基于DSP的脉阶调制器数字控制系统

鉴于目前国内大部分无线电台的短波发射机脉阶调制器控制系统以模拟方式实现的现状,本设计方案在现有的脉阶调制器技术基础上对其控制系统进行数字化、智能化改造。基于TMS320VC33的脉阶调制器数字控制系统采用单极性三角波对称规则同步取样改进算法实现PSM PWM调制,随后又给出了开关模块循环通断的实现方案。计算机仿真结果表明,此方法易于实现,实时性好、精度高。     

Including long-range dependence in integrate-and-fire models of the high interspike-interval variability of cortical neurons

Many different types of integrate-and-fire models have been designed in order to explain how it is possible for a cortical neuron to integrate over many independent inputs while still producing highly variable spike trains. Within this context, the variability of spike trains has been almost exclusively measured using the coefficient of variation of interspike intervals. However, another important statistical property that has been found in cortical spike trains and is closely associated with their high firing variability is long-range dependence. We investigate the conditions, if any, under which such models produce output spike trains with both interspike-interval variability and long-range dependence similar to those that have previously been measured from actual cortical neurons. We first show analytically that a large class of high-variability integrate-and-fire models is incapable of producing such outputs based on the fact that their output spike trains are always mathematically equivalent to renewal processes. This class of models subsumes a majority of previously published models, including those that use excitation-inhibition balance, correlated inputs, partial reset, or nonlinear leakage to produce outputs with high variability. Next, we study integrate-and-fire models that have (nonPoissonian) renewal point process inputs instead of the Poisson point process inputs used in the preceding class of models. The confluence of our analytical and simulation results implies that the renewal-input model is capable of producing high variability and long-range dependence comparable to that seen in spike trains recorded from cortical neurons, but only if the interspike intervals of the inputs have infinite variance, a physiologically unrealistic condition. Finally, we suggest a new integrate-and-fire model that does not suffer any of the previously mentioned shortcomings. By analyzing simulation results for this model, we show that it is capable of producing output spike trains with interspike-interval variability and long-range dependence that match empirical data from cortical spike trains. This model is similar to the other models in this study, except that its inputs are fractional-gaussian-noise-driven Poisson processes rather than renewal point processes. In addition to this model's success in producing realistic output spike trains, its inputs have long-range dependence similar to that found in most subcortical neurons in sensory pathways, including the inputs to cortex. Analysis of output spike trains from simulations of this model also shows that a tight balance between the amounts of excitation and inhibition at the inputs to cortical neurons is not necessary for high interspike-interval variability at their outputs. Furthermore, in our analysis of this model, we show that the superposition of many fractional-gaussian-noise-driven Poisson processes does not approximate a Poisson process, which challenges the common assumption that the total effect of a large number of inputs on a neuron is well represented by a Poisson process.     

Choosing Between Two Classification Learning Algorithms Based on Calibrated Balanced $$5\times 2$$ Cross-Validated F-Test

Ion-channel variability has critical effect on the spike initiation and propagation in nervous system. Noise can play a constructive role leading to increased reliability or regularity of neuronal firing and spike propagation in the nervous system. In this paper we show that memristors can be considered as an electronic analogous of the Hodgkin–Huxley ion channels not only in terms of threshold switching effect but also in terms of stochastic behavior. In other words, memristor can also implement stochastic version of Hodgkin–Huxley equation. Switching effect in memristive devices is thermodynamically driven, which is stochastic in nature. We show that if the intrinsic stochastic behavior of memristor is taken into account, memristor based neuristor can also implement stochastic version of Hodgkin–Huxley axon model in generation of action potential. Ion channel variability in neurons can be modeled by intrinsic stochastic behavior of memristor. We incorporate noise in the memristor model by adding white Gaussian noise to the deterministic part of dynamical state evolution function of the memristor. We study the reliability of spike timing for spike train generated by memristor based neuristor in which the noise included memristor model is used. Also, the reliability of spike propagation along thin axons is discussed. A series connection of neuristors can be used as an axon in which neuristor acts as a node of Ranvier on an axon. Probabilistic nature of spike propagation on thin axons can be modeled using neuristor in which the variability nature of memristor is included.     

一种用于无人机测控系统的DS-BPSK调制的实现

阐述了直扩BPSK调制原理,给出了调制模型,论述了基于FPGA和直接数字频率合成技术的DS-BPSK调制器的设计与电路实现;根据伪码的产生原理,给出了在FPGA中实现平衡Gold码的方法及时序仿真;针对调制器的测试结果,提出了提高频谱纯度的高斯滤波器的优化设计方法,实现了对上行信号的DS-BPSK调制;通过无人机测控系统的搭载实验与应用证明:该调制器不仅实现了遥控数据的扩频功能,而且解决了无人机数据链中上行数据加密和抗干扰问题,扩大了无人机无线电的控制距离。     

Distortion of neural signals by spike coding

Analog neural signals must be converted into spike trains for transmission over electrically leaky axons. This spike encoding and subsequent decoding leads to distortion. We quantify this distortion by deriving approximate expressions for the mean square error between the inputs and outputs of a spiking link. We use integrate-and-fire and Poisson encoders to convert naturalistic stimuli into spike trains and spike count and inter-spike interval decoders to generate reconstructions of the stimulus. The distortion expressions enable us to compare these spike coding schemes over a large parameter space. We verify that the integrate-and-fire encoder is more effective than the Poisson encoder. The disparity between the two encoders diminishes as the stimulus coefficient of variation (CV) increases, at which point, the variability attributed to the stimulus overwhelms the variability attributed to Poisson statistics. When the stimulus CV is small, the interspike interval decoder is superior, as the distortion resulting from spike count decoding is dominated by a term that is attributed to the discrete nature of the spike count. In this regime, additive noise has a greater impact on the interspike interval decoder than the spike count decoder. When the stimulus CV is large, the average signal excursion is much larger than the quantization step size, and spike count decoding is superior.     

基于FPGA的π/4-DQPSK调制设计

传统的π/4四相相对相移键控(π/4-DQPSK)调制器多采用模拟元件构建系统,易受环境因素影响、灵活性也较差。因此需要设计一个以数字信号处理为核心,开放性、灵活性较强的系统。系统采用软件无线电设计方法,在现场可编程门阵列(FPGA)上实现时输入码率1Mbps、中频为2MHz的π/4-DQPSK调制。结果表明,该方法可产生正确的调制波形。系统模块多用IP软核实现,易于修改和实现。     

The impact of spike timing variability on the signal-encoding performance of neural spiking models.

It remains unclear whether the variability of neuronal spike trains in vivo arises due to biological noise sources or represents highly precise encoding of temporally varying synaptic input signals. Determining the variability of spike timing can provide fundamental insights into the nature of strategies used in the brain to represent and transmit information in the form of discrete spike trains. In this study, we employ a signal estimation paradigm to determine how variability in spike timing affects encoding of random time-varying signals. We assess this for two types of spiking models: an integrate-and-fire model with random threshold and a more biophysically realistic stochastic ion channel model. Using the coding fraction and mutual information as information-theoretic measures, we quantify the efficacy of optimal linear decoding of random inputs from the model outputs and study the relationship between efficacy and variability in the output spike train. Our findings suggest that variability does not necessarily hinder signal decoding for the biophysically plausible encoders examined and that the functional role of spiking variability depends intimately on the nature of the encoder and the signal processing task; variability can either enhance or impede decoding performance.     

Error rate performance of Hybrid QAM-FSK in OFDM systems exhibiting low PAPR

Multicarrier transmission systems like orthogonal frequency division multiplexing (OFDM) support high data rate and generally require no equalization at the receiver, making them simple and efficient. This paper studies the design and performance analysis of a hybrid modulation system derived from multifrequency and MQAM signals, employed in OFDM. This modulation scheme has better bit error rate (BER) performance and exhibits low PAPR. The proposed hybrid modulator reduces PAPR while keeping the OFDM transc...     

二维复式晶格光控四波长太赫兹波调制器

给出的基于复式晶格光子晶体的太赫兹波调制器是一种用数字基带信号对太赫兹载波进行强度调制的外调制器。该调制器利用复式晶格一个点缺陷可同时调制两个缺陷模的特点来同时控制四束不同太赫兹波的传输,从而实现对太赫兹载波的通、断调制。这种基于复式晶格光子晶体的调制器具有光子禁带大、体积小,了等许多优点。     

Faraday optical phase modulator on microstructured spun fiber

Optical phase modulator on Faraday effect in microstructured spun fiber is suggested for current sensor. It is showed that such modulator has a high effectiveness which is closed to theoretical one if a period of modulation is more than transit time of light through the fiber. A variation of parameters of optical interferometer with incorporated modulator is experimentally studied under mechanical disturbances on modulator fiber ends. It is discovered that a relative variation of interferometer visibility factor is considerably more than a variation of magneto-optical sensitivity under identical disturbances.     

浅析WDM-PON的再调制方式

再调制波分复用无源光网络（WDM-PON）系统是将ONU端的光源用调制器来替代,就可以不用再ONU端配置光源设备大大降低了成本,也能够达到ONU“无色化”的技术方案。主要有两种实现再调制WDM-PON的方案：一种是采用马赫曾德尔调制器的直接调制方式,另一种是采用RSOA的光环回的再调制方式。而其中主要的是基于RSOA的再调制的WDM-PON系统,由于RSOA自身的一些优点使得它特别适合于再调制WDM-PON系统。     

一种矿用变频器滤波装置

矿用变频器与电动机通过长线电缆连接,脉宽调制(PWM)脉冲在传输过程中存在电压反射现象,从而引起电动机端产生尖峰电压,严重影响变频驱动系统的运行可靠性。目前,矿用隔爆变频器一般采用串联输出电抗器的方式来抑制尖峰电压,但抑制效果有限;而采用RC滤波装置和LRC滤波装置抑制尖峰电压的方法主要针对380,660 V变频器,不能满足煤矿井下1140 V变频器对尖峰电压的抑制要求。针对长线电缆远距离传输引起的尖峰现象,分析了实际应用中电动机负载、PWM上升时间及电缆长度对尖峰电压的影响:长线电缆终端反射系数对电动机负载的变化不敏感,在滤波参数的设计过程中可忽略电动机负载的影响;PWM上升时间越长,电缆长度越短,则电动机端尖峰电压越小。根据上述分析,结合电缆长度和装置功率损耗,提出了一种适用于煤矿井下1140 V变频器的LRC滤波装置设计方案,在PWM脉冲信号传入长线电缆之前,利用该LRC滤波装置延长PWM上升时间,达到抑制尖峰电压和高du/dt的目的。仿真和试验结果验证了该滤波装置的有效性。     

GMSK调制器的FPGA实现

GMSK（高斯最小移频键控）信号优良的频谱特性在跳频通信中有广阔的应用前景。本文分析了GMSK调制器的设计理论，给出了一种全数字实现结构并在FPGA上加以实现。仿真结果表明,这种数字实现结构产生的GMSK基带信号具有良好的功率谱及眼图，同时能够有效避免两条支路信号幅度及正交载波相位失衡。     

频率合成器中Σ-Δ调制器的设计与实现

本文首先介绍了Σ-Δ调制技术的基本原理,分析了一阶及高阶Σ-Δ调制器,最后结合一阶Σ-Δ调制器,给出了在FPGA器件上实现Σ-Δ调制器的设计。仿真结果表明,设计实现了Σ-Δ调制器,通过控制分频器实现了小数分频,方法简单易行。与运用Matlab软件仿真的结果完全一致,并进一步证实了高阶数字Σ-Δ调制对量化相位噪声的高通整形特性,从而有效地解决了小数分频频率合成器中的小数杂散问题,具有很高的实用性。     

高速2CPFSK调制器的设计与实现

针对小型飞行器数据链中信号传输速率的要求,介绍了二进制连续相位的FSK调制原理,提出了基于直接数字频率合成技术的2CPFSK调制器的设计与电路实现.给出了提高频谱纯度的椭圆函数型滤波器的设计,实现了对高速数字信号的2CPFSK调制.通过小型飞行器数据链图像信号的传输应用实验验证:该设计实现了程序自动调节频偏,得到了较小的调制指数,解决了小型飞行器数据链高速数据传输的问题.     

A chaotic communication system of improved performance based on the Derivative-free nonlinear Kalman filter

The Derivative-free nonlinear Kalman Filter is used for developing a communication system that is based on a chaotic modulator such as the Duffing system. In the transmitter’s side, the source of information undergoes modulation (encryption) in which a chaotic signal generated by the Duffing system is the carrier. The modulated signal is transmitted through a communication channel and at the receiver’s side demodulation takes place, after exploiting the estimation provided about the state vector of the chaotic oscillator by the Derivative-free nonlinear Kalman Filter. Evaluation tests confirm that the proposed filtering method has improved performance over the Extended Kalman Filter and reduces significantly the rate of transmission errors. Moreover, it is shown that the proposed Derivative-free nonlinear Kalman Filter can work within a dual Kalman Filtering scheme, for performing simultaneously transmitter–receiver synchronisation and estimation of unknown coefficients of the communication channel.     

基于压电陶瓷相位调制器的外调制相位生成载波法研究

对基于压电换能器PZT(Piezoelectric Transducer)的外调制相位生成载波PGC(Phase-Generated Carrier)法进行了深入的理论分析和实验研究.PZT光纤相位调制器利用电致伸缩效应来改变缠绕在其上面的光纤的长度,进而实现对光纤中光相位的周期性调制.在马赫曾德尔光纤干涉仪MZI(Mach-Zehnder Interferometer)的参考臂中加入该光纤相位调制器便可以将载波信号调制到光纤干涉仪的输出信号当中.计算机仿真分析了调制参数对PGC解调结果的影响.并通过实验验证了这种调制解调方案的可行性.利用美国国家仪器公司的数据采集系统及Labview编写的解调算法,在臂长为200 m的MZI中成功实现了相位解调,恢复出MZI传感臂中的原始相位信息,解调信号与原始信号的相关系数在0.99以上.     

A deterministic study of delta modulation

Delta modulation has often been viewed as a type of PCM and has been analyzed by probabilistic methods. This paper views delta modulation as a hybrid PDM/PAM system. A nonlinear feedback model is constructed and subjected to digital computation on an IBM 650. Computation is enabled by trapezoidal convolution, an approximateZ-transform method for solving dynamical systems. Responses to various steps and ramp inputs for unity and nonunity feedback are considered. Dead space is also introduced into the nonlinearity in the forward link. A series of computer runs is condensed and observations are reported. A typical observation is that a trade-off exists between average error and noise and that both may not be minimized by any one of two versions of the delta modulator.     

Analysis and modelling of variability and covariability of population spike trains across multiple time scales

As multi-electrode and imaging technology begin to provide us with simultaneous recordings of large neuronal populations, new methods for modelling such data must also be developed. We present a model of responses to repeated trials of a sensory stimulus based on thresholded Gaussian processes that allows for analysis and modelling of variability and covariability of population spike trains across multiple time scales. The model framework can be used to specify the values of many different variability measures including spike timing precision across trials, coefficient of variation of the interspike interval distribution, and Fano factor of spike counts for individual neurons, as well as signal and noise correlations and correlations of spike counts across multiple neurons. Using both simulated data and data from different stages of the mammalian auditory pathway, we demonstrate the range of possible independent manipulations of different variability measures, and explore how this range depends on the sensory stimulus. The model provides a powerful framework for the study of experimental and surrogate data and for analyzing dependencies between different statistical properties of neuronal populations.     

基于CORDIC算法的微小卫星发射机设计与实现

针对微小卫星测控应答机体积小、重量轻及其功能灵活的特点,研究了全数字调制发射机的实现方法。全数字调制加两次上变频的发射机结构,可以灵活的实现多种码速率、不同带宽、不同调制方式的调制信号。在全数字调制部分利用NCO和CORDIC算法实现数字频率合成器,不仅可以满足副载波、载波调制的频率精度要求,而且与传统的数字式频率合成技术相比占用了较少的硬件逻辑资源。在一块FPGA上实现了几种常用调制方式的VHDL代码,验证了该方案的可行性。基于CORDIC算法的全数字调制设计方案可以应用到其他可重构的软件无线电设计中。