检测性能约束下目标估计的波形优化设计

为了提高杂波背景下检测性能约束的扩展目标估计性能,提出一种基于凸优化和随机化方法的波形优化设计算法。文中考虑了实际雷达系统应用对目标检测性能的要求,定义了随机目标场景下的信杂噪比,并将之作为约束条件,以最大化接收回波与目标随机冲激响应之间的互信息作为优化准则,利用凸优化和随机化方法进行恒包络相位编码信号的设计。仿真实验结果表明,该算法获得的发射信号能够满足系统最低检测信杂噪比的要求,最大化互信息,提高了目标的估计性能,将扩展目标估计性能和检测性能有效统一起来。     

最大互信息准则下的认知MIMO雷达波形设计

针对杂波背景下对认知多输入多输出(MIMO)雷达波形设计研究较少的问题,提出了一种基于最大互信息准则的波形设计方法。该方法结合一般认知雷达波形设计模型,以雷达发射功率作为约束条件,以最大化目标与接收回波间的互信息为目标,对认知MIMO雷达的波形设计问题进行建模,并采用卡尔曼滤波一步预测的方法对快速运动扩展目标的冲激响应进行预测,实现对目标的精准估计;同时,基于上述分析采用最大能量分配的方法进行波形设计。仿真实验表明,与传统的线性调频信号(LFM)相比,文中所提方法可以获得更多的信息量。     

LMS-like AR modeling in the case of missing observations

This paper presents a new recursive algorithm for the time domain reconstruction and spectral estimation of uniformly sampled signals with missing observations. An autoregressive (AR) modeling approach is adopted. The AR parameters are estimated by optimizing a mean-square error criterion. The optimum is reached by means of a gradient method adapted to the nonperiodic sampling. The time-domain reconstruction is based on the signal prediction using the estimated model. The power spectral density is obtained using the estimated AR parameters. The development of the different steps of the algorithm is discussed in detail, and several examples are presented to demonstrate the practical results that can be obtained. The spectral estimates are compared with those obtained by known AR estimators applied to the same signals sampled periodically. We note that this algorithm can also be used in the case of nonstationary signals     

OFDM稀疏信道估计中基于树状随机搜索导频设计新方法

压缩感知（CS,Compressed Sensing）是一种以低速率对稀疏信号进行采样后在接收端重建信号的技术,基于CS的稀疏信道估计具有更小的导频开销且具有更好的信道估计性能。针对基于CS的OFDM稀疏信道估计中的导频设计问题,提出一种基于树状随机搜索算法（TSS,Tree-based Stochastic Search Algorithm）的导频位置设计新方法,该方法结合了树的结构,以分支的方式进行随机搜索从而避免陷入局部最优问题。仿真结果表明,与传统的导频设计方法相比,使用TSS算法获得的导频图案用于信道估计中能够获得更优的信道估计性能,而且TSS算法的复杂度更低。      

Structurally Constrained Receivers for Signal Detection and Estimation

A general approach to the problem of designing structurally constrained receivers for signal detection and estimation is proposed. The approach is based on the constrained Bayesian methodology wherein risk-minimizing inference (or decision) rules are modified (constrained) by replacement of true posterior probabilities with estimated posterior probabilities. The estimators are structurally constrained minimum-mean-squared-error (MMSE) estimators for random posterior probabilities. This methodology is, in essence, an extension and generalization of the well-known linear MMSE estimation methodology. The approach is employed to design linearly constrained coherent receivers for signals in additive and multiplicative noise, and quadratically constrained noncoherent receivers for signals in additive noise. An analysis of these receivers shows that they are very similar to those that are optimum for additive Gaussian noise. The methodology provides a unified theory of receiver design based on the constrained MMSE criterion. This unification yields new insight into this old approach, clarifying both strengths and weaknesses of the approach.     

基于多通道数据融合的跳频信号频率跳变时刻估计算法

针对低信噪比条件下宽带高速跳频信号的参数估计问题,提出一种多通道数据融合跳频信号频率跳变时刻估计算法。该算法利用无盲区数字信道化预处理实现宽带跳频信号的全概率、全盲接收,通过数据融合得到一路包含全部频率跳变信息的参考信号,并利用该参考信号进行最大似然估计得到频率跳变时刻精确估计值。给出了所提出跳变时刻估计算法的Cramer-Rao下界并进行实验仿真。理论推导和仿真结果表明:针对一定的输入信噪比,适当选择信道化数和估计时间可实现较高的估计精度。在0dB信噪比条件下,采用16通道数字信道化处理,估计方差小于10-3。      

一种基于Burg谱估计和FFT的频偏估计方法

针对星间链路通信中常用的BPSK、QPSK、UQPSK和64QAM等调制信号的载波频偏估计问题,提出了一种基于Burg谱估计和FFT的通用频偏估计方法。采用Burg谱估计方法对信号进行粗频偏估计,补偿该频偏后得到含有较小残留频偏的信号;并进行改进的四次方非线性变换,去除调制信息;再利用FFT估计出较高精度的残留频偏值。仿真结果表明,该方法估计精度高、范围大。     

新的盲信道估计算法

研究了各种盲信道估计算法.提出一种关于信道的假设,并在此基础上提出一种新的盲信道估计算法.新算法能够同时估计出信号和信道.新算法基于MMSE准则,利用m进制通信系统中,在接收端和发射端都已知信号模式且模式个数有限(K=log2m)的特点,结合预置于算法的信道模型,得到信道模型和信号模式的估计.然后依据MMSE准则得到信道和信号的最佳估计.最后给出仿真结果,仿真表明:新的盲信道估计方法能够精确估计实际信道的等效冲击响应,并能够进行有效通信.     

利用互模糊函数实现卫星干扰源定位

介绍了双星体制卫星干扰源定位系统工作的原理,对利用信号互模糊函数(CAF-Cross Ambiguity Function)定位参数估计进行了研究,分析了参数估计的时频特性和参数的时变性对估计方法的影响,提出了提高CAF参数估计性能的优化处理方法.通过对实际转发信号的参数估计和定位实验,证实了优化的CAF参数估计和定位方法的有效性.     

基于小波变换的MSK信号码速率盲估计

针对最小频移键控调制信号的码速率估计问题,提出一种基于Haar小波变换的MSK信号码速率盲估计方法。首先对接收信号作傅里叶变换得到信号频谱,对频谱频点分析粗估计信号的码速率,接着通过粗估计的码速率选取短时傅里叶变换窗函数长度和3个小波尺度,利用短时傅里叶变换得到信号瞬时频率变化,再利用小波的边缘检测特性对信号瞬时频率序列相位跳变点检测,最后对检测结果作频谱分析,估计频率得到MSK信号的码速率。仿真结果表明,高于信噪比门限时本算法可以对MSK信号码速率有效估计。     

基于提升小波与粒子群相结合的混沌信号降噪

提升小波变换用于混沌信号降噪具有良好的效果,阈值选取与混沌信号降噪后信号的畸变具有紧密联系。为了提高混沌信号中提升小波的自适应能力,降低降噪后信号的畸变率,提出了一种基于提升小波和粒子群相结合的混沌信号降噪方法。该方法在对提升小波变换后的细节部分进行阈值处理时,采用阈值自适应选择方法,并结合粒子群算法全局搜索最优阈值。通过对Colpitts模型进行仿真分析,与标准的软阈值降噪相比,能更好地对混沌信号降噪,并且降噪后信号失真度较小,具有很好的应用价值。     

Numerical optimization techniques applied to PPM signal design

A computer-oriented algorithm is developed for designing optimum waveforms for a pulse-position-modulation communication system. Nonlinear modulation threshold effects are incorporated directly into the design by introducing constraints on the sidelobe peaks of the autocorrelation function. The search is performed over the class of signals satisfying constraints on average power, peak power, and bandwidth. The optimum signal in this class is the one whose autocorrelation function has the sharpest central peak while the sidelobe peaks are below the specified constraint level. Numerical results for a realistic problem are presented, and the effect of introducing the correlation and peak power constraints is studied. It is shown that a large reduction in the sidelobe peaks is possible with relatively little loss in the sharpness of the central peak.     

Optimal periodic training signal for frequency offset estimation in frequency-selective fading channels

This paper addresses an optimal periodic training signal design for frequency offset estimation in frequency-selective multipath Rayleigh fading channels. For a fixed transmitted training signal energy within a fixed-length block, the optimal periodic training signal structure (the optimal locations of identical training subblocks) and the optimal training subblock signal are presented. The optimality is based on the minimum Cramer-Rao bound (CRB) criterion. Based on the CRB for joint estimation of frequency offset and channel, the optimal periodic training structure (optimality only in frequency offset estimation, not necessarily in joint frequency offset and channel estimation) is derived. The optimal training subblock signal is obtained by using the average CRB (averaged over the channel fading) and the received training signal statistics. A robust training structure design is also presented in order to reduce the occurrence of outliers at low signal-to-noise ratio values. The proposed training structures and subblock signals achieve substantial performance improvement.     

基于稀疏贝叶斯学习的多跳频信号DOA估计方法

针对多跳频信号空域参数估计问题,该文在稀疏贝叶斯学习(SBL)的基础上,利用跳频信号的空域稀疏性实现了波达方向(DOA)的估计。首先构造空域离散网格,将实际DOA与网格点之间的偏移量建模进离散网格中,建立多跳频信号均匀线阵接收数据模型;然后通过SBL理论得到行稀疏信号矩阵的后验概率分布,用超参数控制偏移量和信号矩阵的行稀疏程度;最后利用期望最大化(EM)算法对超参数进行迭代,得到信号矩阵的最大后验估计以完成DOA的估计。理论分析与仿真实验表明该方法具有良好的估计性能并能适应较少快拍数的情况。     

Fast detection and DOA estimation of the unknown wideband signal sources

The direction of arrival (DOA) estimation analysis requires prior knowledge of frequency‐related information of the incident wideband signals, eg, center frequency and bandwidth, which are not available in many cases. This research is based on applications where DOA estimation of the wideband signal source is unknown, eg, in astronomy and unauthorized transmissions. Therefore, this paper has two major contributions. The first contribution is to identify the frequency spectrum of the wideband signals transmitted from an unknown source. The method use edge detection prestage to identify the frequency spectrum of the received signal. The second contribution is to estimate the DOA of the wideband signal at higher accuracy while keeping a minimum computational cost. The estimation of the DOAs was analyzed by measuring the orthogonal relationship between the signal and the noise subspaces of multiple frequency components of the sources. The introduced method utilizes subband as a reference frequency based on the extracted frequency‐related information rather than examining the complete incoming signal spectrum and exploits the spatial information of a few subbands. The introduced algorithm is implemented based on the well‐known method, test of orthogonality of projected subspaces (TOPS). Tests are conducted on a range of wideband signals with extreme values of signal‐to‐noise ratio (SNR). Considerable performance improvement is obtained.     

Signal Design for Bandwidth Efficient Multiple Access under Asymptotic Effective Energy Constraints

The problem of signal design for bandwidth-efficient multiple access (BEMA) over additive white Gaussian noise (AWGN) channels is addressed under quality of service (QoS) requirements specified by asymptotic effective energies (AEEs). The AEE characterizes the bit error rate (BER) in the low-noise regime, but in contrast to BER, it is tractable and amenable to analysis and signal design. We adopt the BEMA strategy of bandwidth conservation where users are detected successively using minimum mean-squared error decision feedback (MMSE-DF) detection and where signals are designed in a greedy fashion for one user at a time, in the reverse order in which the users are detected. The signal design method proposed here is based on an exact characterization of how a signal update for one user affects the issue of preserving bandwidth with the addition of signals for subsequent users. A geometric insight in the construction of good signal sets and significant improvements in bandwidth over full-rank or orthogonal signaling are obtained. The main result of this paper can hence be seen as providing a tight upper bound on the minimum signature sequence dimension or rank (and hence bandwidth) needed to satisfy individual, possibly distinct user QoS constraints specified in terms of the AEE measure.     

多径传播条件下宽带线性调频信号波达方向估计方法

针对信号出现多径传播情况时现有宽带信号波达方向（direction of arrival, DOA）估计方法性能下降的问题,提出了一种多径传播条件下宽带线性调频（chirp）信号波达方向估计方法,该方法将导向有效投影（steered effective projection, STEP）技术与宽带线性调频信号的时频特性相结合,对具有不同时频特性的信号分量进行分离,逐个处理,并以时频分布矩阵代替传统的协方差矩阵,从而构造有效噪声子空间,实现时域角度估计。本方法无需进行信号聚焦操作,因此理论上不受聚焦误差的影响。仿真结果验证了所提方法的有效性。      

Comparison of the non linear energy operator and the Hilbert transform in the estimation of the instantaneous amplitude and frequency

The instantaneous amplitude (ai) and frequency (fi) parameters of a biomedical signal can be useful for identification of signal physiological states or state changes. In this article the features ai and fi of simulated and experimental (real EEG and ECG) signals, are estimated using three methods: one based on the Hilbert Transform (HT), a modified version of this that improves the fi estimation in experimental signals (HTM), and the energy separation algorithm (DESA1), based on Teager’s energy operator (TEO). The algorithm comparison is made using the average relative error obtained in the signals’ demodulation process, their noise sensitivity, and computational efficiency. The obtained results showed that the HTM method produces the least fi estimation errors in noisy signals, and depending on the kind of signal considered, DESA1 and HTM methods produce the least ai estimation errors.     

Subspace Smoothing for Direction of Arrival Estimation in DS-CDMA Systems

In this paper a subspace processing method is introduced that can be used for direction of arrival estimation of coherent signals in an asynchronous DS-CDMA system. Conventional methods of direction of arrival estimation are not directly applicable to the case of multiple coherent signals that impinge on an antenna array from different directions. Some preprocessing is essential prior to estimation in this case. The proposed method exploits the spreading code and the path delays of the desired user to eliminate the contribution of undesired paths in the signal subspace. To this end, the signal subspace is mapped to a new subspace which contains the spatial-temporal signature of the desired signal. Once the desired subspace is created, conventional methods such as MUSIC and ESPRIT can be employed to estimate the desired directions of arrival. It is proved that the obtained direction of arrival estimator, based on the proposed method, is consistent. Also, the estimation performance is evaluated by comparing the proposed method with conventional estimation methods.     

基于Cadence的DDRⅡ仿真设计

针对DDRⅡ设计中高速信号的完整性和时序匹配问题,使用EDA工具Cadence仿真设计了DDRⅡ存储器的印制板。通过Cadence软件建立DDRⅡ信号拓扑结构、仿真信号的串扰、码间干扰、过冲等与信号质量相关的参数,从仿真波形中可以测量出与信号时序相关的参数,从而计算出信号的时序裕量,并为DDRⅡ信号设置约束进行布线。布线完成后,使用Cadence软件进行板后仿真,验证DDRⅡ信号的完整性和时序关系。并根据仿真结果,总结出部分设计规则。