无线自组网中最大化网络寿命的速率调整问题

该文针对发送速率可以调整的无线自组网,研究了最大化网络寿命的速率调整问题。将该问题模型化为混合整数非线性规划问题,通过分支限界法可以求出最优解。该文还提出了一个基于贪心策略的分布式最大化网络寿命速率调整算法MNLRAA,其基本思想是根据网络中节点的流量和剩余能量,尽可能为每条链路选择较低传输速率发送分组来节能。模拟实验结果表明,同所有节点使用最高传输速率的经典技术相比,MNLRAA可延长网络寿命20%以上。     

支持OTDM的多粒度光交换结构研究

多粒度光交换能减小光交叉连接矩阵的规模,降低光节点的成本,然而现有多粒度光交换结构的最小交换粒度常为波长,该交换粒度太大,会导致核心节点的链路利用率低。在多层MG-OXC基础上,提出了一种新型多粒度交换结构,实现了波带交换和OTDM的结合。该新型MG-OXC结构端口较少,并且可以提高传输速率,同时也因此降低了同等信息量下波长的使用数量,为网络提供了更大的传输容量,能够很好地适应光网络发展的需要。     

多包接收无线传感器网络的跨层优化策略研究

多包接收能有效提高无线传感器网络的网络吞吐量,但由于该思想在物理层实现的复杂性,决定了在上层难以建立充分发挥多包接收性能的最优传输方案。本文根据基于信噪比的物理层数据发送模型,通过研究可同时传输数据的节点集合,建立了链路层的分时传输模型。为了使该模型可在多项式时间内求解,提出了最大可行集合的概念,减少了求解的时间和空间复杂度,最终提出基于多包接收的无线传感器网络跨层优化策略。仿真显示,采用该策略后数据传输速率比传统方案提高了1倍。     

基于拥塞控制的多速率MAC协议的研究

在IEEE 802.11b协议中有四种速率用于数据传输,节点可根据信道情况选择传输速率,致使802.11DCF公平的退避机制不再适用.为了让高速节点能更容易的竞争到信道以体现多速率协议的优势,提出了基于拥塞控制的速率自适应机制.竞争信道的节点根据拥塞情况来选择合适的退避窗口.通过NS2软件仿真证明该机制进一步提高了竞争窗口自适机制的性能.     

移动互联网下分层媒体传输速率优化研究

在移动互联网的多媒体应用中,各参与的用户可能具有不同的处理平台并且以不同的速率连接到网络,处于同一多播会晤的各接收节点可能具有不同的接收带宽。多速率传播允许接收节点根据其接收带宽的大小以不同的接收速率接收网络服务,所以多速率比单速率更适合于具有大量异构接收节点的移动互联网,当前广泛采用的策略主要有三个：复制流、分级编码、多重描述编码。本文研究了分层媒体传输速率优化问题,通过优化分配层速率并最大化所有接收节点的接收速率总和来提高网络吞吐量和各接收节点的平均带宽利用率。     

无线mesh中传输速率抖动抑制策略研究

通过分析无线mesh网络中节点的抖动行为特征,针对节点因拥塞导致的限速行为提出了抖动抑制策略.当访问节点选择流媒体服务提供节点时,通过预测抖动概率效用函数,选择抖动较低的节点为流媒体服务源端节点;构建节点失效恢复策略,当发生拥塞且预测抖动概率较大时,判定节点失效,启动节点替换机制并实现服务迁移.实验结果表明,该策略能有效抑制通信链路的传输速率抖动,提高网络的服务性能,同时验证了网络中节点抖动的客观存在性.     

支持OTDM的多粒度光交换结构研究

多粒度光交换能减小光交叉连接矩阵的规模,降低光节点的成本,然而现有多粒度光交换结构的最小交换粒度常为波长,该交换粒度太大,会导致核心节点的链路利用率低.文章在多层MG-OXC基础上,提出了一种新型多粒度交换结构,实现了波带交换和OTDM的结合.该新型MG-OXC结构端口较少,并且可以提高传输速率,同时也因此降低了同等信息量下波长的使用教量,为网络提供了更大的传输容量,能够很好地适应光网络发展的需要.     

基于多目标的MIMO无线mesh网络信道优化策略

MIMO是一种可有效提高无线网络信道带宽的技术。将MIMO技术应用在无线mesh网络中会遇到信道干扰和无线节点之间无协同策略等问题,导致网络效率降低。基于无线mesh网络中节点的多属性特征,以节点属性和内容分发为约束,提出了基于多目标优化算法与多层分发联合的调度和优化策略。实验结果表明,该算法能有效降低无线mesh网络分发数据过程中的时延,提高网络的吞吐表现和服务质量。     

一种多速率水声传感器网络协商机制

在水下声通信传感器网络中,一个较短的链路可以比一个较长的链路提供更大的带宽。多速率水声传感器网络模型可以在不同长度的链路间动态选择传输速率,提高了带宽的利用率。针对多速率水声传感器网络的速率协商问题,提出了一种基于握手的多速率协商机制。这种协商机制适用于链路长度未知的多速率水声传感网,可以在保证网络连通率的前提下降低端到端延迟和单位比特的能量消耗。仿真验证结果表明,该协商机制可以有效提高水下声通信传感器网络的性能。     

基于吞吐量比例公平的802.11MAC优化机制

802.11DCF MAC机制为单速率网络节点提供相同的信道接入机会,保证节点公平地使用信道。在多速率网络中依然沿用该接入机制,会导致低速率的节点长期占用信道,高速传输的优势得不到充分利用,使得多速率网络中所有节点的吞吐量都等于低速率节点的吞吐量,这就是著名的多速率网络"性能异常"问题。针对这一问题,通过分析建模,提出CCDa P(Change the CWmin according to Data rate and Packet-size)MAC优化机制以改善多速率网络中的节点的吞吐性能。仿真结果表明,该接入机制不仅可以保证节点公平性,还能提高网络整体吞吐量。特别地,在数据包长度不等的多速率WLAN中,该机制能够保证网络节点吞吐量的比例公平。     

基于最优化的多媒体多播速率控制

传输多媒体流的一种有效方法是采用多速率多播,但多速率多播的速率控制面临许多挑战,如异构性、公平性、实时性及服务质量(QoS)等。提出了一种两阶段优化的策略进行多媒体多播速率控制。把问题公式化为求系统效用最大化的最优化问题,推导出有效的算法。方法综合考虑了服务质量、异构性等,且满足协议间的公平性和多播会晤内各接收者间的公平性。仿真实验表明算法的有效性,与现有的算法相比系统总效用大大提高。     

A routing protocol using a reliable and high-throughput path metric for multi-hop multi-rate ad hoc networks

In this paper, a high-throughput routing protocol for multi-rate ad hoc networks using lower layer information is proposed. By choosing the route with the minimum value of the proposed “Route Assessment Index” metric which has the form of entropy function, the selected route is ensured to have high throughput and link reliability among route candidates. Link bottleneck is avoided in the chosen route; hence, the packet drop rate due to buffer overflow is alleviated. Furthermore, an effective route discovery strategy is also introduced along with new routing metric. The correctness of the proposal is proven, and the simulation results show that our new metric provides an accurate and efficient method for evaluating and selecting the best route in multi-rate ad hoc networks.     

Video transmission strategy in multi-rate and multi-node IEEE 802.11 networks

The video transmission strategy VQCW (video queue contention window) was proposed for video transmission fair problem in multi-rate and multi-node IEEE 802.11 networks.The strategy was based on node queue selective packet drop and contention window dynamic adjustment.It deduced a maximum throughput model according to initial contention window size because of the relation between throughput and initial contention window size.This model can provide theoretical upper limit for improving throughput.The theoretical modeling and NS simulation show that the proposed strategy can maintain both video transmission quality and high network overall throughput.     

Blind Channel Estimation for Multi-Rate Multicarrier DS/CDMA Communications

Multi-rate multicarrier DS/CDMA is a potentially attractive multiple access method for future wireless communications networks that must support multimedia, and thus multi-rate, traffic. Several receiver structures exist for single-rate multicarrier systems, but little has been reported on multi-rate multicarrier systems. Considering that high-performance detection such as coherent demodulation needs the explicit knowledge of the channel, based on the finite-length chip waveform truncation, this paper proposes a subspace-based scheme for timing and channel estimation in multi-rate multicarrier DS/CDMA systems, which is applicable to both multicode and variable spreading factor systems. The performance of the proposed scheme for these two multi-rate systems is validated via numerical simulations. The effects of the finite-length chip waveform truncation on the performance of the proposed scheme is also analyzed theoretically.     

Space-Time Receiver for Multi-Rate CDMA Systems: Multi-Code and Variable Spreading Length Access Methods Comparison

This work proposed the linear minimum mean square error (LMMSE) space-timereceivers for synchronous multi-rate direct sequence code devision multipleaccess (DS/CDMA) systems. The performance of the proposed receivers isanalyzed. The high-rate (HR) LMMSE space-time receiver with combiningtechnique can provide essentially the same performance for low-rate (LR) usersas LR LMMSE space-time receiver while eliminate the time delay for the HRusers. The performance of the proposed multi-rate LMMSE space-time receiversare studied in the context of two multi-rate access methods: multi-code (MC)access where high data rate users multiplex their information streams ontomultiple codes, and variable spreading length (VSL) access where signaturesequences of different lengths are assigned to users with different datarates.Through the simulation results, we show that: (a) the proposed multi-rateLMMSE space-time receivers are optimum near-far resistant; (b) the proposedmulti-rate LMMSE space-time receivers have a clear performance improvementcompared to the time only LMMSE dual rate receiver; (c) there is a performancegain of the proposed multi-rate LMMSE space-time receivers compared to themulti-rate decorrelating space-time receiver when near-far ratio (NFR) is low;(d) The performance difference between MMSE combining and MRC in multi-ratesystem is much more pronounced than in single-rate system. Simulations alsoshow that the VSL access method is more robust than MC access methodconsidering changing rate-ratio in multi-rate systems.     

多速率移动Ad hoc网络路由策略研究

在多速率Ad hoc网络中，要充分利用多速率的优势，提高网络的整体性能，妊须设计一种适合网络特点以及满足用户需要的多速率路由策略。文中简要分析了多速率路由策略对网络性能的影响，重点介绍了现有的多速率路由策略。论文还给出了后续的工作——对在多频段和多模式的无线网络中采用改进的多速率路由算法的研究。     

WiMAX中多码率LDPC解码器的设计与实现

针对WiMAX中多码率LDPC码,提出一种多码率LDPC解码器结构,并且在FPGA上实现了该解码器.实验结果表明:该解码器完全可以满足IEEE802.16e标准中多码率的实现要求,而且具有高吞吐率、高性能的特点.     

Blind channel estimation in multi-rate CDMA systems

Multi-rate CDMA is a potentially attractive multiple access method for future broad-band multimedia wireless networks that must support integrated voice/data traffic. The primary impairment for such multi-rate systems is the multipath nature of radio channels that results in intra-user inter-chip interference (ICI) and multi-user interference (MUI) between different users' symbols. Explicit knowledge of the channel is typically needed for high performance detectors (such as coherent demodulation). We propose a subspace method for channel estimation in multi-rate CDMA systems. A unified signal model that applies to three multi-rate CDMA schemes proposed in the literature is developed. The computational complexity for multi-rate scenarios is large and variable-accordingly, a modified approach is devised that offers performance/complexity trade-offs. Performance analysis is conducted based on a close-form expression for the mean square error of the estimator, supported by simulation results that investigate the effectiveness of our method     

面向GEO卫星网络的多速率多播拥塞控制机制

针对GEO卫星网络带宽时延积较大、拥塞控制机制不完善的问题,提出了一种面向GEO卫星网络的多速率多播拥塞控制机制MMCCM_GEO.首先,在保证接收端请求速率最大化的前提下,将GEO卫星网络中的多速率多播问题转化为非线性优化问题,并采用改进的模拟退火算法对其求解,得到了最优的接收端请求速率.其次,通过采用代理节点实现反馈信息的汇集与丢失数据的恢复,有效地解决了反馈内暴及数据恢复问题.仿真结果表明,与目前GEO卫星网络中典型的多速率多播拥塞控制机制相比,本文的拥塞控制机制有效地提高了数据吞吐量和带宽利用率,降低了GEO卫星网络中的数据传输时延,同时也具备了更好的可扩展性.     

High throughput reactive routing in multi-rate ad hoc networks

A reactive routing algorithm for multi-rate ad hoc wireless networks is proposed. It enhances the AODV protocol and achieves higher throughput by utilising the multi-rate capability of the underlying wireless channel via the MAC delay routing metric. Simulations show that the protocol leads to a significant throughput increase over traditional ad hoc routing protocols.