子载波序列调制GO-MC-CDMA系统的性能分析

SIM-GO-MC-CDMA是GO-MC-CDMA与子载波序列调制相结合的系统。分析了SIM-GO-MC-CDMA采用迫零检测时系统性能;比较不同数字调制方式对误比特率(BER)的影响。通过蒙特卡洛仿真分析表明:SIM-GO-MC-CDMA的系统可得到低误码率。     

Effects on correlation between two mobile radio base-station antennas

The correlation between signals received by two mobile radio base-station antennas is investigated to determine spacing requirements for space diversity. Measurements of the fading of UHF signals received by two base-station horn antennas oriented at different angles with respect to the incoming mobile radio signal were made for different antenna spacings. The experimental results are compared with an analytical expression derived in this paper; they agree fairly well. A further experiment was made after removing the possible local scatterers surrounding the base station. Comparing these two experimental results, we find that the following are true. 1) Propagation in the direction of a line connecting the two base-station antennas is the critical case and requires a large separation of 70 wavelengths. As soon as the incoming wave is 10° away from the in-line axis, the spacing requirement drops to 30 wavelengths. 2) Local scatterers at the base station tend to decrease the correlation between signals received at the two antennas. We conclude that an upper limit to the spacing of antennas used for diversity can be obtained and that it is within the achievable range.     

基于SOA的两种干涉仪结构性能分析

对基于半导体光放大器的萨格奈克型(Sagnac)和马赫曾德型(MZ)两种干涉仪结构的性能进行了分析比较.首先讨论了干涉仪在对数据进行逻辑操作时出现的光能量泄漏问题,并给出了试验结果.随后对数据帧宽度、数据流占空比和光纤环长的关系进行了详细分析.     

Breaking two secure communication systems based on chaotic masking

This paper describes the security weakness of two generalized nonlinear state-space observers-based approaches for both chaos synchronization and secure communication, using chaotic masking and chaotic modulation of a Lorenz system. We show that the security is compromised without any knowledge of the chaotic system parameter values and even without knowing the transmitter structure.     

异步DS-CDMA系统中基于符号级相关阵的DOA估计

针对异步DS-CDMA系统多用户环境，本文提出了一种有效的DOA估计算法。首先，将天线阵分为等阵元的两组，并且在符号级构造出不含噪声项的组间相关阵；然后，根据最小二乘准则分离出DOA信息；最后，利用MUSIC算法逐个估计出各路径的DOA。算法具有分辨率高，顽健性强及硬件要求低等优点。仿真实验验证了算法的有效性。     

一种基于Bigram二级哈希的中文索引结构

为通过构建高速的中文索引结构来提高Off-line模式的串匹配速度,提出了一种基于Bigram二级哈希的中文索引结构。该索引采用中文GB2312编码处理中文汉字,以中文Bigram项作为词汇项,并实现了基于二级哈希的词汇表存储结构。实验数据显示,本文索引结构虽然占用存储空间为词索引的2倍多,但其匹配速度是词索引的4倍多。结果表明本文索引在中文匹配中具有速度优势。     

基于混沌参数调制的多进制数字通信系统的性能比较

基于混沌参数调制方式,设计和实现了一种多进制的数字扩频通信方案-CPSM(Chaotic parameter spreading modulation),研究了用不同的混沌系统作为载波信号并在不同的扩频因子条件下,二进制和四进制数字扩频通信系统的性能,并分析了影响系统性能的因素.仿真结果表明加大扩频因子有助于提高这些系统的性能,同时也发现Chua系统的信号更适合于多进制数字通信.此外,这些系统具有较好的抗干扰能力,且易于实现.     

基于蒙特卡罗仿真的多种二进制通信系统性能分析

介绍了在加性高斯噪声干扰条件下,多种二进制通信系统信号的传递与最佳接收．根据蒙特卡罗仿真方法基本思想,建立在加性噪声干扰下的相关检测系统蒙特卡罗仿真模型。模型通过Matlab软件方法实现,最终仿真结果与对应系统的理论误码率基本符合。     

Time-domain channel estimator based on cyclic correlation for OFDM systems with guard interval

Channel impulse response （CIR） can be estimated on the basis of cyclic correlation in time-domain for orthogonal frequency division multiplexing （OFDM） systems, This article proposes a generalized channel estimation method to reduce the estimation error by taking the average of different CIRs. Channel impulse responses are derived according to the different starting points of cyclic correlation. In addition, an effective CIR length estimation algorithm is also presented. The whole proposed methods are more effective to OFDM systems, especialiy to those with longer cyclic prefix. The analysis and the simulation results verify that the mean square error performance is 4-5 dB better than the conventional schemes under the same conditions.     

基于小波分组调制的多码多载波跳频通信系统分析

介绍了一种将多码调制、小波分组调制以及跳频技术相结合的高效通信方式——小波分组多码多载波跳频通信系统.推导了系统在Nakagami-m衰落信道下的误码性能,给出了用户数、小波分组类型、小波分组滤波器长度以及跳频点数与系统性能之间的关系.理论分析与数值计算表明:增加小波分组滤波器长度可以有效降低系统误码率,但不同小波分组类型对系统性能的影响不大;跳频技术的引入不仅增加了系统的安全性,同时也可有效降低多址干扰对系统性能的影响,提高了系统的可靠性.     

Full-duplex radio-over-fiber transport systems based on two modes injection-locked FP LD

A full-duplex radio-over-fiber (ROF) transport system based on two modes injection-locked Fabry–Perot laser diode (FP LD) is proposed and demonstrated. Performances over a 40-km standard single-mode fiber (SMF) full-duplex transmission were investigated. Good performances of bit error rate (BER) and error vector magnitude (EVM) were obtained in our proposed systems. Since our proposed systems use only one FP LD as light source for both down-link and up-link transmissions, it reveals a prominent alternative with advantages in simplicity and cost.     

Performance of two 4×4 guided-wave photonic switching systems

Data from two photonic switching systems are presented, the first is a 4×4 crossbar, and the second is a 4×4 passive splitter/active combiner broadcast switch. The 4×4 crossbar has operated continuously and reliably for 18 months with no noticeable performance degradation. The 4×4 passive splitter/active combiner has operated for six months and yields excellent bit-error-rate (BER) performance at 1.7 Gb/s, showing that the influence of optical crosstalk in a small guided-wave optical switching system does not significantly affect the BER     

Performance evaluation for band-limited DS-CDMA systems based on simplified improved Gaussian approximation

The standard Gaussian approximation (SGA) for error analysis of direct-sequence code-division multiple-access (DS-CDMA) systems is very optimistic in many cases. Improved Gaussian approximation (IGA) is a technique that produces accurate error probabilities, but is still computationally intensive. Simplified IGA (SIGA) has complexity similar to that of SGA and, at the same time, provides sufficient accuracy. In this paper, we consider SIGA for DS-CDMA systems employing random sequences in a band-limited scenario. The validity of IGA for band-limited systems is established in a rigorous mathematical sense. Then a key parameter in SIGA is derived via a frequency-domain approach. Applications to a number of typical chip waveforms, including the popular sinc and raised-cosine pulses, are investigated. Performance comparison with IGA-based lower and upper bounds shows that SIGA yields very accurate probability of error.     

Performance analysis of maximum ratio transmission based multi-cellular MIMO systems

In this paper, we analyze the performance of the uplink of multi-cellular MIMO systems in flat Rayleigh fading. There is co-channel interference from users within the same cell as well as from other cell users. I The channel model includes lognormal shadowing and path loss along with power control, resulting in a statistical model for user powers. Consistent with practical scenarios, the co-channel interference is categorized into two groups: intracell interference from users within the same cell as the desired user and intercell interference from outer cell users. We derive a compact, easily computable closed form outage probability expression in the form of finite sums. This expression allows for simpler and faster analysis of various MIMO configurations. It has been shown that using antennas on the receiver side results in better performance, since transmit diversity does not combat interference from same cell users.     

基于大气信道链路的混合FSO/RF系统性能分析

提出了新的混合FSO/RF系统信道模型,此模型不仅克服了雾和雨对链路的严重影响,而且降低了系统的能量衰减,提高了系统的可用性.该系统在接收端探测器采用比较光电流大小来选择适合信道传输的链路,克服了各种天气状况的影响,最大限度地满足用户对通信性能的要求.     

先拉伸后轧制纯镍中滑移系与位错结构的关系

对柱状晶纯镍样品先拉伸后冷轧,用透射电镜和扫描电镜表征其位错结构.在拉伸变形时形成的结构在后续的轧制变形后保持或改变取决于当应变路径改变时开动的滑移系是否发生了改变.当开动的滑移系发生变化时,最终的结构由第二应变路径中开动的滑移系所决定.这些结果为支持已发表的滑移系活动与位错结构的关系提供了进一步的证明.     

基于矢量范数的一类多发射天线系统的性能分析

用矢量范数定义了一类多发射天线系统，并对各系统的中断概率性能进行了研究。分析表明，虽然各种多发射天线方法根据其接收机和发射机所获得的信道信息不同，采用不同的功率分配算法和发射编码准则，但其中断概率随信噪比的增加呈现相似的渐进性能。     

基于粗糙集的信息安全系统评估指标优化

信息安全系统效能评估指标体系的建立,是实现信息安全系统效能评估的前提。首先通过德尔菲法获取初始评估指标集;其次根据指标统计数据,运用粗糙集理论的知识约简方法,得到初始指标集的核集,即可剔除冗余指标,从而得到优化的评估指标体系;最后对其进行稳定性分析,验证了指标体系的科学合理性。     

Comparison between two approximation methods of state space fractional systems

A large number of real dynamic systems are better characterized using a non-integer order dynamic model based on fractional order differential equations. Nevertheless, their analytical solutions are rather complicated. In this paper we present two alternative methods of simulation of the fractional order dynamical system in state space. We particularly present a comparison between two approximation methods. The first one is based on the differentiation operator approximation and thus uses the usual form of the state space representation D^(α)(x)=Ax+Bu. The second method is based on the approximation of the integration operator and uses, in this case, the new representation w=AI^(α)(w)+Bu. The comparison between these two methods is made on the basis of initial and steady state approximation state and output errors which are characterized in this present paper. Numerical examples are also given to support this comparison.