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双语推荐：媒体接入控制

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由于多媒体业务需要更大的带宽和更高的实时性,所以对服务系统和接入控制提出了更高的要求。文章针对分布式媒体服务系统提出了一种新颖的接入控制方法,与以往方法不同之处在于将请求调度融合在接入控制之中,从而提高了系统的服务性能。我们先为系统建立部分可观Markov决策过程(POMDP)模型,并将请求调度融合在决策中,然后使用基于观测的随机接入控制策略,通过策略梯度优化算法仿真求解模型的最优策略。仿真结果表明,与其他分布式接入控制方法相比,该文所提方法在有效利用系统资源的同时,提高了系统性能。
Multimedia services require larger bandwidth and less response time, which raises higher requirements on the service system and admission control policies. This paper presents a novel admission control method aiming at the distributed media service system, which integrates request scheduling into the admission control, so that improving the system performance. The partially observable Markov decision process is built up to model the service system and the request scheduling is integrated into decision-making, and then the random admission control policy based on observation is used to solve the optimal admission policy of the model by applying the policy-gradient approach through computer simulation. The simulation result shows this policy can make efficient use of system resources and improve system''s performance compared with other distributed admission control methods.

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针对紫外光通信网络中的能量受限问题，为了减少节点的能量消耗和节点间的相互干扰，以延长网络的生命周期并增加系统容量，设计并实现了一种适合紫外光通信的MAC（媒体接入控制）层功率控制机制。仿真和实验结果均表明，该机制可以在保证用户通信QoS（]I~务质量）的前提下实现紫外光通信平台上的功率控制，并为今后紫外光Adhoc（自组织）网络的搭建打下了基础。
In view of energy constraint in ultraviolet communication networks,this paper designs and realizes a Medium Access Control (MAC)layer power control mechanism suitable for ultraviolet communication so as to reduce node energy consumption and inter-node interferences,extend network life cycle and increase system capacity.Simulation and experimental results indi-cate that this mechanism achieves power control on the platform of ultraviolet communications under the premise of ensuring the QoS of user communication and lays a solid foundation for building ultraviolet Ad hoc networks in the future.

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IEEE802．1ie媒体接入控制（MAC）协议不能较好地满足无线多媒体传感器网络不同类型业务节点间的公平性要求。为解决该问题，提出一种基于博弈论的无线多媒体传感器网络MAC协议。将节点间的信道竞争过程建模为非完全信息动态博弈，在不同的负载情况下，通过改变普通业务的权重提高不同业务间的公平性。仿真结果表明，该协议能在保证多媒体业务服务质量的同时，增加普通业务数据流接入信道的机率，提高整个网络的平均吞吐量。
In wireless multimedia sensor networks, IEEE802.11e Medium Access Control(MAC) protocol can not solve the fair access to channel between different services of each node. To solve this problem, this paper proposes MAC protocol for multimedia sensor network based on game theory. The main idea is that the channel contention process is modeled a dynamic game with incompletely information. Under different load conditons, the protocol improves the weight of the ordinary services and reduces the fairness between the different services. Simulation results show that this protocol can guarantee the Quality of Service(QoS) of multimedia services, make ordinary service, get more chance to access channel, and improve the average throughput of the networks.

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在前人研究的基础上提出了一种独立于应用的、适用于集中式会议的会议控制模型。系统实现的集中的会议管理平台,可以有效的管理各种会议资源,方便各种软硬件媒体资源的接入。采用了SIP协议作为会话控制协议。会议控制消息分为命令和通知两种。会议命令使用XMLRPC协议实现,会议消息采用了SIP事件通知机制。该会议控制模型被成功地应用于基于SIP的实时多媒体视频会议系统。实践表明,该会议控制模型是合理的、有效的。
This paper identifies the requirements for conference control and presents a centralized conference system model on the base of some scholar research works. The model employs SIP as singling control protocol and comprises some components such as conference configuration, user management, media control, application session management and net-work management. To implement conference control, message mechanism should be employed. This paper adopts a popular solution in which XMLRPC is used as conference command and SIP event framework as conference notification. The mod-el proposed in this paper has been successfully applied to a SIP-based real-time multimedia conference system. The confe-rence control results demonstrate that this model is applicable and effective.

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对于新一代的无线网络,宽带无线系统的融合将成为一个重要的技术难题。近年来,尽管一些研究人员已经提出了几种技术方案用来增强第二代媒体访问控制协议(MAC),但这些设计主要针对的是数字信息。针对实时宽带信源给出一个了更好的集中控制访问技术,这项技术通过实现信息源的统计复用,并根据不同用户的服务质量需求来对无线终端进行组合,使之形成一个固定的有线宽带网络。同时这项技术将轮询方式与随机接入方式整合在一起,基站中的数据包调度程序负责动态地选择最高传输需求吞吐量的接入方式。对上述方法进行了性能测定,并估算了相关的参数。
For the new generation of wireless networks,the convergence of wireless systems with broadband services is becoming an important technical issue.In recent years,several schemes for enhancing second-generation media access control(MAC)protocols have been proposed,which,however,mainly focus on digital information.In this paper,an enhanced centrally controlled access technique for real-time broadband sources is presented.It enables full integration of wireless terminals into fixed wired broadband networks by realizing the statistical multiplexing of sources and depending on the user''s requirements of quality-of-service. Furthermore,the technique combines random access with polling,and the packet scheduler running at the base station dynamically selects the access method with the highest throughput for transmission of capacity requests. The performance of the method is tested,and the relevant parameters are calculated.

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媒体访问控制（MAC）协议负责协调所有认知用户的空闲信道接入服务,是认知Ad-hoc网络支持服务质量（QoS）的关键技术之一。在二进制指数退避算法基础上,提出一种支持服务区分的多智能体Q学习MAC算法。实时调整传输概率,使系统信道接入服务达到最优,建立传输概率调节的Markov链模型,导出分组的传输概率与协议参数的关系,给出基于服务区分的信道吞吐率模型,建立基于MAC协议参数学习的多智能体Q学习算法。实验结果表明,该算法能满足高优先级业务的QoS,且吞吐率和时延性能优于IEEE 802.11e EDCA机制。
The Media Access Control(MAC) protocol which coordinates idle channel accessing service among cognitive radio users, is one of the key technologies in cognitive Ad-hoc network supporting Quality of Service(QoS). This paper is based on the algorithm of binary exponential backoff, proposes a MAC algorithm with multi-agent Q-learning that supports service differentiation, real-time transmission probability adjusting is introduced to optimum the accessing service of system. Markov chain model is established with transmit probability adjusting, and the relationship between packet transmit probability and protocol parameters are derived. The channel throughput model with service differentiation is given. The multi-agent Q-learning architecture based on MAC protocol parameter is realized. Experimental result shows that this algorithm can satisfy the QoS of high priority service, the throughput rate and delay are better than IEEE 802.11e EDCA mechanism.

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物理层协作通信技术的应用给媒体接入控制（MAC）协议的设计带来了挑战。针对协作通信特点，提出一种适用于Ad Hoc网络的自适应协作MAC（ADCO-MAC）协议。基于最短路径算法，在源、目的节点之间选择最佳的协作节点。根据网络条件，可自适应选择是否进行协作传输。利用OPNET软件实现对ADCO-MAC协议的网络仿真。通过仿真结果表明，ADCO-MAC协议在吞吐量、端到端时延、接收成功率方面性能有显著提升。
The application of cooperative communication technology on physical layer introduces great challenges to MAC protocol design. Based on the characteristics of cooperative communication, an adaptive cooperative MAC (ADCO-MAC) protocol for ad hoc networks is proposed. Based on shortest path algorithm, ADCO-MAC protocol selects the best cooperative node between source node and destination node. While ADCO-MAC protocol adaptively chooses whether cooperative transmission or not according to network conditions. The network simulation of ADCO-MAC protocol is carried out using OPNET. Simulation results show that the performance of ADCO-MAC protocol improves significantly in terms of throughput, end to end delay and reception success rate.

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本文介绍了一种基于跨层思想设计的无线传感器网络时间同步方法。传统的网络设计通常基于开放互联模型，系统的整体设计缺乏层间信息交互。本文提出的后同步改进方法通过预估晶体振荡偏移并进行补偿，这种方法基于媒体接入控制层和物理层的联合设计，并在Si1000无线微控制器平台上通过实验验证，证明此法可以有效的延长同步周期、减少同步开销，对保持网路稳定运行有积极意义。
This paper introduces a typical kind of time synchronization method based on cross layer consideration. The typical design of a network system mainly follows the OSI separated model. The whole design progress is always implemented without considering of the interaction with different layers. The improved post synchronization mechanism proposed in this paper presents a self correction method of estimating the crystal oscillation drift based on the cross layer consideration-the unification design of physical and media access control layer. The experiment results from wireless MCU Si1000 illustrate that the improved post synchronization using cross layer design is able to keep a stable operation of network in the way of prolong the synchronization period and reducing the cost of synchronous actions.

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本文介绍一种廉价的在Linux嵌入式平台下实现移动媒体播放的方案．首先，在嵌入式平台中植入AC5803G网卡驱动，再通过PPP拨号实现3G网络的接入．然后，修改MPlayer源代码并移植到嵌入式平台中，实现在无操作界面下的网络视频LCD定位播放，接着编写一个QT界面程序来控制MPlayer，实现播放器的可视化操作，同时将QT播放器移植到平台中．最后，在嵌入式平台中实现一个利用QT播放器通过3G网络播放网络视频的终端机．实验测试结果表明，本终端可以通过3G网络实现网络电视等网络流媒体的在线点播，经过转化可望投产做成移动电视，网络广告机等终端产品．
A low-cost design of 3G mobile media player in the embedded Linux platform is introduced. First,the driver of AC580 3G network card is implanted in the embedded platform,and 3G network access through PPP dialing is achieved. Second, the source code of the MPlayer is modified and planted in the embedded platform, achieving the fixed playing of the network video on the LCD in no operation interface. Then,a QT interface program is written to control the MPlayer,achieving the visual operation of the player, and meanwhile transplant the QT player in the platform. Finally, the MPlayer and QT program is transplanted in the embedded platform to implement a 3G media player. Test results show that this media player can play streaming media such as web TV online through the 3G network. It’s expected to put into production of mobile TV,online advertising players,etc. after transformation.

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802．11n协议继承并改进了802．11协议物理层和媒体接入控制（ MAC）层技术，提升了无线吞吐量。但是，面对复杂的室内环境，周围存在无线干扰的情况下，无线吞吐量必会受到影响。本文在楼宇办公环境中实测速率为300 Mbps和450 Mbps的802．11n无线网络吞吐量，对比二者在20 MHz和40 MHz带宽下的吞吐量性能，并分析在Android、Windows7和WindowsXP系统下的不同客户端的吞吐量状况，为在楼宇环境下进行802．11n无线局域网的部署提供了有效的参考。
Inherited and improved the physical layer and media access control ( MAC) layer technology of 802.11, 802.11n wireless protocol improved throughput.However, facing with a complex indoor environment and radio interference around, the wireless throughput will be affected.In this paper, the wireless network throughput of 802.11n with the rate of 300 Mbps and 450 Mbps are measured and compared in an office environment with different bandwidth of 20 MHz and 40 MHz.What''s more, the throughput of the different clients with Android, Windows7 and Windows XP systems are analyzed.The result provides an effi-cient reference for 802.11n wireless LAN deployment in the building environment.

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