A Generalized Limit Theorem for Reliability

A new and more general limit theorem is proposed in place of the exponential limit theorem of Drenick. First it is shown that as time goes to zero, the hazard rate can be made to approach an almost arbitrary function. Next it is pointed out that in the exponential limit theorem (and others) the only practical and necessary effect of having the number of elements ``go to infinity' is to force time to go to zero. Therefore the limit theorems are not as useful as was once thought.     

Characteristic Functions for Optimum-Combining Output SINR With AWGN and Correlated Interference

Optimum combining (OC) is a powerful means for combatting co-channel interference. Its performance, however, is difficult to analyze. The prevailing methodology in current use is to neglect the influence of additive white Gaussian noise (AWGN). Inclusion of AWGN into the analysis usually leads to mathematical intractability, except for some extreme cases. In this letter, we formulate the problem in the framework of hypergeometric functions, so that their good properties can be exploited to enable the analysis to account for the influence of AWGN and co-channel interference simultaneously. We obtain closed-form solutions to the characteristic function (CHF) of the signal-to-interference-plus-noise ratio at the OC output for three important operational scenarios in Rayleigh fading, although the general solution still needs further effort to simplify. The assumptions made here are that both signal and interferers suffer from Rayleigh fading, and the number of interferers is not less than the number of antennas. The use of resulting CHF formulas is illustrated through their application to the bit-error and outage performance evaluation of OC     

宽带带通信号的直接采样定理

对起、止频率为ｆｓ_ｆｅ_的带通信号的直接采样,传统上要求信号是窄带的９即ｆ≥ｆ_ｅ／２）,否则只能用经典的Ｓｈａｎｎｏｎ采样定理,以不低于２ｆ_ａ的采样率来采样才能恢复信号。本文采取半均匀采样技巧,突破了这一限制。对满足ｆ_ｓ≥ｆ_ｅ／３的宽带带通信号,建立了精确的恢复公式,采样率为４ｆｅ／３,低于Ｎｙｑｕｉｓｔ率;如果ｆ_ｓ＜ｆ_ｅ／３,用ｔｉｌｉｎｇ分析技术可以证明无论是均匀还是半均匀采样,最低采样率必然是２ｆ_ｅ。这表明本文所给出的宽带条件是最优的。     

On-Chip Evaluation of Oscillation-Based-Test Output Signals for Switched-Capacitor Circuits

This work presents a simple and low-cost method for on-chip evaluation of test signals coming from the application of the Oscillation-Based-Test (OBT) technique. This method extracts the main test signal features (amplitude, frequency and DC level) in the digital domain requiring just a very simple and robust circuitry. Experimental results obtained from an integrated chip demonstrate the feasibility of the approach.     

一种高抗干扰的DSP输入输出信号传输电路的设计

介绍和比较了现有的DSP输入输出信号传输方法,设计了一种高抗干扰的DSP输入输出信号传输电路,论述了该电路工作原理,给出了电路主要参数的设计计算。通过实验验证了该传输电路的可行性。     

A Novel Circulant Approximation Method for Frequency Domain LMMSE Equalization

The coefficients of a Linear Minimum Mean Square Error (LMMSE) equalizer for a stationary random signal are defined by a Toeplitz system. The Toeplitz structure can be exploited to reduce computational complexity. In this paper we investigate the Levinson and Schur algorithm, as well as circulant embedding and circulant approximation methods applied to the Preconditioned Conjugate Gradient (PCG) method and Frequency Domain Equalization (FDE). We develop a novel circulant approximation method which improves the performance/complexity tradeoff. We show that the optimal choice of algorithms largely depends on the antenna configuration. Investigated configurations are Single Input Single Output (SISO), Single Input Multiple Output (SIMO) and Multiple Input Multiple Output (MIMO). All considered algorithms are benchmarked in terms of implementation complexity and capacity achieved by a High Speed Downlink Packet Access (HSDPA) receiver in a multipath fading scenario.     

基于SINR判决的MIMO联合检测算法

一种低复杂度的MMSE-QRD-QRDM检测方法被提出,该算法根据接收端各子流的信干噪比(SINR)和门限值的比较,对各子流分别进行最小均方误差QR分解(MMSE-QRD)检测或QR分解-M(QRD-M)检测。对MMSE-QRD-QRDM算法进行了误码率(BER)性能仿真和算法复杂度分析。结果表明,和OSD-MLD算法相比,MMSE-QRD-QRDM算法可以在大大降低检测算法复杂度的情况下,获得优于OSD-MLD算法的BER性能,同时通过减少运算中的矩阵求逆次数,提高了算法的数值稳定性。     

A rank-reduced LMMSE canceller for narrowband interference suppression in OFDM-based systems

We present a narrowband interference (NBI) canceller that suppresses spectral leakage in an orthogonal frequency-division multiplexing (OFDM)-based system caused by a narrowband (NB) signal. We assume that the spectrum of the NB signal is within the spectrum of the OFDM signal. This can be the case, e.g., on digital subscriber lines (DSL) and in new unlicensed frequency bands for radio transmission. The canceller makes linear minimum mean-square error estimates of the spectral leakage by measuring the NBI on a few modulated or unmodulated OFDM subcarriers. It uses a model of the NB signal's power spectral density as a priori information. Using a frequency invariant design, it is possible to cancel NBI from signals that are changing their frequency location with significantly reduced complexity overhead. The operational complexity of the canceller can be lowered by using the theory of optimal rank reduction and using the time-bandwidth product of the NB signal. Analytical performance evaluations, as well as Monte Carlo simulations, show that, without perfect a priori information, this canceller can suppress the spectral leakage from a strong NB signal (e.g., with equal power as the OFDM signal) to well below the background noise floor for typical applications where it causes negligible signal-to-noise ratio and symbol error rate degradation.     

Computationally Efficient Algorithm for Estimating the Frequency of Signals at the Output of a Channel with White Gaussian Noise and Narrowband Interference

Journal of Communications Technology and Electronics - Abstract—A computationally efficient algorithm is proposed for estimating the frequency of a quasi-harmonic signal in the presence of...     

A modified Min Sum decoding algorithm based on LMMSE for LDPC codes

A new modified Min Sum decoding algorithm based on parameter estimation theory for Low Density Parity Check (LDPC) codes is presented in this paper. First, Linear Minimum Mean Square Error (LMMSE) estimate criterion is used to model the magnitude of check-to-variable message and calculate estimated parameters, furthermore the golden section search algorithm is used to speed up getting the boundary, with which the parameters can be determined. Then, the parameters are modified further on the basis of the relationship between the iteration number and the estimated parameters. Finally, the same estimated parameters are used for different signal to noise ratio (SNR) to ensure the decoding performance and reduce the hardware complexity. The simulation results show that a gain of 0.3–0.5 dB can be achieved in comparison with other kinds of modified Min Sum algorithms, which is very close to that of BP algorithm. What's more, the algorithm has the following characteristics: low computation complexity, small decoding delay, easiness of calculation for estimated parameters, and simplicity in hardware implementation.     

A Test Generation Methodology for Interconnection Opens Considering Signals at the Coupled Lines

Interconnection opens have become important defects in nanometer technologies. The behavior of these defects depends on the structure of the affected devices, the trapped gate charge and the surrounding circuitry. This work proposes an enhanced test generation methodology to improve the detectability of interconnection opens. This test methodology is called OPVEG. OPVEG uses layout information and a commercial stuck-at ATPG. Those signal values at the coupled lines which favor the detection of the opens, under a boolean based test, are attempted to be generated. The methodology is applied to four ISCAS85 benchmark circuits. The results show that a significant number of considered coupled signals are set to proper logic values. Hence, the likelihood of detection of interconnection opens is increased. The results are also given in terms of the amount of coupling capacitance having logic conditions favoring the defect detection. This shows the OPVEG benefits. Furthermore, those lines difficult to test can be identified. This information can be used by the designer to take design for test measures.

OFDM系统中的自适应信道估计

分析了现有的基于导频的OFDM信道估计技术,提出了一种低复杂度的自适应信道估计方法,并给出了最大时延扩展的实时估计方法,最后通过计算机仿真,给出了多径信道下MSE曲线,以及在DVB-T系统中的BER仿真曲线,验证了其可靠性和良好的性能。     

A Minimax Chebyshev Estimator for Bounded Error Estimation

We develop a nonlinear minimax estimator for the classical linear regression model assuming that the true parameter vector lies in an intersection of ellipsoids. We seek an estimate that minimizes the worst-case estimation error over the given parameter set. Since this problem is intractable, we approximate it using semidefinite relaxation, and refer to the resulting estimate as the relaxed Chebyshev center (RCC). We show that the RCC is unique and feasible, meaning it is consistent with the prior information. We then prove that the constrained least-squares (CLS) estimate for this problem can also be obtained as a relaxation of the Chebyshev center, that is looser than the RCC. Finally, we demonstrate through simulations that the RCC can significantly improve the estimation error over the CLS method.     

一种多径线性调频信号的参数估计方法

基于循环互相关变换，提出了一种结合循环频率域的信号分离技术的多径LFM信号参数估计方法。该方法首先利用信号循环相关变换，估计出源信号的特征参数，根据估计出的参数重构出源信号，并将其和观测信号作循环互相关变换，再根据信号循环频率域上的多径信号特征，估计出最强路径信号分量的时延和衰减因子参数，然后重构最强路径分量，最后将其从观测信号中滤去，这样逐次分离出各径信号，从而有效地抑制了强路径信号分量对弱路径信号分量的影响。最后运用计算机进行了仿真实验。     

A Differentiator for Low-Frequency Signals

An electronic differentiator specifically for low-frequency signals is described. The difference between a signal and its staircase approximation is computed; the peaks of this function approximate the time derivative of the input signal. By regulating the width of the steps in the staircase function, very slow signals can be differentiated.     

Alpha稳定分布噪声下基于柯西分布的相位键控信号码速率最大似然估计

针对现有的相位键控(PSK)编码信号码速率估计方法在Alpha稳定分布中性能严重退化的问题,该文提出一种基于柯西分布的码速率最大似然估计(CMLE)新方法,该方法可同时估计码速率与定时偏差.CMLE利用窗口法将信号划分为定时偏差窗和多个宽度一定的非重叠且已同步的时域窗,每个窗只包含一个码元符号;在 Alpha稳定分布噪声下,利用窗中符号信息构造了基于柯西分布的似然函数,可同时获得定时偏差窗宽与码元符号窗宽的最大似然估计.仿真结果表明,该方法能有效抑制Alpha稳定分布噪声并具有良好的参数估计性能.     

实正弦信号频率估计的高精度综合算法

推导了单频信号离散傅里叶变换的的理论表达式,阐述了FFT法测频的基本原理,并详细介绍了2种插值算法:FFT实部法和分段FFT算法。2种算法都是基于FFT谱线的插值算法,属于改进算法,但是2种算法具有测频性能恶化的潜在缺陷,因此综合考虑2种算法的优缺点,提出一种综合二者优势的综合测频算法。计算机仿真表明综合测频算法性能要优于FFT实部法和分段FFT算法,是一种稳定的高精度测频算法。     

A Blind Synchronizer for OFDM Systems Based on SINR Maximization in Multipath Fading Channels

This paper presents a blind synchronizer for orthogonal frequency-division multiplexing (OFDM) systems based on signal-to-interference-and-noise ratio (SINR) maximization. Due to the incurred losses from intersymbol interference (ISI) and intercarrier interference (ICI) introduced by synchronization errors, the SINR of the received data drastically drops. By taking advantage of this characteristic, both the symbol time and carrier frequency offsets are intuitively estimated by maximizing the SINR metric. For the SINR metric, two blind SINR estimations are investigated. The estimations do not need prior knowledge of the channel profiles and transmitted data. As such, the proposed maximum SINR (MSINR) synchronization algorithm is nondata aided so that the transmission efficiency can be improved. Moreover, to reduce the computational complexity, the early–late gate technique is proposed for the implementation of the synchronizer. Simulation results exhibit better performance for the MSINR algorithm than conventional techniques in multipath fading channels.      

GaAs MESFET Regenerator for Phase-Shift Keying Signals at the Carrier Frequency

This paper describes a GaAs metal-semiconductor FET (GaAs MESFET) phase regenerator for biphase phase-shift keying (PSK) signals at the carrier frequency. By using this regenerator, decision and reshaping of the signals can be made without detection, thus repeaters can be simplified. This paper shows that phase regeneration is characterized by the symbol m, which denotes the ratio of the normal signal to the phase-inverted signal. Ideal phase regeneration is obtained for m = 1. An analysis of the ratio m for the MESFET regenerator is presented, and it is shown that, if the gate bias or the local-oscillator power level are selected at a slightly higher point than that minimizing the conversion loss, then m = 1.03 is obtained at an excess loss of 3 dB. To verify this analysis, the ratio m was measured experimentally and it was found to agree with the analysis. Static and dynamic characteristics were also measured, and it is shown that the MESFET regenerator has decision and reshaping ability.     

A Digital Demodulator for PSK Signals

This paper describes a digital demodulator for phase-shift-keyed (PSK) signals in which the phase difference between the received signal and a carrier reference is found by measuring digitally the time interval between the zero crossings of the signal and the reference. In the case of coherent detection the reference is locked to one of theMpossible phases of the signal. The advantage of this demodulator is that bulky low-pass filters and delay lines as well as critical threshold devices can be dispensed with. On the other hand, digital measurement of the phase and the use of a finite-width sampling window lead to degradation of the error performance. This degradation is theoretically analyzed for both coherent and phase-comparison detection. The quantizing error proves to be small enough when the phase difference is coded into a 6-b binary number, and the theoretical results are in good agreement with measurements taken from an experimental phase-comparison demodulator for fourand eight-level PSK signals. The experimental demodulator is also described in the paper.