VODStar视频点播系统的设计、实现及性能测试

以技术报告的形式阐述了一种采用新的信道调度方案的视频点播系统——VODStar系统——的设计、实现及性能测试．该系统综合应用了CM(controlled multicast)与EEB(extended exponential broadcasting)两种新的信道调度方案，采用以信道调度为中心的控制器和以处理媒体数据为中心的“数据泵”相结合的系统结构，基于IP网络实现了RTSP，RTP和SDP等协议．性能测试结果表明，VODStar系统可以有效地缓解传统VOD系统中的服务器I／O或网络带宽的瓶颈问题，是一种性能较高的VOD系统．     

一种分布式视频点播系统模型

视频点播（Video-on-Demand）是现代网络上的一个重要多媒体应用，在传统的集中式视频点播系统中，如何用户数目过多，并可能出现服务器I／O及网络带宽的瓶颈，而采用发布式体系结构的VOD系统可以将负载分布到放置在网络不同位置的各个服务器上，能很好地解决系统瓶问题，本文提出了一种分布式视频点播系统模型，包括系统结构、软件结构、功能定义及实现上的考虑。     

基于代理的视频点播系统设计

视频点播（Video-on-Demand,VoD)是现代网络上的一个重要多媒体应用。在传统的集中式视频点播系统中，如果用户数目过多，将会出现服务器I/O及网络带宽的瓶颈，而采用基于代理服务器的分布式体系结构，可以把VoD系统的负载分布到放置在网络不同位置的各个代理服务器上，能很好地解决系统瓶颈问题，阐述了基于代理的VoD系统的特点，设计原则，以及设计的关键问题，并提出了一种基于代理服务器的VoD系统模型。     

基于文件访问概率预测的VOD代理数据分布策略

针对校园网VOD系统应用中面临的网络带宽和服务器I/O带宽的瓶颈问题,通过对流媒体文件访问次数的统计回归分析,并结合Zipf分布规律和校园网流媒体点播的特征给出了一种流媒体文件访问概率的预测算法.根据该预测算法的结果提出了一种VOD代理服务器的数据分布策略.实验表明,该策略可以有效提高系统的服务性能和减少网络的阻塞.     

IP组播下的视频点播实现技术

一、引言与电视不同,视频点播(VOD)可以让用户自由地选择播放的节目,进行任意的交互操作,并立即得到响应。VOD是很有前途的一种宽带业务,但由于带宽的限制,VOD系统只能在小范围内应用。随着因特网的发展,ADSL、Cable Modem等宽带接入技术的出现,在广域网实现高质量的VOD业务将成为可能。对于因特网来说,最宝贵的资源就是带宽,而对于VOD系统的实现来说,如何有效地利用信道资源也是最关键的。视频数据具有信息量特别大的特点,传统的VOD系统只支持视频服务器和用户之间的单点连结,为每个用户都提供一条     

VOD服务器中共享I/O流的关键技术

VOD服务器的I/O带宽是影响VOD系统性能的关键因素。如何通过使多个用户请求共享一个I/O流,减少对I/O带宽的要求是VOD研究领域中的研究热点之一。文章对VOD服务器中共享I/O流的基本技术Batching、AdaptivePiggybacking、Bridging和Chaining进行了全面的讨论,并对当前的研究现状进行介绍。     

基于多传播路径的VOD服务QoS保证的新构架

提出一种流媒体视频点播服务(VOD服务)的新架构,在应用层上实现VOD服务所需数据的多传播路径,旨在降低网络带宽波动对流媒体VOD服务的影响,克服传统方式下当某一传输数据的路由因请求过多或其他原因发生拥塞时服务质量(QoS)难以保证的问题。还具体给出了多路径传播的协议和实现算法,实验结果也证明该架构能够有效减少对单一路由、特别是中心VOD服务器带宽的压力,使得数据传输能够根据带宽的变化动态变化,从而更好地保证VoD服务的QoS。     

负载平衡算法在分布式视频点播系统中的应用

在分布式体系结构的基础上采用一种基于系统的动态反馈负载平衡算法,使任务负载的分配更加合理。结果表明,该系统能有效缓解传统VoD系统中服务器I／O或网络带宽的瓶颈问题．具有良好的可扩张性。     

采用新的流调度策略的视频点播系统研究

客户多播补块流调度策略——CMP(Client Multicast Patching)——是基于代理缓存的有效的视频点播策略，它采用用户参与流调度的方式，某些用户在播放节目的同时，又作为服务器为后续用户多播一部分节目，因此，在不增加用户I／O带宽的前提下，通过利用局域网络丰富的带宽．有效地节省了服务器及主干网络的资源，并对用户请求提供即时服务，该文给出CMP方案的实现算法，并对系统进行仿真及性能分析，结果表明了CMP方案的有效性和可行性。     

基于周期补丁算法的媒体流调度管理策略

随着计算机网络的日益发展和人们对流式媒体需求的迅猛增加,VoD将得到更广泛的应用。面对巨大的数据量,服务器磁盘I/O和网络带宽成为瓶颈。该文提出媒体流调度和管理策略,合理分配、动态管理系统带宽资源,减少用户等待时间,在同样条件下服务更多用户,提高了VoD系统效率和性能。     

Multicast scheduling for VOD services

Recent developments in networking technologies, coupled with the advent of high-capacity storage devices and improved coding schemes, will make it feasible to provide many advanced multimedia communications services. Among future telecommunication services, the VOD (Video On Demand) service is emerging as one of the most promising services. In this paper, we propose a new VOD service scheme that utilizes the dynamic multicasting capabilities of future networks. We first describe an overall VOD service architecture that consists of CPEs (Customer Premise Equipments), SCCs (Service Control Centers), and ISs (Information Stores). Based on the assumptions that each subscriber has local storage space and the video transfer speed is faster than the playback speed, we develop a new service scheme where video signals are multicasted to multiple subscribers simultaneously. To realize the potential benefits of multicasting, we propose two scheduling algorithms: EDS (Earliest Deadline Scheduling) and MMS (Most Multicasting Scheduling). Finally, we study the performance of multicasting scheme and compare the performance of the two scheduling algorithms via computer simulation. The simulation results show that multicasting increases the service capacity of an SCC significantly.     

基于对等网络的VOD模型研究

随着Internet的快速发展,视频点播的应用越来越广泛,但是目前广泛采用的IP单播传输方式使骨干网和服务器在点播用户增多的时候不堪重负,而目前组播方式和代理服务器方式因为各种原因而不能大规模应用于Internet。本文提出了一种基于对等网络(P2P)的视频点播系统模型,该模型采用了一种全新的滑动窗口机制对用户端缓存进行管理并对用户上行信道加以利用,从根本上解决骨干网和服务器负载过大的难题。     

多用户正交频分复用加权比例公平调度

传统的正交频分复用(OFDM)调度进行资源分配时没有考虑用户间速率比例公平性。针对这一问题,提出了一种新的适合于混合业务的多用户OFDM系统比例公平调度方案,其用户队列承载混合类型业务。该方案在用户间速率成比例约束条件下最大化系统权重容量和;授予用户队列中不同类型的分组不同的权重因子,并通过权重因子计算用户的权重;在子载波分配时不仅定义了信道优先级因子,而且在用户间速率成比例公平约束条件下通过该因子为用户分配子载波;最后推导出一种线性的功率分配方式。仿真结果与分析显示,该方案可以较好地满足用户速率和业务时延的需求,且可以在有效提高系统容量的基础上,严格地保证用户容量公平性。     

基于多对一Gale-Shapley算法的D2D通信资源分配

针对D2D通信复用异构蜂窝网络上行信道产生的干扰问题和频谱资源优化问题进行研究,提出一种基于多对一Gale-Shapley算法的D2D通信资源分配方案。本方案允许多个D2D用户共享一个蜂窝用户信道资源,通过设置信干噪比（SINR）门限保证用户的通信服务质量（QOS）。根据信道分配情况,构建D2D用户和信道的偏好列表,最大化系统总容量。仿真结果表明,该方案收敛较快,复杂度较低,能够有效保证用户的通信服务质量,系统总容量接近最优解。本研究为实现D2D用户和蜂窝用户的频谱资源共享,提高频谱利用率提供了一种有效方案。     

VOD系统批处理调度策略优化研究

大规模视频点播（VOD）业务需要消耗大量的网络带宽和服务器资源，基于多点组播的批处理技术允许服务器的不增加额外系统资源的情况下发送相同数据到多个客户端，从而达到系统资源利用率的最大化，通常使用的批处理调度策略有FCFS、MQL和MFQL三种，但是这些方案没有得到令人满意的结果，本文提出一种新策略，称之为MDP，即最大撤销概念，其基本思想是在组空间搜索用户请救撤概率和最大值，MDP以等待服务的所有组中撤销概率的和最大为调度决策依据。保障到达系统的用户因不能忍受等待时间太长而退出的概念最小，通过分析与仿真实验，MDP方案在系统蚕吐量，平均等待时间，用户请求撤销概率和不公平性等系统性能参量方面获得优良结果。     

多输入多输出—非正交多址接入系统融合用户调度的下行波束赋形设计

针对多输入多输出—非正交多址接入（MIMO-NOMA）技术中用户间干扰较大的问题，提出了一种融合用户调度的波束赋形（BF）算法。首先，在进行用户调度时，为了同时兼顾簇内用户干扰和簇间用户干扰，根据各用户信道的差异性，利用L1-范数正则化方法对所有用户分组情况进行初步稀疏化处理，进而从各用户信道相关性角度出发，将信道相关性大的两个用户分为一簇；其次，结合部分发射功率控制（FTPC）策略实现簇内用户功率分配；最后，根据和速率最大化准则构建一目标优化函数，进而利用连续凸逼近（SCA）算法对其进行求解，以获得波束赋形矩阵。理论分析和链路仿真表明，与传统的正交多址接入技术相比，在系统容量方面实现了84.3%的提升；与传统的相关性用户分簇方法相比，在公平性方面实现了20.2%的提升。实验结果表明，该方案不仅有效地抑制了簇内用户干扰和簇间用户干扰，同时，又保证了用户间的公平性。     

Optimal user scheduling and power control in multi-user cognitive broadcast systems

Cognitive radio systems should not only have the ability to sense and exploit "frequency spectrum holes",but also the ability to sense and utilize "spatial spectrum holes".In this paper,we consider the issue of maximizing the throughput of the cognitive systems by fully utilizing "spatial spectrum holes" brought in by multiple cognitive users,in the scenario where a pair of licensed users and a cognitive broadcast system share multiple spectrum bands.By exploiting the channel reciprocity under the premise that the licensed system adopts the time-division-duplexing (TDD) mode,we propose a more practical cognitive access scheme that can sense the interference at the licensed user caused by the cognitive transmitter,based on the existing feedback signals from the licensed user to the licensed base station.Taking both interferences from the licensed base station to the cognitive receiver and from the cognitive transmitter to the licensed user into consideration,we investigate the optimal user scheduling and power allocation scheme that can maximize the ergodic sum rate of the cognitive system.We show that scheduling the user whose channel gain to interference and noise ratio (CGINR) is the largest for each frequency band is optimal.We also derive the dynamic power allocation scheme meeting the three practical constraints,i.e.,the transmitter’s average transmission power constraint,the power amplifier’s instantaneous transmission power constraint,and the interference power constraint at the licensed user.The result shows that in different coherent time intervals and different frequency bands,the power allocation has a multi-level waterfilling structure.Theoretical analysis shows that the strategy scheduling user with the largest CGINR introduces significant performance improvement compared with the traditional strategy scheduling user with the largest channel gain to noise ratio (CGNR).We also illustrate the impact of power constraints and the number of users on system performance by simulation.     

Cross-layer packet scheduling for downlink multiuser OFDM systems

This paper proposes a channel and queue aware fair (CQAF) packet scheduling scheme for the downlink packet transmission in multiuser orthogonal frequency division multiplexing (OFDM) systems. By making use of the information on the channel conditions and the queue lengths, the proposed CQAF packet scheduling scheme efficiently allocates the subcarriers, transmission power and modulation level to users under the constraints of total transmission power, the number of subcarriers, bit-error-rate (BER) requirement and generalized processor sharing (GPS)-based fairness requirement. The numerical results show that the proposed CQAF packet scheduling scheme can reduce the transmission delay and queue length significantly while maximizing system throughput and maintaining fairness among users.     

Design and analysis of a look-ahead scheduling scheme to support pause-resume for video-on-demand applications

In a video-on-demand (VOD) system, subscribers can choose both the movie they wish to view and the time they wish to view it. In such an environment there are invariably hot videos which are requested by many viewers. The requirement that each viewer be able to independently pause the video at any instant and later resume the viewing with little delay can cause difficulties in batching viewers for each showing. Under batching, a single video stream is shared by multiple concurrent viewers and a resume request has to wait for additional stream capacity to become available before actual resumption can occur. The conventional approach to the support of on-demand pause-resume provides one video access stream to disks for each video request. This can greatly increase the disk arm requirements of a VOD system. In this paper, we propose a more efficient mechanism to support the pause-resume feature usinglook-ahead scheduling withlook-aside buffering. The idea is to use buffering to increase the number of concurrent viewers supportable. The concept of look-ahead scheduling is not to back up each viewer with a real stream capacity so he can pause and resume at any time, but rather with a (look-ahead) stream that is currently being used for another showing which is close to completion. Before the look-ahead stream becomes available, the pause and resume features have to be supported by the original stream through (look-aside) buffering of the missed content. It is shown via simulations that the proposed scheme can provide a substantially greater throughput than the approach without batching. Furthermore, for a given amount of buffer, the improvement in throughput grows more than linearly with the stream capacity of the server. In other words, the look-ahead stream scheduling scheme operates with good economy of scale because it is easier to form look-ahead streams for video servers with larger stream capacity.     

Robust multiuser MIMO scheduling algorithms with imperfect CSI

Robust multiuser multiple-input-multiple-output (MIMO) scheduling algorithms are proposed in this paper.With imperfect channel state information (CSI),traditional scheduling algorithms for the multiuser MIMO system based on the zero forcing precoding scheme will lose some performance due to the multi-user interference (MUI).In order to improve the system average throughput,we study the robust multiuser MIMO scheduling problem with imperfect CSI.From the average capacity formula,we derive a robust factor which can transform the robust multiuser MIMO scheduling problem into the traditional one,thus most existing non-robust scheduling algorithms can be robust if this factor is adopted.Simulation results show that compared with the traditional algorithms,the proposed robust algorithms can improve the system average throughput significantly under the CSI error environment.