Short packet communication in underlay cognitive network assisted by an intelligent reflecting surface

We propose short packet communication in an underlay cognitive radio network assisted by an intelligent reflecting surface (IRS) composed of multiple reconfigurable reflectors. This scheme, called the IRS protocol, operates in only one time slot (TS) using the IRS. The IRS adjusts its phases to give zero received cumulative phase at the secondary destination, thereby enhancing the end-to-end signal-to-noise ratio. The transmitting power of the secondary source is optimized to simultaneously satisfy the multi-interference constraints, hardware limitations, and performance improvement. Simulation and analysis results of the average block error rates (BLERs) show that the performance can be enhanced by installing more reconfigurable reflectors, increasing the blocklength, lowering the number of required primary receivers, or sending fewer information bits. Moreover, the proposed IRS protocol always outperforms underlay relaying protocols using two TSs for data transmission, and achieves the best average BLER at identical transmission distances between the secondary source and secondary destination. The theoretical analyses are confirmed by Monte Carlo simulations.     

Packet Delay Analysis of Symmetric Gated Polling System for DBA Scheme in an EPON

In this paper, we analyze the mean packet delay of a dynamic bandwidth allocation (DBA) scheme in an Ethernet passive optical network (EPON). We propose the interleaved polling system with a gated service discipline and a two-stage queue in order to investigate the delay performance of DBA scheme in an EPON. We assume that input packets arrive at an optical network unit (ONU) according to a Poisson process from several types of users. We use a continuous time queueing model in order to find the mean packet delay and the mean cycle time of an arbitrary packet. We obtain the closed form solution for the mean packet delay of the proposed gated polling system with a two-stage queue. We obtain another result on the mean packet delay by solving a system of linear equations derived from the moments of the queue length distribution. We give some numerical results to investigate the delay performances for the symmetric polling system with statistically identical stations. In addition, we compare numerical results on the closed form solution with numerical results on a system of linear equations.     

Improving TCP performance for vertical handover in heterogeneous wireless networks

The incorporation of wireless local area networks (WLANs) into existing cellular networks as supplementary access technologies has become an issue of great interest. However, vertical handover (VHO), which allows users to roam between a WLAN and a cellular network, causes an abrupt change in certain link characteristics such as the round trip time and data rate. Owing to such changes, reordering problem and premature timeout occur and trigger unnecessarily fast retransmission during VHO, causing throughput degradation. Thus, we propose a new transmission control protocol (TCP) mechanism, which resolves the reordering problem by suppressing unnecessary retransmission caused by spurious duplicate acknowledgments (dupacks) incurred because of the reordering problem, and prevents premature timeout by employing an adaptive retransmission timer. We analytically investigate the throughput of our proposed TCP scheme. The numerical and simulation results show that our proposed TCP performs better in terms of throughput than other schemes appearing in the literature. Copyright © 2009 John Wiley & Sons, Ltd.     

POS信号中IP包提取的设计及实现

针对目前广泛应用的POS技术,文章主要研究了POS信号中PPP／HDLC,LAPS／HDLC,SDL三种映射协议的封装格式及映射方式,提出了从POS信号中提取出IP数据包的方法,并用软件编程实现。     

基于EDA的机会监听中继选择的改进机制

机会监听中继选择机制结合了中继间监听与机会选择,可以充分利用重传机制进一步降低误包率.然而其忽视监听信道和低适应性的不足,使得该机制在某些场景中不能发挥长处.因此,提出了基于分布估计算法的改进方案,使得改进后的机制不仅考虑了监听信道对于中继选择的影响,还具备了不断自我优化的学习性能.通过仿真验证后表明,提出的方案可以进一步提升系统的性能,还具有很强的自适应能力.     

传输误码损伤对数据业务的影响

介绍了误码与丢包的定义,分析了传输误码产生的原因和概率分布,给出了传输误码率与数据丢包率的理论关系,并以GFP-F映射方式为例,分析传输误码对数据丢包的影响。     

基于Gilbert丢包机制的TCP吞吐量模型

 丢包机制是推导TCP吞吐量模型的关键,直接影响模型的准确性.本文利用四状态Gilbert丢包机制来描述端到端路径上的丢包行为,对TCP的拥塞控制过程进行建模,在此基础上提出了一种更精确的TCP吞吐量模型.实验表明,改进的模型能较好的与实际值相拟合,可以更精确地预测实际TCP数据流的吞吐量性能.     

基于双边线性预测的信包丢失隐藏算法

本文提出了一种基于双边线性预测的信包丢失隐藏算法。该方法利用丢失信包的前一信包或邻接信包(在后一信包可获得的情况下)预测丢失信包。线性加权双边线性预测的样点获得最终的重建信号。使用重叠相加和幅度调整操作平滑重建信号和真实信号之间的边界。经过非正式试听和ITU-T P.862协议所推荐的PESQ算法测试,本文建议算法的重建语音信号质量,与其他四种流行重建算法相比有了较为明显的改善。     

分组增强型OTN控制平面技术研究

分组增强型OTN实现了分组传输网络(PTN)和光传送网络(OTN)的进一步有机融合,其网络内部综合了分组交换,VC交叉,ODUk交叉,波长交叉等不同的交换颗粒,引入智能控制层面,实现多交换颗粒、多业务适配网络环境下的资源调度,成为POTN网络应用的重要需求。本文从光传送网络智能化标准化现状出发,对POTN网络控制平面实现机制中的多层信令调度、层间资源调度策略、保护恢复机制实现等问题进行分析研究。     

基于压电陶瓷的风机叶片模型覆冰主动监测

南方山区高湿低温严酷环境易导致冰灾,风机叶片覆冰会导致发电效率降低甚至停机,因此发展高效可靠的风机叶片覆冰监测技术对防冰、除冰具有重要意义。该文提出了一种基于压电陶瓷应力波测量的风机叶片覆冰主动监测方法。开展叶片模型进行模拟覆冰试验,在叶片表面布置伸缩型和剪切型两种压电陶瓷片,根据波动法原理对驱动器输入正弦扫频电压信号作为激励,记录不同传感器在不同结冰厚度下的响应信号,并对测量信号进行小波包能量分析。结果表明,同一压电陶瓷片接收信号的小波包能量与结冰厚度存在明显关系。