Digital Beamforming for Unified Spread Spectrum TT&C System

In TT&C system,unified spread spectrum framework and adaptive antenna digital beamforming technologies are used to track, telemetry and command objects. Constant modulus array (CMA) and adaptive signal canceller estimate the direction of arrival (DOA) of every signal and use the optimum weighted vector to form the beams. The phase weighted vectors estimated from DOA improve the processing gain as well as being utilized in the transmitting of tele command signal to form the beam of specified object. Its processing performance is researched and simulated in this paper.     

Beamforming Technique of the Multi-aircrafts Management System

Under the operation mode of the multi-aircrafts , more aircrafts at the same time in the view area of one TT&C station. Obviously, it is unable to manage them for traditional methods. This paper proposes a new technique, which combines SDMA with spread spectrum CDMA. In SDMA, multi-beamforming is available by parallel data processing and one aircraft is tracked by one beam. Finally, simulation results of digital beamforming are provided.     

近场波束形成声源识别的改进算法

为提高近场波束形成方法的声源识别性能和阵列平面上最大声压贡献量的计算精度,首先基于球面波假设,采用除自谱的互谱波束形成算法,仿真分析了阵列传声器信号幅值校正对声学成像和声源识别的影响,结果表明:幅值的校正在提高阵列平面上最大声压贡献量计算精度的同时也带来了旁瓣水平增大,动态范围缩小等诸多不足.在此基础上,提出并设计了声源定位与强度幅值校正相结合的近场波束形成阵列平面卢压贡献量的改进算法,仿真分析与算例试验结果均表明:改进算法既能准确计算阵列平面上的最大声压贡献量,且旁瓣水平低,声源成像动态范围增大1.0～1.6dB.最后,利用改进算法进行了某车的声学密封性能试验,准确识别了该车的声学密封薄弱位置.     

基于声阵列技术的柴油机噪声源识别

为了准确识别某柴油机的噪声源,为进一步的低噪声改进指明方向,综合采用Beamforming(波束形成)和SONAH(统计最优近场声全息)2种阵列的声源识别方法对该柴油机噪声辐射最突出的进气侧噪声源进行识别。结果表明:噪声贡献量较大的1 650~2 200 Hz频率范围内对应的噪声源为进气总管、汽缸盖罩,920~1 450 Hz对应喷油器,而760~776 Hz和920~936 Hz分别对应油泵传动轴和油泵调速器。进一步的声贡献量分析结果显示:进气总管对该发动机进气侧辐射噪声的声功率贡献量达15.38%,喷油器、油泵调速器声功率贡献度量分别为5.47%和5.11%;汽缸盖罩和油泵传动轴声功率贡献量分别为4.85%和4.26%。综上,结合Beamforming和SONAH在不同频段内具有高分辨率的优点,可以在宽频带内进行声源识别,且试验实现简单,操作方便。     

Group based DBF MUD in CDMA mobile communication system

For the CDMA wireless cellular communication system, a new methodology is proposed to combine digital beamforming (DBF) with multi user detection (MUD) technology which harnesses the co channel interference mitigation and obtains better performance. The proposed approach assigns all the users within a cell into separated groups according to their direction of arrival (DOA). Then, only one DBF branch is employed for a singular group so that the main lobe is steered to the desired users in the group and nulls are directed to the mobile stations in other group. Furthermore, inter group interference is degraded by MUD following the DBF. The new strategy simplifies the weight vector calculation and solves the unorthogonal channel problem. Additionally, it decreases the bit error rate. The analysis and simulation illustrate the fruits of the new mechanism.     

The method of dynamic aperture control technology based on ultrasound imaging system

Dynamic aperture control technology is one of the most important parts in ultrasonic imaging system. Excellent control technology of dynamic aperture can effectively improve the quality of ultrasonic imaging. Based on deep analysis of ultrasonic beam distribution, a control method for dynamic aperture which can eliminate the scanning dead zone of focused beam is presented. The detection region is even divided according to the number of probe array elements. The desired focused beam width is calculated between the next two scan lines at different depths, and then according to the beam width, the required aperture size for different depths is determined. The method is not affected by the probe parameters or detection objects, and it can be widely employed in ultrasonic imaging system. The simulation experiments indicate that the proposed method can effectively improve the whole quality of ultrasonic imaging.     

球形传声器阵列三维波束形成性能

为分析球形阵列结构参数对三维波束形成声源识别性能的影响,基于延迟求和波束形成理论,仿真分析了主瓣宽度和最大旁瓣水平随阵列直径的变化规律,结果表明:在传声器布置形式一致的情况下,直径越大,阵列空间分辨率越好,但对旁瓣抑制能力越弱;模拟计算了5种典型球形阵列的阵列模式径向投影及最大旁瓣水平,结果显示:传声器均匀分布球形阵列的性能最好,在50～100rad/m的波数范围内,最大旁瓣水平约为-12dB,在波数高达220rad/m时最大旁瓣水平也低于-6dB。提高球形阵列传声器分布的均匀程度和密集程度能显著提高阵列性能。     

Minimum variance beamforming combined with MV-Based coherence factor applied to medical ultrasound imaging

In medical ultrasonic imaging, minimum variance beamforming (MV)can effectively improve imaging resolution, but the contrast is not improved. By considering the low contrast of minimum variance beamforming, a medical imaging method combined minimum variance beamforming and MV-based coherence factor is presented. First, the coherent sum in coherence factor is replaced by the output of MV to obtain weighting factor; and then the factor is used to weight the results of minimum variance beamforming. The simulated results indicate that the proposed method in the aspects of resolution and contrast is better than traditional delay and sum, minimum variance beamforming and medical imaging method combining minimum variance beamforming and coherence factor.     

基于声压球谐函数分解的球面波束形成噪声源识别

基于声压球谐函数分解的球麦克风阵列波束形成算法能够同时对三维空间所有方向进行声源定位,特别适用于内场噪声源的识别。该文以典型的50通道刚性球麦克风阵列为例,进行了声源识别性能仿真分析,结果表明：球谐函数截断长度、声源频率和声源位置等参数对阵列响应均具有显著影响,2 000 Hz对应的声压球谐函数最优截断长度为5,且所有声源位置的最大旁瓣水平的最大值可达-15.35 dB。在此基础上,开发了阵列动力学性能分析及声源识别成像软件。利用该软件对已知声源的试验算例进行声源成像,成像结果与声源真实位置吻合,表明该算法能准确识别声源,证实了自主研发程序的正确性。