Joint multi-user space time block coding and beamforming via convolutional weighting

A convolutional weighting （CW） scheme applied to a half-wavelength spacing array was proposed for multi-user system to joint STBC （space time block ceding） and beam forming （BF）. The transmitting beam is equivalent to the product of two sub-beams. One is used to realize interference suppression, while the other is employed to form a couple of uncorrelated channels from base station （BS） to the desited user （to meet the requirement of STBC） and to maximize SINR （signal-to-interference-plus noise ratio） at the desired receiver. As an optimum combination of STBC and beam forming, the proposed scheme can achieve both full diversity order of STBC and array gain of BF. Meanwhile, it can also effec- tively restrain multi-user interference by nulling. Simulation results show that the proposed scheme can significantly improve the BER （Bit Error Rate） performance and enhance system capacity as compared with the conventional eigen-beamforming （EBF） technique applied to a half-wavelength spacing array.

Forming of Space Charge Wave with Broad Frequency Spectrum in Helical Relativistic Two-Stream Electron Beams

We elaborate a quadratic nonlinear theory of plural interactions of growing space charge wave （SCW） harmonics during the development of the two-stream instability in helical relativistic electron beams. It is found that in helical two-stream electron beams the growth rate of the two-stream instability increases with the beam entrance angle. An SCW with the broad frequency spectrum, in which higher harmonics have higher amplitudes, forms when the frequency of the first SCW harmonic is much less than the critical frequency of the two-stream instability. For helical electron beams the spectrum expands with the increase of the beam entrance angle. Moreover, we obtain that utilizing helical electron beams in multiharmonic two-stream superheterodyne free-electron lasers leads to the improvement of their amplification characteristics, the frequency spectrum broadening in multiharmonic signal generation mode, and the reduction of the overall system dimensions.

HIGH RESOLUTION REAL-TIME MEDICAL IMAGING BASED ON PARALLEL BEAMFORMING TECHNIQUE

Improvement of frame-rate is very important for high quality ultrasound imaging of fast-moving structures.It is also one of the key technologies of Three-Dimension(3-D) real-time medical imaging.In this paper,we have demonstrated a beamforming method which gives imaging frame-rate increment without sacrificing the quality of medical images.By using wider and fewer transmit beams in combination with four narrower parallel receive beams,potentially increasing the imaging frame-rate by a factor four.Through employing full transmit aperture,controlling the mainlobe width,and suppressing sidelobes of angular responses,the inherent gain loss of normal parallel beamfomer can be compensated in the maximal degree.The noise and interference signals also can be suppressed effectively.Finally,we show comparable lateral resolution and contrast of ultrasound images to normal single widow weighting beamformer on simulated phantoms of point targets,cyst and fetus of 12th week.As the computational cost is linear with the number of array elements and the same with Delay And Sum(DAS) beamformers,this method has great ad-vantages of possibility for high frame-rate real-time applications.

Robust Broadband Beam-Forming Based on the Feature of Underwater Target Radiated Noise

To the problem of the unknown underwater target detection, according to the feature that the underwater target radiated noise contains the stable line spectrum, a weighted method based on the main-to-side lobe ratio （MSLR） is proposed for broadband beam-forming. This weighted method can be implemented by using the following steps. Firstly, optimize the spatial spectrum of each frequency unit by the second-order cone programming （SOCP）, and obtain the optimized spatial spectrum with lower side lobe. Secondly, construct weighting factors based on the MSLR of the optimized spatial spectrums to from weight factors. Lastly, cumulate the spatial spectrum of each frequency unit via the weight statistical method of this paper. This method can restrain the disturbance of background noise, enhance the output signal-to-noise ratio （SNR）, and overcome the difficulty of traditional four-dimensional display. The theoretical analysis and simulation results both verify that this method can well enhance the spatial spectrum of line spectrum units, restrain the spatial spectrum of background noise units, and improve the performance of the broadband beam-forming.

An introduction to the riometer system deployed at China-Iceland joint Arctic observatory and its beam-forming correction method based on the preliminary data

The China-Iceland joint Arctic observatory(CIAO)has formally been operating since October 18,2018,and an imaging riometer system was deployed at CIAO in August 2019 for the conjunction observation purpose with the co-located ground-based all sky imager auroral observation system.The features of the riometer and antenna system are presented.The riometer’s beam-forming performance were evaluated with the analysis method introduced in detail.The analysis results showed that the mapping of beams was incorrectly ordered,and the correction has been made.The revised ordering result was reasonably verified and the analysis method was proved to be effective.

Design of 2D-Bootlace Lens with Five Focal Feed for Multiple Beam Forming

Utility of microwave bootlace lens is well established. For broadband and wide scanning network, it is required to op-timize and use features of this lens for better communication and scanning device. This report presents the design of a compact 2D bootlace lens with five focal feed for multiple beam forming. This design will help in reducing phase error and will provide power efficiency and better resolution during target tracking. This design will provide better aperture efficiency and scanning angle.

Modelling and Simulation on the Effect of Hot Forming Damage on Three-Point Bending Performance of Beam Components

The effects of forming damage are analyzed,which occur during hot stamping process,on the load-carrying capacity and failure mode of hot stamped beams.A damage-coupled pre-forming constitutive model was proposed,in which the damage during hot stamping process was introduced into the service response.The constitutive model was applied into the three-point bending simulation of a hot stamped beam,and then the influences of forming damage on the load-carrying capacity and cracks propagation were investigated.The results show that the forming damage reduces the maximum load capacity of the hot stamped beam by 7.5%.It also causes the crack to occur earlier and promotes crack to propagate along the radial direction of the punch.

Selection of Optimal Beam Forming Algorithm for Mobile Ad Hoc Networks

Ad hoc networks have drawn considerable attentions of researchers for the last few years. Various applications of ad hoc networks have been reported in the literatures including disaster management, battle field, environmental management, healthcare, and smart grid. Ad hoc networks have some limitations namely short operating life, unreliability, scalability, delay, high interference, and scarce resources. In order to overcome these limitations, numerous researches have been carried out. Smart antenna integration is one of them. It has been shown in the literatures that smart antenna can improve network’s capacity, increase network lifetime, reduce delay, and improve scalability by directing antenna radiation pattern in a desired direction. But, producing a desired antenna radiation pattern is not a simple task for resource constraint ad hoc networks. A careful selection of beam forming algorithm is required. In this paper we show that smart antenna system, consisting of circular microstrip antennas and arranged in a linear arrangement, is the most suitable choice for ad hoc network. We compare a number of smart antenna algorithms in this paper under different noisy conditions. We show that the Least Square Constant Modulus (LSCM) and Least Constant Modulus (LCM) algorithms outperform other algorithms in terms of directivity and minimized side lobes.

New Wideband Beam-forming Method Used in Underwater Communication System

A novel wideband beam-forming structure with constant beam width based on complex coefficients (FIR) digital filters used in underwater acoustic communication is proposed. First,the received signals are compensated with integer sampling period by using delay line. Then their complex envelopes are calculated by using frequency shift method. Finally,the envelopes are weighted by using complex coefficients FIR digital filters whose coefficients are optimized. Simulation results show that,in the communication band,the maximum difference between the designed beam and desired beam is less than 0.3 dB when the ratio of communication band to carrier frequency is 0.85.

Performance Enhancement for Adaptive Beam-Forming Application Based Hybrid PSOGSA Algorithm

Recently researchers were interested in hybrid algorithms for optimization problems for several communication systems. In this paper, a novel algorithm based on hybrid PSOGSA technique (combination of Gravitational Search Algorithm and Particle Swarm Optimization) is presented to enhance the performance analysis of beam-forming for smart antennas systems using N elements for Uniform Circular Array (UCA) geometry. Complex excitations (phases) of the array radiation pattern are optimized using hybrid PSOGSA technique for a set of simultaneously incident signals. Our results have shown tremendous improvement over the previous work was done using Uniform Linear Array (ULA) geometry and standard GSA in terms of normalized array factor and computational speed for normalized fitness values.

The Beam-Forming Technique for Enhancement of Noisy Seismic Refraction Data

We have described a method of obtaining useful information from noisy seismic refraction data. The simple method, tagged beam-forming technique, is based on the basic time-distance equations of refraction seismology. It involves basically of introducing relative time delays to individual seismic traces of seismic refraction spread to correct for the non-coincidence of the incidence seismic energy at different geophones, and averaging the traces to obtain the beam. The assumption here is that the signal is coherent between the geophones while the noise is random, and for groups of geophones corresponding to the same refraction segments of the travel time curve, this basic assumption is valid. The process of beam forming therefore leads to improvement in signal-to-noise ratio (SNR) and correct determination of the intercept times which are subsequently used to compute other geologic layer parameters. The ability of the applied technique to filter out or minimize random noise has been tested using a modified random number routine. The performance test on computation of geologic layer parameters using very noisy synthetic data reveals that the method is still very reliable even with very poor quality data having SNR as small as 0.05.

Optimization of Leaky Feeder Slot Spacing for Better Beam Forming in Mines and Tunnels

The radiating cable (or leaky feeder) is the leading solution for distributed broadband wireless access in underground mines and tunnels. The traditional radiating cable has equally spaced slots along its axis radiating evenly. However, with the new requirement for tracking and localization of miners, this paper shows how to modify the leaky feeder to function as a beam forming antenna array by appropriately optimizing the slot spacing. Optimizing the leaky feeder slot distances using Genetic algorithm has a good impact on the channel parameters, making it an excellent choice for leaky feeder antennas. Linear, as well as bent practical leaky feeder shapes, were considered, and we tested five different optimization algorithms and compared side lobe energies, varying the slot distance which had an impact on side lobe level. Also, we derived the expression for the BER, spectral efficiency and throughput considering a time-varying wireless channel. We observed that as the radius of curvature of the feeder increased (approaching a straight line), the spectral efficiency decreased as expected. Interestingly different optimization algorithms perform differently at different carrier frequencies. An optimization method should be chosen according to the required goal to be achieved (maintaining uniform equal power along the cable, or a more directed beam, or using a certain frequency of operation).

Superplastic formability of Ti-6Al-4V butt-welded plate by laser beam welding

The superplasticity of Ti-6Al-4V butt-welded plates by laser beam welding(LBW)was studied in virtue of hot tensile tests and superplastic bulging tests.Furthermore,microstructural evolution of weld metal upon superplastic forming was systematically analyzed via metallographical tests and scanning electron microscope(SEM).The relation between the microstructure of weld metal and its superplastic ability was discussed.The experimental results show that Ti-6Al-4V butt-welded plates by LBW possess superplasticity.The maximum elongation is up to 154%and the maximum bulge height can be up to 1.81 times the internal radius of the female die.There is an optimum value of the bulge height for bulging gas pressure.

Feasibility of developing composite action between concrete and cold-formed steel beam

Cold-formed steel structures are steel structure products constructed from sheets or coils using cold rolling, press brake or bending brake method. These structures are extensively employed in building construction industry due to their light mass, ductility by economic cold forming operations, favorable strength-to-mass ratio and other factors. The utilization of cold formed steel sections with concrete as composite can hugely reduce the construction cost. However, the use of cold formed steel members in composite concrete beams has been very limited. A comprehensive review of developments in composite beam with cold formed steel sections was introduced. It was revealed that employing cold-formed steel channel section to replace reinforcement bars in conventional reinforced concrete beam results in a significant cost reduction without reducing strength capacity. The use of composite beam consisting of cold-formed steel open or close box and filled concrete could also reduce construction cost. Lighter composite girder for bridges with cold-formed steel of U section was introduced. Moreover, types of shear connectors to provide composite action between cold-formed steel beam and concrete slab were presented. However, further studies to investigate the effects of metal decking on the behavior of composite beam with cold-formed steel section and introduction of ductile shear connectors were recommended.

STIFFNESS EQUATION OF FINITE SEGMENT FOR FLEXIBLE BEAM-FORMED STRUCTURAL ELEMENTS

The finite segment modelling for the flexible beam-formed structural elements is presented, in which the discretization views of the finite segment method and the difference from the finite element method are introduced. In terms of the nodal model, the joint properties are described easily by the model of the finite segment method, and according to the element properties, the assumption of the small strain is only met in the finite segment method, i. e., the geometric nonlinear deformation of the flexible bodies is allowable. Consequently,the finite segment method is very suited to the flexible multibody structure. The finite segment model is used and the are differentiation is adopted for the differential beam segments. The stiffness equation is derived by the use of the principle of virtual work. The new modelling method shows its normalization, clear physical and geometric meanings and simple computational process.

新一代Wi-Fi的新型感知信息压缩方法

通信设备由于和雷达设备的工作存在重叠,也可以实现目标检测。但是传统的通信协议采用显式反馈传输信息,导致采用通信设备检测无法保留感知信息,因此可以对显式反馈的分解流程进行改进,从而在通信的间隙实现对环境目标的感知。在MIMO系统中,波束成型是发射端利用MIMO信道状态信息生成导向矩阵,从而提升接收端接收性能的一种技术。目前显式反馈波束成型是通信中波束成型的主流方式,接收端会对接收到的信道矩阵进行奇异值分解后转换成一系列角度值传回发射端。虽然采用传统的矩阵分解流程获得反馈矩阵可以有效降低反馈的冗余信息量,但是通常会丢失掉通信设备在感知过程中获得的大部分重要信息,从而导致利用Wi-Fi信号进行目标探测的功能受到限制。研究发现对于接收到的信道矩阵利用传统的分解方式获得的反馈矩阵特征向量无法保留目标的距离,速度信息。本文提出了一种新型的分解方式,基于信道矩阵的协方差矩阵,先求解左奇异矩阵,再利用左右两个酉矩阵正交向量的对应关系,进一步求解从而获得改进的右奇异矩阵,所提改进方法保留了目标的距离、速度以及角度信息,极大地提升了有效反馈信息量。最后通过仿真实验验证了所提方法的有效性。

基于波束形成的海上智能天线算法

远距离海上雷达探测由于海上环境的复杂性容易受到杂波干扰,常用的最小均方算法通过在干扰噪声中形成主波束并引导至目标信号,有效解决了杂波干扰问题。通过对自适应智能天线波束形成技术的海上应用进行研究,给出了常用的天线阵列结构模型和信号模型,研究了智能天线中的自适应波束成型算法,目前在这一领域的解决方案中最小均方算法最为常见,但其存在收敛速度差、通用性低等问题。本文将优化遗传算法引入,对传统遗传算法中初始种群规划和交叉操作进行了优化和改进。仿真实验表明,与最小均方算法、传统遗传算法相比,优化遗传算法对杂波的抑制效果提高了28%,收敛速度提升了3倍,具有良好发展前景。

UHF波段无源雷达低仰角波瓣分裂现象分析及校正方法

针对低频段无源雷达低仰角远程预警探测时波瓣分裂影响俯仰向探测空域覆盖的问题,提出了一种波瓣分裂校正方法.首先分析了波瓣分裂形成原因和影响因素;然后基于阵列流型拟合思想,提出了一种利用最小二乘法求解变换矩阵的校正方法;最后通过仿真分析了角度量化间隔、角度变换区间对校正误差的影响,验证了校正方法的有效性.这对改进基于数字广播电视信号的无源雷达性能提供了参考.

基于DDPG的智能反射面辅助无线携能通信系统性能优化

针对智能反射面(IRS, intelligent reflecting surface)辅助的多输入单输出(MISO, multiple input singleoutput)无线携能通信(SWIPT, simultaneous wireless information and power transfer)系统,考虑基站最大发射功率、IRS反射相移矩阵的单位膜约束和能量接收器的最小能量约束,以最大化信息传输速率为目标,联合优化了基站处的波束成形向量和智能反射面的反射波束成形向量。为解决非凸优化问题,提出了一种基于深度强化学习的深度确定性策略梯度(DDPG, deep deterministic policy gradient)算法。仿真结果表明,DDPG算法的平均奖励与学习率有关,在选取合适的学习率的条件下,DDPG算法能获得与传统优化算法相近的平均互信息,但运行时间明显低于传统的非凸优化算法,即使增加天线数和反射单元数,DDPG算法依然可以在较短的时间内收敛。这说明DDPG算法能有效地提高计算效率,更适合实时性要求较高的通信业务。

装配式冷弯厚壁型钢半刚性梁-柱节点抗震性能试验研究

冷弯型钢在装配式结构中应用具有天然的优势,为了扩展冷弯厚壁型钢结构的使用范围,克服冷弯厚壁钢的缺点,设计6个新型分层装配式“十字型”梁-柱节点,进行循环加载试验,对梁-柱节点的破坏模式、初始刚度、骨架曲线、等效黏滞阻尼系数、能量耗散系数、割线刚度、滞回曲线和关键部位应变分布进行研究,主要得到以下结论:通过螺栓和节点板的滑移,半刚性节点具有一定的耗能能力。增设高强螺栓可以提高梁柱节点的承载力,初始刚度和耗能能力也得到提高,避免梁端与连接板孔壁承压。增加可更换节点翼缘板,对梁-柱节点的破坏模式没有明显影响,承载能力、耗能能力、初始刚度分别得到较大提高。