无线传感器网络中重发问题的理论分析*

针对无线传感器网络信道特性和网络布置等具体问题,以Mica2节点为例,从理论上分析了重发次数、时间窗长度、节点通信半径范围内的节点数量等参数的选取对数据可靠性、节点平均寿命等性能的影响.     

基于Fourier矩阵的无线广播重传策略

针对随机网络编码重传的缺陷, 将Fourier矩阵和随机网络编码相结合, 提出一种半固定编码系数的广播重传方案FMWBR。利用广播源节点和接收节点双方已知的Fourier矩阵的行向量作为编/解码向量, 保证接收节点接收到的重传包具有完全可解性。理论分析表明, FMWBR增强了无线传输的安全性、提高了网络的鲁棒性、减少了包头开销。仿真测试结果表明, FMWBR跟其他几种重传策略相比, 有效地减少了平均传输次数, 节省了带宽消耗, 提高了网络吞吐量。     

一种应用干扰消除进行冲突消解的分布式无线MAC协议

媒介接入控制(MAC)用以协调无线节点对公共信道的共享,对无线网络性能有至关重要的影响。传统的MAC协议只能抑制冲突,不能根除及处理冲突。提出了一种基于已知干扰消除技术的新型消解冲突方法,并以此为基础设计了一个全新的MAC协议——CR-MAC。在CR-MAC协议中,无线接入点(AP)通过将部分报文传输与已知干扰消除相结合来解码冲突所包含的所有报文。因此发生冲突的报文传输过程能够被充分利用,且所需的报文重传减少了。实验结果表明,在网络吞吐率及预期报文时延指标上,CR-MAC协议较普遍采用的IEEE 802.11DCF协议均有明显优势。     

SRA-MSDU: Enhanced A-MSDU frame aggregation with selective retransmission in 802.11n wireless networks

The main goal of the IEEE 802.11n standard is to achieve more than 100 Mbps of throughput at the MAC service access point. This high throughput has been achieved via many enhancements in both the physical and MAC layers. One of the MAC enhancements is the frame aggregation in which multiple frames are concatenated into a single large frame before being transmitted. The 802.11n MAC layer defines two types of aggregation, aggregate MAC service data unit (A-MSDU) and aggregate MAC protocol data unit (A-MPDU). The A-MPDU outperforms A-MSDU due to its large aggregation size and the subframes retransmission in erroneous channels. However, in error free channels and under the same aggregation size the A-MSDU performs better than the A-MPDU due to its smaller headers. Thus, adding a selective retransmission capability to the A-MSDU would improve the system performance. In this paper, we have proposed an MSDU frame aggregation scheme that enables selective retransmission at the MSDU level without altering the original MAC header. In this proposed scheme an implicit sequence control mechanism has been introduced in order to keep the frames in sequence and preserve their correct order at the receiver side. The results show that the proposed scheme improves the system performance in terms of throughput and delay even under highly erroneous channels.     

Improving fairness in IEEE 802.11 networks using MAC layer opportunistic retransmission

This paper introduces DAFMAC (Decode And Forward MAC), a scalable opportunistic cooperative retransmission enhancement for the IEEE 802.11 MAC protocol which operates without the need for additional explicit control signalling. Distributed opportunistic retransmission algorithms rely on selecting a single suitable relay without direct arbitration between nodes. Simulations show that DAFMAC offers a significant improvement in fairness for both throughput and jitter, giving multiple parallel data flows a more equal opportunity to utilise the channel. DAFMAC cooperative retransmissions are shown to reduce node energy consumption for a given throughput. Further, the DAFMAC relay selection algorithm is shown to scale very well in terms of complexity and memory requirements in comparison to other cooperative retransmission schemes.     

MANET环境下的TCP Veno性能研究

采用NS2对运行在MANET环境下的TCP Veno的性能进行仿真测试,仿真结果表明,在有背景流、随机丢包且存在拥塞的 MANET网络中,TCP Veno的性能优于TCP Reno,且背景流越大、达到拥塞的时间越短、随机丢包越大,TCP Veno的优越性就越明显。但2种协议的兼容性较差,导致数据包的重传率增大。     

特高压输电塔实时监测系统的数据传输方法研究

对特高压输电塔安全状态进行实时在线监测是保障国家电网安全的一个重要手段,而特高压输电塔处于的复杂强干扰、弱无线信号的环境对数据可靠传输提出了较高要求。以基于无线传输信道建立的远程数据传输系统为基础,在分析了特高压输电塔环境特性对无线信道的影响基础上,提出建立一种基于应答确认与自适应数据动态重传机制的数据传输方法,该方法能自动根据无线信道情况,采用"快速启动"、"线性增长"、"回归发送"的动态机制来实时调整数据包大小,从而在保证数据传输可靠性基础上实现数据的最大效率传输。该数据传输方法经过实验验证,相比传统直接发送数据方法具有很高的可靠性和抗干扰性。     

500 kV输电系统切机信号通道改造

根据500kV阳淮输电系统切机传输回路运行原理,通过对运行情况的分析,对传输回路中转发接点潜在的缺陷提出合理的改造方案,制定切实可行的措施,解决了设备存在的问题,消除了系统隐患,防止误切机信号的传递,确保切机传输回路的安全可靠,提高了电力线载波通道的运行可靠性。     

层次编码流媒体发送调度的研究

文章针对层次编码流媒体数据在Internet上进行传输的问题,研究服务端包发送调度技术。根据发送缓冲区中层次编码流媒体数据包之间存在的多重依赖关系和传输时间限制,提出了服务端发送调度的马尔科夫模型,在该模型的基础上,用值迭代法实现一个最优的发送策略。该策略能够在带宽受限的条件下,保证重要性较高的数据包优先发送出去。通过实验证明,与顺序发送方法比较,该调度算法能够在客户端获得更好的播放质量。     

一种基于RCPT码的混合ARQ方法及其在衰落信道下的性能

本文基于码率匹配截短Turbo(RCPT-Rate Compatible Punctured Turbo)码,综合利用"码字校验交替重传"方案及Chase组合技术,提出了一种新型混合ARQ(Hybrid Automatic Repeat reQuest)方法,并进一步在瑞利衰落信道上对该方法的性能进行了仿真验证,同时将其与几种现有基于RCPT码的混合ARQ方法进行了比较.数值结果表明,本文所提方法能以较低的系统实现复杂度获得较好的性能.