双正交电磁矢量阵列低角估计方法研究

电磁矢量阵列由于利用了信号的极化信息,能显著提高阵列的环境感知性能。建立双正交电磁矢量阵列低仰角测高多径模型,提出利用极化平滑与空间平滑结合的预处理方法对直达波和多径进行解相干,同时利用极化和空域信息提高低仰角角度估计性能;并推导低仰角多径模型下双正交电磁矢量阵列的Cramer-Rao界,分析极化参数对测角性能的影响。仿真实验结果表明,低角情形下电磁矢量阵列相较于标量阵列测角性能更优;所提的极化空间平滑算法由于结合了极化平滑和空间平滑的优点,较现有方法解相干效果更好,精度更高,特别适用于直达波和多径极化状态差异较小的低仰角情形。     

基于波束域的米波雷达低仰角波达方向估计

针对米波雷达低仰角工作时除了收到目标的直达波外,还会收到与直达波相干的地(海)面反射的多径信号,提出了一种基于波束域的米波雷达低仰角波达方向估计的新算法.利用阵列输出数据协方差矩阵构造一个Toeplitz矩阵,以实现对雷达回波数据的解相干;在波束域对降维后的数据协方差矩阵应用基于信号子空间的角度超分辨算法实现波达方向估计;最后,研究了波束域下米波雷达低仰角波达方向估计的特点,分析了不同信噪比、波束个数对算法性能的影响.所提算法不但可以有效地克服多径效应,还极大地降低了运算量,理论分析和计算机仿真都证明了新算法的优越性.     

多径信道中基于盲波束成形的CDMA多用户检测和伪码估计

在分析阵列天线接收的多径CDMA信号的基础上,发掘阵列信号子空间与扩频用户伪码序列的关系,对传统的子空间波束成形器结构做了改进,提出一种新的基于盲波束成形的伪随机码序列盲估计算法。算法采用复独立分量分析法迭代,得到盲波束成形器系数,能在波达方向未知的情况下,估计各个用户的扩频序列。本文同时提出一种基于盲波束形成的异步多径CDMA信号多用户检测算法,可以在未知各个用户扩频码和波达方向的先验知识条件下,完成多径异步CDMA信号的多用户检测。算法由于同时利用了扩频增益和阵列天线分集增益,相比于单天线多用户检测算法性能有所提高。理论分析和仿真结果验证了算法的可行性。      

基于多径分布源模型的米波雷达测高算法

针对复杂环境下的米波雷达低仰角测高问题,建立多径信号服从高斯分布源的阵列信号模型,提出一种广义约束多重信号分类(MUSIC)算法。该算法将多径信号作为约束,通过限制信号子空间包含多径导向矢量,来提高直达波的估计精确度。算法性能不受信号相干和地面反射系数的影响。与传统的测高算法相比,该方法在复杂反射地形下能有效进行目标高度估计。计算机仿真结果验证了该算法的可行性。     

米波雷达低仰角DOA估计及阵列通道误差校正

现有的阵列校正算法几乎都没有考虑存在多径效应时的情况,对此提出了一种米波雷达低仰角环境下波达方向估计和阵列通道误差校正的新算法.先对各子阵接收信号做预处理,使通道误差对每个子阵的影响一致,这样阵列旋转因子就与通道误差无关.再对各子阵接收数据进行线性变换和差分处理,利用阵列旋转不变性,实现波达方向估计.最后利用精确求得的波达方向值进行阵列通道误差的校正,算法避免了以往自校正算法联合波达方向和误差矩阵进行最大似然多维寻优的缺点,不但运算量小,还可以有效地克服多径效应.理论分析和计算机仿真都表明了新算法的优越性.     

复杂阵地米波雷达低仰角测高算法研究

针对复杂阵地下的米波雷达低仰角测高问题,建立多径信号服从高斯分布源的阵列信号模型,提出一种基于多维交替投影的合成导向矢量最大似然算法。该方法将回波信号的相关矩阵,在各个模型参数中交替投影,该方法可以同时对直达波角度和多径信号分布源参数进行精确的估计,并可以有效地对低仰角低空目标进行高度测量。与现有的测高算法相比,该方法在复杂阵地下能有效进行目标高度估计。计算机仿真结果和实测数据处理结果证实了该算法的可行性。     

波束域最大似然测高方法

针对雷达在低仰角搜索和跟踪目标时波束打地、受阵地反射多径影响严重的问题,提出了波束域最大似然雷达低仰角测高方法。该方法首先形成俯仰多波束覆盖目标,然后使用最大似然算法对多波束的目标数据进行处理,通过空间谱能量最大化的角度信息估计目标仰角和高度。与传统的和差波束及多波束比幅测角方法相比,该方法受多径影响小,具有较高的角度分辨率和高测量精度。计算机仿真和实测数据的处理结果验证了该算法可行有效。     

互相关矩阵重排获取信号子空间的二维DOA估计算法

本文提出一种L型阵列的二维子空间DOA估计算法,该算法通过重排阵列接收数据的互相关矩阵获取信号子空间,然后根据信号子空间生成一个二维谱函数,最后通过二维搜索估计信号的来波方向。由于该算法采用二维谱峰搜索,所以不需要对俯仰角和方位角进行配对。与二维MUSIC算法相比,该算法的估计精度略有下降,但该算法不需要对矩阵做特征值分解,计算量降低且易于实现。文中给出了该算法的推导过程和具体实现步骤,并进行了实验仿真,仿真结果说明了算法的有效性。      

一种双基地嵌套MIMO雷达快速角度估计算法北大核心CSCD

针对双基地嵌套多输入多输出雷达现有算法复杂度较高的问题,文中提出了一种基于泰勒展开离散傅里叶变换(DFT)的快速角度估计算法。该算法首先将匹配滤波输出转化为等效虚拟阵列接收信号的DFT空间谱,随后通过谱峰搜索得到波离方向(DOD)和波达方向(DOA)的初始角度估计,然后通过相位旋转技术在角度初始估计值附近搜索得到DOD和DOA的二次角度估计,最后根据虚拟阵列等效方向矩阵的一阶泰勒级数展开式对角度二次估计值进行误差修正,计算得到修正后的DOD和DOA的精确角度估计。与子空间算法相比,该算法避免了协方差矩阵计算和特征值分解,不仅提高了估计性能,而且显著降低了计算复杂度。仿真结果验证了所提算法的有效性和优越性。     

相干分布式信源二维波达方向估计算法

针对相干分布式信源二维波达方向估计算法多采用谱峰搜索导致计算复杂度较大的问题,该文提出了一种二维波达方向分离估计算法。该算法通过将积分形式的相干分布式信源方向向量化简为点信源方向向量与实向量的Schur-Hadamard积,对子阵X接收的数据构造二阶统计量;利用传播因子最小二乘估计子阵X与Z,X与W之间的旋转不变矩阵。由二阶统计量与旋转不变矩阵分别估计方位角与仰角,对于接近90的仰角也可给出有效的估计。与传统子空间算法相比,无需任何谱峰搜索和特征值分解,降低了计算复杂度。仿真实验表明了所提算法的有效性。     

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     

Coastal multipath fading

While flight testing airborne satellite communication systems, two-ray multipath fading has been regularly encountered at low satellite elevation angles during over water flights. In addition, an unexpectedly fast multipath fading was experienced as the aircraft transitioned from over land to over water. This unusual multipath fading occurred at medium and high elevation angles where the antenna discrimination should have reduced the reflected signal to an insignificant value. The coastal multipath has been recorded on over twenty occasions by different aircraft using a variety of antennas and flying over various north and central American coastlines. The rate of the multipath fading and fading amplitude suggests that the ocean has a very high reflection coefficient near shore and that some other mechanism such as dielectric wedge diffraction may play a part in the unexplained multipath fading.     

基于双极化圆阵天线的多路径干涉仪测向研究

当低空掠海反舰导弹攻击目标舰船时,因为海面多路径散射波的存在,导致舰船上传统的相关干涉仪测向不准,从而不能有效反击拦截导弹。提出了一种基于双极化圆盘阵列天线的多路径相关干涉仪的测向方法,其工作原理为(假设反舰导弹天线是垂直极化方式)当圆盘阵列天线选择垂直极化方式时,干涉仪接收到导弹直达和海面多路径散射的混合信号;当圆盘阵列天线选择水平极化时,干涉仪仅接收到海面多路径总散射信号。在仿真中,根据相关干涉仪算法和多信号分类(MUSIC)算法,可以画出混合信号和总散射信号的空间坐标分别为方位角3°,4°,俯仰角82°,86°,然后比较两者空间向量之间的关系,得出导弹的空间坐标方位角小于3°,俯仰角小于82°,最后通过最小方差无失真响应(MVDR)空域滤波和波束形成算法抑制干扰信号的影响, 通过仿真可以看出总散射信号方位角被抑制大约23 dB,俯仰角被抑制大约17 dB,并通过与仿真场景中导弹的实际空间坐标进行比较,可看出该方法依然存在一定的差距,但也为消除散射多路径对测向的影响提供一种思路与方法。     

Characteristics of L-band multipath fading due to sea surface reflection

For lowG/Tship-based earth stations in future maritime satellite communications, the effect of multipath fading due to sea surface reflection will be very important at low elevation angles. However, a practical model of theL-band multipath fading for fade prediction has not been available so far. A practical fading model is presented based on the shadowed Kirchhoff approximation theory for the coherent and incoherent components of the scattered power as a function of sea surface conditions. Using this model, theoretical fading depths are presented as a function of elevation angle, wave height, and antenna gain. The results indicate that intense fading occurs for wave heights greater than 50 cm, and the dependence on wave height is small under these conditions atL-band frequencies. Theoretical results presented agree well with experimental results obtained by field experiments.     

Subspace-based approach for DOA estimation using pilot symbol channel identification

In the paper, antenna processing is applied in the radio localisation frame. For a source of interest, the multipath directions of arrival (DOA) are estimated and the shortest/direct propagation path is identified. First, an unstructured estimate of the sampled channel impulse response is derived by use of pilot symbols. The channel response samples are then separately processed to recover the DOA of the relative paths. For stationary channels, it is suggested that smoothing be used in the case of a uniform and linear antenna array (ULA) to recover the source subspace. For fast fading channels, which is typically the case for high speed mobiles, it is shown that using a MUSIC like algorithm allows source subspace recovery by exploiting the gain diversity over a reduced number of slots with unchanged DOA and time delays. Separate processing of channel response samples reduces the constraint on antenna array size and allows comparison of the path lengths.     

Multipath fading at L band for low elevation angle, land mobilesatellite scenarios

We characterize multipath fading at low elevation angles for unshadowed line-of-sight propagation over a land-mobile satellite link. Equipment aboard a van recorded a CW signal from INMARSAT's geostationary satellite MARECS-B2 while driving in the states of Utah, Nevada, Washington, and Oregon. Elevation angles ranged from 7° to 14°. The van carried a tracking helix antenna with beamwidths in the principal planes of approximately ±18°. Multipath fading was observed in flat and hilly terrain and is compared with an example of fading due to tree shadowing. The measurements demonstrate that multipath effects at low elevation angles may result in fades exceeding 7 dB for approximately 1% of the driving distance for a worst case scenario corresponding to driving in rolling, hilly terrain where the satellite is in front or behind of the vehicle. Fading in such a case is typically dominated by a single multipath reflection from a terrain feature. On the other hand, tree shadowing at low elevation (7°) may result in fades which exceed 25 dB at the 1% level     

柱面共形阵列天线盲极化波达方向估计算法

针对柱面共形阵列天线的单曲率特点,建立了柱面共形阵列天线的快拍数据模型,基于高分辨波迭方向(DOA)估计的子空间原理与秩损理论,结合合理的阵元排列结构设计,将信源极化状态、俯仰角以及方位角去耦合,通过参数的一维搜索与方程求解,实现了信源极化状态未知条件下的2D DOA估计.针对相干信源情况,推导了柱面共形阵列天线的解相...     

Experiment on coherent adaptive antenna array for wideband DS-CDMAmobile radio

A four-element pilot symbol-assisted coherent adaptive antenna array diversity receiver for 4.096 Mchip/s wideband direct sequence code division multiple access mobile radio is implemented and its performance in a multipath fading environment is evaluated by a laboratory experiment using hardware fading simulators. The receiver comprises an adaptive antenna array using the normalised least mean square algorithm and Rake combiner. It is demonstrated that, for the three-user case, the required average signal-to-interference ratio obtaining average BER of 10^-3 can be reduced by ~8 dB compared to four-branch antenna diversity     

BER performance of CMA adaptive array for high-speed GMSK mobilecommunication-a description of measurements in central Tokyo

This paper describes the performance of an adaptive array as a countermeasure to multipath fading for a 256 kbps Gaussian-filtered minimum shift keying (GMSK) mobile communication system operating in the 1.5 GHz band. An adaptive array having four antenna elements is implemented using the digital beam forming concept. The constant modulus algorithm (CMA) is employed for the adaptation process to ease the implementation. Measurements in central Tokyo of the bit error rate (BER) performance and an array pattern arising in the multipath environment are presented. Analysis of the array pattern confirms that the array succeeds in directing nulls to the delayed signals. BER performance shows an improvement in E_b/N₀, compared with that of a single antenna system, of 17.5 to 22 dB at a BER of 1.0×10^-2 in a frequency-selective fading channel     

Novel Directional Radiation Pattern by Genetic Algorithms in Indoor Wireless Local Loop

The genetic algorithm is used to synthesize the radiation pattern of the directional circular arc array to minimize the bit error rate (BER) performance in indoor wireless communication system. The impulse responses of the indoor channel for any transmitter-receiver location are computed by shooting and bouncing ray/image techniques. By using the impulse response of multipath channel, the performance of the synthesized antenna pattern on BPSK (binary phase shift keying) system with phase and timing recovery circuits can be calculated. Based on the topography of the antenna and the BER formula, the synthesis problem can be reformulated into an optimization problem and solved by the genetic algorithm. The novelty of our approach is choosing BER as the object function instead of sidelobe level of the antenna pattern, i.e., BER performance is defined as a object function to optimize the excitation coefficient of array by the genetic algorithm. The strong point of the genetic algorithm is that it can find out the solution even if the performance index cannot be formulated by simple equations. Besides, the genetic algorithm will converge to global extreme instead of local extreme and achieves a good antenna pattern. Numerical results show that the synthesized antenna pattern is effective to combat the multipath fading and can increase the transmission rate of indoor millimeter wave system.