基于校园网带宽利用率最优的视频组播机制

传统的视频点播系统为每个点播用户分配单独的静态通信通道,其系统资源利用率低的缺点使得总体时间段上能并发的点播用户数少。针对网管可控的宽带校园网环境,文章提出了一个采用自适应动态缓存的组播策略,它通过差别服务(Diffserv)比例带宽分配机制保证了一定的视频播送服务质量(QoS),并基于服务端综合调度和客户端回馈的方法动态调整各视频流的播送速度,从而优化了系统整个过程的整体资源利用率,提高了系统的点播性能。     

P2P点播系统的数据调度策略研究

提出了适用于点播系统的推拉结合的内容分发方案,该方案通过对调度窗口的划分,解决了方案中存在较多冗余数据的问题,同时通过调度带宽的动态调整和片段预定的转移,使得所提方案更加适应于高动态性及缓存不连续的点播环境.     

流媒体资源调度策略的研究与应用

流媒体系统资源调度策略是流媒体系统中的关键技术和重要研究方向。本文提出了一套资源调度解决方案,利用节目切片、分布式存储解决节目存储问题,利用单播、组播和单、组播切换解决流的播放问题,并给出一种调度策略解决流的调度问题。测试结果显示该方案具有良好的效果。     

一种分布式VOD系统的方案设计

视频点播(VOD)是目前广受网络用户欢迎的应用服务,而节目调度问题始终是VOD系统方案设计和实现中的一个重要问题。该文针对互联网的用户点播特点,从用户行为和节目流行度入手,详尽分析了系统体系和用户点播流程。通过改进基于流行度的节目调度策略,采用每个节目不同片段分块备份存储和不同时间实时调度相结合的方案。实验表明,该方案的边缘Server资源利用率较高,系统能达到较好的服务性能。     

一种基于IP/DVB双通道环境的视频点播调度算法

研究了点播业务在广电IP、DVB通道共存环境下支撑问题,提出一种基于稳态带宽的联合通道调度PBHS(Prediction Baaed Hybrid Schedule)算法.此算法充分发挥了IP单播和DVB广播优势,实现对不同特征(带宽、时长、热度)点播片源的自适应接纳决策(单播、周期性补丁和广播).PBHS调度算法分为带宽不受限和受限两部分:前者依据对稳态带宽的估计,与基于流行度的带宽凋度算法相比,带宽资源需求可减少约20%;后者依据带宽分配效能因子,与基于流行度的带宽调度算法相比,确定性的拒绝对部分片源请求的同时,降低用户拒绝率.     

基于负载均衡的医院云计算系统资源调度方案

医院云计算系统存在需求的不确定性和节点资源的异构性问题,导致节点的负载失衡。为此,提出一种新的医院云计算系统资源调度方案。该方案基于混合蛙跳算法设计,并针对混合蛙跳算法容易陷入局部最优解的不足,给出一种基于讨论机制混合蛙跳算法改进的医院云计算系统资源调度方案,通过增加自适应讨论次数,提高算法的搜索能力。仿真实验结果表明,与传统负载均衡方案相比,该方案具有更好的负载均衡度性能,可解决混合蛙跳算法陷入局部最优的问题。     

一种新的基于流合并的调度策略

分析了Patching调度策略的特点,指出Patching流满足了70％左右的用户请求而只消耗8％左右的系统资源。以此为依据,提出了PatchingFirst连续媒体播放调度策略,并基于该策略设计了MPQL和MFPQ通道分配算法。试验结果表明,与MQL算法比较,这两种算法可以明显地缩短用户等待时间、减少用户请求撤消率、降低调度的不公平性。通过试验结果分析,证明了Patching First策略增强了Patching流合并调度算法的优势,是一种非常有效的连续媒体播放通道调度策略。     

基于最佳并行度的任务依赖图调度

基于最佳并行度的任务依赖图调度策略充分利用编译时刻所得到的全局信息,采用横向和纵向任务合并,处理节点预分配,静态调度和动态调度相结合、集中式调度和分层调度相结合等措施,是一种简单的、具有较高效率的实用化调度方案.该调度方案能够在尽量压缩调度长度的情况下节约系统资源.     

采用分区缓存调度策略的P2P点播系统

针对在当前的P2P点播系统中,由于节目热度的差异导致数据副本分布不合理的问题,提出一个采用分区缓存调度策略的P2P流媒体点播系统设计方案。该策略将用户节点缓存区分为2个部分,分别考虑节点自身的需求和整个网络的全局需求进行调度,以优化节目数据在各节点间的分布,从而提高播放质量。通过仿真实验,验证了该系统设计与策略的有效性。     

基于云计算神经网络物流车辆调度算法研究

研究了物流车辆调度优化问题。针对云计算下任务调度算法没有考虑调度的服务质量和用户满意度的问题,特别是在物流任务调度问题中存在复杂的计算网络,造成计算率降低,为了解决上述问题,提出了一种新的有关云计算和神经网络相结合的物流作业调度算法。算法充分考虑了调度的服务质量以及用户满意度,建立一个参数化的处理模型,计算用户在各个资源上的综合满意度,再将任务分配到满足用户需求和使系统资源达到均衡的资源上执行,最后采用改进的神经网络进行优化车辆调度。实验结果表明,改进算法不仅能满足用户的多种需求,提高了用户的满意度,同时也提高了资源调度率和系统资源的利用率。     

Simulating the performance of SW-ARQ schemes within molecular communications

This paper provides results on an investigation concerning the application of five tailored Stop-and-Wait Automatic Repeat reQuest (SW-ARQ) schemes to a diffusion based molecular communication system. Each scheme is numerically simulated and evaluated to determine its performance with regards to average time cost and energy consumption. It is shown that all five schemes are beneficial depending upon the application scenario. Scheme 1 is the best choice for adjacent communications although, if a slightly higher energy budget can be afforded, schemes 2 and 3 will provide better performance than scheme 1 as the communication distance increases. Schemes 4 and 5 are designed to benefit scenarios with either a varying channel or for a channel with unknown parameters although will also benefit a static channel if again, further system energy can be utilised. This optimisation and trade-off between time and energy requirement for a complete successful transmission will become more important in future applications involving molecular communications where energy efficiency is a design consideration.     

Realizing high-accuracy transmission in high-rate data broadcasting networks with heterogeneous users via cooperative communication

This paper considers a broadcasting network in which multiple single-antenna (weak) and multiantenna (strong) users are receiving simultaneously spatial-multiplexed data streams from the multiantenna base station (BS). In order to improve the received data quality for the single-antenna users while preserving the transmission rates of the multiantenna users, we propose user cooperation schemes without the employment of space–time codes or retransmission from the BS which reduce the data rates and the spectral efficiency. Three cooperation schemes among single-antenna users, namely, decode-and-forward (DF), amplify-and-forward (AF), and hybrid cooperation, are examined and compared. Simulation results demonstrate that single-antenna users through cooperation can achieve comparable or superior error-rate performance as compared with noncooperative multiantenna users. Various configurations of the proposed cooperation schemes are studied to show the tradeoff in terms of cooperation overhead, receiver complexity, and system performance. The acquisition of the channel information and the effect of channel estimation errors on the system performance are also investigated for practical implementation of the proposed schemes. The proposed schemes are capable of avoiding modification to the multiple-input multiple-output (MIMO) transceivers, and are readily applicable to existing MIMO broadcasting networks.     

UpdateSearch: A New Dynamic Channel Allocation Scheme for Mobile Networks That Can Adjust to System Loads

Distributed dynamic channel allocation techniques are an integral part of distributed mobile computing systems where nodes communicate among themselves via wireless radio channels. The channel allocation schemes can be broadly categorized as search based or update based. Search based techniques have low messaging complexity and are suited for high system load and low request rates. On the other hand update based schemes have higher messaging complexity but are more suitable for low system load and high request rates. This paper presents a combined scheme, called UpdateSearch, which provides the advantages of both types of schemes. UpdateSearch is parameterized by the number of channel classes k, 1kn, where n is the total number of channels in the system. The parameter k can be adjusted to control the number of concurrent searches and degree of contention between cells competing for channels in the system. For k=1 and k=n the scheme respectively behaves as basic search and basic update scheme [2]. A simple analytical model is used to compare the performance of UpdateSearch for various values of k with the basic update and search techniques in terms of channel allocation time and number of simultaneous channel selections allowed in the system under different system loading conditions.     

Adaptive Distributed Dynamic Channel Allocation for Wireless Networks

Channel allocation schemes in a mobile computing (wireless) environment can be either static or dynamic. Static allocation offers negligible channel acquisition time and zero message complexity and works well at a low system load; the performance steadily decreases as system load increases since many calls are dropped. In the case of even temporary hot spots many calls may be dropped by a heavily loaded switching station even when there are enough idle channels in the interference region of that station. On the other hand, dynamic schemes provide better utilization of the channels at higher loads albeit at the cost of higher channel acquisition time and some additional control messages. Our purpose in the present paper is to propose a combined channel allocation scheme so that each switching station can tune to its own load independent of other stations in its interference region; the objective is to minimize the call drop rate and at the same time maintain a minimum average channel acquisition time and minimum control message complexity.     

Link-level traffic scheduling for providing predictive QoS in wireless multimedia networks

A set of centralized burst-level cell scheduling schemes, namely, First Come First Served with Frame Reservation (FCFS-FR), FCFR-FR+, Earliest Deadline First with Frame Reservation (EDF-FR), EDF-FR+, and Multitraffic Dynamic Reservation (MTDR), are investigated for transmission of multiservice traffic over time division multiple access (TDMA)/time division duplex (TDD) channels in wireless ATM (WATM) networks. In these schemes, the number of time slots allocated to a virtual circuit (VC) during a frame-time is changed dynamically depending on the traffic type, system traffic load, the time of arrival (TOA)/time of expiry (TOE) value of the data burst and data burst length. The performances of these schemes are evaluated by computer simulation for realistic voice, video and data traffic models and their quality-of-service (QoS) requirements in a wireless mobile multimedia network. Both the error-free and the correlated fading channel conditions are considered. Simulation results show that the EDF-FR+ and MTDR schemes outperform the other schemes and can provide high channel utilization with predictive QoS guarantee in a multiservice traffic environment even in the presence of bursty channel errors. The EDF-FR+ scheme is found to provide better cell multiplexing performance than the MTDR scheme, Such a scheme would be easy to implement and would also result in a power conservative TDMA/TDD medium access control (MAC) protocol for broadband wireless access. Burst-level cell scheduling schemes such as EDF-FR+ can be easily adapted as MAC protocols in the emerging differentiated services (DS) enhanced wireless Internet protocol (IP) networks.     

Performance analysis of a threshold based distributed channel allocation algorithm for cellular networks

Rapid advances of the handheld devices and the emergence of the demanding wireless applications require the cellular networks to support the demanding user needs more effectively. The cellular networks are expected to provide these services under a limited bandwidth. Efficient management of the wireless channels by effective channel allocation algorithms is crucial for the performance of any cellular system. To provide a better channel usage performance, dynamic channel allocation schemes have been proposed. Among these schemes, distributed dynamic channel allocation approaches showed good performance results. The two important issues that must be carefully addressed in such algorithms are the efficient co-channel interference avoidance and messaging overhead reduction. In this paper, we focus on our new distributed channel allocation algorithm and evaluate its performance through extensive simulation studies. The performance evaluation results obtained under different traffic load and user mobility conditions, show that the proposed algorithm outperforms other algorithms recently proposed in the literature.     

Dynamic radio resource and interference management for MIMO–OFDMA mobile broadband wireless access systems

A multi-user multi-cell Multiple-Input Multiple Output/Orthogonal Frequency Division Multiple Access (MIMO/OFDMA) system for next generation Broadband Wireless Access (BWA) networks is studied, in which the Base Station (BS) or evolved Node B (eNB) has only knowledge of the statistics of the channel. A combination of MIMO and OFDMA could increase the spectral efficiency in a high speed network. We investigate methods with scalable channel feedback and we analyze the trade off between the amount of Channel State Information (CSI) to the transmitter and the system performance. The proposed schemes with limited feedback are combined with other cell interference reduction strategies based on cooperation for improving the performance of a coordinated multi-cell system under very dynamic conditions like high velocity and fast fading. Simulation results demonstrate that substantial gain is obtained by the proposed schemes which take advantage of the statistical information of the highly dynamic channel.     

采用压缩感知的协作多点信道反馈算法研究

协作多点技术（ Coordinated Multiple Points,CoMP）作为LTE-A的最重要候选技术之一,已经得到广泛的关注。在协作多点中,有很多种传输方案,其中一种基于联合传输下的全局预编码方案能够获得极佳的系统性能,而实现该方案的前提是基站可以得到较为完整的信道状态信息。因此在信道反馈时选择显式反馈,因为相比较其他反馈方式,它可以反馈更为完整的信道状态信息,而显式反馈的缺点为需要的反馈量过大。文中利用一种采用压缩感知的信道反馈新方法对联合传输下的全局预编码方案信道显式反馈信息进行压缩,仿真结果显示在不影响系统性能的前提下,能够有效地减少反馈量,使得系统发挥最佳性能。     

Real-Time Virtual Channel Flow Control

Real-time communication system support for large scale parallel multicomputers becomes an important issue as the number of real-time applications developed on these systems increases. Flow control is a key component that affects the performance of the communication subsystem. We develop a range of new real-time virtual channel flow control schemes for wormhole networks. The flow control schemes differ in their priority mapping strategies, priority adjustment methods, and arbitration functions. The priority mapping strategy and priority adjustment method of a flow control scheme determine the priority of a message. The priority of a message is used for the virtual channel assignment and the physical channel arbitration. We discuss the trade-off between the performance and the hardware cost of each flow control scheme. A simulator is implemented for studying the performance of the schemes, and simulation experiments are designed to compare the importance of priority mapping, priority adjustment and arbitration toward the system performance. As wormhole networks scale to larger sizes, the average distance between source and destination nodes increases. The flits of messages in wormhole networks, which are buffered in nodes along the path from the source to the destination, consume network resources in these nodes. Therefore, increased scaling may lead to increased resource consumption, congestion, and late messages. In real-time systems, messages lose their value when they miss their deadlines. In order to reduce congestion, we provide a scheme for dropping messages that miss their deadlines.     

认知无线电网络信道交汇研究综述

认知无线电技术被认为是解决目前频谱资源利用率低下问题最有前景的技术,基于该技术,认知无线电网络采用动态频谱接入方式有效地提高了授权频段的利用率.然而,动态变化的信道可用性极大地增加了认知无线电网络组网的难度.信道交汇旨在为用户通信提供公共传输媒介,是实现无线网络组网的基础.介绍了认知无线电网络信道交汇的基本概念和特点,并阐述了信道交汇策略设计面临的挑战以及应考虑的性能指标.提出了信道交汇策略的分类标准和系统模型,根据该分类标准,详细剖析了当前信道交汇策略相关的研究工作.最后,讨论了认知无线电网络信道交汇研究的开放性问题,以期为未来的研究指出可能的方向和重点.