A new unwindowed lattice filter for RLS estimation

Adaptive lattice algorithms are derived for the solution of unwindowed least squares estimation problems for AR and FIR models. The basic approach is to embed the unwindowed problem in a larger prewindowed problem and then eliminate superfluous terms in the lattice. Initializations are given to allow the lattice to use no initial parameter estimates or to include initial parameter estimates with desired weightings in the quadratic criterion for parameter estimation. A numerical example is given     

Frequency shift keyed narrowband interference rejection: optimal exponential weighting factor for the RLS algorithm

Cochannel narrowband interference can limit the performance of direct sequence spread spectrum (DSSS) and high frequency (HF) systems. Narrowband interference (NBI) can be single tone, chirped or frequency shift keyed (FSK) in nature and numerous techniques for its removal have been proposed. Linear adaptive prediction filters based on autoregressive modelling have been suggested owing to their ability to perform in a non-stationary environment. In the FSK narrowband interference case, adaptive filters are susceptible to excess residual errors owing to instantaneous frequency step changes and the finite convergence time required for the filter to adapt to a new interference frequency. The signal degradation owing to this type of interference becomes greater in high SNR regimes and has been found to be a function of the frequency parameters of the FSK interference signal. The paper discusses the convergence and frequency tracking properties of the recursive least squares (RLS) adaptive lattice filter using a posteriori estimation errors in the presence of FSK narrowband interference. An optimal exponential weighting factor that balances convergence time and steady state error is derived for this case of NBI. Results are compared to those of a previously proposed fast converging minimum frequency error (FCMFE) RLS lattice filter.     

Rejection of narrowband interference in DS spread spectrum systemsemploying minimum redundant nonlinear filters

A new nonlinear filter structure, the minimum redundant nonlinear filter (MRNF), for combating narrowband interference in direct sequence spread spectrum systems is proposed. Analytical expressions for the signal-to-noise ratio improvement factors are derived under the condition of single tone interference. The results show that the MRNF provides significantly better performance than the minimum redundant transversal filter     

An adaptive ARMA four-line lattice filter for spectral estimationwith frequency weighting

A method for designing an adaptive four-line lattice filter which can perform frequency-weighting spectral estimation, which provides more accurate spectral estimation for some frequency bands than for others, is proposed. Using a suitable frequency-weighting function, denoted as an ARMA (autoregressive moving-average) model, an estimated spectrum is obtained by arbitrarily weighing some frequency bands more heavily than others. if the frequency-weighting function has the property of a low-pass filter, the spectrum of the reference model can be estimated accurately with a reduced ARMA order in the low-frequency band. Spectra of time-varying models can be estimated with an exponentially weighted sliding window, and the input signal of the reference model can be estimated by assumption. The order-update and the time-update recursive formulas and the frequency-weighting method for the filter are described. The algorithm is verified by experimental results     

Blind channel estimation for multicarrier systems with narrowband interference suppression

We present herein a novel blind channel estimator for multicarrier (MC) systems in the presence of unmodeled narrowband interference. A generalized multichannel minimum variance principle is invoked to design an equalizing filterbank that preserves desired signal components and suppresses the overall interference. While a channel estimate may be obtained by directly maximizing the filterbank output power through multidimensional nonlinear searches, such an approach is computationally prohibitive and suffers local convergence. To overcome this difficulty, we derive an asymptotically (in SNR) tight lower bound of the filterbank output power and use it for channel estimation, which reduces the problem to a quadratic minimization. Numerical examples show that the proposed scheme compares favorably with a subspace blind channel estimator in the presence of unknown narrowband interference.     

FIR filter design over discrete coefficients and least square error

The difference routing digital filter (DRDF) consists of an FIR filter followed by a first-order integrator. This structure with power-of-two coefficients has been studied as a means of achieving low complexity, high sampling rate filters which can be implemented efficiently in hardware. The optimisation of the coefficients has previously been based on a time-domain least-squares error criterion. A new design method is proposed that includes a frequency-domain least-squares criterion with arbitrary frequency weighting and an improved method for handling quantisation of the filter coefficients. Simulation studies show that the new approach yields an improvement of up to 7 dB over existing methods and that oversampling can be used to improve performance     

DS/FH快跳频系统设计和窄带干扰抑制

跳频通信具有一定的抗窄带干扰的能力,跳速越高抗窄带干扰的能力越强.在DS/FH跳频系统中,解跳之后干扰信号存在于部分的扩频信号,相当于扩频信号内存在时变的干扰信号.文中将Turbo纠错码和分集合并技术联合应用于DS/FH快跳频系统中,利用信号的分集特性,采用奇异值分解的算法检测受干扰的跳频信号,将未受干扰的跳频信号合并,结果表明采用Turbo码的快速跳频方式时可以实现窄带干扰抑制.     

A new normalized subband adaptive filter under minimum error entropy criterion

A new normalized subband adaptive filter based on the minimum error entropy criterion (MEE-NSAF) is proposed for identifying a highly noisy system. The MEE-NSAF utilizes a kernel function and a number of past errors in adaptation, whereas the classical NSAF relies only on the current error signal. Moreover, the stability of the MEE-NSAF is analyzed. To further improve the performance of the MEE-NSAF under the sparse impulse responses, an improved proportionate MEE-NSAF (MEE-IPNSAF) algorithm is proposed. Simulation results show that the proposed algorithms can achieve improved performance as compared with the conventional NSAF when noise gets severe.     

On adaptive minimum probability of error linear filter receiversfor DS-CDMA channels

Receiver architectures in the form of a linear filter front-end followed by a hard-limiting decision maker are considered for DS-CDMA communication systems. Based on stochastic approximation concepts a recursive algorithm is developed for the adaptive optimization of the linear filter front-end in the minimum BER sense. The recursive form is decision driven and distribution free. For additive white Gaussian noise (AWGN) channels, theoretical analysis of the BER surface of linear filter receivers identifies the subset of the linear filter space where the optimal receiver lies and offers a formal proof of guaranteed global optimization with probability one for the two-user case. To the extent that the output of a linear DS-CDMA filter can be approximated by a Gaussian random variable, a minimum-mean-square-error optimized linear filter approximates the minimum BER solution. Numerical and simulation results indicate that for realistic AWGN DS-CDMA systems with reasonably low signature cross-correlations the linear minimum BER filter and the MMSE filter exhibit approximately the same performance. The linear minimum BER receiver is superior, however, when either the signature cross-correlation is high or the background noise is non-Gaussian     

A simplified lattice factorization for linear-phase paraunitary filter banks with pairwise mirror image frequency responses

In this paper, by extending our previous work on general linear-phase paraunitary filter banks even-channel (LPPUFBs), we develop a new structure for LPPUFBs with the pairwise mirror image (PMI) frequency responses, which is a simplified version of the lattice proposed by Nguyen et al. Our simplification is achieved through trivial matrix manipulations and the cosine-sine (C-S) decomposition of a general orthogonal matrix. The resulting new structure covers the same class of PMI-LPPUFBs as the original lattice, while substantially reducing the number of free parameters involved in the nonlinear optimization. A design example is presented to demonstrate the effectiveness of the new structure.     

The performance of a direct-sequence spread-spectrum acquisition system using a linear prediction filter for narrowband interference suppression

The coarse acquisition performance of a direct sequence spread-spectrum receiver is analyzed when a linear prediction filter is used for narrowband interference suppression. We show that once an appropriate matching strategy is identified, the linear prediction filter can provide favorable performance when narrowband interference is present over a considerable range of both interference power and bandwidth. In addition, the presence of the filter dramatically improves the performance over the case where there is no filter, except when the interference bandwidth and the power are both small (i.e., when the processing gain provides sufficient interference immunity without the filter). If long spreading sequences are used with moderately sized observation windows, the acquisition performance can be severely degraded when a parallel acquisition scheme is used due to the linear predication filter. We show, however, that a slower serial receiver will provide reliable performance.This work was supported in part by the Office of Naval Research under contract ONR N00014-91-J-1234, the Army Research Office under contract ARO DAAL03-91-0071, and the NSF Center for Ultra-High Speed Circuits and Systems (ICAS).     

Filters for data transmission with minimum intersymbol interference

Lowpass filters for data transmission with and without finite imaginary-axis transfer zeros are considered. The transfer-function poles adjust the equidistance between the rectangular pulse response zeros and the minimum intersymbol interference is automatically attained. The improvement in filter selectivity is provided by the imaginary-axis zeros.     

一种导航信号频域干扰抑制方法及其FPGA实现

针对双频导航接收机在导航战中面临的窄带干扰问题,提出了一种频域抑制压制式窄带干扰的方法,并把该方法应用在军用导航接收机中提高导航系统的抗干扰能力。介绍了基于快速傅里叶变换的干扰抑制算法,并对频域干扰抑制方法进行了加窗、混叠、数字自动增益控制处理等设计处理;考虑实际工程应用情况,在较小资源占用的前提下完成了现场可编程门阵列(Field Programmable Gate Array, FPGA)工程实现。将实现的频域抗窄带干扰工程移植到接收机基带中,完成了抗干扰试验,验证了其抗干扰性能,为导航接收机系统双频抗窄带干扰提供了理论和实际工程应用参考。     

Effect of correlated noise on error probability of binary frequency shift keying with limiter-discriminator-detector and narrowband filters

In investigations of frequency shift keying (FSK) with a limiter-discriminator-integrator (LDI) detector it was assumed that the noise at two consecutive sampling points is uncorrelated. Here we study the effect of correlated noise on error probability. We show that the error probability is reduced when the correlation is positive and increased when the correlation is negative. For optimal values of filter bandwidth the error probability remains unchanged.     

The research on channel estimation and signal-noise ratio estimation based on minimum error entropy kalman filter for single carrier frequency domain equalization system

In this paper, the channel estimation and signal-to-noise ratio (SNR) estimation technique of single-carrier frequency domain equalization (SC-FDE) system under low SNR in aeronautical multipath channel are studied, a SNR estimation algorithm which is easy to implement in engineering and an improved LS channel estimation algorithm based on Kalman filter using minimum error entropy (MEE-KF) are proposed. This paper first introduces the SC-FDE system and introduces the principle of MEE-KF, and then, the channel estimation flow based on MEE-KF is obtained by combining it with the traditional LS channel estimation algorithm, which makes the estimation results perform better. Simulation results show that after getting more accurate noise variance, the channel estimation results can better follow the changes of the channel after MEE-KF processing, so as to resist the doppler frequency offset effect and make the channel estimation results more accurate, that is the channel response results of the data part can be closer to the real situation, so that the communication performance of SC-FDE system has also been greatly improved.     

最小移频键控信号的检测和误码性能分析

首先介绍了MSK信号差分检测原理。其次,分析了存在相关高斯噪声和信道有瑞利衰落时MSK的抗噪声性能。结果表明,在高斯噪声时的差分MSK的误码率与DPSK相同;而当信道存在瑞利衰落时将严重影响系统的抗噪声性能。所得结论能为系统的设计提供重要依据。     

Quantising for minimum error with particular reference to speech

A mathematical solution is given for the design of a quantiser suitable for quantising, with minimum mean-square error, a signal with an exponential amplitude probability-density function. This is particularly relevant to speech, the probability-density function of which approximates to the exponential case.     

基于频域递推算法的窄带滤光片光束传输特性研究

多腔窄带薄膜滤光片在倾斜入射时中心透射波长会向短波方向移动,由此可制备角度调谐滤波器。但其透射光斑在倾斜入射时会出现明显的斑展宽现象,由此产生的接收端耦合度及干涉级次的降低会导致其透射光谱的插入损耗迅速增大,会限制其有效波长调谐范围。传统的多光束叠加法可以对窄带滤光片斜入射时的透射光斑展宽现象进行仿真,但是在光强分布上与实验结果有着较大的误差。本文基于快速傅里叶变换及菲涅尔公式,提出了一种新颖的频域递推算法来计算光斑的展宽程度及透射光强分布,计算了从0度到60度倾斜入射范围内光斑展宽以及透射率的变化情况。理论计算和实验结果都表明该方法较之传统的多光束叠加算法结果更准确且计算效率高。