N＊DPT／D／1排队系统分析

多路离散周期串到达，单个服务台定长服务排队系统，是在研究ＣＢＲ业务下ＡＴＭ网络中间节点性能时所遇到的一种排队模型，在有线ＡＴ 的ＣＢＲ精力接进无线ＡＴＭ网时也会遇到这种排模型，本文分析了这一排队系统，得到 队长剩余分布的计算公式     

基于前向神经网络的Banyan通信网输入开窗排队研究

本文提出了采用前向神经网络实现ＡＴＭ交换网中信元输入开窗排队的方法，并从仿真角度证明了这一新方法的性能比传统排队技术有显著提高。     

分布式排队双总线协议的光纤宽带综合业务通信网

本文介绍“八五”国家自然科学基金重大项目──光波与微波相结合的光纤宽带综合业务通信网研究。该通信网的实验网采用ＡＴＭ技术和ＩＥＥＥ８０２．６ＤＱＤＢ（ＤｉｓｔｒｉｂｕｔｅｄＱｕｅｕｅＤｕａｌＢｕｓ）ＭＡＣ协议，可以为卫星广播电视系统、微波网。以太网和ＶＳＡＴ网等子网提供宽带互连服务。本文讨论了该实验城域网的总体结构、性能指标、结点站体系结构及结点配置等几方面内容。该项目的研究为“九五”期间宽带网的实用化打下了基础。     

ATM网络中CBR业务排队性能分析

分析了ATM网络中CBR业务排队性能,给出了一种简单的计算信元丢失率和信元平均时延的表达式.分析结果表明,一方面在较小的缓冲区容量下,即使CBR业务被分配的带宽大于等于其峰值速率,也还存在着较大的信元丢失;另一方面,当复用的CBR业务源数目很大时,只需要分配相对较小的缓冲区容量就可以满足十分低的信元丢失率要求.该结果对于ATM设备中相应的缓冲区设计、带宽分配以及连接允许控制机制的研究具有重要的意义.     

一个具有随机丢弃分组机制的GI/M/1/N排队系统

由于标准GI/M/1/N排队系统仅当等待队列中没有空闲位置时才丢弃到达的分组,不适合为QoS控制中的缓存队列管理建模。利用随机过程中输入流稀疏化的方法,在标准的GI/M/1/N排队系统中嵌入随机丢弃分组的机制,建立了一个具有随机丢弃分组机制的扩充的GI/M/1/N排队系统,以及该排队系统的分组丢失率、系统利用率、队列长度的均值/方差、平均等待时间等性能评价指标。     

小缓冲容量时N＊Burst／D／1／K服务系统丢失率

Ｎ＊Ｂｕｒｓｔ／Ｄ／１／Ｋ随机服务系统，是在研究ＡＴＭ网络中的流量控制问题时被广泛采用的排队模型。该排队模型手丢失率了缓冲容量改变而变化的曲线可以用一个负指数函来描述。     

B—ISDN的AAL1规程及其发展

本文首先从支持面向连接的恒定比特率业务，在收侧恢复源端定量关系，结构数据转移和比特误码及信元丢失的检测与校正等功能要求方面详细介绍了基本的ＡＡＬ１规程，然后以减少时延为为目标讨论了对ＡＡＬ１规程可能的改进方案最后介绍适于支持低比特率话音的候选的ＡＡＬ规程。     

通信网交换系统的发展趋向

本文对宽带综合通信网交换系统几个主要方面技术的发展趋向作了概括介绍，内容包括：电子交换的分布结构、ＡＴＭ交换的开始应用，个人通信的无线进网，宽带交换引用光子技术和多媒体交换结构分析。     

一种基于差分技术的CBR业务时钟自适应恢复算法与方案

信元在ATM网内传输时,由于网内缓存的存在,造成了信元延时抖动。信元延时抖动对基于PLL的恒定比特率业务时钟的自适应恢复有很大影响,即时钟的抖动/漂移比较明显。这使得这种基于PLL的CBR业务时钟恢复方案在某些场合不能应用。本文提出了一种基于差分技术的时钟自适应恢复新方案,该方案可以明显地降低由于信元延时抖动而造成的CBR业务时钟的抖动和漂移,同时不增加缓存的容量。     

均匀业务下反压型输入/输出排队ATM交换机的性能分析

本文利用矩阵几何分析法分析了内部无阻塞输入/输出排队反压型ATM交换机在均匀贝努利输入下的信元丢失、信元延时及吞吐量等性能指标。本文结论对实际设计一反压型输入/输出排队分组交换机具有一定参考意义。     

OCT系统二维图像形成分析

在弱物体近似下分析了ＯＣＴ系统横向二维图像形成过程，研究表明，对于高斯像面图像传输，ＯＣＴ系统相当于一复振幅线性空间不变系统，所得二维相干传递函数表明系统具有低通特性，选用较小光纤－透镜间隔，对成像性能影响不大，减少所用透镜焦距、增大光瞳孔径，均有助于增宽系统带宽，改善成像性能．     

PERFORMANCE ANALYSIS OF TRAFFIC CONTROL METHODS ON MIXED TRAFFIC CLASSES IN ATM LAN

We treat traffic control methods for the multimedia ATM LAN, in which two service classes are considered; one is for high-speed data transfer based on a fast reservation protocol (FRP service class) and the other is for the continuous bit rate (CBR) traffic such as motion video (CBR service class). Through an analytic method, the performance of the CBR service class traffic is shown to be heavily affected by the FRP service class traffic. Thus, we introduce a reserved bandwidth for the CBR service class to guarantee some appropriate level of performance for the CBR service class. With the reserved bandwidth for CBR service class, the performance of CBR service class can be preserved from being affected by the FRP class traffic load.     

Performance analysis of RTS/CTS scheme in WLAN with the impact of bit errors

To estimate the system performance of RTS/CTS scheme in an error‐prone WLAN channel, this paper proposes a new three‐dimensional Markov model, which considers the impact of bit error on all kinds of frames, and both station short retry limit and long retry limit. The system performance parameters including saturation throughput, packet drop probability, drop time, and average delay are derived using the new Markov model. By comparing the numerical results with simulation results, the model is proved to be more accurate than previous work. The numerical results show that the channel bit error rate has a significant impact not only on system performance, but also on the sensitivity of other system parameters including network scale, channel data rate, and packet length. Copyright © 2010 John Wiley & Sons, Ltd.     

基于SC分集的混合FSO/RF航空通信系统性能分析

研究了基于选择合并(SC)分集的混合激光/射频(FSO/RF)航空通信系统性能,该系统设计简单且在发射端无需信道状态信息(CSI)。激光链路服从平均孔径效应下的Exponentiated Weibull大气湍流分布模型,射频采用Nakagami-m衰落信道模型,推导求出混合FSO/RF航空通信系统接收端信噪比的累积分布函数,进一步利用Meijer′s G函数推导了混合FSO/RF通信系统中断概率以及平均误码率的闭合表达式,通过仿真对比分析了不同湍流强度、调制方式及分集通信方案对系统中断、误码性能的影响。仿真结果表明,混合FSO/RF航空通信系统有效地利用了FSO及RF链路在不同大气信道条件下的互补性质,具有更优的中断和误码性能;采用BPSK调制能有效降低大气湍流对混合FSO/RF航空通信系统的影响;信噪比高时,并行传输、分集接收的通信方案对系统误码性能的改善要优于低阶调制对误码性能的改善。     

Packet Scheduling Algorithm Considering a Minimum Bit Rate for Non‐realtime Traffic in an OFDMA/FDD‐Based Mobile Internet Access System

In this letter, we consider a new packet scheduling algorithm for an orthogonal frequency division multiplexing access/frequency division duplex (OFDMA/FDD)‐based system, e.g., mobile broadband wireless access or high‐speed portable internet systems, in which the radio resources of both time and frequency slots are dynamically shared by all users under a proper scheduling policy. Our design objective is to increase the number of non‐realtime service (e.g., WWW) users that can be supported in the system, especially when the minimum bit rate requirement is imposed on them. The simulation results show that our proposed algorithm can provide a significant improvement in the average outage probability performance for the NRT service, i.e., significantly increasing the number of NRT users without much compromising of the cell throughput.     

Modelling and simulation of a Ka-band DBPSK/DQPSK mobile satellite channel

For the prospective personal satellite communications in the early 21st century, this paper presents a general exploration of a K_a-band DBPSK/DQPSK land-mobile satellite channel model and its BER performance from system design, modelling and simulation. A forward-link (i.e. outbound from the hub) channel design is introduced in brief. A complete model of channel multipath fading and shadowing is proposed for the first time, including a basic model and various derivative submodels corresponding to different actual propagation environments. Computer simulation results are given for a Rician channel model, a shadowed channel model and different combinational-fading channel models by complete curve sets of BER performance, which coincide with the results of the analysis, and could be used as valuable references in further research and implementation.