JOINT MF COMBINING AND TURBO EQUALIZATION FOR WIRELESS COMMUNICATIONS OVER ISI CHANNELS WITH DIVERSITY RECEPTION

A new method called joint Matched Filter (MF) combining and turbo equalization is proposed for wireless communications over Inter-Symbol Interference (ISI) channels with diversity reception. This method takes diversity combining and equalization as integrity and need just one turbo equalizer for all diversity branches. Computer simulations prove that our method can take advantage of turbo equalization and diversity reception to combat fading of wireless channels.

UPLINK PERFORMANCE OF CWP-MC-CDMA WITH SPACE DIVERSITY COMBINING TECHNIQUE OVER RAYLEIGH FADING CHANNEL

In this paper, a Complex Wavelet Packet （CWP-MC-CDMA） system uplink model is proposed, based Multi-Carrier Code Division Multiple Access based on the analysis of the principle of MC-CDMA and the use of the optimized complex wavelet packet. Considering that the base station can adopt multiple re- ceiver antennas in the uplink, we employ the Space Diversity Combining （SDC） technique to improve the sys- tem pertbrmance via multiple antennas. The uplink performance of proposed CWP-MC-CDMA system with SDC technique is investigated over Rayleigh lading channel, and corresponding bit error rate analysis is given in detail. The system can avoid the decrease of spectrum efficiency of conventional MC-CDMA due to inserting cyclic prefix. Theoretical analysis and simulation result show that the application of SDC technique can improve the CWP-MC-CDMA system ability to combat spatial lading and various interferences effectively. Moreover, the proposed system based on SDC technique has superior Bit Error Rate （BER） performance over the Discrete Fourier Transform （DFT） and SDC based MC-CDMA system and the real wavelet packet and SDC based MC-CDMA system.

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.

Collaborative Spectrum Sensing for Cognitive Radio: Diversity Combining Approach

In this paper it is shown that cyclostationary spectrum sensing for Cognitive Radio networks, applying multiple cyclic frequencies for single user detection can be interpreted (with some assumptions) in terms of optimal incoherent diversity addition for “virtual diversity branches” or SIMO radar. This approach allows proposing, by analogy to diversity combining, suboptimal algorithms which can provide near optimal characteristics for the Neyman-Pearson Test (NPT) for single user detection. The analysis is based on the Generalized Gaussian (Klovsky-Middleton) Channel Model, which allows obtaining the NPT noise immunity characteristics: probability of misdetection error (PM) and probability of false alarm (Pfa) or Receiver Operational Characteristics (ROC) in the most general way. Some quasi-optimum algorithms such as energetic receiver and selection addition algorithm are analyzed and their comparison with the noise immunity properties (ROC) of the optimum approach is provided as well. Finally, the diversity combining approach is applied for the collaborative spectrum sensing and censoring. It is shown how the diversity addition principles are applied for distributed detection algorithms, called hereafter as SIMO radar or distributed SIMO radar, implementing Majority Addition (MA) approach and Weighted Majority Addition (WMA) principle.

The Analysis of Secure HARQ with Chase Combining over Block Fading Channel

In this letter, the physical layer security of hybrid automatic repeat request with chase combining(HARQ-CC) scheme is investigated from the viewpoint of information theory. Different from the literature which used Wyner code, our analysis focuses on the general scenario without specific code. We firstly obtain the outage probability of both main channel and wiretap channel. Since retransmissions are completely determined by main channel, we then prove that its achievable diversity order equals to maximum transmission number() while this order of wiretap channel is only one. Furthermore, we evaluate the metric of secure gap which demonstrates the difference between main channel and wiretap channel with reliable and secure constraints. As increases, the secure gap decreases monotonously. When is large enough, the security can be guaranteed even if wiretap channel is better than main channel.

Distributed Relay Diversity Systems for OFDM-Based Networks

In this paper, distributed relay diversity systems are analyzed, modeled and evaluated in an Orthogonal Frequency Division Multiplexing (OFDM) based networks. The investigated distributed relay diversity schemes extend the ideas of a single hop transmit antenna schemes such as Cyclic Delay Diversity (CDD), Space Time Transmit Diversity (STTD), transmit Coherent Combining (CC) and Selection Diversity (SD) to distributed diversity systems. In contrast to the classical single hop system, the antennas in the distributed systems belongs to distributed relays instead of being co-located at the transmitter. The distributed relay diversity methods considered in this paper: Relay CDD (RCDD), Relay Alamouti (i.e.STTD), Relay CC (RCC) and Relay SD (RSD) are compared to the traditional 1-hop system. Analytical expressions for the received Signal to Interference Noise Ratio (SINR) are derived and used in a dynamic multi-cell multi-user simulator. Results show considerable SINR gains for both Round Robin and Max-SINR schedulers. The SINR gains translate into substantial cell throughput gains, up to 200%, compared to 1-hop systems. Despite its low complexity, the RCDD scheme has similar performance to that of other more sophisticated 2-hop schemes such as Relay Alamouti and Relay Coherent Combining. Marginally better results are observed for the Relay Selection Diversity scheme.

Cooperative TDD reciprocity calibration with diversity combining for distributed large-scale MIMO systems

Thanks to channel reciprocity,the time-division duplexing operation is typically used for distributed large-scale multiple-input multiple-output systems.With the knowledge of uplink channel state,APs(Access Points)perform the downlink precoding to cooperatively communicate with multiple UEs(User Equipments).Unfortunately,the channel reciprocity is often jeopardized by the non-symmetric transceiver RF(Radio Frequency)circuits at both sides of the link.By excluding UEs from the calibration procedure,the TLS(Total Least Squares)method is extended to the case of partial calibration,where only the APs are involved to exchange calibration signals to compensate for RF mismatches.Nevertheless,channel fluctuations between APs significantly degrade system performance.Therefore,we propose a scheme to obtain the diversity gain,by performing a calibration with the combination of the calibration signals of different channel coherent times.Simulation results confirm the effective performance and robustness of our scheme.

抽水蓄能电站防沙措施研究

以典型抽水蓄能电站为研究对象,开展了水库防沙措施研究。针对复杂工程条件,在分析各种防沙布置措施的基础上,考虑以沉代拦、导沉结合,提出导沙堤和尾水明渠相结合的防沙布置型式。经过数值模拟和物理模型验证,该型式减少过机泥沙效果明显,水力学参数合理。研究成果可为类似工程规划、设计和运行提供参考。

不同施肥组合对科尔沁沙地南缘沙地土壤健康指标的影响

为研究不同施肥组合对沙地土壤改良的效果,以辽宁省阜新市彰武县的沙地土壤为考察对象,开展了试验研究。试验以不施肥为对照(CK)处理,设置生物有机肥分别与含腐殖酸肥料(OH)、含聚谷氨酸肥料(OP)和中微量元素肥(OM)混施3个施肥处理,测定施肥后6、12、18个月的土壤中微生物数量和土壤理化性状的变化。结果表明:不同施肥处理的土壤中微生物数量均呈现细菌>放线菌>真菌的变化趋势,其中OH处理的细菌数量最多,3个取样时间的细菌数量平均值为1.510×10^(7)cfu/g,是CK处理的5.2倍;施肥处理的土壤中全磷、全钾和有机质含量均得到提高,OP处理的全钾含量平均值最高,质量分数为5.96 g/kg;施肥处理的土壤pH均呈下降趋势;施肥处理的地上部植物生物量提高。施用不同组合的肥料可以有效提高土壤微生物的数量,改善土壤理化性状,提高地上部植物生物量,是一种合理的沙地改良措施。

基于软硬件结合的控制流完整性保护技术

针对影子栈难以兼顾安全性和性能,软件实现的前向CFI(control-flow integrity)技术性能开销过大、难以进行实际部署,提出基于软硬件结合的CFI(control-flow integrity based on the combination of software and hardware,SHCFI)技术。通过二进制重写器对程序反编译,生成中间语言,并判断转移指令类型。对于后向控制流的保护,提出基于返回地址加密的平行影子栈方案,使用随机数对栈上的返回地址进行异或加密,将加密结果备份到原始栈固定偏移处的影子栈中,在函数返回时对影子栈中的地址异或解密,将解密结果作为实际的返回地址。对于前向控制流的保护,使用硬件ENDBRANCH状态机指令标记间接转移指令的目标地址,在运行时对目标地址进行合法性检查,以降低性能开销。实验结果表明,SHCFI加固后的程序能够有效地防御代码重用攻击,且具有良好的运行开销。

旱作区农田土壤AM真菌对长期有机无机施肥的响应

AM真菌群落动态变化对于长期有效的土壤生态系统管理非常重要。为揭示旱作区农田土壤丛枝菌根(AM)真菌对长期有机、无机培肥管理的响应机制,利用单因素随机区组设计,基于连续11年的定位试验及高通量测序方法,研究了不施肥(T0)、长期单施化肥(T1)、长期化肥与牛粪有机肥(T2)和长期化肥与羊粪有机肥(T3)对土壤的影响,比较了土壤AM真菌群落组成及多样性间的差异,探究了驱动土壤AM真菌群落组成及多样性变化的土壤环境因子及其相互作用效应。结果表明:随培肥时间延长,与T0处理相比,T2、T3处理的土壤全氮、有机质含量显著增加,pH显著下降(P<0.05);与2018年相比,2021年的T0、T1和T3处理土壤全磷和速效钾含量显著下降。有机无机肥配施下,球囊霉属(Glomus)和类球囊霉属(Paraglomus)是土壤AM真菌的优势属,但近明球囊霉属(Claroideoglomus)的相对丰度显著下降,从优势属变为非优势属。近明球囊霉属较球囊霉属和类球囊霉属相对丰度而言,更容易受长期培肥影响而发生显著改变。连续有机无机肥配施到2018年后,T2、T3处理的土壤近明球囊霉属和两性球囊霉属(Ambispora)的相对丰度与T0间有显著差异(P<0.05);培肥至2021年后,T2、T3处理土壤近明球囊霉属和两性球囊霉属的相对丰度与T0处理间无显著差异。随培肥时间延长,不同处理间土壤AM真菌群落的α多样性差异消失。NMDS分析结果表明:长期培肥改变了土壤AM真菌群落的β多样性,但T2与T3处理间土壤AM真菌群落相似性较一致。连续培肥改变了土壤AM真菌群落结构组成和多样性,驱动AM真菌群落变化的土壤环境因子由土壤全氮、pH转变为土壤全磷。长期有机无机培肥没有同步提升土壤全磷、速效钾等主要理化性状。随培肥年限增加,驱动土壤AM真菌群落结构和多样性变化的土壤因子发生了显著改变,AM真菌群落会随土壤环境因子的变化倾向于更加敏感的驱动因子。

非满管流对渠管结合输水系统水力特性的影响

【目的】了解非满管状态下的渠管结合输水系统水力特性。【方法】采用物理模型试验与理论分析相结合的方法,对不同充满度下主渠流速分布与水面线变化、管道流速、分流比的变化规律进行了研究。【结果】不同充满度下主渠各断面紊动强度沿程均呈先升高后降低的变化趋势,在距管道入口纵向2倍、横向1.5倍管径的主渠区域内流速变化较为剧烈;在有管道存在的主渠壁面附近水面线变化剧烈,沿程呈先降低后增大再降低的变化趋势。通过量纲分析得到非满管流速表达式,采用线性回归分析法拟合得到非满管流速系数计算式,计算值与实测值之间的相对误差不超过8.81%。当主渠流量不变时,非满管流速系数随主渠傅汝德数的增大而增大,随水深比、充满度的增大而减小,分流比随充满度的增大而增大;当充满度不变时,随着主渠流量的增大,非满管流速系数增大,分流比减小。【结论】非满管流对主渠的影响范围有限,在安装闸阀以及量水设备时要尽量避开相关影响区域,采用本研究推导的流速系数公式只需获得主渠的傅汝德数与水深值,即能快速计算非满管流速值,在来水流不变的情况下可通过增大主渠水深来获得较大的管道流量。

Spatial diversity and combination technology using amplitude and phase weighting method for phase-coherent underwater acoustic communications

The UWA channel is characterized as a time-dispersive rapidly fading channel, which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate inter- symbol interference caused by multipath propagation, spatial diversity equalization is the main technical means. The paper combines the passive phase conjugation and spatial processing to maximize the output array gain. It uses signal-to-noise-plus-interference to evaluate the quality of signals received at different channels. The amplitude of signal is weighted using Sigmoid function. Second order PLL can trace the phase variation caused by channel, so the signal can be accumulated in the same phase. The signals received at different channels need to be normal- ized. It adopts fractional-decision feedback diversity equalizer （FDFDE） and achieves diversity equalization by using different channel weighted coefficients. The simulation and lake trial data processing results show that, the optimized diversity receiving equalization algorithm can im- prove communication system＇s ability in tracking the change of underwater acoustic channel, offset the impact of multipath and noise and improve the performance of communication system. The performance of the communication receiving system is better than that of the equal gain combination. At the same time, the bit error rate （BER） reduces 1.8%.

玉带溪流域合流制片区截污方案溢流污染特征分析

为明确玉带溪流域合流制片区不同截污方案的溢流污染特征及溢流控制效果,选择玉带溪北支上游合流制片区为研究区域,构建排水系统模型,在全年各等级降雨情景下,对合流制片区末端截污和截流式分流两种工程方案的合流制溢流污染特征指标进行对比研究。结果表明,截流式分流改造方案在溢流频次、溢流总量、溢流历时、溢流量均值、溢流量峰值和溢流污染负荷方面总体优于末端截污方案。其中,在全年各等级降雨情景下,末端截污方案的溢流量削减率为12.9%~77.5%,而截流式分流改造方案的溢流量削减率为40.6%~98.8%。在溢流污染负荷削减方面,降雨等级为中雨或大雨时,末端截污方案对3种污染物(化学需氧量、氨氮、总磷)的溢流污染负荷削减率均达到64%以上,而截流式分流改造方案的削减率均达到89%以上;降雨等级为暴雨及以上时,末端截污方案的溢流污染负荷削减率均小于50%,而截流式分流方案的削减率均达到60%以上。因此,通过溢流污染特征分析研究有利于掌握不同截污方案的污染物排放规律及溢流削减效果,对经济有效地控制合流制溢流污染具有指导性意义。

采样方式对苍山采集昆虫群落的比较研究

为明确不同采样方式对分析昆虫群落结构特征的影响,以苍山东坡中山湿性常绿阔叶林为研究地点,采用马氏网(MS)、地陷阱法(XJ)、灯诱法(DY)以及扫网法(SW)4种采样方式,进行为期1年的昆虫群落调查,比较不同采样方式及组合采集的昆虫群落结构特征,分析结果的差异性,明确不同采样方式的优劣及可替代性。结果显示:在采集的59科13340头昆虫中MS捕获41科6896头,XJ捕获31科6201头,DY捕获24科141头,SW捕获22科102头;比较不同采样方式采集到的各目数、科数、物种数和个体数,MS最佳,XJ和DY次之,SW最差;不同采样方式的优势类群存在差异;4种采样方式的群落相似性相互间差异较大(Cs≤0.60);除SW+XJ、DY+XJ及SW+XJ+DY组合外,其余的组合采样效果相当,可以酌情替换。

一种适用于空间相关信道的分集接收方法

针对空间相关信道下信号检测误码率性能下降的问题,提出一种多天线分集接收方法。该方法通过增加接收机天线个数,减小信道空间相关性对信号检测的影响,可根据实际工程需求灵活配置相应的接收天线数量,在避免引入高复杂度检测算法的同时具有较优的检测误码率性能。采用等增益合并方式对所提方法进行仿真分析,仿真结果验证了方法的有效性。

东江水源涵养林不同混交组合林下植物多样性研究

为揭示东江水源涵养林5年生8种不同混交组合林下植物多样性的差异及其规律。对8种不同混交组合林分样地开展植物多样性调查,对每种混交组合林下的灌木、藤本、草本层进行植物多样性评价。结果表明,林下植物丰富度指数均不高,Simpson指数与种间相遇机率(PIE)在数值上相等,但其与Shannon-Wiener指数间则相差较大;从林下植物多样性指标的聚类分析看,混交组合楠木×锥栗、红苞木×枫香、火力楠×红锥、椆木×红锥、格木×海南红豆的植物多样性指数较高,而混交组合红锥×枫香的植物多样性指数较低。

黑臭水体的源头整改设计——以合肥蜀山区为例

以合肥市蜀山区十五里河雨水排出口污染治理工程为例,根据实际情况制订了相应的污染问题解决方案。在对十五里河上游管网进行排查中发现,该区域住宅小区内存在了合流制排水体制、阳台雨废水混接、雨污水管网混接、管道及附属设施淤积、破损等问题,严重污染了下游河道。本次设计中因地制宜地提出了对应的整改方案,基本实现了雨污分流,施工运行后效果良好。

引排结合多工况泵站总体布置型式探讨

泵站工程从功能上来说可分为引水和排涝两大类。某些平原圩区泵站枢纽工程要求同时具备机排、机引、自排、自引多种工况调度功能,相对于传统泵站,其具有节省投资、减少占地、管理集中等优点。引排结合泵站的设计要点和难点在于总体布置型式的选择及运行调度方案的确定。文章结合阜阳市某水系连通项目,对引排结合多工况泵站的几种总体布置方案进行了介绍及分析,设计方案均合理可行,可为其他相关的引排结合泵站设计提供思路和借鉴。