光网络中的OXC研究

本文介绍了光交叉连接(OXC)节点在光网络中所处的位置,分析了透明OXC节点和非透明OXC节点两种结构的构成方式.同时分析了OXC节点的串扰性能和利用GMPLS协议实现OXC节点的控制方式.     

基于OCP接口的片上网络性能评估平台

针对片上网络性能评估的通用性问题,提出将OCP协议运用到片上网络性能评估平台中,设计与实现了一个具有OCP接口的片上网络资源节点,该资源节点通过OCP协议与片上网络路由节点进行通信。以资源节点为主要构成单元,构建了片上网络性能评估平台。该评估平台采用集成化的设计方式,将流量产生机制、接收机制和性能分析逻辑单元集成在资源节点内部,使得平台易于灵活配置。本文结合具体的片上网络实例验证了该平台的正确性。     

基于邻居节点的拓扑控制算法研究与仿真

拓扑控制是移动自组织网络提高网络能量利用率和网络容量的一种重要机制。针对移动自组织网络拓扑易变、带宽和能量有限等特点,简要介绍了一种节约节点能耗,有效提高整个网络寿命的拓扑控制算法;通过对基于邻居个数的拓扑控制协议K-Neigh算法的仿真,研究了不同k值的选择下拓扑控制对节点功耗和网络性能(包括吞吐量、丢包率和时延等)的影响。其结果表明选择合适的k值可以取得节点功耗和网络性能的平衡,而且经过K-Neigh拓扑控制后的网络具有很好的鲁棒性。     

无线自组织网传输功率控制与跨层优化

无线自组织网节点功率有限，如何有效利用节点电量、改善网络性能是自组网领域研究的关键问题。首先讨论了节点传输功率对各协议层的影响，并归纳出功率控制的设计原则；然后分类介绍和比较了几种主要的控制机制。在传统协议分层研究的基础上，提出了对传输功率控制进行跨层优化的设计思想，并对运用跨层优化的困难给予了阐述；最后给出了传输功率控制领域最新的一些研究方向。     

基于带宽估计的ad hoc网络拥塞控制机制

针对ad hoc网络提出了一种基于带宽估计的拥塞控制机制.该机制通过实时的监测无线节点链路的工作状态,来估计节点的可用带宽,从而获得节点的拥塞程度指标,根据包的类型进行拥塞控制.由于带宽估计不需要与其他节点进行状态信息交换,降低了系统开销.同时拥塞控制机制缓解了无线网络的拥塞状态,提高了网络性能.     

无线传感器网络中基于效用模型的分布式功率控制机制

本文将效用模型引入无线传感器网络的功率控制设计中,提出了一种基于效用模型的分布式功率控制机制(简称UMDPC).该机制建立了网络中所有传感器节点的功率与效用模型的对应关系,将链路可靠性、网络能耗归纳到统一的网络效用优化框架中,并证明该效用优化问题是凸优化问题,构造基于对偶分解的分布式的优化算法,获得网络效用最大化条件下各节点的优化发射功率.最后,通过模拟实验对所提机制及其实现算法的性能进行比较和评价.实验结果表明,本文所提机制最大化了网络的效用,提高了网络的能量利用效率.     

基于移动代理的一种减少网络负载的数据更新机制

针对分布式控制中，节点间的信息广播武交换，占用了大量网络资源这一问题，文章介绍了基于移动代理的负载均衡结构，在传统负载信息更新的基础上，提出了基于移动代理的减少网络负载的新更新机制ULIMA算法，较大的提高了系统的性能和效率，并通过仿真实验证明了该数据更新机制的有效性。     

基于信誉值维护的机会网络自私节点检测机制

机会网络中自私节点的存在严重影响路由转发的性能。为在路由时避开此类节点、消除其对网络性能的影响,提出了一种基于信誉值维护的自私节点检测机制,通过两跳ACK消息来监测节点行为,利用监测信息计算节点的信誉值,并将其作为判断节点是否自私的依据。在多种路由算法上加载该检测机制进行仿真实验,结果表明该检测机制可准确识别机会网络中的自私节点,提高消息投递的成功率,并能有效控制消息副本数和网络开销。     

3G网络与WLAN的综合结构设计

本文回顾了多种3G和WLAN相结合的网络结构，在讨论了它们的性能后提出两种新的结构设计方案，即把UMTS网络分别通过节点SGSN和GGSN接入WLAN网络，介绍了利用OPNET对这两种网络结构进行仿真的方法，并进行性能分析和比较。     

基于蚁群优化的高性能拥塞控制路由机制

为了有效地解决偏远地理区域通信网络存在的网络拥塞严重、数据成功传输率低、数据冗余率高以及网络整体性能不佳等问题,通过考虑网络节点运动区域性特点,基于蚁群优化机制,设计出一种新型的容延容断网络 (DTN) 拥塞控制路由优化算法。该算法结合蚁群优化机制中的信息素因子,在同一对源、目的网络节点之间进行多次数据信息传输操作。在数据信息传输方向上,获取各个网络节点的中转跳数平均值,评估各个网络节点的中转价值;参考蚁群优化机制中的启发值因子,将网络节点的中转价值与剩余存储容量相关联,构成网络节点作为中转节点的评定参数,选取评定参数最大的网络节点完成其中转任务。实验表明：该算法有效控制了网络拥塞,提高了数据成功传输率,降低了数据信息冗余率,使网络整体性能得到进一步优化。     

PERFORMANCE OF ACCESS RATE CONTROL FOR CORRELATED SOURCES IN HIGH-SPEED NETWORKS: SPECTRAL ANALYSIS

In this paper we study the performance trade-offs of leaky-bucket control in a high speed network with correlated sources. The emphasis is placed on the interrelationship between access control queueing and network queueing, as affected by degrees of control in response to differing input power spectrum characterizing the source correlations. Both stochastic and deterministic analyses are developed. Whereas the stochastic analysis based on multi-state Markov modulated sources provides exact performance measures of the access rate control in random traffic environment, the deterministic analysis based on sinusoidal sources complements the stochastic analysis, leading to good engineering insights into the control performance in the complex scenarios where the stochastic analysis is intractable. Interesting observations are made between the control performance and the low-frequency input power. In the stochastic analysis, we use a novel technique to characterize a rather general class of input power spectrum and are able to derive not only the power spectrum of the leaky-bucket controlled source but also the distribution of a network queue fed by the controlled source.     

A gradient‐based binary feedback scheme for congestion control in computer networks

In this paper, we propose a binary feedback scheme for congestion control in computer networks using a gradient‐based mechanism which employs neural network modelling of the system dynamics. The optimal direction for rate adjustment at the source is based on a single bit feedback signal which depends upon the sign of the sensitivity of the system performance index with respect to queue input rate. The paper presents the scheme and the analysis that went into the choice of the various decision mechanisms. Simulation results are presented to show the performance of the gradient based technique as compared to the conventional queue‐based approach. Copyright © 2000 John Wiley & Sons, Ltd.     

A fail-safe self-routing fiber-optic ring network using multitailedreceiver-transmitter units as nodes

A fiber-optic component consisting of N receivers, each with one fiber input port, and one transmitter with n fiber output ports, with a circuit in between, form a multitailed node. This is the basic building block for a self-routing `filled-ring network' with many stations, which can be disconnected without affecting the ring integrity. The token-passing medium-access protocol is found to have a several times better performance, in terms of the average delay-traffic intensity characteristic, in a filled-ring network than in a conventional ring network with the same number of stations. In a realistic example with 64 stations the improvement is by a factor of two to three. Using the multitailed nodes and self-routing, the network can easily be expanded to more complex configurations without introducing a routing overhead to keep the network under control     

On the characteristics of queueing and scheduling at encoding nodes for network coding

Synchronization can greatly influence the performance of network coding. In this paper, we shall investigate the synchronization issue based on the use of queueing theory. We shall first propose a queueing model, referred to as the classic model, to investigate the characteristics of the encoding process. It will be proved that given the packet arrival processes are stationary, i.e. the distribution of the arrival processes does not depend on time, and obey independently and identically Poisson distribution and that the encoding time is exponentially distributed, the output flow will be an asymptotically Poisson flow with the same parameter. Through simulation we shall show that the network is sensitive to the arrival rate of input flows and becomes unstable with the input queue size increasing to infinity. This indicates that the classic coding scheme would impose strict requirements on synchronization over the whole network. In order to address this, we shall propose a combined opportunistic scheduling and encoding (COSE) strategy, in which the classic coding scheme and the traditional forwarding algorithm are well integrated. Theoretical analysis and simulation will demonstrate that the COSE strategy is able to control the input queue sizes and keep the network operating in a stable state while maintaining a relatively high throughput, low blocking probability and small waiting delay under various levels of traffic load. Copyright © 2009 John Wiley & Sons, Ltd.     

Cognitive radio CDMA networking with spectrum sensing

In this paper, the performance of cognitive radio (CR) code division multiple access (CDMA) systems is analyzed. More precisely, CR users belong to a cognitive radio network (CRN), which coexists with a primary radio network (PRN). Both CRN and PRN are CDMA‐based, with colocated base stations. Soft hand off and power control are considered in both the CRN and the PRN. Upon the development of an accurate simulator for a representative three‐cell cellular scenario, we evaluate the performance of the proposed CR system in terms of outage probability, blocking probability and average data rate of secondary users. Three different spectrum sensing techniques are. Two new schemes, based on interference limit, are proposed and compared with an existing adaptive spectrum sensing scheme. Spectrum activity measurements and spectrum sharing decisions have been considered for evaluating the performance of the three schemes. The paper proposes a new CR‐CDMA networking model and a simulation testbed for evaluating performances of secondary users and primary users in terms of outage, blocking, BER and average data rate in the presence of soft hand‐off and power control. For comparison purposes, the analysis in the absence of spectrum sensing is also investigated.Copyright © 2012 John Wiley & Sons, Ltd.     

Power control and clustering in heterogeneous cellular networks

Recently, it is widely believed that significant coverage and performance improvement can be achieved through the deployment of small cells in conjunction with the well-established macro cells. However, it is expected that the high density of base stations in such heterogeneous cellular networks will give rise to multiple design problems related to both co-tier (small-to-small) and cross-tier (between small and macro cells) interference. Fortunately, cooperation between base stations will play a major role to cope with these problems and hence to enhance the users’ data rates. In this paper, we consider a two-tier cellular network comprised of a macro cell underlaid with multiple small cells where both co-tier and cross-tier interference are taken into account. We study the scenario where the small cell base stations seek to maximize a common objective by forming multiple clusters through cooperation. These base stations have also to allocate power to their associated users and, at the same time, control the total aggregate interference caused to the macro cell user which has to be kept below a threshold prefixed by the macro cell base station. We consider two utility functions: the overall sum rate of the small cell network and the minimum data rate of the small cell users. We formulate the studied problems as mixed integer nonlinear optimization problems and we discuss their NP hardness. Therefore, due to the complexity of finding the optimal solution, we design heuristic algorithms which resolves efficiently the tradeoff between computational complexity and performance. We show through simulations that the designed heuristics approach the optimal solution (obtained using the complex exhaustive search algorithm) with highly reduced computational complexity.     

超高站对LTE网络性能影响的评估方法研究

超高站覆盖范围广,对周边基站形成广泛的重叠覆盖,对于同频组网的TD-LTE网络,意味着同频干扰、速率下降。但是在实际建网过程中,由于种种原因已建成了大量超高站,如果将已建成的超高站全部关闭,重新选址建站,则会带来巨大的成本。提出了一种评估超高站对网络性能影响的方法,基于路测数据,量化一个超高站对网络性能的影响程度,并结合实际案例对现网中的超高站进行了评估,根据评估结果来决定对超高站的处理方式,不仅改善了网络性能,而且降低了建网成本,提高优化效率。     

Throughput Analysis of IEEE802.11 Multi-Hop Ad Hoc Networks

In multi-hop ad hoc networks, stations may pump more traffic into the networks than can be supported, resulting in high packet-loss rate, re-routing instability and unfairness problems. This paper shows that controlling the offered load at the sources can eliminate these problems. To verify the simulation results, we set up a real 6-node multi-hop network. The experimental measurements confirm the existence of the optimal offered load. In addition, we provide an analysis to estimate the optimal offered load that maximizes the throughput of a multi-hop traffic flow. We believe this is a first paper in the literature to provide a quantitative analysis (as opposed to simulation) for the impact of hidden nodes and signal capture on sustainable throughput. The analysis is based on the observation that a large-scale 802.11 network with hidden nodes is a network in which the carrier-sensing capability breaks down partially. Its performance is therefore somewhere between that of a carrier-sensing network and that of an Aloha network. Indeed, our analytical closed-form solution has the appearance of the throughput equation of the Aloha network. Our approach allows one to identify whether the performance of an 802.11 network is hidden-node limited or spatial-reuse limited     

New nodal design for high throughput data vortex optical interconnection network

This paper proposes a new three input nodal structure within the data vortex packet switched interconnection network. With additional optical switches, the modified architecture allows for two input packets in addition to a buffered packet to be processed simultaneously within a routing node. A much higher degree of parallel processing is allowed in comparison to previously proposed enhanced buffer node with two input processing or the original network node with single input processing. Unlike the previous contention prevention mechanism, the new network operates by introducing the packet blocking within the node if no exit path is available. This eliminates the traffic control signaling and the strict timing alignment associated with the routing paths which simplifies the overall network implementation. This study shows that both data throughput and the latency performance are improved significantly within the new network. The study compares the three input node with the two input node as well as the original single input data vortex node. Due to additional switch count and nodal cost, networks that support the same I/O ports and of the same cost are compared for a fair comparison. The limitation introduced by the blocking rate is also addressed. The study has shown that under reasonable traffic and network condition, the blocking rate can be kept very low without introducing complex controls and management for dropped packets. As previous architectures require operation under saturation point, the proposed architecture should also operate at reasonable level of network redundancy to avoid excessive packet drop. This study provides guidance and criteria on the proposed three input network design and operation for feasible applications. The proposed network provides an attractive alternative to the previous architectures for higher throughput and lower latency performance.     

CoopMAC: A Cooperative MAC for Wireless LANs

Due to the broadcast nature of wireless signals, a wireless transmission intended for a particular destination station can be overheard by other neighboring stations. A focus of recent research activities in cooperative communications is to achieve spatial diversity gains by requiring these neighboring stations to retransmit the overheard information to the final destination. In this paper we demonstrate that such cooperation among stations in a wireless LAN (WLAN) can achieve both higher throughput and lower interference. We present the design for a medium access control protocol called CoopMAC, in which high data rate stations assist low data rate stations in their transmission by forwarding their traffic. In our proposed protocol, using the overheard transmissions, each low data rate node maintains a table, called a CoopTable, of potential helper nodes that can assist in its transmissions. During transmission, each low data rate node selects either direct transmission or transmission through a helper node in order to minimize the total transmission time. Using analysis, simulation and testbed experimentation, we quantify the increase in the total network throughput, and the reduction in delay, if such cooperative transmissions are utilized. The CoopMAC protocol is simple and backward compatible with the legacy 802.11 system. In this paper, we also demonstrate a reduction in the signal-to-interference ratio in a dense deployment of 802.11 access points, which in some cases is a more important consequence of cooperation