激光触发多级多通道开关研究

研究了200kV激光触发多级多通道开关的运行机理,该开关在直流电压下以四倍频Nd:YAG激光器为触发源进行的实验结果表明：开关触发延迟时间及其抖动随开关电压、激光能量和充气压力上升呈指数下降趋势,对混合气体则随气体密度上升而上升。随透镜焦距的增大延迟时间及其抖动呈上升趋势。该开关实现了多通道放电。     

离子通道电子束回旋脉塞的等离子体波效应

研究了离子通道回旋电子束脉塞（ICECM）中的等离子体波非线性效应。利用流体理论与自洽非线性理论方法对ICECM中等离子体波效应的微观机理进行了分析。研究发现,等离子体波加强了电子束的纵向群聚,束-波互作用的能量交换效率及系统增益得到明显提高。数值模拟计算表明,对于中等等离子体密度、1.5kA电流和1MV加速电压的电子束,系统能够获得的脉冲功率和频率分别为200MW和280GHz的毫米波束。     

A multi-port D-R mutator using CCIIs with current followers

A multi-port D-R mutator with new current conveyors (CFCCIIs) as the four-port active element is proposed. Each CFCCII consists of a current follower added to a second-generation current conveyor (CCII). This proposed circuit is a simple configuration using CCIIs, CFCCIIs and grounded capacitances and is applied to higher order high-pass filters. This configuration can realize a superior transmission characteristic, inheriting the characteristic of the conventional LC filter. Since all the passive elements are grounded, the influence of parasitic elements of current conveyors can be reduced with this circuit configuration. As a result, this circuit is considered a suitable configuration for monolithic integration. Results obtained from the SPICE simulations show the realized filters have excellent performance and the circuit is effective.     

Analysis of LDPC with optimum combining

Low density parity check (LDPC) codes have shown exceptionally good performance for single antenna systems over a wide class of channels. LDPC when implemented with a single input multiple output system with maximum ratio combining is optimum from the standpoint of maximising signal-to-noise ratio at combiner output without the presence of interferer. Optimum combining outperforms maximal ratio combining (MRC) in the presence of interferer(s). In this article, the performance of the LDPC codes with multiple receiver antennas with optimum combining in the presence of single interferer is investigated. The simulation results showed that LDPC codes of irregular construction are able to give high coding and diversity gain with optimum combining. The proposed LDPC optimum combined (LDPC–OC) system in Rayleigh fading channel in the presence of a single interferer improves the signal to interferer plus noise ratio by 2.62 dB with four receiver antennas and by 1.98 dB when the number of receiver antennas is three.     

多用户MIMO双向中继信道鲁棒预编码

在多用户MIMO双向中继系统中,若使用非理想信道模型,中继处仅能获得部分下行信道状态信息,这样将导致系统性能大幅度下降。由此提出基于最小信干噪比最大化的鲁棒预编码方案。仿真表明,该方案不仅可以使最差信干噪比最大化,也有效地改善了系统的比特误码率性能。     

基于多版本的多级安全并发控制机制的研究

在多级安全数据库系统中，如果采用传统的并发控制机制，则通过多级事务的协作可以很容易的创建隐通道，因此我们必须研究适合于多级安全数据库的并发控制机制。本文提出了一个基于多版本的安全的并发控制机制，它能阻止隐通道的创建而不会导致检索异常和高级事务的饿死，同时还能提供一个多级事务的可串行化调度。     

Performance comparison of dual‐hop hybrid decode‐or‐amplify‐forward relay schemes for M‐ary quadrature amplitude modulation burst transmission over Rayleigh fading channels

This paper shows the analytical performance expressions of M‐ary quadrature amplitude modulation burst symbol transmission for hybrid decode‐or‐amplify‐forward (HDAF) relay schemes over quasi‐static Rayleigh‐fading channels. First, we derive the probability density function of the received instantaneous signal‐to‐noise ratio as the simplified form, which is related to all the possible occurrence probabilities of error‐events for M‐ary quadrature amplitude modulation burst transmission. On the basis of the derived probability density function, we express average bit error probability, average symbol error probability, and average burst error rate as closed forms, which can be also applied to both amplify‐and‐forward and adaptive decode‐and‐forward (ADF) schemes. The analysis and simulation results show that HDAF scheme for burst transmission can achieve the performance of ADF scheme with symbol‐by‐symbol transmission, which is the achievable lower bound. Furthermore, the outage probability, the normalized channel capacity, and the goodput performance are also derived as closed forms. The analysis shows the superiority of HDAF scheme to ADF scheme. Comparison with simulations confirms that the derived analytical expressions are accurate over all signal‐to‐noise ratio regions and for different numbers of relays and modulation orders.     

Interleaved coding and sequential transmission scheme for packet‐level forward error correction over burst loss channels

Burst packet loss is a common problem over wired and wireless networks and leads to a significant reduction in the performance of packet‐level forward error correction (FEC) schemes used to recover packet losses during transmission. Traditional FEC interleaving methods adopt the sequential coding‐interleaved transmission (SCIT) process to encode the FEC packets sequentially and reorder the packet transmission sequence. Consequently, the burst loss effect can be mitigated at the expense of an increased end‐to‐end delay. Alternatively, the reversed interleaving scheme, namely, interleaved coding‐sequential transmission (ICST), performs FEC coding in an interleaved manner and transmits the packets sequentially based on their generation order in the application. In this study, the analytical FEC model is constructed to evaluate the performance of the SCIT and ICST schemes. From the analysis results, it can be observed that the interleaving delay of ICST FEC is reduced by transmitting the source packets immediately as they arrive from the application. Accordingly, an Enhanced ICST scheme is further proposed to trade the saved interleaving time for a greater interleaving capacity, and the corresponding packet loss rate can be minimized under a given delay constraint. The simulation results show that the Enhanced ICST scheme achieves a lower packet loss rate and a higher peak signal‐to‐noise‐ratio than the traditional SCIT and ICST schemes for video streaming applications.     

LEMP 空间表达式求解及分布规律研究

利用偶极子理论对Maxwell方程组进行了求解,得到了垂直通道与斜向通道模型的雷电电磁场解析表达式。基于此表达式分析了不同高度处雷电电磁场的空间分布规律。研究结果表明,在垂直通道与斜向通道模型中,垂直电场和磁场受观测点高度的影响随水平距离的增加而减小,但是对水平电场而言,在垂直通道模型中其初始峰值随着观测点高度增加而增加,在斜向通道模型中,当观测点在通道下方时电场峰值随着观测点高度的增加而增加,当观测点在通道上方时高度越高电场峰值越小。     

雷电通道模型研究与应用

雷电的研究必须基于雷电本身,而闪电通道模型的建立可以很好地模仿自然雷电。通过建立逼真的雷电通道模型,可以更有效地研究雷电及开发雷电防护产品。通过对常见的雷电回击通道模型进行分析,重点阐述了雷电通道的工程模型,分析其中TL,TCS,BG和DU等模型之间的关系,并对其优劣做出比较。利用Matlab工数学软件分析了双指数模型与海德尔模型雷电流模型的波形和频谱,经对结果进行分析比较发现,海德尔模型相比双指数模型更符合实际的雷电流。