Estimation of directions of arrival of multiple scattered sources

We consider the problem of estimating the directions of arrival (DOA) of multiple sources in the presence of local scattering. This problem is encountered in wireless communications due to the presence of scatterers in the vicinity of the mobile or when the signals propagate through a random inhomogeneous medium. Assuming a uniform linear array (ULA), we develop DOA estimation algorithms based on covariance matching applied to a reduced-size statistic obtained from the sample covariance matrix after redundancy averaging. Next, a computationally efficient estimator based on AR modelling of the coherence loss function is derived. A theoretical expression for the asymptotic covariance matrix of this estimator is derived. Finally, the corresponding Cramer-Rao bounds (CRBs) are derived. Despite its simplicity, the AR-based estimator is shown to possess performance that is nearly as good as that of the covariance matching method     

Estimation of the directions of arrival of signals in unknowncorrelated noise. I. The MAP approach and its implementation

The authors propose a method of direction of arrival (DOA) estimation of signals in the presence of noise whose covariance matrix is unknown and arbitrary, other than being positive definite. They examine the projection of the data onto the noise subspace. The conditional probability density function (PDF) of the projected data given the signal parameters and the unknown projected noise covariance matrix is first formed. The a posteriori PDF of the signal parameters alone is then obtained by assigning a noninformative a priori PDF to the unknown noise covariance matrix and integrating out this quantity. A simple criterion for the maximum a posteriori (MAP) estimate of the DOAs of the signals is established. Some properties of this criterion are discussed, and an efficient numerical algorithm for the implementation of this criterion is developed. The advantage of this method is that the noise covariance matrix does not have to be known, nor must it be estimated     

Estimation of the directions of arrival of signals in unknowncorrelated noise. II. Asymptotic behavior and performance of the MAPapproach

For pt.I see ibid., vol.40, no.8, p.2007-17 (1992). The asymptotic behavior and the statistical performance of the maximum a posteriori (MAP) estimate of the directions of arrival (DOAs) of signals applicable in an environment where the sensor noise is unknown and correlated. Computer simulations were performed to confirm the correctness of the performance analysis, and a comparison of the performance of the MAP estimate with other methods is also presented     

Angles of arrival of indoor multipath

Some preliminary results of the angles of arrival of multipath components in indoor radio channel measurements are reported. The results show that strong multipath components arrive at the receiver in various directions.<>     

Estimating directions of arrival of completely and incompletelypolarized signals with electromagnetic vector sensors

We are concerned with direction-of-arrival estimation and signal classification with electromagnetic vector sensors for scenarios where completely and incompletely polarized signals may co-exist. We propose an efficient ESPRIT-based method, address the identifiability of the proposed method, and compare its performance against CRB     

The estimation of the directions of arrival of the spread-spectrum signals with three orthogonal sensors

An effective technique in estimating the directions of arrival (DOAs) of incoming signals using three orthogonal sensors is proposed. The channel model with multipath transmissions for code-division multiple access (CDMA) users whose signals are modulated with binary phase-shift keying (BPSK) is used. Utilizing the maximum-likelihood (ML) method, the channel impulse response vectors of the three sensors can be estimated, then all of the corresponding propagation delays and amplitude weights of the three sensors' channels can be obtained. By comparing the propagation delays of the three channels, we can identify the same signal replica, then its DOA can be estimated by the relation of the three corresponding attenuation weights. Calculating results show this method can reach fairly high accuracy, and it needs only three sensors while in other techniques the required number of sensors is greater than the number of estimated signals.     

相干多径环境下信号空间特征及波达方向估计

以均匀直线阵和四阶累积量为基础,提出了一种新的空间特征盲估计算法.该算法首先利用阵列输出四阶累积量构造了一种空间特征矩阵,对其作特征分解可以得到各用户的空间特征估计.然后,在空间特征估计基础上,结合前向/共轭后向空间平滑技术进行了多径波达方向(Direction of Arrival,DOA)估计.该方法突破了传统MUSIC、ESPRIT等算法的局限,可以利用M阵元估计2M2/3个DOA,且各DOA与信源自动配对.该算法不依赖于信号具体特征,适用于任意加性高斯噪声(如有色噪声)环境.理论分析和仿真结果说明了算法的有效性和鲁棒性.     

On arrival of paths in fading multipath indoor radio channels

Arrival of the paths in fading multipath channels obtained from several manufacturing floors and college campus laboratories at 910 MHz are studied. The discrepancies between the empirical distribution of the arriving paths and Poisson arrivals are discovered. The modified Poisson process is shown to fit the arriving paths closely.<>     

Adaptive beam-space nulling of multipath signals

A beam-space adaptive nulling technique that has potential for applications in communication circuits degraded by multipath signals is described. The technique is based on a well-known vector relationship in beam space. A linear transformation is used to prevent the degradation of the desired signal reception. Results are presented from tests of the technique that were conducted using real multipath data. The data used in these tests were recorded using a 32-element sampled aperture antenna (SAMPAR). These measurements were carried out on an over-water path. The direct signal, i.e. the signal that propagates via the shortest path from the transmitter to the receiver antenna, is selected as the desired signal; its reception is enhanced by suppressing the unwanted signals, i.e. the multipath signals that propagate via a reflection from the surface of the water. Examples are given in which the wanted and unwanted signals are separated by less than a beamwidth     

Estimation of multipath parameters in wireless communications

In a parametric multipath propagation model, a source is received by an antenna array via a number of rays, each described by an arrival angle, a delay, and a fading parameter. Unlike the fading, the angles and delays are stationary over long time intervals. This fact is exploited in a new subspace-based high-resolution method for simultaneous estimation of the angle/delay parameters from multiple estimates of the channel impulse response. A computationally expensive optimization search can be avoided by using an ESPRIT-like algorithm. Finally, we investigate certain resolution issues that take the fact that the source is bandlimited into account     

密闭狭小环境中多径信号对码环的影响

基于提高北斗接收机在密闭狭小环境中定位效果的目的,通过建立密闭狭小环境中多径信号的数学模型,选取直视信号与6路反射信号组成的复合信号进行分析,使用归一化非相干超前减滞后幅值法对信号进行鉴相,得到密闭狭小环境中多径信号造成的码相位误差,分析误差产生的原因。提出了一种通过布置吸波材料来减小北斗多径信号造成的码相位误差的方法,使多径信号造成的码相位误差减少90%。     

多径信道下MPSK信号的调制分类算法

针对多径信道中MPSK信号的调制分类问题,提出一种新的基于小波变换的分类算法.算法所用的小波变换相位信息特征对平坦衰落信道具有衰落不变性,对频率选择性衰落信道也具有很强的抗多径能力.与已有方法相比,新算法极大地降低了对多径信道冲激响应模式的限制,更具有普适性.理论分析和计算机仿真试验都证明了新分类算法的稳健性和有效性.     

Errors in estimating local average power of multipath signals

Narrow-band field strength measurements of mobile radio signals are often averaged over some small interval to determine the effect due to shadowing. It is demonstrated that that part of the remaining variation is due to the local averaging process itself, and that the shadowing effect has been overestimated.<>     

Estimation of multipath channel response in frequency selectivechannels

A novel discrete-time method is proposed for estimating the impulse response of a frequency-selective digitally modulated communication channel. The received signal is first demodulated and sampled and then the fourth-order cumulants of the resulting discrete-time sequence are estimated. The method estimates the channel impulse response from the complex cepstrum of the aforementioned fourth-order cumulants (i.e. tricepstrum). The method depends only on the second- and fourth-order statistics of the transmitted sequence and is capable of reconstructing nonminimum-phase impulse responses. Monte Carlo simulation results demonstrate the effectiveness of the method, its low sensitivity to observation noise, and its improved performance in terms of probability of error or the reconstructed transmitted sequence     

多径信道中MPSK信号的调制识别算法

针对多径信道中MPSK信号的调制分类问题，提出一种新的基于高阶累量的分类算法，算法所用特征对平坦衰落信道具有衰落不变性，对频率选择性衰落信道也具有很强的抗多径能力。与已有方法相比，本文算法极大地降低了对多径信道冲激响应模式的限制，更具适应性。理论分析和计算机仿真试验都证明了新分类算法的稳健性和有效性。     

Blind detection of multirate asynchronous CDMA signals in multipath channels

Blind detection of a desired user's signal in a multirate direct sequence code division multiple access (DS-CDMA) system [using either variable sequence length (VSL) or multicode (MC) access] is considered. A code-constrained inverse filter criterion (IFC)-based blind detector for equal-rate CDMA signals to detect a desired user's signal was presented by Tugnait and Li (2001). The IFC method exploits the higher order statistics of the data. In multirate CDMA systems, a high-rate user signal may be treated as the superposition of several virtual basic-rate signals. The code-constrained IFC-based detector may be used to detect a given basic-rate virtual signal. This, however, does not solve the problem of combining the detected virtual basic-rate signals to yield the original high-rate signal since the former may be delayed by different equalization delays, may be multiply extracted, and may be in different "order." In this paper, novel approaches combining the code-constrained IFC and a penalty function are developed to cope with this problem for VSL and MC multirate access methods. Global minima of the proposed cost functions are analyzed. Three illustrative simulation examples are presented, including an example where the proposed algorithms are compared with an existing subspace approach (and its modifications), a clairvoyant matched filter receiver, and a known channel linear minimum mean-square error (MMSE) receiver.     

On the combining of multipath signals in narrowband Rayleigh fadingchannels

This paper deals with the process of constructive and destructive addition of multipath signals in a Rayleigh fading channel. It derives closed formulas associating the number of multipaths with the Rayleigh statistics of the channel and it displays the accuracy of these formulas by means of simulation. The primary conclusion is that multipaths add constructively with high probability, thus the more the multipaths the larger the mean power level experienced at the receiver. In this context, multipath propagation exhibits a beneficial property that could be exploited for designing improved performance receivers     

密集多径环境下超宽带信号的快速捕获

提出了一种新颖的密集多径环境下超宽带信号的快速捕获方法,即分块量化比特翻转搜索。这种方法综合了比特翻转搜索(bit reversal search)与分块量化搜索并作出了改进。仿真结果表明此方法可以显著提高在密集多径环境下超宽带信号的捕获速度。     

Feedback beamforming technique for receiving multipath coherent signals

A novel feedback beamformer is proposed for receiving multipath coherent signals. First, a subtraction-based minimum variance distortionless response beamformer is utilized to obtain an estimation of the desired signal. Then its output is fed back to the original full aperture array where a minimum mean square error (MMSE) beamformer is applied. Due to multipath-matched feature of the MMSE beamformer, the novel feedback beamformer can combine multipath signals without aperture loss. Two feedback schemes are proposed and their effectiveness is verified via simulation.     

An angle difference of directions arrival algorithm with channel inconsistency

This article proposes a new angle difference of directions arrival (ADOA) estimation algorithm. It can estimate the values of ADOA of incidence signals even under channel incoherence environments. It performs an eigenvalue decomposition of a covariance matrix to obtain signal and noise subspace eigenvectors, then estimates the values of ADOA of signals based on the orthogonality between the noise subspace eigenvectors and steering vectors. Its main advantage is that the performance is not degenerated by array elements channel incoherence. In addition, the system complexity is also reduced. Finally, the numerical simulations have been conducted to verify the performance improvement of this algorithm.