QoS敏感的802.11e分组调度算法

分析并总结无线网络中基于QoS的分组调度算法,针对802.11e EDCA机制中多媒体数据分组调度的不公平问题,提出QoS敏感的802.11e数据分组调度算法.首先,根据不同数据业务延时敏感性需求,提出新的基于紧急度的数据分组调度指标.然后,在802.11e协议中根据业务流的紧急度,调整不同业务流所对应AC队列的参数,改变AC队列信道访问优先级,使紧急业务流有更多机会竞争到信道访问权.最后,进行大量仿真实验,实验结果验证了所提算法的有效性.     

基于业务流均衡的802.16无线分组调度算法

基于对802.16 2004标准所提出的四种业务流的分析,结合802.16网络的实际应用场景,提出了一种基于业务流均衡的802.16系统无线分组调度算法,并对该算法进行了Matlab仿真类比。仿真结果表明,新算法能够很好地解决分组调度的优先权问题和“饥饿”情况,具有重要的实际意义。     

基于探测的多信道无线网状网机会路由算法

多信道无线网状网的性能在很大程度上依赖于信道分配和路由选择.现有的多信道无线网状网路由大多没有考虑信道之间的干扰问题,从而导致通信性能下降.针对这一问题,提出一种基于探测的多信道无线网状网机会路由(POR)算法.首先,根据干扰能量,选出最佳通信信道集来降低信道间的传榆干扰.在此基础上,采用探测方式计算路径期望传输时延,确定候选链路集并运用机会路由机制进行数据传输以最小化端到端的传输时延.实验结果表明,POR可以显著地降低平均端到端时延,提高数据包投递率,为数据传输提供实时性和可靠性保证.     

基于分组管理的无线mesh网多信道分配算法*

为了合理利用多信道来提高无线网络吞吐量,针对基于802.11标准无线mesh网的业务特点,提出了基于分组管理的分布式多信道分配算法。该算法将节点接口分为回程接口与转发接口,并使回程接口分配到在干扰区域内干扰值尽可能小的信道。仿真实验结果表明,该算法可以减少区域干扰,并可充分利用信道的多样性和得到较高的网络吞吐量。     

M-WiMAX网络中预测LWDF调度算法的稳定性分析

移动无线城域网作为4G标准无线移动网络,其无线信道具有用户依赖和时变信道的特性,具有服务质量保证机制,分组调度算法是系统保证服务质量的核心要素之一。建立一个多用户泊松到达业务流,用Markov链建模一个无线时变信道,Pre-LWDF调度算法在各个用户间调度实时业务流,这样,移动无线城域网在PMP模式下形成了一个M/G/1的排队系统。根据队列理论计算并推导出无线城域网的信道容量域和系统的稳定域,在此基础上,用李雅普诺夫漂移稳定性理论分析证明Pre-LWDF调度算法具有分组级稳定性。进一步在NS2仿真平台上搭建一个移动无线城域网仿真环境,验证Pre-LWDF调度算法的稳定性。仿真结果表明,该算法在移动无线城域网中具有分组级稳定性。     

基于修正CQI反馈参数的分组调度方法

无线信道的非理想特性会使用户设备反馈给演进型基站(eNode B)的下行信道质量指示(CQI)参数值产生误差,从而降低调度器灵活调度的性能。为此,给出一种基于修正CQI反馈参数的快速分组调度方法,该方法在指数平滑预测模型及二次移动平均预测模型的基础上,利用CQI先验信息,通过组合预测对eNode B接收到的CQI参数值进行修正。仿真结果表明,该方法的吞吐性能够得到有效提升。     

AD hoc网络中的机会分组调度算法

无线多跳Adhoc网络中节点在业务发送过程中需要竞争共享信道,容易发生局部拥塞导致网络性能下降,而且节点内部采用的先入先出（FIFO）队列容易使队头阻塞,影响队列中后续分组的发送。本文提出了一种机会分组调度算法CBOS,发送节点采用多播RTS的方式同时指向多个接收节点,可以支持可变长分组,提高了Adhoc网络的空间重用率,接收节点根据拥塞程度按照一定概率返回CTS,有利于节点网络的拥塞控制。仿真结果表明,该算法提高了网络端到端的饱和吞吐量和信道利用率,并提高了业务流之间的公平性。     

增强超宽带无线网络QoS的调度算法

基于对UWB网络中已有调度算法性能的分析,提出了一种用于增强UWB无线网络QoS的调度算法。该算法采用跨层设计的思想,能根据无线物理层信道状态和应用层业务传输速率的变化进行动态带宽分配,分配过程主要采用带宽借贷的思想,即在具有不同优先级的业务流之间进行带宽调度,以尽最大可能满足具有不同优先级的业务流QoS要求。仿真结果表明,该算法能有效地增强网络的QoS,提高整个网络的性能。     

AD hoc网络中的机会分组调度算法

无线多跳Ad hoc网络中节点在业务发送过程中需要竞争共享信道,容易发生局部拥塞导致网络性能下降,而且节点内部采用的先入先出(FIFO)队列容易使队头阻塞,影响队列中后续分组的发送。本文提出了一种机会分组调度算法CBOS,发送节点采用多播RTS的方式同时指向多个接收节点,可以支持可变长分组,提高了Ad hoc网络的空间重用率,接收节点根据拥塞程度按照一定概率返回CTS,有利于节点网络的拥塞控制。仿真结果表明,该算法提高了网络端到端的饱和吞吐量和信道利用率,并提高了业务流之间的公平性。     

移动无线网分组调度策略的研究

提出了一种支持时延限制的无线多媒体流公平调度算法，算法根据无线信道的服务质量，动态调整该信道连接的业务速率，并根据各个业务请求当时的时延因子的大小来公平地补偿和再分配带宽。支持对时延敏感的流和对差错敏感的流，能做到区别补偿调度，满足各自的QoS需求。     

一种OSTBC-OFDM下行链路中的跨层自适应算法

本文从跨层目标出发,分析了OSTBC-OFDM下行链路中支持多业务混合传输的特性与质量要求,提出一种兼顾媒体业务传输质量(QoS)保障及最大化传输效率的动态BER/PER目标调整算法.该算法根据无线传输系统的容量和信道质量,调整传输手段,并根据媒体业务包的质量要求,为发送缓冲区的各个业务包指定不同等级的BER/PER要求,并加载于各个子信道中,从而达到兼顾媒体业务传输质量和最大化传输效率的目的.     

Enhanced handoff scheme based on efficient uplink quality estimation in LTE-Advanced system

Asymmetric traffics cause downlink–uplink asymmetric interference. It can lead to a critical unbalance between a downlink and an uplink channel qualities in cell edge areas. This paper proposes an enhanced handoff scheme including an efficient uplink channel estimation method. The proposed handoff scheme determines an appropriate handoff-timing and handoff-direction according to an estimated uplink channel quality and a measured downlink channel quality. In the proposed scheme, an uplink or downlink, whose quality dominantly affects a link failure, becomes the main handoff-criterion. An efficient uplink channel estimation method is also proposed to exploit an uplink channel quality in handoff. The proposed method estimates an uplink signal strength from the measured downlink signal strength and predicts an uplink interference based on the interference-level information from neighbor base stations. We propose two different uplink estimation modes such as the simple and the precise modes. The simple estimation mode calculates the uplink channel quality for the overall bandwidth for a general handoff process. The precise estimation mode finds the best uplink band for the handoff user who wants an elaborate handoff process. In the elaborate handoff, a target base station allocates the best uplink band to a handoff user to provide the better uplink channel quality. Simulation results show that the proposed uplink estimation method can accurately compute the uplink channel quality of neighbor cells where the estimation error rate is less than 0.7% The simulation results also show that the proposed handoff scheme reduces handoff-call-dropping probability by up to 69% compared to LTE-Advanced system. In addition, the end-to-end delay of the proposed scheme can be better than that of LTE-Advanced system by 26%.     

Using traffic asymmetry to enhance TCP performance

A wealth of recent work has gone into optimizing the performance of Transmission Control Protocol (TCP) on the downlink channel of wireless networks such as for example, honing its congestion awareness mechanism so that it is minimally affected by random wireless losses, and optimizing achieved fairness of the end-to-end TCP rates. Other work has gone into balancing the allocation of a shared resource between the downlink and uplink in order to optimize TCP performance. We build on such previous research by proposing a cross-layer algorithm for resource allocation in OFDMA systems aiming not only to achieve optimal throughput for competing TCP flows but also to allocate resources appropriately between the downlink and uplink. This is important due to the increasing number of Internet applications where the mobile terminal is the TCP sender (social networking, peer-to-peer, etc.). Therefore, our scheme makes use of the asymmetry in the traffic and by defining the boundary between downlink and uplink capacity dynamically, enhance the TCP performance. Through numerical investigations we show the performance of the proposed scheme in terms of achieved fairness to the receivers and efficient allocation of downlink to uplink ratios based on the TCP traffic.     

信道估计误差下多用户MIMO／OFDM下行系统自适应传输

以系统总速率最大化为目标，提出在非理想信道信息情形下基于空分复用的多用户MIMO／OFDM下行系统的自适应资源分配方案，并满足用户的QoS要求。该方案首先根据用户信道估计误差模型和用户QoS对用户进行子载波分配，然后在各个子载波上进行功率和比特分配。仿真结果表明，该方案相对静态分配方案可获得更大的总速率，而且对信道估计错误更加强健，可应用到信道信息不确定的实际系统中。     

无线传感器网络中一种抗无线局域网干扰的信道分配机制

无线传感器网络(WSN)易受到与其共享信道的无线局域网(Wifi)干扰,造成通信可靠性及吞吐量下降.当具有不同优先级的多个WSN受到Wifi干扰时,如何按优先级分配信道,并兼顾整体通信可靠性及吞吐量是一个重要问题.针对该问题,作者提出了一种抗Wifi干扰的信道分配机制EasiCAP(Channel Allocation for wireless sensor networks with Priority).该机制利用基于干扰强度和活跃比率的干扰特征模型(External Interference Model,EIM)度量WSN中各信道的Wifi干扰;同时,采用以接收端为中心的模型(Internal Interference Model,IIM)度量各WSN之间的干扰.然后,各WSN根据EIM和IIM度量的结果,采用局部化贪婪信道分配算法独立、实时地选择信道,通过保持信道、切换信道及抢占信道操作实现按优先级分配信道,并尽可能降低所有网络所受干扰之和.实际测量和仿真结果表明,EasiCAP可为各WSN提供与其优先级相对应的通信可靠性和吞吐量;而且该机制下的平均通信可靠性及吞吐量也比现有方法高.此外,EasiCAP未带来过大的开销.     

基于演化博弈的用户接入机制

用户接入问题就是无线终端选择接入某个服务基站的问题。用户接入可以看作无线资源管理的第一步,对于网络性能有着重要的影响,在实现负载均衡、控制干扰、提高频谱和能量效率等方面起着非常重要的作用。针对包含宏基站和全双工小基站的多层异构网络特点,考虑了分离多接入机制,即允许一个终端在上行和下行接入到不同的多个基站,从而实现性能的提升。在此基础上,将异构网络中的上行下行分离多接入的用户接入问题建模成一个演化博弈问题,其中用户是博弈方,相互之间进行资源的竞争,基站的接入选择就是博弈中的策略,每个用户希望能通过策略的选择实现自身效用的最大化。此外,基于演化博弈和强化学习设计了低复杂度自组织用户接入算法,用户可以根据当前的策略选择收益来进行策略调整,并最终达到均衡状态,实现了用户公平性。最后通过大量的仿真实验验证了所提方法的有效性。     

Interference suppression with iterative channel and spatial covariance matrix estimation for LTE downlink

In LTE downlink systems with a high frequency reuse factor, inter-cell interference has been viewed as a predominant factor limiting system performance. Therefore, we develop an iterative interference suppression receiver to mitigate inter-cell interference for LTE downlink systems in this paper. The key challenge here is how to accurately estimate the channel state information and spatial interference covariance matrix by using limited available pilots to improve the interference suppression capability and the successful probability of signal detection. To overcome the challenge, an iterative receiver making full use of the time–frequency correlation of channel is proposed. Simulation results show that the proposed iterative receiver can obtain a lower packet-error ratio compared with the existing algorithms.     

基于服务质量机会测量的传感器网络协作控制机制*

为了消除制约无线传感器网络性能的因素和提高网络控制效率,基于实时网络服务质量机会测量,提出了传感器网络协作控制机制。首先,基于发送端节点和接收端节点状态以及中继节点的协作,测定无线传感器网络实时状态。其次,分析能耗品质和负载品质对网络性能的影响规律。接着,讨论不同分频调制方式对网络性能的影响规律。最后,制定了网络状态感知的机会分频调制的传感器网络协作控制机制。数学分析和实验结果表明,所提出的传感器网络协作控制机制对无线传感器网络的实时性、可靠性和吞吐率等方面具有较强的保障能力。     

Optimizing the radio resource utilization of multiaccess systems with a traffic-transmission quality adaptive packet scheduling

In this paper we state a general framework for radio resource allocation based on a matrix which highlights the trade-offs of complexity and efficiency. This framework is outlined for the systematic definition of scheduling algorithms that are jointly adaptive to traffic and to transmission quality in order to improve the radio resource utilization and the achievable throughput of cellular networks for the support of best-effort traffic. We consider the application of the matrix concept to both time division and code division multiple access, the latter scheme also bringing about mutual interference among competing users. Then we propose a scheduling algorithm for wireless systems, called channel adaptive open scheduling (CHAOS). The CHAOS performance in terms of throughput and delay is extensively compared with those resulting from a load adaptive channel independent scheduling (CIS). A major result of this work is the quantitative assessment of the performance advantage allowed by jointly accounting for traffic congestion and transmission quality. Moreover the main implementation issues related to the proposed algorithms are investigated.     

Enhancing multi-hop communication over multi-radio multi-channel wireless mesh networks: A cross-layer approach

The multi-channel multi-radio technology represents a straightforward approach to expand the capacity of wireless mesh networks (WMNs) in broadband wireless access scenarios. However, the effective leveraging of this technology in WMNs requires (i) enhanced MAC protocols, to coordinate the access to multiple channels with a limited number of radio interfaces, and (ii) efficient channel allocation schemes, to mitigate the impact of co-channel interference. The design of channel assignment schemes and MAC protocols is strictly interrelated, so that joint design should be considered to optimize the mesh network performance. In this paper, a channel assignment and fast MAC architecture (CAFMA) is proposed, which exploits the benefits provided by the multi-channel multi-radio technology to (i) enhance the performance of multi-hop communications, (ii) maximize the resource utilization, and (iii) support differentiation of traffic classes with different quality of service (QoS) requirements. CAFMA is designed with a cross-layer approach and includes (1) a novel MAC scheme, which provides multi-channel coordination and fast data relaying over multi-hop topologies, and (2) a distributed channel allocation scheme, which works in cooperation with the routing protocol. Simulation results confirm the effectiveness of CAFMA when compared with other single-layer and cross-layer solutions for multi-radio multi-channel WMNs.