Near theoretical upper bound new loosely synchronous complementary spreading sequences

A new class of loosely synchronous (LS) spreading sequences with zero correlation window (ZCW) was presented. It was constructed by making Kronecker product of orthogonal matrix and ZCW complementary sequences. This new LS sequence increases the number of perfect complementary pairs and extends ZCW within the same group. Moreover, both auto-correlation and cross-correlation of ZCW in the same group remain identical. The minimum ZCW among different groups is the same as that of basic LS sequences. The method for constructing these new LS sequences is presented and ZCW properties are also verified. The number of these new LS sequences is only smaller than theoretical upper bound by one. __________ Translated from Journal of Beijing University of Posts and Telecommunications (Natural Science), 2007, 30(2): 1–5 [译自: 北京邮电大学学报 (自然科学版)]     

Medical image lossless compression based on combining an integer wavelet transform with DPCM

To improve the classical lossless compression of low efficiency, a method of image lossless compression with high efficiency is presented. Its theory and the algorithm implementation are introduced. The basic approach of medical image lossless compression is then briefly described. After analyzing and implementing differential plus code modulation (DPCM) in lossless compression, a new method of combining an integer wavelet transform with DPCM to compress medical images is discussed. The analysis and simulation results show that this new method is simpler and useful. Moreover, it has high compression ratio in medical image lossless compression. __________ Translated from Journal of Northeastern University (Natural Science), 2007, 28(10): 1454–1457 [译自 : 东北大学学报 (自然科学版)]     

An AM-RLC scheme with adaptive acknowledgement interval

The acknowledged mode radio link control (AM-RLC) protocol is one of the most important radio protocols in wideband code division multiple access (WCDMA) and time division-synchronization code division multiple access (TD-SCDMA) mobile communication systems. A modified AM-RLC scheme with adaptive acknowledgement interval is proposed. At the receiver, the acknowledgement interval is dynamically changed according to the channel status. The simulation results show that the proposed AM-RLC scheme outperforms the fixed acknowledgement interval AM-RLC scheme in terms of frame delivery delay and protocol overhead. __________ Translated from Journal on Communications, 2008, 29(3): 119–122 [译自: 通信学报]     

Absorption of electromagnetic wave by inhomogeneous, unmagnetized plasma

In this article, a novel and normalized Z-transform finite-difference time-domain (ZTFDTD) method is presented. This method uses a more general form of Maxwell’s equations using the E, H, D fields. The iterative model of D-E-H-D can be obtained by using the Z-transform resulted frequency-dependent formula between D and E. The advantages of the ZTFDTD consist in that the discrete equations are simple, the results are precise, easy to program and capable of dealing with the key technologies of finite-difference time-domain (FDTD), such as absorbing boundary conditions (uniaxial anisotropic perfectly matched layer, UPML) and near-to-far-field transformation. The ZTFDTD method is then used to simulate the interaction of electromagnetic wave with plasma. Using a simplified two-dimensional model, the stealth effect of inhomogeneous, unmagnetized plasma is studied both in different electron densities of plasma, different electromagnetic wave frequencies and different plasma collision frequencies. The numerical results indicate that plasma stealth is effective in theory and a reasonable selection with the plasma parameters that can greatly enhance the effectiveness of plasma stealth. __________ Translated from Journal of Huazhong University of Science and Technology (Nature Science Edition), 2006, 35(6): 57–59 [译自: 华中科技大学学报(自然科学版)]     

Blind source separation algorithm for communication complex signals in communication reconnaissance

Most blind source separation algorithms are only applicable to real signals, while in communication reconnaissance processed signals are complex. To solve this problem, a blind source separation algorithm for communication complex signals is deduced, which is obtained by adopting the Kullback-Leibler divergence to measure the signals’ independence. On the other hand, the performance of natural gradient is better than that of stochastic gradient, thus the natural gradient of the cost function is used to optimize the algorithm. According to the conclusion that the signal’s mixing matrix after whitening is orthogonal, we deduce the iterative algorithm by constraining the separating matrix to an orthogonal matrix. Simulation results show that this algorithm can efficiently separate the source signals even in noise circumstances. __________ Translated from Journal of Huazhong University of Science and Technology (Natural Science Edition), 2007, 35(4): 33–36 [译自: 华中科技大学学报(自然科学版)]     

Robust adaptive beamforming algorithm based on Bayesian approach

The performance of adaptive array beamforming algorithms substantially degrades in practice because of a slight mismatch between actual and presumed array responses to the desired signal. A novel robust adaptive beamforming algorithm based on Bayesian approach is therefore proposed. The algorithm responds to the current environment by estimating the direction of arrival (DOA) of the actual signal from observations. Computational complexity of the proposed algorithm can thus be reduced compared with other algorithms since the recursive method is used to obtain inverse matrix. In addition, it has strong robustness to the uncertainty of actual signal DOA and makes the mean output array signal-to-interference-plus-noise ratio (SINR) consistently approach the optimum. Simulation results show that the proposed algorithm is better in performance than conventional adaptive beamforming algorithms. __________ Translated from Journal of Northeastern University (Natural Science), 2007, 28(6): 793–796 [译自: 东北大学学报 (自然科学版)]     

Parameter estimation for MIMO system based on MUSIC and ML methods

The frequency offset and channel gain estimation problem for multiple-input multiple-output (MIMO) systems in the case of flat-fading channels is addressed. Based on the multiple signal classification (MUSIC) and the maximum likelihood (ML) methods, a new joint estimation algorithm of frequency offsets and channel gains is proposed. The new algorithm has three steps. A subset of frequency offsets is first estimated with the MUSIC algorithm. All frequency offsets in the subset are then identified with the ML method. Finally, channel gains are calculated with the ML estimator. The algorithm is a one-dimensional search scheme and therefore greatly decreases the complexity of joint ML estimation, which is essentially a multi-dimensional search scheme. __________ Translated from Journal of Electronics and Information Technology, 2008, 30(7): 1552–1556 [译自: 电子与信息学报]     

Study and simulation of video communications under wireless environment based on blind source separation

A new scheme is proposed to separate several compressed video signals transferred in multiple wireless channels using the blind source separation method. The scheme selects IEEE 802.11b and XVID compression as the wireless communications channel and MPEG-4 video compression, respectively. A simulation model is then made for the video communications under a wireless environment. The model can separate several video signals using blind source separation. Simulations show that the normalized whiten plus cyclic whiten based on cyclostationary (NWCW-CS) algorithm based upon the cyclostationary characteristics of signals has the best separation performance and fast convergence. Besides, the algorithm can solve the mixing of video signals. The image of the transferred video signals decompressed by XVID is nearly consistent with the source ones. The new method meets the requirement of real-time video communications. __________ Translated from Journal of Southeast University (Natural Science Edition), 2007, 37(1): 13–17 [译自: 东南大学学报(自然科学版)]     

A PO-CI/MC-CDMA scheme for high modulation styles

Through analyzing the theoretical spreading principle, it has been proved in this paper that the benefit of pseudo-orthogonal carrier interferometry (PO-CI) spreading code is not supported when complex signal modulation (e.g., quadrature phase-shift keying (QPSK) and quadrature amplitude modulation (QAM)) types are employed. On this basis, a novel and feasible structure for this problem is brought forward. Within the structure mentioned, instead of complex modulation patterns, pulse amplitude modulation (PAM) combined with PO-CI spreading code is utilized. This allows us to maintain the throughput increase of a multi-carrier code division multiple access (MC-CDMA) system with minimal loss in performance and no bandwidth expansion. __________ Translated from Journal of Beijing University of Posts and Telecommunications, 2007, 30(4): 14–18 [译自: 北京邮电大学学报]     

PRF-ambiguity resolution for SAR by contrast minimization in range-Doppler domain

An algorithm was developed to accurately estimate the Doppler centroid, which is needed for high-quality synthetic aperture radar (SAR) image formation by resolving the SAR pulse repetition frequency (PRF) ambiguity. The algorithm uses the SAR range migration to resolve the PRF-ambiguity by searching for a PRF-ambiguity number that minimizes the intensity contrast in the range-Doppler domain. Experimental results show that the approach, compared with traditional methods for resolving the SAR PRF ambiguity, is more suitable for both high contrast scenes such as urban areas and low contrast scenes such as mountains. Moreover, the approach is more computationally efficient for there are no time-consuming correlations or fast Fourier transform (FFT) operations needed in the range-Doppler domain and only part of the range cells are used in the calculation. Translated from Journal of Tsinghua University (Science and Technology), 2006, 46(7): 1 259–1 261 [译自: 清华大学学报(自然科学版)]     

New mutual coupling compensation method and its application in DOA estimation

A new mutual coupling compensation method based on a new mutual impedance matrix, as well as its application to dipole arrays, are proposed. This new mutual impedance matrix is deduced by electromotive force (EMF) method, based on the current distribution obtained by the characteristic basis function method. It appears in a concise and explicit formulation that facilitates the numerical calculation. The compensation performance is demonstrated and evaluated through its application in direction of arrival (DOA) estimation. Numerical results show that the proposed method exhibits excellent compensation performance compared with conventional mutual impedance matrix approaches. __________ Translated from Chinese Journal of Radio Science, 2007, 22(4): 541–545 [译自: 电波科学学报]     

Single-trial EEG classification using in-phase average for brain-computer interface

Communication signals should be estimated by a single trial in a brain-computer interface. Since the relativity of visual evoked potentials from different sites should be stronger than those of the spontaneous electroencephalogram (EEG), this paper adopted the time-lock averaged signals from multi-channels as features. 200 trials of EEG recordings evoked by target or non-target stimuli were classified by the support vector machine (SVM). Results show that a classification accuracy of higher than 97% can be obtained by merely using the 250–550 ms time section of the averaged signals with channel Cz and Pz as features. It suggests that a possible approach to boost communication speed and simplify the designation of the brain-computer interface (BCI) system is worthy of an attempt in this way. __________ Translated from Journal of Huazhong University of Science and Technology (Nature Science Edition), 2007, 35(1): 11–13 [译自: 华中科技大学学报(自然科学版)]     

High-speed ground moving target detection research using triangular modulation FMCW

The frequency modulated continuous wave (FMCW) radar has the characteristics of low probability of interception, good hidden property and the ability to counter anti-radiation missiles. This paper proposes a new method for high-speed ground moving target detection (GMTD) using triangular modulation FMCW. According to the characteristic of the opposite range shift induced by the upslope and downslope modulation FMCW, the upslope and downslope are imaged, respectively. After compensation of continuous motion of the platform and time difference between upslope and downslope signals for imaging, the moving target can be detected through displaced phase center antenna (DPCA) technology. When the moving target is detected, the moving target image is extracted, and correlation processing is used to obtain the range shift, which can be used to estimate the target radial velocity, and further to find the real position of the target. The effectiveness of this method is verified by the result of computer simulation. __________ Translated from Journal of Xidian University, 2008, 35(4): 586–591 [译自: 西安电子科技大学学报(自然科学版)]     

Analysis on two novel spherical helical antennas

Two novel spherical helical antennas are designed by projecting the planar equiangular spiral antenna onto hemisphere and partial sphere surfaces. Their radiation properties are analyzed by the moment method with curved basis and test function, and the curves of the voltage standing wave ratio (VSWR), gain, polarization and pattern that change with frequency are also given, respectively. It can be seen that the circular polarization band of the novel hemispherical helical antenna is broader. The gain curve of the partial spherical helical antenna is flatter and the structure is simpler. __________ Translated from Journal of Xidian University, 2008, 35(1): 144–147 [译自: 西安电子科技大学学报 (自然科学版)]     

Performance analysis of WCDMA wireless access standard

Based on the transmitting power of a mobile station and the maximum cell capacity, the analysis of a wide-band code-division multiple access (WCDMA) standard and the comparison of the corresponding parameters with CDMA2000 or evolution-data only (EV-DO) are given in this paper. The result proves that the mobile station of WCDMA cannot provide the required transmitting power on the specified frequency band and data rate, and the symmetrical capacity in an up-downlink cannot meet the requirement of a mobile Internet. It is questionable for the International Telecommunication Union (ITU) to select the frequency band of 2 GHz for vehicular mobile telecommunication and unreasonable to distribute it over the downlink and uplink channels symmetrically. Only CDMA2000 1X EV-DO or enhanced data rate for GSM evolution (EDGE), which adopts the Time Division Multiple Access (TDMA) mode, can provide the high-speed data rate for a wireless access. Translated from Journal of Nanjing University of Posts and Telecommunications (Natural Science), 2006, 26(3): 42–48 [译自: 南京邮电大学学报(自然科学版)]     

A dynamic,secure,and efficient group key agreement protocol

The key challenge of dynamic peer communication is how to realize secure and efficient group key management. A two rounds key agreement protocol for dynamic peer group (DPG) is proposed in this paper. The protocol, which was obtained by combining the ElGamal encryption scheme with the ElGamal signature scheme, is efficient and simple. The protocol is proven secure against passive attack by using indistinguishable method. Moreover, both perfect forward secrecy (PFS) and key independence (KI) were achieved. Because the protocol is based on the broadcast channel, it is also suitable for key agreement in wireless communications, especially in ad-hoc networks. Translated from Journal of Shandong University, 2006, 41(2): 89–93 [译自: 山东大学学报(理学版)     

Preprocessing of ionospheric echo Doppler spectra

The real-time information of the distant ionosphere can be acquired by using the Wuhan ionospheric oblique backscattering sounding system (WIOBSS), which adopts a discontinuous wave mechanism. After the characteristics of the ionospheric echo Doppler spectra were analyzed, the signal preprocessing was developed in this paper, which aimed at improving the Doppler spectra. The results indicate that the preprocessing not only makes the system acquire a higher ability of target detection but also suppresses the radio frequency interference by 6–7 dB. __________ Translated from Journal of Wuhan University (Natural Science), 2006, 52(1): 114–118 [译自: 武汉大学学报(理学版)]     

Delay-dependent robust H ∞ controller design for a class of nonlinear uncertainty time-delay systems with input delay

Based on an appropriate Lyapunov function, this paper analyzes the design of a delay-dependent robust H _∞ state feedback control, with a focus on a class of nonlinear uncertainty linear time-delay systems with input delay using linear matrix inequalities. Under the condition that the nonlinear uncertain functions are gain bounded, a sufficient condition dependent on the delays of the state and input is presented for the existence of H _∞ controller. The proposed controller not only stabilized closed-loop uncertain systems but also guaranteed a prescribed H _∞ norm bound of closed-loop transfer matrix from the disturbance to controlled output. By solving a linear matrix inequation, we can obtain the robust H _∞ controller. An example is given to show the effectiveness of the proposed method. __________ Translated from Journal of Nanjing University of Aeronautics and Astronautics, 2007, 39(2): 159–163 [译自: 南京航空航天大学学报]     

Joint optimization in MIMO multiple relay channels

The joint optimization of cooperative relays in a multiple-input multiple-output (MIMO) multiple relay aided communication system is discussed in this article. A simple linear optimization solution is designed and a multi-user scheduling algorithm is proposed. The new algorithm chooses users with larger cooperation diversity gains from the waiting list to serve; it can reduce inter-user interference and maintain space diversity caused by parallel transmission of multiple relays, and achieve higher system throughput. __________ Translated from Journal on Communications, 2008, 29(3): 40–46 [译自: 通信学报]     

Indoor and outdoor people detection and shadow suppression by exploiting HSV color information

An adaptive background model based on maximum statistical probability and a shadow suppression scheme for indoor and outdoor people detection by exploiting hue saturation value (HSV) color information is proposed. To obtain the initial background scene, the frequency of R, G, and B component values for each pixel at the same position in the learning sequence are respectively calculated; the R, G, and B component values with the biggest ratios are incorporated to model the initial background. The background maintenance, or the socalled background re-initiation, is also proposed to adapt to scene changes such as illumination changes and scene geometry changes. Moving cast shadows generally exhibit a challenge for accurate moving target detection. Based on the observation that a shadow cast on a background region lowers its brightness but does not change its chromaticity significantly, we address this problem in the article by exploiting HSV color information. In addition, quantitative metrics is introduced to evaluate the algorithm on a benchmark suite of indoor and outdoor video sequences. The experimental results are given to show the performance of the algorithm. __________ Translated from Journal of Huaqiao University (Natural Science), 2007, 28(1): 30–33 [译自: 华侨大学学报 (自然科学版)]