Multi‐band pattern reconfigurable Yagi‐Uda antenna

In this study, novel designs of single‐band and tri‐band pattern reconfigurable antennas are proposed. The design of single‐band pattern reconfigurable antenna is accomplished by the use of varactor diodes with the parasitic elements placed on both sides of the driven conventional printed dipole antenna. By tuning the capacitance of varactor, the antenna operates in four different configurations of radiation pattern which include bi‐directional end‐fire, broadside, and uni‐directional end‐fire radiation patterns. The tri‐band pattern reconfigurable antenna design is achieved by the use of parasitic elements on both sides of a tri‐band driven dipole antenna. Dual‐band LC resonators are used as loading elements along the arms of printed dipole to get two lower order modes in addition to the reference dipole mode, resulting in a triband operation of the driven element. The electrical lengths of the parasitic elements with respect to the tri‐band driven element are controlled by suitably embedding varactor and PIN diodes with them. The proposed tri‐band antenna operates in ten different configurations of radiation patterns in the three operating bands. Fully functional prototypes of single‐band and tri‐band pattern reconfigurable antennas along with the DC bias networks have been fabricated to validate the results obtained in simulation.     

PSO算法的稳定性分析及算法改进

种群多样性的缺失是导致PSO算法易陷入早熟早收敛的重要原因,因此对基于线性定常离散系统的PSO算法的稳定性作了理论分析,并分析了种群多样性缺失的原因,根据此特性提出了一种·贯r}权重因子在一定范围内随机取值且学习因子取恒定常数的改进Pso算法,该算法可以使粒子速度具有一定的概率发散,以保持种群的多样性。通过对3个约束优化问题的仿真实验表明,该算法跳出局部极值的概率很大,可有效地避免早熟早收敛。     

基于分级策略的演化算法

为了避免演化算法过早收敛,保持种群多样性,增加算法的搜索能力,本文提出基于分级策略的演化算法．即通过对种群进行分级,来度量种群的多样性,衡量算法是否陷入局部最优,协调种群多样性和精英策略之间的矛盾,再根据种群分布的多样性设计一种有效的半一致交叉算子与单重均匀变异算子。     

LTE双层网中MIMO技术性能分析*

Femtocell技术以其较好的热点覆盖、较高的传输速率以及较大的网络容量,成为LTE网络中补充覆盖的重要途径之一。但同时,也造成了网络中复杂的CCI,严重影响了异构网络的性能。为了减少LTE双层网络中的CCI,提高网路容量,本文将基于MIMO的本征波束赋形、正交空时编码、天线选择技术应用于LTE双层网络,详细给出了无Femtocell覆盖半径、Femtocell最优密度以及Macrocell覆盖半径的精确数学表达形式,并对其所带来的干扰抑制效果进行了分析。通过仿真我们发现,相对于SISO来说,本征波束赋形的干扰抑制效果最好,可以使网络性能有个很大的提高,天线选择次之,正交空时编码所带来的增益最小,而当综合考虑性能增益以及复杂度的情况下,选择分集是一种比较合适的选择。     

Hierarchic Social Entropy: An Information Theoretic Measure of Robot Group Diversity

As research expands in multiagent intelligent systems, investigators need new tools for evaluating the artificial societies they study. It is impossible, for example, to correlate heterogeneity with performance in multiagent robotics without a quantitative metric of diversity. Currently diversity is evaluated on a bipolar scale with systems classified as either heterogeneous or homogeneous, depending on whether any of the agents differ. Unfortunately, this labeling doesn't tell us much about the extent of diversity in heterogeneous teams. How can it be determined if one system is more or less diverse than another? Heterogeneity must be evaluated on a continuous scale to enable substantive comparisons between systems. To enable these types of comparisons, we introduce: (1) a continuous measure of robot behavioral difference, and (2) hierarchic social entropy, an application of Shannon's information entropy metric to robotic groups that provides a continuous, quantitative measure of robot team diversity. The metric captures important components of the meaning of diversity, including the number and size of behavioral groups in a society and the extent to which agents differ. The utility of the metrics is demonstrated in the experimental evaluation of multirobot soccer and multirobot foraging teams.     

Application of a Recurrent Neural Network to Space Deversity in SDMA and CDMA Mobile Communication Systems

Linear and non-linear adaptive algorithms are investigated for Space Division Multiple Access (SDMA). SDMA is one of the emerging techniques for multiple access of users in mobile radio, which uses spatial distribution of users for their differentiation. The performance of the linear Square Root Kalman (SRK) algorithm for SDMA is compared to that of the non-linear Recurrent Neural Network (RNN) technique. The proposed SDMA-RNN technique is evaluated over Rician fading channels, and it shows improved Bit Error Rate (BER) performance in comparison with the linear SRK-based technique. The performance of SDMA-RNN is also compared with that of Code Division Multiple Access (CDMA) systems, showing that it could be used as a viable alternative scheme for multiple access of users. Finally, a Hybrid CDMA-SDMA system is proposed combining CDMA and SDMA-RNN systems. Hybrid CDMA-SDMA exhibits a very good potential for increase in the capacity and the performance of mobile communications systems.     

遗传算法中交叉算子对群体多样性的影响

在遗传算法中,群体多样性对于避免早熟收敛、提高搜索效率以及保证搜索的全局性是至关重要的。本文分析了遗传算法在进化处理过程中导致群体多样性下降的原因,并着重就交叉算子与替换策略（或后期选择）的共同作用对群体多样性的影响作了较深入的探讨,完成交叉算子关于群体多样性损失的量化分析,并据此对如何平衡算法的“探测
测”与“开发”性能做了讨论。     

结合机会调度和迫零接收机的SM．rvnMo系统研究

为了充分利用多用户MIMO系统中固有的多用户分集,采用机会调度方案,根据接收端反馈的信道 状态信息选择有着最大信噪比的用户进行数据传输,同时为了有效地利用复用增益,提高系统的容量,在平 坦瑞利信道中,提出并分析了结合机会调度和空间复用的采用迫零接收机的MIMO系统方案．在不同信道估 计下,根据基于多项式展开的方法,分别推导出了采用M-QAM和M-PSK调制的系统的误码率、分集增益量 化值以及总速率容量,并用基于泰勒级数的方法对其进行渐近分析．通过蒙塔卡罗仿真很好地验证了理论分 析的正确性,表明该方案相对于没有机会调度的系统提供了更大的分集和更高的容量     

Temporal shifts in the biodiversity of nearshore small fishes in Lake Simcoe

Nearshore small fish species represent a large proportion of fish biodiversity in Lake Simcoe, a large inland lake in southern Ontario, Canada. Over the past 30 years, Lake Simcoe has experienced several changes to its aquatic habitat, benthic invertebrate communities and predatory fish populations. This study compared samples of the nearshore small fish community in three geographic areas of Lake Simcoe. Fish community data were grouped into two time periods: a contemporary period (2007–2009) and a historical period (1982–1995). The fish community was compared across time periods for each area to assess if observed ecological changes had an impact on the small fish community. Species richness significantly declined between time periods in two areas (Cook's Bay and the southeast shoreline), the number of individuals captured declined between time periods in one area of the lake (Kempenfelt Bay) and Simpson's diversity index declined between time periods in one area of the lake (southeast shoreline). There were no significant differences in the Shannon–Weiner evenness index between time periods in any of the study areas. Additional analyses of intra- and inter-annual variation in fish sampling results generally supported the findings that shifts in the fish community occurred between time periods. Overall, this study suggests that the nearshore small fish biodiversity of Lake Simcoe has shifted over time but these shifts are not clearly related to recent increases in water clarity, macrophyte growth and nearshore benthic invertebrate densities.     

Action diversity in a simulation of the Israeli-Palestinian conflict

This article explores the strategies used by Israeli students to resolve the Israeli-Palestinian conflict in the interactive computer game, PeaceMaker. Students played PeaceMaker in the roles of both the Israeli Prime Minister and the Palestinian President in random order. Students must take actions satisfying constituents on both sides of the conflict in order to win the game. The diversity of actions taken in each role was measured. Several hypotheses test the degree to which Israeli students, depending on which role they played and their own demographic variables, exploited a consistent set of actions or explored a more diverse range of actions across three main types: construction, political, and security. The results show that (1) greater action diversity increases success in both roles, (2) Israeli students engaged in less diverse actions when playing the Israeli role than when playing the Palestinian role, (3) students’ religiosity and political Hawkishness negatively predicted action diversity when playing the Palestinian role, and (4) action diversity mediates the relationship between a student’s background knowledge about the conflict and success in the Israeli role. The significance of these findings for understanding attitudes about the Israeli-Palestinian conflict are discussed, including implications for conflict resolution more generally.