-based rectifier regulator for AC/DC/AC converters

A voltage-sourced rectifier control scheme for use with AC/DC/AC variable speed drives is presented. A control scheme is derived that directly calculates the duration of time spent on the zero state and on each switching state adjacent to the reference vector, over a constant switching interval, in order to drive the line current vector to the reference vector. In addition, under transient conditions, when deadbeat control is not possible, a control scheme is presented that ensures that the line current vector is driven in the direction of the reference current vector. The current reference for the rectifier controller is derived from the bus voltage error and a feedforward term based on the estimated converter output power. The proposed space vector-based rectifier regulator is shown to exhibit improved harmonic and transient performance over existing per-phase duty cycle prediction methods, especially at modulation indices near unity. The deadbeat control of the rectifier input current is accomplished every half-cycle with constant switching frequency while still symmetrically distributing the zero state within the half-cycle period     

A novel detection criterion for weak m-ary signals and its application to ultrawideband multiple access systems

In this paper, we propose a novel criterion for the detection of weak m-ary signals. In the sense of minimizing the error probability, the proposed criterion is optimal when the signal strength approaches zero. Based on the proposed criterion, a detection scheme for ultrawideband multiple access systems is proposed and analyzed in the presence of impulsive interference. Numerical results show that the proposed detector requires less complexity than, and possesses almost the same performance as, the maximum likelihood detector. In impulsive interference, the proposed detector also offers significant performance improvement over the detector optimized for a Gaussian environment.     

基于零知识证明的电子现金

在零知识证明系统的基础上提出了一种不同于以往的构造电子现金的方案。它不基于特定的盲签名方案和零知识证明系统,从而提供了基于任意零知识证明系统和盲签名方案构筑电子现金的方法。在合理的密码学假设前提下,证明了方案的安全性。     

A Full Rate Quasi‐orthogonal STF‐OFDM with DAC‐ZF Decoder over Wireless Fading Channels

In this letter, we propose a quasi‐orthogonal space‐time‐frequency (QOSTF) block coded orthogonal frequency division multiplexing (OFDM) that can achieve full symbol rate with four transmit antennas. Since the proposed QOSTF‐OFDM cannot achieve full diversity, we use a diversity advantage collection with zero forcing (DAC‐ZF) decoder to compensate the diversity loss at the receiving side. Due to modulation advantage and collected diversity advantage, the proposed scheme exhibits a better bit‐error rate performance than other orthogonal schemes.     

A New Audio Watermarking Scheme Based on Singular Value Decomposition and Quantization

In this paper, we propose a new robust and blind audio watermarking algorithm based on singular value decomposition and quantization index modulation. The watermark insertion and extraction methods are based on quantization of the norm of singular values of the blocks. Audio quality evaluation tests show high imperceptibility of the watermark in the audio signal. Simulation results demonstrate that this algorithm is robust against signal-processing and stirmark attacks. The false negative error probability under the proposed scheme is close to zero. Moreover, the proposed algorithm has higher data payload and better performance than the other related audio watermarking schemes available in the literature.     

Cooperative interference power allocation in physical layer security under imperfect time synchronization

In physical layer security,considering imperfect time synchronization,a power allocation scheme was proposed to maximize the system secrecy capacity.By analyzing the residual interference power at the authorized receiver caused by imperfect time synchronization,the optimal power distribution method was given,and the relationship between the optimal interference power and the relative channel quality was discussed.Theory and simulation analysis show that when the synchronization error is small,the synchronization error consumes extra power to reach the preset secrecy capacity,and the interference power increases with its increase.As the synchronization error increases,the secrecy capacity of the system gradually fails to reach the preset target,and may even drop to zero.