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范品忠 《激光与光电子学进展》2002,39(5):25-28
密集波分复用(DWDM)系统能满足对光纤干线传输容量日益增长的需求,其近期研究活动已转向太比特的传输[1]。为了增加此系统的总容量和传输距离,必须研究克服各种限制的技术。图1示出关于提高密集波分复用系统三个重要参数性能有希望的技术,这三个参数是光谱效率、带宽利用率和传输距离。为获得高容量传输必须增加光谱效率和扩展光学带宽。光谱效率就是波分复用信号的密度,它等于平均容量除以通道间隔。在普通二进制信号的DWDM实际系统中,最大的光谱效率为0.4bit/s/Hz,在其中40 Gbit/s光学信号以100 GHz通道间隔被复用[2]。获得… 相似文献
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本文首先介绍光波分复用的概念、光波分复用器件的类型和主要特性参数,在介绍熔融型光波分复用器的复用原理后,讨论光波分复用在有线电视中的应用方法及其特性参数对有线电视传输系统指标的影响。最后,介绍上海有线电视台利用熔融型光波分复用器有效解决过黄浦江光纤紧缺问题的例子。该例利用两根光纤实现了两路数字信号和两路模拟有线电视信号的传输,为利用光波分复用充分挖掘现有光纤网的潜力提供了成功的例子。 相似文献
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研究平坦信道上采用收发天线选择的恒包络正交频分复用系统的误码性能。采用矩生成函数方法,推导矩形M进制正交幅度调制的恒包络正交频分复用系统的平均误符号率下界的解析表达式。仿真表明在大信道衰落参数、小相位调制系数和高信噪比时下界与平均误比特率非常吻合。数值计算和仿真结果均阐明收发天线数目、信道衰落参数与相位调制系数对分集接收恒包络正交频分复用系统误码性能影响。 相似文献
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MPEG-4多媒体移动通信系统的一种有效复用结构 总被引:1,自引:1,他引:0
介绍了一种基于MPEG-4标准的移动多媒体的两层复用结构。第一层对有相似服务质量(QoS)要求的基本数据流进行打包,形成具有较少QoS要求的数据流;第二层为每个数据流提供相应的防误码措施,形成可在易误码链路进行传输的单一数据流,达到既满足各个基本数据流防误码的要求,又使复用开销最小。 相似文献
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本文研究了最优化方法在蜂窝通信系统信道复用,信道配置中的应用,通过研究共信道干扰总概率Pt与系统各参数间的关系,应用最优化方法求出使pt最小的各参数值,从而达到信道最佳复用,通过系统呼叫失败概率pt与信道配置参数间的关系,应用最优化方法求出使pt最小的信道配置参数,从而达到信道的最佳配置,文中还给出了设计实例。 相似文献
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本文提出了一种新的基于H 32 3多媒体会议系统的终端媒体流复用模型 ;对其进行了理论计算和计算机仿真 ;得到了模型中信元的循环时间、返回时间、缓冲区中平均数及时延的解析表达式 ;讨论了k2 ,λ2 ,μ等参数对循环时间、缓冲区中信元的平均时延的影响。结果表明通过调整相关参数 ,采用新的复用模型能够满足一定的时延和媒体流同步等实时性要求 相似文献
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文章首先讨论了与光突发交换(OBS)相关的一些问题。接着讨论了OBS如何应用于下一代光互联网中,特别是偏置时间和延迟预留协议有助于避免使用光缓存,能在波分复用(WDM)层支持服务质量(QoS)服务。 相似文献
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Balance power control is based on the idea of balancing Carrier to Interference Ratio (CIR) of all wireless links. Unbalance power control means that different traffics can achieve different CIR at receivers. This paper proposes a forward link partial-balance power control algorithm, which can provide necessary Quality of Service (QoS) for multimedia traffics in Wideband CDMA(W-CDMA) systems. The proposed algorithm is the integration of grading traffics priority and allocating and adjusting forward link power levels. For higher priority traffics, the unbalance power control is used. Whereas for lower priority traffics, balance power control is adopted. Computer simulation results show that the proposed algorithm can guarantee the special QoS requirements of the traffics with higher priority orders and maximize the CIR of the traffics with lower priority orders. 相似文献
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IEEE 802.11 is a widely used standard for MAC and PHY layers of WLANs. Unfortunately, the access methods offered in this standard
cannot support QoS (Quality of Service) for real-time traffics. Using multimedia applications over WLANs is increasing and,
on the other hand, it seems that the access methods employed in this standard causes high variations in delay or jitter and
wastes bandwidth due to collisions. There are many methods to enable DCF—basic access method in 802.11—with service differentiation
and QoS. The difficulty in majority of these methods is unfair bandwidth allocation among low and high priority traffics at
high loads resulting starvation for low priority traffics. In this paper, we modify the way that the CW (Contention Window)
size is calculated after a successful transmission and study the effect of the CW size on performance and fairness. Results
of our simulations show that the performance of DCF with this modification is better, specially, for traffics in which throughput
is the most important parameter. Besides, this method provides better fairness among low and high priority traffics. We also
employ a scheme to enable 802.11 with service differentiation which grants dynamic priority to low priority traffics to prevent
starvation, specially, in high loads. 相似文献
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随着网络和应用的飞速发展,Internet不仅要提供尽力转发(Best Effort)的服务,还要支持各种传输类型和多个优先级的QoS服务.目前普遍认为区分服务体系机构是很有前途的提供QoS保证的Internet框架,而网络节点机制是其关键技术之一.我们提出了一种在网络节点上实现的区分服务机制comBAQ(combining Buffer Management and Active Queue Management),它综合了适当的缓存管理和主动队列管理方法.我们详细介绍了它的服务框架和分组处理判决算法,实验模拟结果显示,它能满足我们提出来的五个设计目标,可以在网络节点上实现多个丢失优先级的区分服务:为需要可靠传输的多媒体应用提供"有保证"服务,为传统TCP传输提供"无保证"服务. 相似文献
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本文基于EMBRACE脉冲神经网络硬件实现方案提出了一种片上网络路由器的动态优先级仲裁策略,来解决脉冲神经网络脉冲传输的交通负载非均衡问题.该方案使用二维网格片上网络系统实现神经元之间的互连通讯,其基于脉冲发送频率的动态优先级仲裁策略能够降低高频路径的平均延迟及系统丢包风险,提高系统工作稳定性.使用Noxim片上网络模拟器搭建实验平台,测试结果表明采用提出的动态优先级仲裁策略较轮询及固定优先级仲裁器,高频路径延迟平均降低32.33%和34.69%,降低幅度最大达到84.86%和86.20%.在90nm CMOS工艺下,提出的路由器架构硬件面积为213,471μm2,具有较好的扩展性. 相似文献
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优先级队列(PQ)算法虽然能够保证高优先级业务的服务质量,但低优先级业务的性能较差,整体性能不佳,公平性较低。针对这些不足,提出优先级与带宽需求相结合的调度算法(PRQ),在优先级调度的基础上,使用带宽需求对调度概率进行调整,提高低优先级业务的调度概率,进而改善其服务质量,同时改善整体性能,提高公平性。仿真结果表明,PRQ算法能够显著改善低优先级业务的性能和整体性能,公平性较PQ算法高。 相似文献
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LI Xiao-hui HAN Ming YI Ke-chu TIAN Bin Key Laboratory of Integrated Services Networks Xidian University Xi’an China 《中国邮电高校学报(英文版)》2007,14(2):45-50
According to the quality of service (QoS) requirements of differentiated service (DiffServ), a cross-layer resource allocation algorithm for multi-user orthogonal frequency division multiplexing(OFDM)systems is presented. The constant rate is maintained by adjusting the power dynamically for the voice traffics with high priority, whereas the fairness amongst the data traffics is guaranteed by weighted fairness queued (WFQ) algorithm. The two above-mentioned strategies are used for video traffics to realize variable data rate with the constraint of the minimum rate. Combing all these methods, both the throughput and the fairness are ensured when there are multiple users in the OFDM system. Simulation results indicate the validity of the proposed algorithm, which can work well even if the SNR is less than 0 dB. 相似文献
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The authors study a bandwidth allocation strategy with access restriction and pre-emptive priority for the integration of wide-band and narrow-band traffics. This control strategy is analysed by the matrix geometric approach, and its performance is compared with those of other schemes.<> 相似文献