基于半定松弛的长码DSSS信号扩频波形估计

针对非合作通信中的长码DSSS信号,提出了一种基于半定松弛的扩频波形估计方法,并在确定信号模型下推导了扩频波形估计的CRB.首先推导了长码DSSS信号扩频波形的极大似然估计,由于该极大似然估计为非凸的组合优化问题,提出通过松弛约束条件将其转化为具有多项式计算复杂度的半定规划问题,实现对该极大似然估计问题的近似求解.仿真表明本文提出方法性能优于现有方法,并随着信噪比的提高逐渐逼近CRB.     

一种特征波提取速率自适应的波形内插语音编码方案

该文提出了一种特征波形提取速率自适应于输入语音帧特性的波形内插编码方案。基于双加权长时预测增益最大原则并利用前向基音判决实现了较为可靠的基音周期估计算法,用基音周期、浊音度和波表面平坦度决定波形提取速率以及SEW(Slowly Evolving Waveform)和REW(Rapidly Evolving Waveform)的更新速率。实验证明,该文提出的波形内插(WI)编码算法相比固定波形提取速率的WI算法在平均码率和计算复杂度上均有一定程度的降低,且合成语音质量明显优于4.8kbps的CELP语音编码算法。     

一种高效DSO波形显示算法的实现

介绍一种应用于液晶显示的数字存储示波器波形显示的算法。通过分析相邻采样数据之间的大小关系,得到逼近波形的系列直线段;通过分析不同通道直线段的位置关系,得到最佳的线段合成效果;通过分析待清除线段和需绘制线段的位置关系,得到最优的清除和绘图列表。算法可有效地提升示波器的显示速度。     

Concatenated orthogonal/PN spreading sequences and theirapplication to cellular DS-CDMA systems with integrated traffic

In this paper, we investigate the application of the concatenated orthogonal/PN spreading scheme for a cellular direct sequence code-division multiple access (DS-CDMA) system with integrated traffic. The performance of the system is evaluated in terms of user capacity. In order to incorporate traffic with a wide range of source rates, line rates (adjusted data rates before spreading) have to be selected for transmission. For traffic with source rates higher than the line rate of concern, we propose the use of concatenated orthogonal/PN spreading sequences to subdivide a high rate stream into parallel line rate streams. Therefore, in this paper, we first analyze the properties of the concatenated orthogonal/PN spreading sequences. The results are used to evaluate their performance for homogenous voice traffic in various cellular mobile environments with multipath fading, lognormal shadowing, and path loss. Our results show that the proposed spreading scheme offers a significant improvement in the forward link capacity as compared to using the conventional nonconcatenated long PN sequence, especially if the multipath fading is Rician (e.g., microcellular and indoor picocellular systems). Incorporating the notion of line rate, we then evaluate the performance of a system with integrated voice and video traffic. Special emphasis is placed on the effect of line rate selection on the overall capacity which leads to the optimal selection of line rates     

汉明距离发生器实现方案的研究

汉明距离是用来衡量2个二进制码字之间的相似程度的,本文主要针对用FPGA实现的汉明距离发生器,详细研究了其关键部件累加器的几种实现方案,给出了波形仿直结果时延及战胜FPGA资料的统计结果,提出了一种能大在缩短电路时延、提高运算速度并节省资源的实现方案,最终用FPGA实现并应用于一种卫星通信的帧同步系统中。     

GLRT receivers for UWB systems

This letter investigates generalized-likelihood-ratio-test (GLRT) detectors for ultra-wideband (UWB) impulse radio systems employing two alternative signaling schemes. One is the so-called transmitted reference method where, in each time frame, a reference pulse is transmitted prior to the data pulse. The other is the differential transmitted reference scheme, wherein the data pulse received in the previous frame is used as a template waveform in the current frame. The two detectors are compared in terms of bit error rate performance.     

32 Mbit/s Transmission of NTSC Color TV Signals by Composite DPCM Coding

A composite DPCM coding System was developed, which is capable of coding and transmitting an NTSC color TV signal without component separation at a 32.064 Mbit/s rate. The DPCM prediction method used is based on the algorithm that a luminance component prediction valuehat{y}and a carrier chrominance component prediction valuehat{c}are calculated individually, and then the composite signal prediction valuehat{x}is determined byhat{x} = hat{y} + hat{c}. In order to utilize horizontal blanking (HBL) intervals for transmitting active video signals,HBL signals are not transmitted in each line but their representative signals are transmitted once a frame during a vertical blanking interval. A dual word-length coding and quantizing method is adopted, which uses 4 bit and 8 bit words with average word-lengths of 4.4 bits/sample. Codec equipment was fabricated, and coding and transmitting experiments were conducted, using NTT's PCM-100 M digital repeatered line. Experimental results show that this composite DPCM coding system can be employed for digital transmission of NTSC color TV signals, such as color ITV signals, at a 32.064 Mbit/s rate.     

An optimal signal design for band-limited asynchronous DS-CDMAcommunications

An optimal signal design for band-limited, asynchronous, direct-sequence code-division multiple-access (DS-CDMA) communications with aperiodic random spreading sequences and a conventional matched filter receiver is considered in an additive white Gaussian noise (AWGN) channel. With bandwidth defined in the strict sense, two optimization problems are solved under finite bandwidth and zero interchip interference constraints. First, a chip waveform optimization is performed given the system bandwidth, the data symbol transmission rate, and the processing gain. A technique to characterize a band-limited chip waveform with a finite number of parameters is developed, and it is used to derive optimum chip waveforms which minimize the effect of multiple-access interference (MAI) for any energy and delay profile of users. Next, a joint optimization of the processing gain and the chip waveform is performed, given the system bandwidth and the data symbol transmission rate. A sufficient condition for a system to have lower average probability of bit error for any energy profile is found, and it is used to derive some design strategies. It is shown that the flat spectrum pulse with the processing gain leading to zero excess bandwidth results in the minimum average probability of bit error. Design examples and numerical results are also provided     

Effects of Digital Demodulation on Component Coding of NTSC Color Signals

Effects of nonideal filtering in the digital demodulation of the composite NTSC signal into luminance and chrominance components on the coding of the luminance component are discussed. The residual chrominance component is shown to cause degradation in prediction and/or motion detection algorithms which are based on line or frame difference signals. Simple techniques for reducing these effects using chrominance-band rejection filters are presented and the efficacy of these methods are verified by simulation.     

Time-domain scattering parameters of an exponential transmissionline

The scattering parameters of an exponential line are studied in detail in both the frequency and time domains. By taking the causality condition into consideration, the time-domain scattering parameters are cast in a rapid-convergence power series. Each term of the power series represents a signal component generated by the exponential line when the signal travels a round trip. The time-domain scattering parameters of an exponential line lay the foundation for studies of interaction between nonuniform lines and linear/nonlinear loads, and pulse waveform alteration in the time domain     

Theoretical analysis of M-ary/SS communication systems using racingcounters and a Hadamard matrix

The performance of M-ary spread spectrum (M-ary/SS) communication systems is discussed. Firstly, the initial acquisition time is evaluated. Secondly, the retention time, which is the average number of frames holding correct frame timing, and the recovery time, which is the average number of frames required to establish synchronization, are derived. Lastly, the bit-error rate (BER) performance is evaluated. M-ary/SS communication systems, which have more than one spreading code, can improve the BER performance under conditions in which there is additive white Gaussian noise (AWGN). However, the synchronization of M-ary/SS communication systems is difficult because they have several spreading codes. The frame synchronization method uses a Hadamard matrix and “racing counters.” As a result, the retention time becomes longer than the recovery time when the size of the lower counter differs greatly from that of the upper counter in the racing counters. Then the BER gets close to the performance which is achieved under complete synchronization     

A model-based estimator-correlator (EC) structure

The estimator-correlator (EC) is the optimal (maximum likelihood) detector for Gaussian (or exponentially distributed) signals embedded in similarly distributed interference and is applicable to the detection of delay Doppler spread sonar echoes. A discrete EC representation is derived by expanding continuous echo time series data with basis functions that are replications of the transmitted waveform. Scattering function (SF) models of the echo and backscattered interference spreading processes comprise prior information that is required for EC implementation. The effects of SF misinformation are illustrated by comparing the receiver operating characteristics (ROC curves) for the EC with perfect information, a mismatched EC with partial information, and the ideal but unrealizable prescient receiver. An EC implementation called hop code EC (HOPEC) is proposed that uses a frequency-shift-keyed (FSK) waveform (hop code) and is implemented with efficient FFT processing. Prior SF information is introduced via the frequency domain data covariance matrix, the elements of which are obtained as the Fourier transforms of the echo and interference scattering functions. The associated matrix Frobenius norm is shown to be a measure of the underlying scattering function variance and serves as a scalar spreading characteristic     

Spectral characterisation and frame synchronisation of optical fibre digital PPM

The discrete time decoding of data in pulse position modulation calls for accurate timing synchronisation, particularly at the frame rate. The spectral properties of optical fibre digital PPM are considered. An original expression is presented for predicting the spectrum and it is shown that, unlike satellite PPM, a component exists at the frame rate which may be used for timing extraction purposes. Further, it is illustrated that the modulation index can be used to enhance this component by up to 19 dB. This has been verified practically, with the results agreeing to within 1 dB of those predicted from the original expression presented.<>     

一种220GHz 波段太赫兹合成孔径成像雷达

微波频段的机载合成孔径成像雷达在对地观测方面具有广泛应用,但其合成孔径成像积累时间长,成像帧率低,提高雷达工作频率能够减小合成孔径所需转角,提高成像帧率。设计了一种工作在220GHz 波段的太赫兹合成孔径成像雷达系统,采用收发天线分置、发射宽带线性调频连续波的体制,最大信号带宽4. 8GHz,输出信号功率约20mW。宽带回波信号幅度相位经外标校补偿,通过成像试验,验证了太赫兹ISAR 与SAR 成像分辨率约3.2cm,可实现5Hz 的成像帧率,证明太赫兹波段能够大幅提升成像帧率,满足快速成像的要求。     

机载MIMO雷达收发联合降维STAP算法统一理论框架

该文研究了机载多输入多输出（Multiple-Input Multiple-Output,MIMO）雷达杂波抑制的收发联合降维空时自适应处理（Space Time Adaptive Processing,STAP）算法统一理论框架。首先,基于机载MIMO雷达发射波形分集的特性,构建了机载MIMO雷达降维联合自适应STAP处理的统一理论框架结构。在此基础上,建立了3种降维STAP处理结构。最后,针对上述3种降维结构,给出了相应的3类适用于MIMO体制的降维STAP处理算法。仿真实验表明:机载MIMO雷达联合降维自适应算法具有较好的杂波抑制性能和较强的抗干扰能力。      

Differential Addressing of Clusters of Changed Picture Elements for Interframe Coding of Videotelephone Signals

In a conditional replenishment coder for videotelephony only those picture elements (pels) which have changed significantly since the previous frame are transmitted. The amplitudes as well as the locations of these pels within the frame must be sent. In [2] locations are sent by addressing clusters of changed pels with respect to the beginning of the line. Increased addressing efficiency results if clusters of changes are positioned not with respect to the beginning of the line, but with respect to another cluster in the previous line or previous frame which has already been transmitted. Computer simulations using digitally stored videotelephone signals were carried out to evaluate such differential schemes. Results showed that differential addressing of this type and the use of variable word-length codes can yield about a 50 percent saving in bits required to address beginnings of clusters. The overall bit rate saving is much smaller, however, ranging from 10-15 percent depending on the efficiency with which pel amplitudes are coded.     

基于缺失数据模型的长码直扩信号的伪码估计

 在信号截获应用背景下,提出了一种新的缺失数据模型用于长码直扩信号的盲同步和伪码估计.在同步环节中,传统短码同步算法Frobenius范数最大法被扩展至缺失数据模型并验证了渐进有效性;在伪码估计环节,提出了一种低计算复杂度的用于加权低秩逼近的交替投影算法.由于本文提出的方法能够直接利用接收数据,而不仅仅是它的自相关矩阵,仿真表明其性能明显好于传统的只依赖自相关矩阵的算法,特别是在短数据场合.     

64位声表面波可编程抽头延迟线

本文叙述了一种64位声表面波可编程抽头延迟线的结构及性能参数,采用专门设计的有源三极管作开关阵列单元,获得一个时钟速率大于1MHz,可编程速率为15kbit/s的器件。该器件性能基本满足系统实验要求,但在稳定性及波形一致性方面有待进一步提高。     

引入直接序列扩频的线列阵通信信道均衡技术

在空间多径信道垂直线列阵通信中,由于多阵元码间干扰导致信道失衡,误码率较高,需要进行信道均衡设计。传统方法采用随机码扩频方法进行通信信道均衡,扩频信号经高放和混频后导致非线性失真,均衡效果不佳。文中提出一种基于直接序列扩频的线列阵通信信道均衡算法。基于PTRM技术构建了垂直线列阵通信的空间多径信道模型,采用直接序列扩频方法设计码间干扰抑制算法,利用垂直线列阵结构对PTRM时间压缩性能,接收到的扩频信号经高放和混频后,对中频扩频的调制信号进行相关解扩,重组多垂直线列阵的径分量,实现信道均衡。仿真结果表明,采用该算法进行垂直线列阵通信,信道均衡性能和码间干扰抑制性能较好,并有效降低了误比特率,改善了通信质量。     

A Model-Based Controller for A Three-Phase Four-Wire Shunt Active Filter With Compensation of the Neutral Line Current

This paper presents a model-based controller for a three-phase four-wire shunt active filter, which uses a three-leg split-capacitor topology to implement the voltage source inverter. The controller is aimed to compensate reactive power and harmonic distortion in the general case of distorted and unbalanced source voltages and load currents, including distorted loads connected between a phase and the neutral line. In addition, the controller is able to compensate for the homopolar component of the load current, that is, the current flowing to the source via the neutral line can be considerably reduced without modifying the actual topology. The complete model in (fixed frame) alphabetagamma-coordinates is presented. Special attention is given to the homopolar component (referred here as the gamma-component) of the line current, source voltage and control input, which are instrumental for the control design purpose. Experimental results in a 2 kVA prototype are provided to illustrate the benefits of the proposed solution.