晶体型二阶偏振模色散模拟器

报道了一种新型的二阶晶体型偏振模色散(PMD)模拟器,其由3片可产生不同的一阶PMD差分群延迟(DGD)的晶体和1个法拉第旋转器组成,法拉第旋转器理论上可在180°内连续变化。该二阶PMD模拟器实验上能近似模拟从50到200 ps2的二阶PMD。给出了二阶PMD随偏置电压变化的曲线。实验表明,该器件输出的重复性好,响应时间小于1 ms,实验值与理论值近似符合。     

Power-conserving routing of ad hoc mobile wireless networks based on entropy-constrained algorithms

This paper presents an approach to power-conserving routing of ad hoc mobile wireless networks. This approach relies on entropy-constrained routing algorithms, which were developed by utilizing the information-theoretic concept of the entropy to gradually reduce the uncertainty associated with route discovery through a deterministic annealing process. Entropy-constrained routing algorithms were tested using a single performance metric related to the distance between the nodes and to the power consumption associated with packet transmission. This paper also expands the versatility of entropy-constrained routing algorithms by making them capable of discovering routes based on multiple performance metrics. In this study, the second performance metric employed for route discovery relied on the power availability in the nodes of the network. The proposed routing approach was evaluated in terms of the power consumption associated with the routing of packets over an ad hoc mobile network in a variety of operating conditions.     

超宽带多址通信信号的功率谱分析

超宽带(UWB)多址通信是继CDMA技术之后迅速发展的一种宽带传输技术.本文在介绍了各种UWB通信调制方式后,针对产生的UWB多址信号,分析了信号特征,结合数学模型,以简明方式分析了TM-UWB与DSC-UWB多址通信信号的功率谱密度分布,它是UWB通信系统设计与用户干扰分析的基础.     

一种新的优化动态信道分配策略及建模分析

本文提出一种新的动态信道分配策略,称之为分级紧致的动态信道分配(CCDCA),所谓分级就是基于引入的"冷态"和"热态"的概念,将小区所处的状态分为冷态与热态;所谓紧致就是对处于不同状态的小区给出不同的紧致模型.该策略在对"热态"的处理过程中利用了"冷态"的先验信息,有机地结合了局部信息与整体信息,同时能保证小区间有较小的服务偏差,提高了整个系统的服务质量.文中还从理论上给出了冷、热态阈值的分析模型,计算出了模型的主要参数,该模型也可以用来分析系统性能.仿真结果证明该方案有较小的呼阻率和较高的频谱利用率,所提出的模型比较接近实际系统.     

Cooperative schemes for path establishment in mobile ad-hoc networks under shadow-fading

The performance of routing protocols for multi-hop path-establishment in Mobile Ad-hoc NETworks (MANET) is examined when the individual radio links undergo shadow fading of parameterized severity. Such propagation modeling is typical of ground-level networking along with node mobility. The metrics of main interest are the probability of having a reliable multi-hop path plus the temporal statistics of such availability under a Markovian model. Such availability is an indicator for the suitability of the network to carry delay-sensitive applications (push-to-talk voice, streaming video) in uninterrupted manner. It is shown that high levels of diversity are necessary in such adverse environments, as obtained either by multiple independent paths or via concurrent cooperative transmission. Analytical and simulation comparisons of typical routing options are presented on the above metrics, plus on the required nodal engagement for supporting such diversity.     

Bacterial communication systems: A mathematical formulation of negative chemotaxis

The emergence of molecular communication (MC) has provided a new paradigm for communication at nanoscale, besides the electromagnetic one. Numerous biological systems have been proposed that could be used for communication, using mostly bacteria as information carriers, ensuring biocompatibility and low complexity requirements. In this work, message dissemination dynamics in a bacterial communication system was under investigation by means of a simulation framework that was designed and developed based on a commercial tool. A mathematical formulation is proposed, in an effort to accurately predict the system's behavior under the presence of chemotactic‐like nodes. Simulation results are in strong agreement with the respective mathematical model, for a wide range of biological processes, including phenomena such as chemotaxis, bacterial growth cycle, and biological message transformation dynamics. In the case of a simple simulation scenario exhibiting chemotaxis, the mean accuracy improvement reaches values of up to 19% .     

Mitigating adjacent channel interference in vehicular communication systems

In the last few decades, dedicated wireless channels were specifically allocated to enable the development and implementation of vehicular communication systems. The two main protocol stacks, the WAVE standards proposed by the IEEE in the United States and the ETSI ITS-G5 in Europe, reserved 10 MHz wide channels in the 5.9 GHz spectrum band. Despite the exclusive use of these frequencies for vehicular communication purposes, there are still cross channel interference problems that have been widely reported in the literature. In order to mitigate these issues, this paper presents the design of a two-stage FIR low-pass filter, targeting the integration with a digital baseband receiver chain of a custom vehicular communications platform. The filter was tested, evaluated and optimized, with the simulation results proving the effectiveness of the proposed method and the low delay introduced in the overall operation of the receiver chain.     

Optical Communications Research Activities at COM RD1 Siemens S.A.

Abstract

This article summarizes the research activities carried out by the R&D Optical Networks Communications group (COM RD1), at Siemens S.A., in collaboration with both universities and other research institutes. These activities cover various aspects of advanced modulation formats, all optical wavelength conversion, optical quality of signal monitoring in transparent WDM networks, routing, and wavelength assignment in optical networks.     

Impacts of user-selfishness on cooperative content caching in social wireless networks

Cooperative caching can be an effective mechanism for reducing electronic content provisioning cost in Social Wireless Networks (SWNETs). These networks are formed by a collection of mobile data enabled devices physically gathering in settings such as university campus, malls, airport and other public places. In this paper, we first propose an optimal collaborative object caching policy in order to minimize the object provisioning cost in SWNETs with homogenous user requests and a peer-rebate model for promoting collaboration. Then using an analytical model we study the impacts of user selfishness on the provisioning cost and the earned rebate when certain nodes in an SWNET selfishly deviate from the optimal policy. User selfishness is motivated in order to either increase individually earned rebate or to reduce content provisioning cost. The analytical model is validated by experimental results from simulated SWNETs using the network simulator ns2.