数字滤波技术在电阻率测井仪器中的应用探讨

以微球测井仪为例建立了对采集数据作数字滤波处理的数学模型,并进行了仿真研究.其结果表明,与传统模拟处理方法相比,数字滤波器不仅能有效减少硬件,而且更因其阶数高、幅频特性更理想、无温度漂移、处理精度和可靠性较高,从而提高了数据处理的质量,其处理速度也能够满足测井实时性的要求.此方法对其它电阻率仪器也可适用.     

Performance of 60 GHz Virtual Cellular Networks Using Multiple Receiving Antennas

During the past years, research covering propagation, channelcharacterization and wireless systems performance have yield asubstantial knowledge of the 60 GHz channel. The unlicensed 60 GHzfrequency band presents many attractive properties for wirelesscommunications. The environments in which the 60 GHzinfrastructure are to be designed are typically propagation- andcoverage-limited. This paper describes the important factors thatmust be taken into account when designing a wireless local areanetwork (WLAN) architecture operating in this frequency band.Therefore, we motivate the reasons of using distributedtransmitting antennas and multiple receiving antennas (MRA) inorder to mitigate the poor Direction of Arrival (DoA) diversityand to exploit the spatial diversity at the receiver. Such asystem can be considered as a multiple input multiple output(MIMO) system. We investigate the advantages of combining aVirtual Cellular Network (VCN) (using single frequency network anddistributed antennas) and MRA for the downlink. Several ways tocombine the signals with different levels of complexity arepresented. In the most complex case using Singular ValueDecomposition (SVD), it is possible to add coherently thecontribution of each antenna in a virtual cell while retaining thepath diversity inherent to the VCN infrastructure. The schemesyield several advantages: symbol diversity is improved, pathdiversity is still present, antenna gain using multiplebeamformers is increased and the multipath can be reduced. Theconcept is applicable to most types of single frequency networksbut it is especially well appropriate for the 60 GHz VCN/WLANusing orthogonal frequency division multiplexing (OFDM).Simulations give a realistic performance for QPSK, 8-PSK, and16-QAM baseband modulations with a 256-subcarrier OFDM using arate 1/2–convolutional code for a 2 ×2 VCN system.Results show a E_b/N₀ improvement of up to 6.2 dB usingthesingular value decomposition method with 16-QAM compared to thesingle input single output (SISO) coded reference.     

Two-dimensional flow towards a guarded downhole sampling probe: An experimental study

The guarded-probe concept for downhole fluid sampling is analogous to that of focused electrodes for borehole electrical measurements. The guard part of the probe surrounds the sample probe and draws fluid from the near-wellbore region of the rock formation where pore fluid is contaminated with drilling fluid filtrate (invasion fluid). Fluid entering the central sample probe comes from points deeper in the formation, where contamination is lower. We report experiments performed to study the guard probe concept in two dimensions. For these experiments, glass beads contained in a thin cell formed the porous medium. The original, uncontaminated pore fluid was an optical index-matching oil. The invasion fluid was the same oil with a dissolved dye. A camera recorded the displacement of the dyed fluid by the clear fluid and the dye concentration was measured in the flow lines through which fluid was withdrawn. The experiments verify that in 2 dimensions a guarded probe produces clean samples of original pore fluid faster than would a simple probe. The experiments were successfully modeled, without adjustable parameters, by means of a finite-difference numerical reservoir simulator and by computations based on an approximate velocity field given by a complex variable solution of the Laplace equation.     

基于软件无线电的相控阵雷达系统研究

从软件无线电的概念出法,论述了在相控阵雷达系统中采用软件无线电技术的必要性和可能性;其次详细地论述了相控阵雷达系统中软件无线电的实现形式:即天线子系统,收、发子系统,信号处理子系统。最后对软件无线电技术在现代雷达中的发展进行了展望。     

四元数矩阵重构鲁棒波束形成算法

极化敏感阵列的四元数信号模型保持了偶极子阵元分量之间固有的正交性,因而四元数MVDR（Q-MVDR）算法具有比传统复数域MVDR算法更优的性能,但在强期望信号和导向矢量失配的情况下,Q-MVDR算法性能严重下降,甚至会出现期望信号相消现象.针对此问题,提出一种基于四元数矩阵重构的鲁棒波束形成算法.首先建立极化敏感阵列的四元数模型,将协方差矩阵重构方法扩展到四元数域,利用子空间方法得到干扰信号的导向矢量估计,并采用Capon谱估计方法获得干扰信号的功率,重构出干扰噪声协方差矩阵;然后根据信号子空间与噪声子空间的正交性,以及期望信号导向矢量与信号子空间属于同一子空间的特性,将权矢量投影到四元数信号子空间,对期望信号导向矢量失配误差进行修正;最后通过仿真实验验证了算法的有效性.仿真结果表明,在强期望信号和期望信号导向矢量失配时,与传统算法相比,本文算法有效避免期望信号相消引起的性能下降,增强了算法的鲁棒性,可以达到接近最优值的输出信干噪比(SINR).     

多天线无人机通信系统中的安全波束成形方案

针对第6代移动通信系统中多天线无人机通信下行链路传输系统,在有多个合法用户和单个窃听者的场景以及已知窃听者统计信道状态信息的情况下,提出了2种安全波束成形方案：一种是基于迫零算法的波束成形方案,在系统传输总功率受限条件下最大化系统可达安全速率,得到了波束成形权矢量和功率分配因子的闭合解;另一种是基于增强信漏噪比算法的波束成形方案,采用一种分式规划和交替方向乘子法（ADMM）相结合的迭代算法,实现波束成形权矢量和功率分配因子的设计.仿真结果表明,相比较于迫零算法,基于ADMM的增强信漏噪比算法能够有效地提升系统的安全性能.     

LCMV分频的改进维纳滤波后置波束形成算法

针对封闭环境中语音信号受到混响影响,提出了LCMV分频的改进维纳滤波后置波束形成算法。该算法通过计算麦克风阵列接收到含混响信号的短时傅里叶变换得到频域阵列信号,对频域阵列信号分频处理,将分频的信号进行线性约束最小方差波束形成滤波处理,该波束滤波根据每个频段上混响时间不同的特性对频域阵列信号进行分频处理后,将波束形成算法分别应用到高低频中,以提高混响抑制的精度;再由频域阵列信号的组合功率谱进行维纳后置滤波以抑制混响,由麦克风阵列接收到混响信号的直达波和反射波之间不相关性及麦克风阵列接收信号的空间信息解决维纳滤波器的精确估计问题;最后由逆短时傅里叶变换恢复出时域信号。仿真结果表明,该算法对混响抑制具有明显的改善;且在混响时间600 ms条件下语音增强系统的PESQ值提高了0.26。     

弹性网正则化广义逆波束形成算法改进

广义逆波束形成凭借其空间分辨率高,抑制旁瓣能力强等优势得到广泛关注。为了提升一般广义逆波束形成的声源识别性能,基于弹性网正则化波束形成既能保证声源识别结果的稳健性又能体现声源信号的稀疏性。然而,在测量声源信号的过程中所产生的非相干噪声对声源结果产生不可避免的误差,为抑制测量过程的干扰噪声,结合对角降噪和特征值改进法重构波束形成正则化参数,提出了一种改进弹性网正则化的广义逆波束形成,以重构正则化参数区别干扰噪声和目标声源。进行了数值仿真和实验验证,结果表明该算法在中高频时主瓣宽度误差低于10 dB,且比弹性网正则化波束形成具有更高的空间分辨率以及稳健性,衰减旁瓣能力强。     

多天线中继系统中人工噪声辅助的安全波束成形

针对放大转发中继系统中转发信息易被窃听者截获的问题,提出了在中继节点处采用人工噪声辅助的安全波束成形方法。该方法以系统的安全速率最大化（SRM, secrecy rate maximization)为目标,在中继节点的总功率和单个天线功率受限情况下,联合设计最优的中继波束成形矩阵和人工噪声协方差矩阵。由于该SRM问题非凸,设计了双层优化算法,其中采用一维搜索解决外层优化问题,采用半定松弛及内点法解决内层优化问题。理论推导证明,内层优化问题总存在秩为1的最优解,即所采用的松弛技术是紧的。仿真结果表明所提的方法可以显著提高系统的安全性能。     

Labeling-based Zero-forcing Beamforming for LTE MU-MIMO

提出了一种聪明的TD-LTE MIMO操作模式,它结合了波束成形技术和闭环反馈MIMO的优点。当eNB获得UE上行SRS参考信号的信道信息,L1进行基于码本的信道估计量化和标签化。L1将标签上传到L2,L2基于标签进行多用户调度,这样较好地解决了基于迫零的UE配对和L1/L2间跨层资源分配这两个问题。 L1无需更多计算便可生成波束成形的预编码矩阵。同时,提出了在可接受的次优性能下一种易实现的一般性框架。为了达到目标,给出了新的码本设计标准和快速预编码矩阵的生成算法。