An effective scheduling scheme for multi-hop multicast in wireless mesh networks

With the utilization of concurrent transmission strategy, a throughput-enhanced scheduling scheme is devised for multicast service in wireless multi-hop mesh networks. Since the performance of a multicast mechanism is constrained in a wireless setting due to the interference among local wireless transmissions, the interference relationships are first characterized by introducing a graph transformation method. Based on the graph transformation, the multicast scheduling problem is converted to the graph coloring problem, and then a capacity greedy algorithm is designed to provide concurrent transmission scheduling so that the demanded multicast transmission rate can be achieved. Moreover, the necessary and sufficient conditions of multicast schedulable feasibility are derived. Through corresponding simulations, it is shown that the proposed strategy can enhance the throughput of wireless multi-hop multicast systems significantly.     

认知无线电网络中QoS组播路由调度

在多跳认知无线电网络中,组播的信息通常要经由多个中间节点的转发才能到达最终的目的节点。现有的研究中已经有很多的组播路由协议,然而这些协议都是基于传统无线网络的,并不适合新型的认知无线电网络。本文解决的的问题是:在多跳无线网络中,给定一个具有QoS要求的组播请求,如何建立组播路由以及对路径节点进行传输调度,使得在满足QoS要求下整个传输过程的带宽消耗最小。本文提出了一个分布式的组播路由协议来解决该问题,该协议不仅实现了路由过程的建立,同时还完成了对节点传输过程的合理调度。实验结果证明本文的传输调度策略能有效地减少网络的带宽消耗,同时增加组播请求响应的成功率。     

无线多跳网络中吞吐量优化的多播路由算法研究*

现有网络中提高多播吞吐量的算法通常是以提高链路速率为目的,但单纯地提高链路速率而忽略多播树的度也限制了多播吞吐量的提高。主要研究了多跳无线网络中多播吞吐量最优化问题,深入分析了无线多跳网络特点,并在综合考虑链路速率和多播树度对多播吞吐量影响的基础上,提出了应用于节点发射功率相同环境下的UUP_MTOA算法和应用于节点发射功率不同环境下的UNP_MTOA算法。通过仿真实验与同类近似最优化算法相比,UUP_MTOA算法和UNP_MTOA算法能够获得更高的吞吐量,更适应于多跳无线网络环境。     

Gray physical interference model based link scheduling algorithms

To improve the concurrent data transmission capability of wireless multi-hop networks,this paper proposes adopting a gray physical interference model instead of using the threshold physical interference model.The model allows non-ideal links to be involved in scheduling,under the premise of not affecting the quality of existing transmission links.In addition,we design two greedy algorithms to schedule more links with SINR values located in the transition region.The results show that a gray physical interference model is more accurate than a threshold physical interference one,the concurrent transmission capability of a network based on the gray physical interference model is significantly increased,and network throughput is increased by 20%.     

一种优化时延的机会协同组播调度策略

无线组播面临的最大问题是各个用户信道状态的不均匀性和波动性,无法同时满足所有用户的服务质量需求。无线蜂窝通信系统中,为实现可靠组播,数据包不可避免地需要被重传多次,组播的时延也因此增加。本文我们首先分析了协同组播调度CMS策略的时延,并且推导了基于信道信息全知条件下的最小时延。另外,我们在部分信道信息未知条件下提出了一种机会协同组播策略来优化组播时延。仿真数据显示,我们提出的机会协同组播调度OCMS策略在时延性能上几乎达到了我们所分析的CMS策略的最小值而且明显优于其他调度策略。     

基于网络编码和多访问点协作的视频多播方案

随着智能手机和平板等无线设备的普及,基于互联网的视频浏览成为无线设备的重要功能。然而,由于无线网络的链路间存在干扰、可靠性较低,为了提高视频多播传输的可靠性,文中分析了覆盖区域发生重叠的访问点间相互协作对于提高系统增益和系统公平性的作用,提出一种基于网络编码和多访问点协作的视频多播方案。该方案首先将每个视频划分为大小相同的报文段,并利用RLNC机制对每个段的报文进行编码。然后以使用户接收到的报文数量的期望值最大化的同时,实现公平调度为目标,考虑了访问点间的完全干扰和非完全干扰两种模型,将访问点间的传输范围发生重叠时的视频多播问题建模为线性规划优化问题,提出了双阶段启发式算法来进行求解,该算法通过利用多个访问点来获取空间和时间分集增益,提高了数据传输的可靠性,通过允许发生干扰的访问点并行传输数据,提高了系统效用。最后的仿真实验也验证了本文方案在接收报文总量、解码报文数量和公平性方面的有效性。     

Utility-based scheduling in wireless multi-hop networks over non-deterministic fading channels

In this paper, an innovative scheduling scheme is proposed for interference-limited wireless multi-hop networks with non-deterministic fading channels. The scheduling problem is considered as a network utility maximization (NUM) problem subject to link rate constraints. By jointly taking into account of the link scheduling and the statistical variations of signal and interference power, the convex sets for the NUM are derived. Two types of non-deterministic fading channels (i.e., Rayleigh fading channel and Ricean fading channel) are characterized into our NUM models as examples. To solve the convex optimization problem, the subgradient projection method based on dual decomposition is employed. Then, a heuristic algorithm is designed for the TDM mode wireless multi-hop networks by minimizing the discrepancy between the expected network cost and the optimal one in each timeslot. At last, the source–destination session rate and network utility are evaluated in a dedicated wireless multi-hop network scenario. The numerical results demonstrate that the session rates convergence and the network utility is improved by our proposed scheme.     

基于调度集合的多播单播数据联合调度算法

首先定义和分析了IEEE802.16e无线城域网中的一个新问题,即如何在保证移动终端服务质量的前提下,通过合理地调度终端的单播业务和多播业务来降低终端能耗.针对该问题,提出一种基于调度集合的联合调度算法(scheduling set based integrated scheduling,简称SSBIS).SSBIS算法将所有移动终端划分到多播调度集合或单播调度集合中,并利用多播数据的传输特点,在多播数据传输的相邻时隙内发送多播调度集合中所有终端的单播数据,而对于单播调度集合中的终端,则通过凸优化方法求得使终端休眠时间最长的单播业务调度方案,以达到降低终端能耗的目的.仿真实验显示,SSBIS算法在满足移动终端的最小数据速率要求的同时,可以明显地降低终端能耗.     

无线Mesh 网络低干扰组播

不同于无线传感器网络和移动Ad Hoc网络,无线Mesh网络中的组播主要侧重于提高吞吐量,而干扰是影响吞吐量的重要因素。在构建组播拓扑时,传统的方法主要考虑最小价值或最短路径,而通过减少干扰来提高组播性能的研究较少,且它们的干扰计算方法都采用单播的思想,并不适合于组播。例如,当n个接收节点同时从一个节点接收数据时,在组播中这n个接收节点之间不存在干扰,而在单播中认为存在干扰。因此,提出了组播冲突图来计算组播干扰,给出组播树干扰的定义。可以发现,求最小干扰组播扰树是NP完全问题,然后提出基于万有引力的启发式算法构建具有较小干扰的组播树。为了适用于多信道的情况,提出了满足不同干扰范围的多跳信道分配算法。最后,仿真结果显示,与MCM相比,所提出的算法无论是在单天线单信道还是多天线多信道下,都能取得较高的吞吐量和较低的延迟。     

Ad Hoc网络中的多播路由协议

无线Ad Hoc网络是指一组无线移动节点组成的多跳的,临时性的,无基础设施支持的无中心网络。多播是一种面向群组计算的通信传播方式,它使用单一的源地址把数据发给一组主机。如何在移动自组网中实现有效的多播路由技术是当前此领域研究中亟待解决的问题。文中对当前一些典型的多播路由协议进行了研究,并对它们各自的工作方式进行了分析,最后对它们各自的特点进行了比较。     

可变频宽无线网络中信道频谱分配与链路调度

考虑信道频宽对链路传输距离和链路间干扰的影响,对可变频宽无线网络现有的累积干扰模型进行了改进,并基于改进的干扰模型对可变频宽无线网络的信道频谱分配和链路调度问题进行了建模分析。设计了一种两层优化算法对信道频谱分配和链路调度问题进行解耦,提出了一种考虑链路负载需求满足程度的链路优先级指标,启发式地构建并发传输信道分配矩阵的方法。仿真结果表明,两层优化算法能够在合理时间内收敛,启发式方法能够高效地构建并发传输信道分配矩阵。     

物联网分布式调度算法研究

根据无线网络的传输特点,对分布式调度背景进行了简要介绍,考虑无线网络传输的衰减和干扰等因素,规划出了物联网中的无线物理干扰模型,在无线干扰模型作用下,复杂网络关系抽象成一个简单的有向图或者无向图,通过对无线网络中每一个节点状态的研究,以及对Schneider状态的分析,设计了分布式极大独立集算法,实现了物联网分布式调度。     

Ad Hoc网络中的多播路由协议

无线Ad Hoc网络是指一组无线移动节点组成的多跳的,临时性的,无基础设施支持的无中心网络。多播是一种面向群组计算的通信传播方式,它使用单一的源地址把数据发给一组主机。如何在移动自组网中实现有效的多播路由技术是当前此领域研究中亟待解决的问题。文中对当前一些典型的多播路由协议进行了研究,并对它们各自的工作方式进行了分析,最后对它们各自的特点进行了比较。     

Fuzzy Logic-Based Multicast Routing in Multiradio Multichannel Wireless Mesh Networks

The availability of bandwidth in wireless mesh networks (WMNs) introduces it as a prominent choice for implementing bandwidth sensitive services. Multicast services such as teleconferencing, push-based systems, multiplayer games, etc., can be implemented in an efficient way in such networks. Moreover, the severe performance degradations that can result from the interference generated by concurrent data transmissions and environmental noises call for the development of interference-aware routing mechanisms. This paper investigates the impact of wireless interference on network performance for multicast transmission in WMNs. We show that by taking wireless interference into consideration in the design of routing mechanisms, better resource usage can be achieved. Hence, a fuzzy logic–based approach is proposed to choose optimal routes from source to the multicast group in multichannel case. Three fuzzy variables are considered in route selection phase, which are interference, available bandwidth, and hop count. Extensive simulations are conducted aiming at verifying the high performance of the proposed algorithm. Simulation results demonstrated that our proposed algorithm outperforms Link-Controlled Multi-Rate Multi-Channel (LC-MRMC) and Channel Assignment with Multiple Factor (CAMF) algorithms in terms of throughput, packet delivery ratio, and end-to-end delay.     

Scheduling and performance analysis of multicast interconnects

Multicast is an important operation in various emerging computing/networking applications. In particular, many multicast applications require not only multicast capability but also predictable communication performance, such as guaranteed multicast latency and bandwidth, called quality-of-service (QoS). In this paper, we consider scheduling in multicast interconnects, which aims to minimize the multicast latency for a set of multicast requests. Unfortunately, such a problem has been proved to be NP-Complete, which means that it is unlikely to find a fast exact algorithm for the multicast scheduling problem. We then turn to propose a simple, fast greedy multicast scheduling algorithm and derive a lower bound and an upper bound on the performance of the algorithm. As can be seen, while a lower bound is fairly straightforward, the upper bound is much more difficult to obtain. By translating the multicast scheduling problem into a graph theory problem and employing a random graph approach, we are able to obtain a probabilistic upper bound on the performance of the multicast scheduling algorithm. Our analytical and simulation results show that the performance of the proposed multicast scheduling algorithm is quite close to the lower bound and is statistically guaranteed by the probabilistic upper bound. The research work was supported in part by the U.S. National Science Foundation under grant numbers CCR-0073085 and CCR-0207999.     

用于Ad Hoc网络的自适应多速率多播拥塞控制策略

多播提高了链路的传输效率,但易于造成网络拥塞.因此,在网络中实施多播拥塞控制至关重要.然而,由于AdHoc网络的两个本质特点,为Internet设计的多播拥塞控制不适合AdHoc网络:(1)无线多跳连接引起了信息流之间在时间域和空间域的竞争;(2)节点频繁移动导致了网络状态不断变化.首先提出了链路干扰集的概念来描述信息流竞争的特点,将网络状态不变的小时间段内的多速率多播拥塞控制问题表达成一个非线性优化问题,联合运用罚函数法和次梯度法获得此问题的优化解,相应地提出了一种有效的分布式迭代算法.在此算法基础上,针对网络状态的时变性,设计了一种基于状态检测和滚动优化的自适应多速率多播拥塞控制策略——AC2M2.仿真结果表明,分布式算法能够快速收敛到最优解;AC2M2(adaptive congestion control strategy for multirate multicast sessions)策略对网络状态的变化具有较好的自适应能力,所获得的网络性能比TCP-Reno要优越得多.     

一种无线多媒体传感器网络分区链路调度算法

链路干扰是无线多媒体传感器网络实现大容量、实时、可靠传输的主要困难。为提高多跳传输模式下无线网络性能,基于MAC层的调度算法得到了广泛关注。调度算法为每条链路分配合理的传输时槽,降低了冲突和重传次数,能显著提高网络传输性能。但随着网络规模的增大,无论是集中式还是分布式调度算法,都存在调度开销增大和性能降低的问题。针对这一问题,根据节点分布密度和承载网络流量大小,将网络划分为密集区域和稀疏区域。稀疏区域的节点传输冲突较小,直接采用CSMA的协议。密集区域的节点传输冲突大,采用基于队列长度的分布式调度。分区调度能够有效降低网络规模扩大导致的调度算法复杂性增大的问题。仿真实验表明,分区调度算法无论是在队列长度,还是在延时性能上,较传统算法有明显改善。     

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。     

多跳无线 Ad hoc网络的分布式公平调度算法

为兼顾无线Ad hoc网络信道资源的公平利用及网络吞吐量,提出针对多跳无线Ad hoc网络的分布式公平调度算法。该算法采用链路竞争图说明网络中各子流的竞争关系,通过着色算法得到最大无竞争流的集合,通过邻居节点之间的信息交换得到局部(本地)流的信息,而无需全局流的信息交换。实验模拟结果表明,该算法可以在保证Ad hoc网络中各流公平性的同时,有效提高网络资源的利用率。     

无线传感器网络中一种基于虚拟MIMO多播的多跳传输策略

虚拟MIMO技术能够有效减少信道衰落对无线链路的影响,节省无线传输时的能耗.结合MIMO多播和LEACH协议,提出新的虚拟MIMO多跳传输策略(VMMM),由于该策略避免了多跳数据转发时的簇内广播过程,从而提高整个网络的能量有效性.为优化该传输策略的性能,本文对VMMM策略的能耗进行建模分析,并在此基础上通过联合优化以确定满足最小能耗时的网络参数.仿真结果表明,与已有的虚拟MIMO多跳传输策略—vMISO协议相比,VMMM策略能够显著提高网络的能量有效性,有效延长网络生存时间达50%以上.