iM-SIMPLE: iMproved stable increased-throughput multi-hop link efficient routing protocol for Wireless Body Area Networks

Wireless Body Area Networks (WBANs) are envisaged to play crucial role in psychological, medical and non-medical applications. This paper presents iM-SIMPLE; a reliable, and power efficient routing protocol with high throughput for WBAN. We deploy sensor nodes on human body to measure the physiological parameters such as blood pressure, temperature, glucose, lactic acid, EMG, acceleration, pressure, and position. Data from sensors is forwarded to intermediate node, from where it is transmitted to sink. An end user can access the required information available at sink via internet. To minimize energy consumption of the network, we utilize multi-hop mode of communication. A cost function is introduced to select the forwarder; node with high residual energy and least distance to sink has minimum cost function value and is selected. Residual energy parameter balances the energy consumption among the sensor nodes, and least distance improves packet delivery to sink because of reduced less path loss. We formulate the minimum energy consumption and high throughput problems as an Integer Linear Program. In order to support mobility, we also consider two body postures. Simulation results confirm the performance advantage of iM-SIMPLE compared to contemporary schemes in terms of maximizing stability period and throughput of the network.     

Model checker aided design of a controller for a wafer scanner

For a case-study of a wafer scanner from the semiconductor industry it is shown how model checking techniques can be used to compute (1) a simple yet optimal deadlock avoidance policy, and (2) an infinite schedule that optimizes throughput. in the absence of errors. Deadlock avoidance is studied based on a simple finite state model using Smv, and for throughput analysis a more detailed timed automaton model has been constructed and analyzed using the Uppaal tool. The Smv and Uppaal models are formally related through the notion of a stuttering bisimulation. The results were obtained within 2 weeks, which confirms once more that model checking techniques may help to improve the design process of realistic, industrial systems. Methodologically, the case study is interesting since two models were used to obtain results that could not have been obtained using only a single model. Supported by the European Community Project IST-2001-35304 (Ametist), http://ametist.cs.utwente.nl/.     

RED的网络性能研究*

在很多网络中, 支持新的拥塞避免机制( 如RED 和ECN) 的节点将会和支持传统丢尾缓存( Drop-Tail) 的节点共存。研究含有两个拥塞节点的混杂网络中TCP 流集的性能, 比较了几种控制算法的数据流公平性, 仿真结果显示采用Adaptive 算法并不能增加数据流的公平性; 仿真也显示混杂网络中单个RED 参数的设置情况会影响整个网络的性能, 具体可以从网络吞吐量、响应时间等判断。RED 的参数设置在双瓶颈情况下再次变得重要, 正如在单瓶颈的情况下一样。     

基于BD预编码和时分复用的MIMO广播传输方案

在MIMO系统中,块对角化(BD)预编码用来消除多用户的共信道干扰(CCI)。BD预编码要求系统发射天线数大于全部用户接收天线数目的总和。当用户数增多时,用户接收天线总数随之增多,BD算法的复杂度将急剧增大。为了解决这个问题,同时使系统支持的用户数最大化,提出了一种基于BD预编码和时分复用(TDM)相结合的广播传输方案。该方案通过对用户进行分组,对组内的用户进行BD预编码,并对组间进行时分复用,从而降低系统对发射天线数目的要求和算法的复杂度。仿真结果表明,这种组合方案在支持更多用户的同时还可以获得较高的吞吐率。     

一种基于移动自组网的联合检测MAC协议性能分析

在ad hoc移动自组网中,隐藏终端和暴露终端问题严重影响着MAC层的网络吞吐量性能。为了更好的解决隐藏／暴露终端问题,文献[3,4]提出了一种信道接入方法,即联合检测法。论文对此算法进行了改进,对RTS／CTS控制分组采用了载波侦听／冲突检测（CSMA／CD）策略,而对数据分组采用了基于发射端的码分配法。通过理论分析和仿真,表明提出的信道接入策略可获得较大吞吐量增益。     

分数频率复用的帧结构及性能分析

针对现代无线通信系统在干扰控制方面越来越高的要求,利用通信帧中子载波的重新分配,提出了帧结构设计中一种新的分数频率复用方法—时频分分数频率复用,并将其与传统的分数频率复用方式进行比较。这一新方法是在对系统容量进行建模之后,综合资源块分配中的时分和频分模式提出的,其对应的帧结构相对于传统的FFR具有更高的调节粒度。实验结果验证了这种设计以少量系统容量为代价,在提升系统公平性、提高边缘用户吞吐率方面的性能优势。     

Garbage collection: Java application servers’ Achilles heel

Java application servers are gaining popularity as a way for businesses to conduct day-to-day operations. While strong emphasis has been placed on how to obtain peak performance, only a few research efforts have focused on these servers’ ability to sustain top performance in spite of the ever-changing demands from users. As a preliminary study, we conducted an experiment to observe the throughput degradation behavior of a widely-used Java application server running a standardized benchmark and found that throughput performance degrades ungracefully. Thus, the goal of this work is three-fold: (i) to identify the primary factors that cause poor throughput degradation, (ii) to investigate how these factors affect throughput degradation, and (iii) to observe how changes in algorithms and policies governing these factors affect throughput degradation.     

OPNET网络仿真技术及其应用

网络仿真是一种新的网络设计和优化技术,它能够为网络的规划设计提供可靠的定量依据,也能够验证实际方案或比较多个不同的设计方案.介绍了OPNET网络仿真软件,并对其主要特性、建模机制以及仿真步骤进行了深入的阐述.最后,给出了OPNET软件在预测网络性能方面的一个应用实例.实验结果表明,OPNET网络仿真软件能够准确地分析复杂网络的性能和行为.     

Throughput analysis and bandwidth allocation for IEEE 802.11 WLAN with hidden terminals

Motivated by observations from real world wireless local area network (WLAN) deployments, we develop in this paper a novel analytical model to characterize the saturation throughput of an IEEE 802.11-based access point (AP) and stations under the influence of hidden terminals. Unlike existing models, our model can accommodate different numbers of hidden nodes without increasing the model complexity. Given any number of hidden nodes, only four constraints are needed to describe the interaction between stations and the AP with the consideration of both uplink and downlink traffic. Simulation evaluation shows that our model predicts network performance accurately over a wide range of network sizes and indicates the existence of a throughput starvation problem. To address this problem, based on our model, we formulate a bandwidth allocation problem to optimize the network throughput and fairness under some predefined requirements by systematically tuning the AP and stations contention windows. Simulation results show that the starvation problem is resolved with our approach, and the target throughput is met.     

Throughput analysis of STS-based CDMA system with variable spreading factor in non-frequency selective Rayleigh fading channel

The throughput enhancement of space-time spreading (STS)-based code division multiple access (CDMA) system is investigated in this paper. Variable spreading factor (VSF) is utilized to improve the data throughput of the system in non-frequency selective Rayleigh fading channel. In this contribution, an analytical approach is proposed to compute a new expression for the bit error rate (BER) performance of the STS-based CDMA system against pre-despreading signal-to-noise-ratio (SNR) for different values of spreading factor. The other contribution of the paper is deriving a new analytical expression for the throughput enhancement of the VSF STS-based CDMA system in non-frequency selective Rayleigh fading channel. Simulation and analytical results demonstrate that using VSF method in STS-based CDMA system improves the throughput of the system by keeping the BER performance at a target level.