多业务蜂窝CDMA系统中的呼叫接纳控制策略

基于码分多址(CDMA)技术的第三代(3G)移动通信系统将支持多种业务传输,有效的呼叫接纳控制策略将使系统在满足各类业务不同QoS要求的同时,能够为更多的用户提供服务,该文首先分析了多业务蜂窝CDMA系统的剩余容量与QoS约束间的关系,接着提出了适用于任意多类业务环境、基于信号干扰比(SIR)测量的两种呼叫接纳控制策略,局部策略与全局策略,并通过大量计算机仿真研究了两种策略在业务均匀分布和非均匀分布环境下的性能,仿真结果表明,在两种业务分布情况下,全局策略的性能部优于局部策略。     

多业务蜂窝CDMA系统的干扰与容量分析

基于码分多址接入（CDMA）的第三代移动通信系统将支持语音、视频、email,FTP,Web浏览等多种业务传输，该文提出了一种多业务蜂窝CDMA系统上行链路的干扰特性与容量的一般分析方法，考察了在不同的业务混合条件下，分别采用高斯分布与对数正态分布来近似干扰的统计特性时，系统的中断性能与容量关系。理论分析与仿真结果表明，采用对数正态分布来近似干扰的统计特性可以获得更加精确的分析结果。此外，该文还研究了阴影衰落、功率控制误差和非理想扇区天线这些实际因素对系统干扰与业务容量的影响。     

多业务传输的WDM-ROF-PON系统研究

针对多业务传输的WDM-ROF-PON(融合光载无线技术的波分复用-无源光网络)系统的稳定性和业务间串扰问题,设计了一种能同时传输两种无线业务的WDM-ROF-PON系统。实验过程中,对下行链路的4路ROF信道进行了测试,系统能同时传输60GHz 2.5Gbit/s的毫米波信号和5GHz 155Mbit/s的DPSK(差分相移键控)信号,传输距离为20km。各信道中低频业务传输20km后功率代价为0.4～2.8dB,毫米波信号传输20km后功率代价为1.5～3.2dB;仅传输毫米波业务时,接收机灵敏度提升0.6～2dB。实验结果表明,各信道中两种业务的信号传输性能均良好,系统较稳定,低频业务对毫米波业务的干扰较小。     

Normal-type approximation for multi-service systems with trunk reservation

In this paper we consider a transmission link of a broadband system. A number of heterogeneous streams with different traffic intensities, different call holding times and different bandwidth requirements use the link in a complete sharing mode with trunk reservation. A normal-type approximation formula for individual blocking probabilities is described. Some numerical examples are presented to show the accuracy of the approximation.     

多业务CDMA蜂窝移动通信系统的功率控制

本文提出了多业务CDMA蜂窝移动通信系统的一种下行链路功率控制策略，系统的最优功率分配可以归结为求解归一化链路增益矩阵在有约束条件下的最大实特征值。在对系统的最优功率分配进行理论分析的基础上，给予了相应的仿真结果，并针对实际系统负载过重的情形，提出了按照业务优先级别逐步去除小区用户的功率控制策略。     

Energy considerations in open and closed waveguides

Energy relations derived for a lossless closed uniform and periodic structure show that the total complex Poynting vector integrated over the cross section is identically zero for the case of an arbitrary complex wave. These results are also applicable to open structures provided certain conditions are satisfied. The application of these results in the field of leaky wave antennas is discussed. Two illustrative examples, those of the sinusoidally modulated reactance surface and the sheath helix, are worked out. It is shown that although the slope of the dispersion curve can no longer be associated with the direction of net power flow, the knowledge of the slope may still be helpful in selecting certain modes for representing a given source.     

多业务MIMO-OFDMA/SDMA系统跨层调度与动态资源分配

对多业务MIMO-OFDMA/SDMA 系统下行链路跨层调度与动态资源分配问题进行了研究.首先,在满足各种约束条件的前提下,以最大化系统吞吐量为目标建立了相应的优化模型;然后,提出了一种基于业务类型和子空间距离的用户分组算法,该算法采用聚类分析的方法在每个子载波上对配置有多根接收天线的用户进行分组,从而降低了调度时所需搜索的用户空间的维数;接着,基于所提出的用户分组算法并结合不同业务的优先级提出了一种新的跨层调度和资源分配算法,该算法充分利用跨层信息为每个子载波调度相应的用户组,并为调度到的用户分配相应的系统资源,从而通过最大化每个子载波的吞吐量近似实现了系统整体吞吐量的最大化.仿真结果表明,与现有的方案相比,所提算法更好地满足了不同业务用户的QoS要求,并获得了更好的吞吐量性能.     

Computer-algebra systems and electromagnetic problems

This paper presents some computer-algebra systems, and explains how these systems are likely to be relevant in addressing electromagnetic problems. After a historical survey, we discuss the various systems and their features. Some examples are given, with an important bibliography. A listing of Web sites (of interest to the antennas and propagation community) is also given. Finally, we outline how a given problem can be formalized and analyzed using symbolic-algebra systems, and show an example calculation for a conformal-microstrip antenna     

Design of microstrip wide stopband quad-band bandpass filters for multi-service communication systems

This paper presents two planar high performance quad-channel bandpass filters, which are designed based on a novel circular multi-mode resonator. In this paper and for the first time, the proposed resonator is utilized to achieve quad passbands. It consists of diverged feeding lines that are coupled to etched circular cells. The first filter has quite close channels at 2.62, 2.88, 4.34 and 4.67 GHz, which make it appropriate for frequency division duplex (FDD) scheme. Meanwhile, the second filter is designed for WCDMA and WiMAX applications. Both filters are able to attenuate the harmonics up to 19 GHz with a maximum harmonic level of −20 dB. The insertion losses and return losses of both filters at all channels are better than 1.2 dB and 17.5 dB, respectively. The harmonic attenuation method is presented employing a LC equivalent circuit of the proposed resonator. In order to verify the designing methodology, the proposed filters are fabricated and measured where there are good agreements between the simulation and measurement results.     

Robust adaptive multi-service transmission with hierarchical modulation for OFDM systems in high mobility scenarios

Wireless communications play a key role in intelligent transportation systems for bearing multiple application services with different quality of service (QoS) requirements. Hierarchical modulation (HM) is an effective technique to increase the spectral efficiency (SE) of differentiated services multiplexing transmissions. In high mobility scenario, due to the impact of the feedback delay and channel estimation error, only the imperfect channel state information is available at the transmitter. Thus, the performance of the existing HM schemes degrades severely. In this paper, we propose a robust adaptive HM scheme to increase the overall SE in the mobile orthogonal frequency division multiplexing system. The bit error rate of the HM symbol is derived for the reliable QoS-aware multi-service transmission, and the strategies of bit assignment and modulation parameters selection for different services are designed. Finally, comparing with the traditional uniform modulation scheme, the proposed robust adaptive HM scheme increases the overall SE of multiplexing transmissions by \(15\%\) at \(300\,\hbox { km}/\hbox {h}\).     

降低环境中电磁辐射污染的电磁兼容策略

根据电磁场的分类及其特性，以及电磁辐射对人体的各种生物效应的分析，提出解决环境中电磁辐射污染的一些电磁兼容策略，从而有效地降低或阻隔电磁辐射造成的污染，保护人类的生活环境。     

城市电磁环境污染及其防治对策

分析了城市电磁环境污染的产生、类型和现状,指出城市电磁工业规划布局不够合理,城市空域电磁辐射污染和危害日趋严重.提出了城市电磁环境污染的防治对策,即依法加强对城市电磁辐射源的合理规划和监管,加大投入提高城市电磁环境污染的综合防治水平.     

生物系统中受激的相干电磁辐射

最近B.Ruth用最精密的物理仪器重新研究了生物细胞的超弱光子发射现象,被认为是一种相干的受激过程,引起一些科学家们的热烈讨论。本文从物理学角度分析了生物细胞产生相干受激发射的条件与可能性,并认为这是一个值得重视的发展。     

Pervasiveness in a competitive multi-operator environment:the daidalos project

This article briefly describes the EU-funded Daidalos project, which designs and develops a communications infrastructure for next-generation networks to enable personalized, context-aware, composite services to mobile users. The fundamental concepts rely on federation of operators who create a pervasive environment for service provisioning, on integrated mobility, security, virtual identity for users, and resource management. The project validates concepts by means of specification, implementation, and integration in a large research testbed.     

Stability problem in electromagnetic systems and possible solutions

The letter is concerned with dispersion relations of active electromagnetic systems which are polynomial functions of either frequency or wavenumber. In this case, the search for saddle and branch points needed for stability analysis can be performed by 2-dimensional rather than 4-dimensional search.     

Combined admission control and scheduling in multi-service networks

Providing the required metrics for different service respectively is a basic characteristic in multi-service networks. The different service can be accessed and forwarded differently to provide the different transmission performance. The state information between admission control and scheduling can be exchanged each other by the defined correlation coefficient to adjust the flow distribution in progress. The priority queue length measured by scheduler implicitly can describe the priority flows load. And the fair rate can describe the non-priority flows load. Different admission decision will be made according to the state of scheduler to assure the time-delay upper threshold for the priority flows under heavy load and the fairness for elastic flows in light load, respectively. The stability condition was conduced and proved. Simulation results show the policy can ensure both the delay for the priority flows and the minimal throughput for non-priority flows.     

Energy and power considerations in injection and optically pumped lasers

The topics of power and energy output from lasers are treated. Both three- and four-level lasers are considered in the pulsed and continuous modes of operation. The theoretical power and energy estimates are compared, when possible, with experimental data.     

Switching considerations to combat spectral pollution in TDMA forsatellite broadcasting

A better switching technique for combating spectral pollution i.e. spectral spreading of burst time-division multiple access (TDMA) digital FM and π/4-QPSK (quadrature phase-shift keying) systems, is proposed. The effects of rectangular, linear, and raised cosine ramp on/off switching are examined for two prototypes using both hardware experimental methods and computer simulation for different gating rates, duty cycles, roll-off factors of transmitter filter and ramp on/off times. The measures results agree with the computer simulation results and indicate that the adjacent channel interference (ACI) caused by the burst operating in TDMA π/4-QPSK is significantly reduced by raised cosine switching in comparison with other types of switching     

Miniaturized quad-channel microstrip diplexer with low insertion loss and wide stopband for multi-service wireless communication systems

Wireless Networks - In this paper, a compact four-channel diplexer is designed using a microstrip structure to separate input signals at 2.07/3.94 GHz and 2.37/4.49 GHz and load...