Lower bound on BER performance for maximal ratio combining with weighting errors

The theoretical lower bounds on mean squared channel estimation errors for typical fading channels are presented by the infinite-length and non-causal Wiener filter and the exact closed-form expressions of the lower bounds for different channel Doppler spectra are derived. Based on the obtained lower bounds on mean squared channel estimation errors, the limits on bit error rate （BER） for maximal ratio combining （MRC） with Gaussian distributed weighting errors on independent and identically distributed （i. i. d） fading channels are presented. Numerical results show that the BER performances of ideal MRC are the lower bounds on the BER performances of non-ideal MRC and deteriorate as the maximum Doppler frequency increases or the SNR of channel estimate decreases.

Hybrid transmit antenna selection and maximal-ratio transmission systems

Maximal-ratio transmission systems with transmit antenna selection is investigated. According to the order statistics of channel fiat fading coefficients, the closed-form expressions axe derived for average SNR with any amount of RF chains and average BER with two RF chains, respectively. The algorithm for calculating the minimum of total transmit antennas is presented in terms of reduced RF chains. The method of quantizing transmit precoders is employed in this study to decrease feedback information. Simulation results demonstrate the superiority of the proposed systems under full and quantized transmit precoders. The SNR of the proposed systems has been less degraded by the quantization of transmit precoder than that of pure maximal-ratio transmission systems.

EFFICIENT BIT ERROR PROBABILITY EXPRESSION AND VERY TIGHT BOUND FOR MAXIMAL RATIO COMBINING DIVERSITY SYSTEMS OVER RAYLEIGH FADING CHANNEL

Bit Error Probability (BEP) provides a fundamental performance measure for wireless diversity systems. This paper presents two new exact BEP expressions for Maximal Ratio Combining (MRC) diversity systems. One BEP expression takes a closed form, while the other is derived by treating the squared-sum of Rayleigh random variables as an Erlang variable. Due to the fact that the extant bounds are loose and could not properly characterize the error performance of MRC diversity systems, this paper presents a very tight bound. The numerical analysis shows that the new derived BEP expressions coincide with the extant expressions, and that the new approximation tightly bounds the accurate BEP.

A Cooperative Diversity Analysis of Two User Mobile Communication System with Maximal Ratio Combining

Cooperative communication is going to play a vital role in the next generation wireless networks. In this paper we derive the expression for symbol error probability (SEP) of a two-user cooperative diversity system, where two users cooperate through the decode-and-forward (DF) relaying with binary phase-shift keying (BPSK) modulation in a flat Rayleigh fading environment. We compare the computational results obtained by the SEP expression with the simulation results using maximal-ratio combining (MRC), equal-gain combining (EGC) and selection combining (SC) techniques. Numerical results show the performance of a cooperative diversity system with maximal-ratio combining is giving better results compared to SC and EGC techniques.

基于EM-KF算法的微地震信号去噪方法

针对微地震信号能量较弱,噪声较强,使微地震弱信号难以提取问题,提出了一种基于EM-KF(Expectation Maximization Kalman Filter)的微地震信号去噪方法。通过建立一个符合微地震信号规律的状态空间模型,并利用EM(Expectation Maximization)算法获取卡尔曼滤波的参数最优解,结合卡尔曼滤波,可以有效地提升微地震信号的信噪比,同时保留有效信号。通过合成和真实数据实验结果表明,与传统的小波滤波和卡尔曼滤波相比,该方法具有更高的效率和更好的精度。

基于QAM的协作通信系统物理层认证技术

针对两用户协作通信系统的身份认证问题,提出了一种基于正交幅度调制(QAM)的协作物理层认证机制。在该机制中,两个单天线用户分别使用同相与正交分量传输自己及伙伴的消息和标签,从而实现两用户消息和标签的唯一分解。基站采用最大比合并检测用户消息和标签,并通过标签对比完成物理层身份认证。在等功率分配且用户上行信道对称的典型场景下,给出了消息和标签的误码率闭合表达式。结果表明:在信噪比(SNR)为6~15 dB时,所提机制的认证概率与非协作物理层认证相比提高了12%~20%,非法攻击认证概率仅保持在10^(-3)量级,所提认证机制具有更好的身份认证性能。

基于小波奇异特征约束的期望最大时延估计算法

针对低信噪比条件下非平稳信号时延估计精度低的问题,提出基于小波奇异特征约束的期望最大时延估计算法。设计小波奇异性特征尺度广义互相关矩阵,构建多尺度小波奇异特征约束下的期望最大化模型。推导参数更新公式,利用期望最大化算法并行迭代,求取奇异性特征显著性最大条件下信号的自适应尺度以及该尺度下声源信号的最优时延估计值。仿真和实验结果表明,所提算法在低信噪比条件下,相较于传统广义互相关时延估计算法以及改进算法具有较高的时延估计精度,并且有效提高了误差约束范围内的有效估计成功率。

基于分式二次规划的互模糊函数赋形方法

在开展认知雷达波形设计时,由于发射波形与接收滤波器的非匹配体制,互模糊函数赋形相比传统模糊函数赋形优化自由度更高。该文针对强杂波条件下微弱运动目标检测问题,以最大化信干噪比为优化准则,提出了一种联合发射相位编码序列与接收滤波器设计的互模糊函数赋形方法。在恒模约束下,优化问题被建模为二次分式规划形式;然后通过引入辅助变量,并利用共轭梯度法求解Stiefel流形空间上的最小化问题,非凸优化据此转化为恒模约束二次优化问题;通过交替循环和类幂迭代算法求得最优解。此外考虑到发射波形受硬件限制而难以实现严格恒模,该文构建了一种低峰均比约束二次优化问题模型,并利用最近邻向量法求得最优解。最后,不同参数下的仿真与实测数据实验表明,该文赋形方法相较于传统方法具有较高的信干噪比增益和收敛速度。

单站卫星外辐射源无源雷达布站方法研究

由于障碍物会对电磁波的传播形成遮挡效应,为了避免遮挡盲区对无源雷达系统探测性能造成影响,以接收信噪比最大为优化目标,将接收站部署区域限制和障碍物遮挡作为约束,建立遮挡条件下单站卫星外辐射源无源雷达接收站部署的数学模型,并用粒子群优化算法给出接收站最佳部署位置的求解方法。仿真分析表明:上述基于接收信噪比最大化的布站方法解决了遮挡条件下的单站卫星外辐射源无源雷达布站问题。

基于邻居重叠比与结构洞的影响力最大化算法

影响力最大化是社交网络研究领域备受瞩目的问题之一,其目的是通过选择少量种子节点,尽量将影响力的传播范围最大化。传统的启发式算法往往只关注节点的单一特征,忽略了多个网络中心性指标的结合,受网络结构的影响较大,且容易导致“富人俱乐部”现象。为此,提出一种基于邻居重叠比与结构洞的影响力最大化算法ORSH,通过邻居重叠比和结构洞性质两个指标衡量一个节点是否拥有成为种子节点的特征。在6个真实网络数据集中进行实验,发现该算法的影响传播范围相较基于节点覆盖范围与结构洞的NCSH算法平均提高了5.4%,表明ORSH算法能有效选取最有影响力的节点。

最大化用户信噪比几何均值以提高信噪比公平性

提出一种双可重构智能超表面辅助(Reconfigurable Intelligent Surface,RIS)的多用户下行无线通信系统,在基站(Base Station,BS)周围对称部署两个可重构智能超表面以增强通信信号的传输。通过联合优化基站的波束成形和智能超表面的可编程反射系数,最大化用户的几何平均(Geometric Mean,GM)信噪比(Signal-to-Noise Ratio,SNR)。同时,提出一种基于闭式解的交替下降迭代算法,有效地增加用户信噪比并提高信噪比公平性。仿真实验验证了所提算法的可行性,同时说明了部署双可重构智能超表面系统的性能优势。

Easy proft maximization method for open-pit mining

A methodology applicable at any phase of a surface mining project for evaluating its current technical and economic feasibility is presented.It requires the typically available quantitative data on the ore-body,with its three-dimensional block model developed upon accurate interpolations.Thus it allows estimations of exploitable reserves in function of various cut-off grades,such as the average grade of mineable ore,the tonnages of ore and waste rock,stripping ratios and proft estimates for different production levels.If cost evaluations of essential mine operations are available(such as ore mining,waste removal,ore concentration,transportation,indirect project costs and expected concentrate selling prices),the methodology will provide clear indications on the economic feasibility of mining,including the best available options at any moment.Simple expressions are developed on the basis of a proft mathematical function and an application example is presented with data available from an existing iron ore deposit.

日粮中添加石吊兰粉对三穗鸭产蛋性能及蛋品质的影响

为了解日粮中添加石吊兰粉对三穗鸭产蛋性能及蛋品质的影响,试验将72只36周龄三穗鸭母鸭随机分为4组,分别为试验Ⅰ、Ⅱ、Ⅲ组及对照组,每组3个重复,每个重复6只。对照组饲喂基础日粮,试验Ⅰ、Ⅱ、Ⅲ组分别饲喂基础日粮加2%、4%、6%的石吊兰粉,预试期为7 d,正试期为28 d。试验结束后测定产蛋性能指标(日均蛋重、日均产蛋量、日均采食量、料蛋比)、蛋品质指标(蛋形指数、蛋壳强度、蛋壳厚度、蛋黄重、蛋白高度、哈氏单位、蛋黄颜色)。结果表明:试验Ⅰ、Ⅱ、Ⅲ组日均产蛋量均高于对照组,其中试验Ⅱ、Ⅲ组比对照组高16.61%、12.45%,差异显著(P<0.05);试验Ⅰ、Ⅱ、Ⅲ组料蛋比均显著低于对照组(P<0.05),其中试验Ⅱ组比对照组低20.19%。各组间蛋形指数、蛋壳厚度、蛋白高度和哈氏单位差异不显著(P>0.05)。试验Ⅱ、Ⅲ组的蛋壳强度比对照组高14.88%、11.18%,差异显著(P<0.05);试验Ⅱ组蛋黄重比对照组高15.22%,差异显著(P<0.05)。试验Ⅰ、Ⅱ、Ⅲ组的蛋黄颜色均显著低于对照组(P<0.05)。说明日粮中添加石吊兰粉能够提高三穗鸭的产蛋量,降低料蛋比,增加蛋壳强度和蛋黄重,降低蛋黄颜色,对蛋形指数、蛋壳厚度、蛋白高度和哈氏单位无显著影响,添加量为4%时效果最佳。

基于改进阻塞矩阵的DMA小信号主瓣保形与导向失配恢复方案

传统阵列天线在运用阻塞矩阵预处理对抗主瓣强干扰过程中,期望小信号会出现主瓣失真,峰值偏移和旁边电平上升,造成一定的信息损失,影响阵列天线接收信号的输出信干噪比(Signal-to-Interference-Noise Ratio,SINR)。为解决这个问题,提出一种基于改进阻塞矩阵的动态超材料天线(Dynamic Metamaterial Antenna,DMA)小信号主瓣保形与导向失配恢复方案。首先,基于DMA结构特性设计改进阻塞矩阵,对接收信号进行预处理;其次,采用权矢量补偿方法对小信号的导向矢量进行变换;最后,通过自适应空域滤波算法设计求解DMA的方向图状态向量,在天线射频前端实现了空域滤波小信号匹配接收。仿真结果表明,经过阻塞矩阵预处理后的DMA比传统天线具有更好的空域波束赋形能力。所提方案能够有效对抗主瓣存在强干扰的情况,降低主瓣失真,恢复小信号主瓣峰值偏移的导向矢量,进一步提高期望小信号的接收增益,证明所提算法的有效性以及优于传统天线阵列波束形成方法的优势。

Virtualization of Wireless Communication Systems and Its Maximal Ratio Combining Macrodiversity To Extend CDMA Capacity

The concept of virtualization of wireless communication systems is based on the open and scalable hardware platform of software radios in the personal communication network. The base station is divided into four components according to their functions: antenna, IF, baseband, and control, which are connected by the ATM network. Virtualization provides great benefits such as fast handoff and easy realization of different macrodiversity algorithms. Macrodiversity can not be easily realized in conventional cellular systems. An exact analysis is presented for the performance of maximal ratio combining (MRC) macrodiversity in virtualized wireless communication systems. The results show that compared with soft handoff in CDMA systems, MRC can greatly increase the reverse link capacity.

Pretreatment serum albumin/globulin ratio as a prognostic biomarker in metastatic prostate cancer patients treated with maximal androgen blockade

The pretreatment serum albumin/globulin ratio (AGR)has been used as a prognostic biomarker for various cancer types.However, the prognostic value of the AGR for prostate cancer,especially for metastatic prostate cancer (mPCa)after maximal androgen blockade (MAB),remains unclear.The aim of this study was to evaluate the prognostic value of the pretreatment serum AGR for mPCa treated with MAB.This retrospective study included 214 mPCa patients receiving MAB from October 2007 to March 2017. The correlation of the AGR with survival was estimated using Kaplan-Meier analysis and Cox proportional hazards models.The cutoff value of the AGR was 1.45 according to the receiver operating characteristic curve.Kaplan-Meier analysis demonstrated that patients with a low AGR (<1.45)had poor outcomes in terms of progression-free survival (PFS)and cancer-specific survival (CSS). Multivariate Cox analyses showed that the AGR was an independent predictor of PFS (hazard ratio [HR]=0.642;95%confidence interval [CI]:0.430-0.957;P=0.030)and CSS (HR =0.412;95%CI:0.259-0.654;P<0.001).Furthermore,in a subset of 79 patients with normal serum albumin levels (≥40.0 g l^-1),the serum AGR remained an independent predictor of CSS (P=0.009). The pretreatment AGR was an independent prognostic biomarker for PFS and CSS in patients with mPCa receiving MAB.In addition,the AGR remained effective for the prediction of CSS in patients with normal albumin levels (≥40 g l^-1).However,further prospective studies are needed to confirm our conclusions.

Physical layer security of underlay cognitive radio using maximal ratio combining

We investigate the secrecy outage performance of maximal ratio combining(MRC) in cognitive radio networks over Rayleigh fading channels. In a single-input multiple-output wiretap system, we consider a secondary user(SU-TX) that transmits confidential messages to another secondary user(SU-RX) equipped with M(M ≥ 1)antennas where the MRC technique is adopted to improve its received signal-to-noise ratio. Meanwhile, an eavesdropper equipped with N(N ≥ 1) antennas adopts the MRC scheme to overhear the information between SU-TX and SU-RX. SU-TX adopts the underlay strategy to guarantee the service quality of the primary user without spectrum sensing. We derive the closed-form expressions for an exact and asymptotic secrecy outage probability.

瑞利衰落信道中最大比合并系统性能及多路信号合并算法研究

分集是数字通信中最有效的抗多径裹落技术,在无线通信中采用分集技术可以改善系统的差错性能。本文详细分析了空间分集中性能最佳的最大比合并方式(MRC)的差错性能,并通过计算机仿真,给出了误码曲线。最后本文还给出了一种可行的最大分集合并的具体算法和仿真结果。

水力裂缝分形扩展对压裂效果的影响

为深入认识裂缝分形扩展对压裂效果的影响,研究了裂缝扩展分形性对裂缝延伸净压力及裂缝尺寸的影响规律。分析裂缝分形几何形态及其尖端应力场特征,并应用分形断裂力学理论对线性扩展净压力模型进行修正,得到了分形扩展净压力模型;在此基础上,结合力平衡模型及Sneddon最大裂缝宽度模型,建立了裂缝分形扩展与线性扩展的裂缝高度比模型和裂缝最大宽度比模型。数值分析结果表明:裂缝的分形扩展增加了裂缝高度、最大缝宽以及延伸所需的净压力;当50m缝长处的裂缝扩展形态的分形维数由1.20增大至1.80,净压力比由1.50增大至6.30。在给定地层力学参数条件下,当分形维数由1.30增大至1.60时,20m缝长处的裂缝高度比由1.04增大至1.11,裂缝最大宽度比由1.70增大至2.70。研究表明,分形扩展对裂缝几何尺度的影响明显,裂缝分形扩展程度越剧烈,裂缝高度和裂缝最大宽度的增量越大。

骆驼蓬提取物对玉米种子萌发和壮苗的影响

用不同浓度骆驼蓬提取物浸种处理玉米,研究对玉米种子萌发和壮苗的影响.结果表明,浸种处理后玉米种子的萌发及胚根和胚芽生长明显受抑,且随处理浓度提高抑制增强;但随培养时间的延长,对萌发的抑制减弱,根长和株高增加.0.1g/mL、0.2g/mL、0.3g/mL浓度的骆驼蓬提取液浸种可显著提高玉米幼苗根系活力,促进植株生长,根体积和植株生物量增加,根苗比增大.