A simple interpolation technique for the DFT for joint system parameters estimation in burst MPSK transmissions

In this paper, we propose a simple frequency-domain interpolation technique for the discrete Fourier transform (DFT). This interpolation technique can significantly improve the frequency and phase resolution capabilities of the DFT without increasing the size of the DFT (the number of points used for the DFT). This new technique employs a dividing point in the amplitude and phase spectra. Suitable areas of application include joint estimation of fine frequency and phase offsets in burst-mode digital transmission.     

Structure-Based Low Complexity MMSE Channel Estimator for OFDM Wireless Systems

Wireless communication systems utilizing orthogonal frequency division multiplexing (OFDM) transmissions are capable of delivering high data rates over multipath frequency selective channels. This paper deals with joint estimation/interpolation of wireless channel using pilot symbols transmitted concurrently with the data. We propose a low complexity, spectrally efficient minimum mean square error channel estimator which exploits the correlation structure of channel frequency response for reducing the complexity. Specifically, it is shown that if pilots are inserted appropriately across OFDM subcarriers, the proposed algorithm requires no matrix inversion, thereby significantly relieving the computational burden without deteriorating the performance. Moreover, the knowledge of channel correlation is also not required for the proposed estimator. Simulation results validate that the proposed technique outperforms existing low-complexity variants in terms of mean square error and computational complexity.

     

大频偏条件下PN码捕获改进算法

针对大频偏条件下PN码捕获的问题,提出了一种改进的PN码捕获算法,即基于谱线插值的联合码捕获算法.首先对现有的码捕获技术进行了分析,然后在部分相关值作FFT的码捕获算法的基础上,提出了基于谱线插值的联合码捕获算法.算法的核心思想是对部分相关值作FFT处理,并利用插值公式计算出载波频偏的精确估计值,使得后续的载波跟踪环更有利于载波跟踪.介绍了新的码捕获系统的工作原理,推导了载波频偏估计的插值公式,并将非相干累加技术应用于码捕获系统,从而提高了低信噪比条件下载波频偏估计的精度.最后,通过仿真证明了此算法对现有GPS接收机性能有5dB的改善.     

基于插值的多普勒频偏和频率斜升联合估计算法

为解决卫星移动通信系统中突发传输在低信噪比条件下的载波快速同步问题,该文提出一种基于插值的频偏和频率斜升联合估计算法。先通过对多普勒斜升搜索结合低复杂度频偏估计获得频偏和频率斜升的粗估计结果,再以频率斜升粗估计结果为中心、计算3个频率斜升值所对应的对数似然函数并据此对频率斜升进行二次插值以获得频率斜升估计值,最后在该估计值下计算出对应的频偏估计值,完成频偏和频率斜升的联合估计。仿真结果表明,该文算法的信噪比门限较低,估计性能接近克拉美罗下界(CRLB),而且计算复杂度远低于最大似然估计算法,非常适于实际应用。     

A gaussian sum approach to blind carrier phase estimation and data detection in turbo coded transmissions

We present a joint phase estimation and decoding method for convolutional turbo codes in the presence of strong phase noise. In order to overcome the problem of phase ambiguity and cycle slips, a combined state-space model for the time varying phase and the component convolutional codes is introduced. The proposed algorithm uses a Gaussian sum approach to approximate the multimodal a posteriori probability density function (pdf) of the phase in a blind context. We compare our method to the well known alternative consisting in discretizing the phase.Monte-Carlo simulations for the turbo code used in the DVB-RCS standard show that the performances of the proposed scheme are close to decoding with perfect knowledge of the phase.     

多径信号到达角和时延高分辨联合估计算法

本文提出了一种新的高分辨高精度的多径信号到达角和时延联合估计算法.该方法通过对多径信号与参考信号进行相关处理,再根据PRO-ESPRIT算法的思想,实现了DOA(Direction-Of-Arrival)估计;并对相关延迟向量进行变换,从互功率谱相位中提取时延信息,完成了高分辨的TOA(Time-Of-Arrival)估计.最后,本文推导了频域模型下到达角和时延联合估计的Cramer-Rao下界.并将通过仿真对本算法的性能进行了评估.     

一种低复杂度线性调频信号参数估计算法

为降低线性调频(LFM)信号参数估计的复杂度,该文提出一种二次估计算法。首先通过短时相干积分与非相干累加对频率斜升和起始频率进行预估计;然后以预估计结果为中心,利用多路并行部分匹配滤波快速傅里叶变换(PMF-FFT)和二次插值对参数进行精确估计;最后综合预估计和精确估计结果得到参数的最终估计值。仿真结果表明,该算法信噪比门限较低,估计精度接近克拉美罗下界,其计算复杂度和资源消耗均远低于频率斜升试探算法和插值联合估计算法。     

数字并行接收机在时变信道下的信道估计与均衡方法

为了适应高速宽带无线通信的需要,本文在一种高速数字并行接收机(APRX)结构的基础上,提出了一种时变信道下的信道估计和均衡方法。使用伪随机(pseudo-randomnumber,PN)序列相关进行信道估计,将所得到的信道频率响应粗估计按照一个DFT块的长度在一帧内进行线性内插得到信道频率响应细估计,将其用来在频域进行信道均衡。这种结构能适应高速率传输的要求,并且能有效地对抗时间和频率选择性衰落。仿真结果表明,在多径衰落信道下,APRX已经无法工作,而本文提出的数字并行接收机的信道估计和均衡方法有较好的性能,并且该方法实现简单,便于应用。     

突发OFDM系统中的同步算法研究

提出了一种应用于突发OFDM通信系统的同步算法。在粗同步阶段,采用两路延迟相关结构,通过适当选择两路的延迟量和累加量,可以有效实现估计精度与方差的折中,提高小数频偏的估计精度,在细同步阶段,在FFT之后进行整数频偏和残留时偏的联合估计,利用子载波上的线性相位得到更加精确的时偏估计。仿真显示,该算法具有较高的同步精度和较快的同步速度,能够适应于突发OFDM传输系统。     

Performance analysis of channel estimation for OFDM systems with residual timing offset

The authors present an analysis of the effect of timing offset on channel estimation for comb-type pilot-aided orthogonal frequency division multiplexing (OFDM) systems. Residual timing offset does not negatively affect the channel estimation of the pilot subcarrier, but does corrupt the channel information obtained via interpolation. This paper provides the mean square error (MSE) channel estimation performance when a linear interpolation technique is used in a comb-type pilot-aided OFDM system. Analysis shows that the performance degradation of the channel estimator due to imperfect frame synchronization is dependent on the frequency correlation of the channels and the amount of timing offset     

基于分形插值的频域散斑相关法面内位移测量

针对传统频域数字散斑相关法在测量物体面内位移测量精度较低的问题,提出一种基于分形插值的频域数字散斑相关法。该方法在频域数字散斑相关法的基础上,引入Hanning窗函数对图像进行滤波处理,克服了图像边缘效应对最终位移值的影响;同时利用散斑图像的子区域与整幅图像在结构形态和灰度特征的自相似性,采用分形插值的方法进行亚像素插值,进而能精确定位相关点,得到更精确的亚像素位移值。实验结果表明:该方法保持了频域散斑相关法的测量速度,且将测量的绝对误差降低在0.01~0.03 pixel以内,并进一步通过刚体平移实验测试了算法的可靠性。     

一种适用于DVB-T系统的信道估计算法

提出了一种基于导频的信道估计算法,该算法在最小平方误差(LS)算法的基础上采用两维插值的方法估计出无线信道的频域响应,即在时域上进行线性插值,然后利用最大似然(ML)算法进行频域插值。在地面数字视频广播(DVB-T)系统中的仿真结果表明,该复合算法具有较高的性能。     

Sequence Design for Data-Aided Estimation of Synchronization Parameters

In this letter, we propose a systematic technique for optimum data-sequence design for data-aided (DA) estimation of synchronization parameters. It is assumed that the system operates in burst mode, transmitting a linearly modulated information signal over an additive white Gaussian noise channel. The method is based on the minimization of the corresponding Crameacuter-Rao lower bound subject to a power constraint and is applied in four practical receiver synchronization contexts: estimation of the symbol timing with known carrier frequency offset and either known or unknown carrier phase, joint estimation of the symbol timing and carrier phase with known carrier frequency offset, and joint estimation of the carrier phase and carrier frequency offset with known symbol timing     

Performance Evaluation of Timing Estimation Technique Using Extended Cyclic Prefix for Correlation Sequence for OFDM Systems

This paper presents an analysis of symbol timing offset (STO) estimation method for orthogonal frequency division multiplexing systems. The proposed method does not require any preamble and with the use of available cyclic prefix (CP) samples we have proposed an extended CP. The extended CP is used to exploit more number of correlation products in correlation sequence so that a more accurate starting point of any symbol can be estimated. A simplified maximum likelihood estimation process for proposed timing estimation technique is given which enables us much more accurate timing estimate due to decreased error variance. The performance of the proposed method is evaluated in terms of mean square error of timing estimator against different signal to noise ratio values and in terms of error distribution of the estimators with and without the effect of carrier frequency offset in various channel scenarios such as AWGN, HIPERLAN/2A and HIPERLAN/2E. Simulation results shows that proposed method has significantly better performance compared to the CP based method for STO estimation.     

Performance Analysis of Analytic Interpolator for Comb-Type Pilot-Aided Channel Estimation in OFDM Systems Without ICI

Pilot-aided channel estimation in orthogonal frequency division multiplexing (OFDM) systems often needs an interpolation technique to construct the channel frequency response on nonpilot subcarriers. Many studies on interpolations have been published; however, the performance of interpolations such as cubic spline interpolation and linear interpolation is limited by either the number or the position of the pilot subcarriers. This paper proposes an analytic interpolator developed using a linear least square criterion to replace conventional interpolation techniques for comb-type pilot-added channel estimation in OFDM systems without inter-carrier interference. The performance evaluation of the analytic interpolator is performed both on the basis of theory and through simulation, and the results from both the analyses are found to be in good agreement. The simulation results show that the proposed method can effectively mitigate the ill-influences of limitations on the number and position of the pilot subcarriers and that it also outperforms the cubic spline interpolation and linear interpolation, especially for short or nonequidistant pilot patterns.     

New improved fractional order integrators using PSO optimisation

This article investigates the optimal results of new improved fractional order integrators (FOIs) of different orders. Mathematical models of FOIs have been first developed by a single-step procedure of direct linear interpolation of fractional integrators based on Al-Alaoui operator in fractional domain itself, instead of using three steps of the well-known conventional method, namely, digital interpolation, series expansion and truncation. Later, these transfer functions (TFs) are optimised for their coefficient values for finding a minimum error function by particle swarm optimisation (PSO) algorithm. Simulation results of magnitude responses, phase responses and relative magnitude errors (dB) for all the proposed half integrators have validated the effectiveness of this new technique of interpolation of fractional order operators, mixed with PSO algorithm. A parallel comparison has been also drawn between the proposed optimised half integrators and those obtained by discretisation of PSO optimised integer order digital integrators (DIs) to properly support the proposed novel combination of interpolation and PSO, both applied together in fractional domain.     

A fully digital fast convergence algorithm for nonlinearity correction in multistage ADC

This paper describes a fast digital background calibration algorithm for pipeline or cyclic analog-to-digital converters. The proposed method corrects for the finite gain/bandwidth of the interstage operational amplifier and for capacitor mismatch in multiplying digital-to-analog converters stages. The new algorithm, fast gain error correction, converges more than 100 times faster than other correlation-based correction techniques presented in literature. The high speed of convergence of the error estimation is due to the use of a polynomial interpolation that cancel the interference in the error estimation process caused by the input signal. This new method does not need any added analog circuitry, does not perturb the output samples, and requires only a digital finite-impulse response filter to implement the polynomial interpolation as opposed to existing fast converging correlation techniques.     

A joint TDOA and FDOA estimation algorithm based on second-order cone programming

ABSTRACT

Considering the low estimation accuracy of the traditional interpolation method, this paper, on the basis of second-order cone programming (SOCP), proposes a novel joint time difference of arrival (TDOA) and frequency difference of arrival (FDOA) estimation interpolation method, which can attain the sub-sample precision. The proposed method uses several discrete samples produced by cross ambiguity function (CAF) to structure the convex optimization models with regard to the interpolation surface. Then, the SOCP is utilized to obtain the interpolation surface which matches the discrete surface of CAF well. Finally, the method achieves the precision superior to the traditional TDOA and FDOA estimation directly through the search for the maximum of the continuous approximate surface. This method decreases the computational load without loss of precision and can efficiently reduce the limitation of finite sampling interval and sampling time in estimation precision. Numerical simulations show that the method in this paper is efficient and outperforms existing interpolation algorithms about estimation precision.     

DVB-RCS2卫星交互网的调制编码技术

DVB-RCS2规范在调制编码技术方面较DVB-RCS作出了重要改进,分别研究了前向链路的自适应编码调制方式,以及回传链路突发所采用的两种传输模式,即Turbo码线性调制模式和卷积码连续相位调制模式。通过对其实现方式和关键参数的分析,探讨了DVB-RCS2体制的灵活性和高效性。     

LFM信号参数估计的DAF插值算法

为实现LFM信号起始频率和调频斜率的高精度参数估计,对基于离散模糊函数的DAF算法进行了研究。该算法具有计算量小的优点但估计精度受到采样频率和采样点数的限制。针对此问题,提出了一种可提高参数估计精度的DAF插值方法:首先利用DAF将LFM信号转换为正弦信号,分别通过两次FFT并进行峰值搜索得到起始频率和调频斜率的粗估计值,然后基于Rife插值利用最大谱线和次大谱线进行修正得到预估计值,再利用两次单点DFT的频谱细化技术得到该值两侧相邻0.5个量化频率点处的谱线,最后重新进行插值计算。该算法突破了频谱离散化带来的频率分辨率限制,在增加运算量较少的情况下,提高了参数估计的精度。仿真实验结果验证了算法的有效性。