基于ULV更新算法的DS-CDMA自适应检测研究

通过研究多径信号码空间和数据矢量空间,采用噪声子空间技术进行异步DS-CDMA系统期望信号矢量估计,以利于把盲线性滤波优化技术应用于稳健的干扰抑制。提出一种修改的ULV更新算法进行噪声子空间跟踪,该算法不需要相关矩阵的秩估计,直接估计噪声子空间,不进行信号子空间跟踪。仿真结果验证了该文算法的有效性。     

Implementation of low-swing differential interface circuits for high-speed on-chip asynchronous interconnection

A novel low-swing interface circuit for high-speed on-chip asynchronous interconnection is proposed in this paper. It takes a differential level-triggered latch to recover digital signal with ultra low-swing voltage less than 50 mV, and the driver part of the interface circuit is optimized for low power using the driver-array method, With a capacity to work up to 500 MHz, the proposed circuit, which is simulated and fabricated using SMIC 0.18-pm 1.8-V digital CMOS technology, consumes less power than previously reported designs.     

The multiple-parameter fractional Fourier transform

The fractional Fourier transform （FRFT） has multiplicity, which is intrinsic in fractional operator. A new source for the multiplicity of the weight-type fractional Fourier transform （WFRFT） is proposed, which can generalize the weight coefficients of WFRFT to contain two vector parameters m,n ∈ Z^M . Therefore a generalized fractional Fourier transform can be defined, which is denoted by the multiple-parameter fractional Fourier transform （MPFRFT）. It enlarges the multiplicity of the FRFT, which not only includes the conventional FRFT and general multi-fractional Fourier transform as special cases, but also introduces new fractional Fourier transforms. It provides a unified framework for the FRFT, and the method is also available for fractionalizing other linear operators. In addition, numerical simulations of the MPFRFT on the Hermite-Gaussian and rectangular functions have been performed as a simple application of MPFRFT to signal processing.     

Low-complexity 2D coherently distributed sources decoupled DOAs estimation method

The existing directions-of-arrival (DOAs) estimation methods for two-dimensional (2D) coherently distributed sources need one- or two-dimensional search, and the computational complexities of them are high. In addition, most of them are designed for special angular signal distribution functions. As a result, their performances will degenerate when deal with different sources with different angular signal distribution functions or unknown angular signal distribution functions. In this paper, a low-complexity decoupled DOAs estimation method without searching using two parallel uniform linear arrays (ULAs) is proposed for coherently distributed sources, as well as a novel parameter matching method. It can resolve the problems mentioned above efficiently. Simulation results validate the effectiveness of our approach. Supported by the National Natural Science Foundation of China (Grant No. 60772146), and the Program for New Century Excellent Talents in University (Grant No. NCET-05-0806)     

Min-max model predictive control for constrained nonlinear systems via multiple LPV embeddings

A min-max model predictive control strategy is proposed for a class of constrained nonlinear system whose trajectories can be embedded within those of a bank of linear parameter varying (LPV) models. The embedding LPV models can yield much better approximation of the nonlinear system dynamics than a single LTV model. For each LPV model, a parameter-dependent Lyapunov function is introduced to obtain poly-quadratically stable control law and to guarantee the feasibility and stability of the original nonlinear system. This approach can greatly reduce computational burden in traditional nonlinear predictive control strategy. Finally a simulation example illustrating the strategy is presented. Supported by the National Natural Science Foundation of China (Grant Nos. 60774015, 60825302, 60674018), the National High-Tech Research & Development Program of China (Grant No. 2007AA041403), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20060248001), and partly by Shanghai Natural Science Foundation (Grant No. 07JC14016)     

A digital authentication watermarking scheme for JPEG images with superior localization and security

The drawbacks of the current authentication watermarking schemes for JPEG images, which are inferior localization and the security flaws, are firstly analyzed in this paper. Then, two counterferiting attacks are conducted on them. To overcome these drawbacks, a new digital authentication watermarking scheme for JPEG images with superior localization and security is proposed. Moreover, the probabilities of tamper detection and false detection are deduced under region tampering and collage attack separately. For each image block, the proposed scheme keeps four middle frequency points fixed to embed the watermark, and utilizes the rest of the DCT coefficients to generate 4 bits of watermark information. During the embedding process, each watermark bit is embedded in another image block that is selected by its corresponding secret key. Since four blocks are randomly selected for the watermark embedding of each block, the non-deterministic dependence among the image blocks is established so as to resist collage attack completely. At the receiver, according to judging of the extracted 4 bits of watermark information and the corresponding 9-neighbourhood system, the proposed scheme could discriminate whether the image block is tampered or not. Owing to the diminishing of false detection and the holding of tamper detection, we improve the accuracy of localization in the authentication process. Theoretic analysis and simulation results have proved that the proposed algorithm not only has superior localization, but also enhances the systematic security obviously. Supported by the National Natural Science Foundation of China (Grant No. 60572027), the Program for New Century Excellent Talents in University of China (Grant No. NCET-05-0794), the Sichuan Youth Science & Technology Foundation (Grant No. 03ZQ026-033), the National Defense Pre-research Foundation of China (Grant No. 51430804QT2201) and the Application Basic Foundation of Sichuan Province, China (Grant No. 2006 J13-10)     

On the linear span of the p -ary cascaded GMW sequences

In this paper, a recursion is derived to compute the linear span of the p-ary cascaded GMW sequences. It is the first time to determine the linear span of the p-ary cascaded GMW sequence without any restriction on the parameters completely. Whereas, the known result on the p-ary cascaded GMW sequence with the specific parameters in the literature could be viewed as a special case of the new result. Supported by the National Natural Science Foundation of China (Grant No. 60302015), the Foundation for the Author of National Excellent Doctoral Dissertation of China (Grant No. 200341), and Sichuan Youth Science Foundation (Grant No. 04ZQ026-048)     

SAR-GMTI investigation in hybrid along- and cross-track baseline InSAR

A joint-pixel clutter suppression method based on slope compensation is proposed in this paper. In order to eliminate the effect of the terrain interferometric phase caused by the cross-track baseline in hybrid baseline InSAR, the local independent identical distribution of the clutter is satisfied by using the slope compensation technique, and thus the clutter can be suppressed successfully by using the orthogonality of the clutter subspace and the noise subspace. This approach utilizes the information contained in the current pixel as well as in its neighbors, showing robustness to the image coregistration errors. Both the simulated data and the real airborne data are used in proving the validity of the presented approach. Supported in part by the National Nature Science Foundation of China (Grant No. 60802074) and the Program for New Century Excellent Talents in University     

Efficient Optimization of Multiple Subspace Skyline Queries

We present the first efficient sound and complete algorithm （i.e., AOMSSQ） for optimizing multiple subspace skyline queries simultaneously in this paper. We first identify three performance problems of the na/ve approach （i.e., SUBSKY） which can be used in processing arbitrary single-subspace skyline query. Then we propose a cell-dominance computation algorithm （i.e., CDCA） to efficiently overcome the drawbacks of SUBSKY. Specially, a novel pruning technique is used in CDCA to dramatically decrease the query time. Finally, based on the CDCA algorithm and the share mechanism between subspaces, we present and discuss the AOMSSQ algorithm and prove it sound and complete. We also present detailed theoretical analyses and extensive experiments that demonstrate our algorithms are both efficient and effective.     

SNR estimation algorithm based on the preamble for wireless OFDM systems

Based on the analysis of the performance of Boumard＇s SNR method for wireless orthogonal frequency division multiplexing （OFDM） systems, a new estimation algorithm of the noise variance is proposed by only using the data samples of the two training symbols in the preamble, and the second order moment of these data samples is employed to estimate the signal power. The average SNR and the SNRs on the subchannels can all be estimated by the proposed algorithm, and its performance is independent of the channel＇s frequency selectivity. Simulation results show that the performance of the proposed method is highly improved and much better than that of Boumard＇s method.     

Oversampling analysis in fractional Fourier domain

Oversampling is widely used in practical applications of digital signal processing. As the fractional Fourier transform has been developed and applied in signal processing fields, it is necessary to consider the oversampling theorem in the fractional Fourier domain. In this paper, the oversampling theorem in the fractional Fourier domain is analyzed. The fractional Fourier spectral relation between the original oversampled sequence and its subsequences is derived first, and then the expression for exact reconstruction of the missing samples in terms of the subsequences is obtained. Moreover, by taking a chirp signal as an example, it is shown that, reconstruction of the missing samples in the oversampled signal is suitable in the fractional Fourier domain for the signal whose time-frequency distribution has the minimum support in the fractional Fourier domain. Supported partially by the National Natural Science Foundation of China for Distinguished Young Scholars (Grant No. 60625104), the National Natural Science Foundation of China (Grant Nos. 60890072, 60572094), and the National Basic Research Program of China (Grant No. 2009CB724003)     

Forward/backward prediction solution for adaptive noisy FIR filtering

An important and hard problem in signal processing is the estimation of parameters in the presence of observation noise. In this paper, adaptive finite impulse response (FIR) filtering with noisy input-output data is considered and two developed bias compensation least squares (BCLS) methods are proposed. By introducing two auxiliary estimators, the forward output predictor and the backward output predictor are constructed respectively. By exploiting the statistical properties of the cross-correlation function between the least squares (LS) error and the forward/backward prediction error, the estimate of the input noise variance is obtained; the effect of the bias can thereafter be removed. Simulation results are presented to illustrate the good performances of the proposed algorithms. Supported by the National Natural Science Foundation of China for Distinguished Young Scholars (Grant No. 60625104), the Ministerial Foundation of China (Grant No. A2220060039) and the Fundamental Research Foundation of BIT (Grant No. 1010050320810)     

Hermite variational implicit surface reconstruction

We propose a new technique for reconstructing surfaces from a large set of unorganized 3D data points and their associated normal vectors. The surface is represented as the zero level set of an implicit vol-ume model which fits the data points and normal constraints. Compared with variational implicit sur-faces,we make use of surface normal vectors at data points directly in the implicit model and avoid of introducing manufactured off-surface points. Given n surface point/normal pairs,the proposed method only needs to solve an n×n positive definite linear system. It allows fitting large datasets effectively and robustly. We demonstrate the performance of the proposed method with both globally supported and compactly supported radial basis functions on several datasets.     

New delay-dependent criterion for the stability of recurrent neural networks with time-varying delay

This paper is concerned with the global asymptotic stability of a class of recurrent neural networks with interval time-varying delay. By constructing a suitable Lyapunov functional, a new criterion is established to ensure the global asymptotic stability of the concerned neural networks, which can be expressed in the form of linear matrix inequality and independent of the size of derivative of time varying delay. Two numerical examples show the effectiveness of the obtained results. Supported by the National Natural Science Foundation of China (Grant Nos. 60534010, 60728307, 60774048, 60774093), the Program for Cheung Kong Scholars and Innovative Research Groups of China (Grant No. 60521003) and the National High-Tech Research & Development Program of China (Grant No. 2006AA04Z183), China Postdoctoral Sciencer Foundation (Grant No. 20080431150), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 200801451096)     

Performance analysis of a random ARQ initialized cooperative communication protocol in shadowed Nakagami-<Emphasis Type="Italic">m</Emphasis> wireless channel

In this paper, we develop and analyze an energy efficient ARQ (automatic repeat request) initialized transmit diversity protocol for cooperative communications. Medium access control (MAC) layer packet retransmission limit (similar to aShortRetryLimit or aLongRetryLimit [802.11–1997]) has been used as an actuator for transmit cooperative diversity initialization. We take the channel state information (CSI) as a function of retransmission tries and the number of retransmission tries is modeled as a random variable. Relays close to the source node are chosen for the transmit cooperation. Closed form expressions are obtained for symbol error rate (SER), outage capacity and outage probability for the proposed scheme in shadowed fading channels. This cooperative scheme achieves lower signal-to-noise ratio (SNR), stumpy outage probability, higher bandwidth, and transmit energy efficiencies for desired average symbol error rate (ASER) than the preceding ARQ based cooperative protocols. Finally, the results of computer simulations are included to demonstrate the efficacy of the proposed scheme and to verify the accuracy of the analytical expressions. Supported by the National Natral Science Foundation of China (Grant No. 60602058), the National High Technology Research and Development Program of China (Grant No. 2006AA01Z257)     

Theory of （n） truth degrees of formulas in modal logic and a consistency theorem

The theory of (n) truth degrees of formulas is proposed in modal logic for the first time. A consistency theorem is obtained which says that the (n) truth degree of a modality-free formula equals the truth degree of the formula in two-valued propositional logic. Variations of (n) truth degrees of formulas w.r.t. n in temporal logic is investigated. Moreover, the theory of (n) similarity degrees among modal formulas is proposed and the (n) modal logic metric space is derived therefrom which contains the classical logic metric space as a subspace. Finally, a kind of approximate reasoning theory is proposed in modal logic. Supported by the National Natural Science Foundation of China (Grant Nos. 10331010 and 10771129), and the Foundation of 211 Construction of Shaanxi Normal University     

传输损耗条件下基于循环平稳检测的空时分组码盲识别方法

针对传输损耗条件下空间复用（SM）和Alamouti空时分组码的盲识别问题,提出一种单接收天线下的基于循环平稳检测的盲识别算法。首先通过理论推导,证明Alamouti空时分组码具有循环频率的特性;然后,求取接收信号的四阶循环累积量来观察循环频率;最后使用循环平稳检测的方法,构造检测不同空时分组码循环频率的假设检验,从而对2种码的接收信号进行区分。该方法可在单接收天线下进行,蒙特卡洛仿真结果表明,该算法不需要预先知道信道信息、调制方式、载波相位和时间偏移,不需要精确知道载波频偏,识别效果较好。     

Fast frequency-domain equalization for single-carrier V-BLAST systems over multipath channel

A low complex minimum mean-square error frequency-domain decision feedback (MMSE-FDDF) equalization algorithm is proposed in this paper for the single-carrier V-BLAST systems. Exploiting the factor that the discrete Fourier transform (DFT) is unitary, the proposed receiver can equalize the signals by the MMSE detecting to the spectrums in the frequency domain instead of the waveforms in the time domain. In order to obtain the right decisions, the detector must be able to equalize the overall spectrum with regard to each layer. This work can be performed very efficiently since the system matrix has been designed as a special block-circulant-block matrix. Similar to other V-BLAST-like systems, the detecting order has strong impact on the performance of MMSE-FDDF. Therefore, we further give a fast optimally sorting scheme for the MMSE-FDDF architecture. By using the newly constructed matrix, the coefficients computation and the sorting can be combined into one process, and then we employ the modified Gram-Schmidt (MGS) to simplify the process. The simulation results and the computational complexity analysis show that the proposed MMSE-FDDF has better tradeoff between the performance and the complexity than the existing algorithms. In addition, MMSE-FDDF can avoid the performance floor caused by the overlap-and-save technique in the severe dispersive channel. Supported partially by the National Natural Science Foundation of China (Grant Nos. 60572046, 60502022, 60772095), the National High-Tech Research and Development Program of China (“863” Program)(Grant No. 2006AA01Z220)     

Multiple accumulated-crossover parallel concatenated SPC codes

By constructing an accumulated-crossover relationship in multiple parallel concatenated single parity check (M-PC-SPC) codes, a class of error-correcting codes, termed multiple accumulated-crossover parallel concatenated single parity check (M-ACPC-SPC) codes, is proposed. M-ACPC-SPC codes possess linear encoding complexity and can be decoded iteratively with low complexity by the sum-product algorithm (SPA). Simulation results show that M-ACPC-SPC codes have lower error floors than M-PCSPC codes with the same dimension, and when the dimension is 5, M-ACPC-SPC codes achieve bit error rate (BER) better than (3, 6) regular low density parity check (LDPC) codes. Supported by the National High-Tech Research & Development Program of China (Grant No. 2007AA01Z288), the National Science Fund for Distinguished Young Scholars (Grant No. 60725105), the Program for Changjiang Scholars and Innovative Research Team in University and the 111 Project (Grant No. B08038)     

Solution to the Generalized Champagne Problem on simultaneous stabilization of linear systems

The well-known Generalized Champagne Problem on simultaneous stabilization of linear systems is solved by using complex analysis and Blondel’s technique. We give a complete answer to the open problem proposed by Patel et al., which auto-matically includes the solution to the original Champagne Problem. Based on the recent development in automated inequality-type theorem proving, a new stabiliz-ing controller design method is established. Our numerical examples significantly improve the relevant results in the literature.