一种应用于Ad Hoc无线局域网的随机接人协议

本文分析了应用于Ad Hoe无线局域网的BSAC(Buffered Slotted ALOHA CDMA)随机接入协议，并且首次提出了采用Markov(马尔可夫)链方法的分析模型．此模型应用两个Markov链模型，一个表示节点中的M／M／I／k排队模型，另一个表示网络中活动节点数量．两个Markov链模型通过节点空闲概率相互联系．在此模型基础上，本文详细分析了扩频增益、队列长度与最大允许重传次数等输入参数对网络吞吐量、平均延迟与丢包概率等性能尺度的影响，推导得出了BSAC协议的吞吐量极限．另外，本文还引入多数据包接收技术一延迟捕获技术，该项技术可以有效降低数据包冲突概率，相对于没有采用延迟捕获技术的BSAC协议，平均提高吞吐量29．1％，最大吞吐量提高20．8％，使网络性能接近于理论极限．     

无线传感器网络DCF改进模型建模分析

针对无线网络的IEEE802.11的DCF机制,文章构建一种基于冲突概率p的分析模型,该模型综合考虑了无线网络中的节点数、网络负载及退避算法中的退避阶数及重传次数等影响因素,利用M/G/1/K队列模拟无线网络终端的饱和与非饱和状态,采用二维Markov对无线网络系统建模,由该模型得到网络系统的归一化吞吐量,并分析不同的数据包到达率对网络性能的影响,为预测和优化系统的性能提供理论依据。     

ISDN分组处理器接口(PHI)的性能分析

采用M/M/1/K的排队模型分析了PHI的性能,包括分组的损失概率、吞吐量、平均延迟、PHI上所能支持的最大用户分组业务量等。     

6LoWPAN网络能耗性能建模分析

为了改进6LoWPAN网络能耗性能,提出了一种基于超帧睡眠期的信道竞争机制,并对其进行Markov建模.基于本模型,对发送状态概率、信道检测冲突概率等网络参数和节点平均能耗进行了数学分析,并研究了参数λ、minBE和NB对能耗等网络性能的影响.理论分析表明,该模型能够较好的描述和评价6LoWPAN网络MAC协议,新机制降低了网络能耗,也改善了协议的性能.     

基于捕获效应的传感器网络MAC层研究

基于Markov链理论提出了一种新的理论模型用于描述无线传感器网络MAC层回退机制,该模型重点考虑了密集分布的无线传感器节点中普遍存在的捕获效应,并给出了新模型下节点发送概率的解析解。在此基础上,进而提出了一种新的无线传感器网络吞吐率计算模型,通过仿真分析,基于该模型计算所得到的网络吞吐率理论值要大于没有考虑捕获效应的网络吞吐率理论值。因此提出的新模型能够更准确地描述捕获效应对无线传感器网络的影响。     

无线Mesh网中基于网络编码的多路径TCP研究

在无线多跳网络中,本地重传和网络编码已经被成功地应用到多路径技术上以增加吞吐量并减少丢包。然而,在提高UDP传输性能的同时,也产生了数据包重排序和延迟等副作用,严重影响了TCP性能。针对此问题,主要提出一种基于网络编码的多路径传输方案NC-MPTCP,即在无线mesh网络的多条路径中引入网络编码、执行拥塞控制以及使用一个基于信用的方法控制节点的传输速率,提高网络的吞吐量以及增加网络传输的可靠性。该方案使用一个简单的算法,评估丢包率以及发送线性组合数据包的速率,用来降低目的节点的数据包解码延迟和防止TCP的超时重传。仿真结果表明设计的NC-MPTCP有效。     

无线Adhoc网络中一种基于网络编码的协同MAC协议

协同通信中,中继节点通常用来转发源节点的数据分组.但是从中继节点的角度出发,帮助其它节点转发数据会降低其自身的性能,导致中继低效率问题的出现.针对此问题,该文基于网络编码设计了一种适用于无线Ad hoc网络的协同MAC协议.该协议将网络编码和协同机制相结合,在需要协同传输时,利用网络编码让中继节点在发送源节点数据的同时也发送自身的数据,利用网络编码来解决协同传输中中继低效率问题,进一步提升协同传输的性能.该文还在2维Markov退避模型的基础上,加入了网络编码和协同机制,对所提协议在多跳网络中进行了吞吐量性能分析,并探讨了网络节点数、多跳和信道质量对吞吐量性能的影响.仿真结果表明,相比一般的协同MAC协议,采用网络编码的协同MAC协议可以显著的改善系统性能,是解决协同传输中的中继低效率问题的有效手段.     

基于TDMA支持实时应用的多跳时隙预留协议

提出一种基于时分多址接入(TDMA)的多跳时隙预留的协议(TMSR)以支持Ad Hoc网络中的实时应用,协议中节点为实时数据包的多跳转发预留信道时隙,通过超帧把数据包从源节点传输到远端的目的节点。通过NS2对提出的协议性能进行评估,重点分析了静态和移动环境下该协议的平均端到端时延和平均吞吐量,同时,在单跳仿真场景中,对TMSR协议与ETDMA进行对比,仿真结果表明随着数据流量的增加,TMSR提供了比E-TDMA更好的数据包吞吐量和时延性能。在多跳仿真场景中,采用TMSR协议的节点间的平均端到端的时延满足了实时应用的端到端多跳时延要求。     

一种基于ε-greedy的领导选举方法

随着区块链的广泛部署,无人协同等延迟敏感型的应用对区块链系统的低时延需求日益提高。在协同场景下,区块链节点通常跨地域部署,节点异构性较强。在基于领导节点的拜占庭容错(Byzantine Foult Tolerant, BFT)共识协议中,不稳定的或能力较差的领导节点将导致不必要的高延迟,并降低区块链的可用性,特别是在资源有限的移动或传感器网络下。针对上述问题,提出了ε-LE,一种带有网络感知的领导选举方法,基于节点到领导节点的通信延迟测量结果,采用ε-greedy策略对领导节点进行选择,使得当前性能较优或网络中关键位置的节点具有更高概率成为领导节点,从而优化共识延迟。相较于AWARE等方法,ε-LE实现O(N)的通信复杂度,更加适用于具备线性通信复杂度的共识协议。实验结果表明,ε-LE能够选择可优化集群共识延迟的节点作为领导节点,在线性拓扑网络中实现了约21%的吞吐量提升。     

带有接入阈值和超时隙的认知无线网络频谱分配策略

为了提高认知用户的响应性能,并降低传输中断的概率,通过限制进入系统的认知用户数据包数量,并令授权用户以超时隙为单位优先使用信道,提出一种带有接入阈值和超时隙的集中式认知无线网络频谱分配策略。结合时隙序号及系统中认知用户数据包的数量建立2维离散时间Markov链模型,给出认知用户数据包的平均延迟、吞吐量及信道切换率等性能指标的表达式。建立系统收益函数,针对不同的超时隙大小给出接入阈值的优化设置方案,并利用优化结果,进行系统实验。实验结果显示：合理的接入阈值和超时隙大小可以有效提高认知用户的传输质量。     

A central-limit-theorem-based approach for analyzing queue behaviorin high-speed networks

In this paper, we study P(𝒬>x), the tail of the steady-state queue length distribution at a high-speed multiplexer. In particular, we focus on the case when the aggregate traffic to the multiplexer can be characterized by a stationary Gaussian process. We provide two asymptotic upper bounds for the tail probability and an asymptotic result that emphasizes the importance of the dominant time scale and the maximum variance. One of our bounds is in a single-exponential form and can be used to calculate an upper bound to the asymptotic constant. However, we show that this bound, being of a single-exponential form, may not accurately capture the tail probability. Our asymptotic result on the importance of the maximum variance and our extensive numerical study on a known lower bound motivate the development of our second asymptotic upper bound. This bound is expressed in terms of the maximum variance of a Gaussian process, and enables the accurate estimation of the tail probability over a wide range of queue lengths. We apply our results to Gaussian as well as multiplexed non-Gaussian input sources, and validate their performance via simulations. Wherever possible, we have conducted our simulation study using importance sampling in order to improve its reliability and to effectively capture rare events. Our analytical study is based on extreme value theory, and therefore different from the approaches using traditional Markovian and large deviations techniques     

Analysis of nonblocking ATM switches with multiple input queues

An analytical model for the performance analysis of a multiple input queued asynchronous transfer mode (ATM) switch is presented. The interconnection network of the ATM switch is internally nonblocking and each input port maintains a separate queue of cells for each output port. The switch uses parallel iterative matching (PIM) to find the maximal matching between the input and output ports of the switch. A closed-form solution for the maximum throughput of the switch under saturated conditions is derived. It is found that the maximum throughput of the switch exceeds 99% with just four iterations of the PIM algorithm. Using the tagged input queue approach, an analytical model for evaluating the switch performance under an independent identically distributed Bernoulli traffic with the cell destinations uniformly distributed over all output ports is developed. The switch throughput, mean cell delay, and cell loss probability are computed from the analytical model. The accuracy of the analytical model is verified using simulation     

Performance analysis of slotted ALOHA and network coding for single-relay multi-user wireless networks

Deployment of wireless relay nodes can enhance system capacity, extend wireless service coverage, and reduce energy consumption in wireless networks. Network coding enables us to mix two or more packets into a single coded packet at relay nodes and improve performances in wireless relay networks. In this paper, we succeed in developing analytical models of the throughput and delay on slotted ALOHA (S-ALOHA) and S-ALOHA with network coding (S-ALOHA/NC) for single-relay multi-user wireless networks with bidirectional data flows. The analytical models involve effects of queue saturation and unsaturation at the relay node. The throughput and delay for each user node can be extracted from the total throughput and delay by using the analytical models. One can formulate various optimization problems on traffic control in order to maximize the throughput, minimize the delay, or achieve fairness of the throughput or the delay. In particular, we clarify that the total throughput is enhanced in the S-ALOHA/NC protocol on condition that the transmission probability at the relay node is set at the value on the boundary between queue saturation and unsaturation. Our analysis provides achievable regions in throughput on two directional data flows at the relay node for both the S-ALOHA and S-ALOHA/NC protocols. As a result, we show that the achievable region in throughput can be enhanced by using network coding and traffic control.     

Queuing Analysis of HCCA for Multi-Rate Wireless LANs with Truncated ARQ Protocol

In this paper, a novel queuing analytical framework is introduced to analyze the performance of the HCF controlled channel access designed as a medium access mechanism in wireless local area networks. The queuing model defines a multi-rate medium using adaptive modulation and coding which is a key point in wireless networks to increase effective transmission rate. Based on a MAP (Markovian arrival process)/PH (phase type)/1 queue with vacation and time-limited service, the model considers a limited node buffer and non-ideal channel with the automatic repeat request protocol. Using a MAP for traffic arrival process and PH distribution for packet service process, the inclusion of the non-transmission and vacation processes makes our analysis very general and comprehensive to support various types of practical traffic streams. To formulate the model, the powerful matrix-geometric method is employed, and the mutual impacts of some parameters in the MAC and the PHY layers are then evaluated to improve system performance. Finally, optimization of parameter settings to maximize throughput is discussed.     

A unified performance model for reservation-type multiple-accessschemes

This paper presents a unified performance model for an integrated voice/data wireless system using reservation type multiple-access (MA) schemes. It is observed that although these schemes are different in the frame structure and resource assignment procedure, all of them can be described by several common state variables whose evolvement exhibits the Markovian property. Based on this observation, a general Markovian model is developed in this paper. Three performance measures, namely, voice-packet-loss probability, data throughput, and data delay are defined. As a special case, the performance evaluation model for the voice-only system is also presented. Numerical results are given and verified by simulation under both voice-only and integrated scenarios using packet-reservation MA (PRMA), dynamic time-division multiple access (D-TDMA), and resource auction multiple access (RAMA) as examples. It is found that our analytical model is quite accurate, especially in the region of interest. The impact of system parameters (such as the voice-permission probability, data-retransmission probability, maximum number of voice slots per frame, etc.) on the integrated system performance is also investigated for these three example systems     

A Large Deviations Analysis of Scheduling in Wireless Networks

In this correspondence, we consider a cellular network consisting of a base station and N receivers. The channel states of the receivers are assumed to be identical and independent of each other. The goal is to compare the throughput of two different scheduling policies (a queue-length-based (QLB) policy and a greedy policy) given an upper bound on the queue overflow probability or the delay violation probability. We consider a multistate channel model, where each channel is assumed to be in one of L states. Given an upper bound on the queue overflow probability or an upper bound on the delay violation probability, we show that the total network throughput of the (QLB) policy is no less than the throughput of the greedy policy for all N. We also obtain a lower bound on the throughput of the (QLB) policy. For sufficiently large N, the lower bound is shown to be tight, strictly increasing with N, and strictly larger than the throughput of the greedy policy. Further, for a simple multistate channel model-ON-OFF channel, we prove that the lower bound is tight for all N     

Performance Analysis of Network Coding Based Two-Way Relay Wireless Networks Deploying IEEE 802.11

In this paper, we investigate the performance analysis of the IEEE 802.11 DCF protocol at the data link layer. We analyze the impact of network coding in saturated and non-saturated traffic conditions. The cross-layer analytical framework is presented in analyzing the performance of the encode-and-forward (EF) relaying wireless networks. This situation is employed at the physical layer under the conditions of non-saturated traffic and finite-length queue at the data link layer. First, a model of a two-hop EF relaying wireless channel is proposed as an equivalent extend multi-dimensional Markovian state transition model in queuing analysis. Then, the performance in terms of queuing delay, throughput and packet loss rate are derived. We provide closed-form expressions for the delay and throughput of two-hop unbalanced bidirectional traffic cases both with and without network coding. We consider the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queuing systems for the buffer behavior at the relay node. To overcome the hidden node problem in multi hop wireless networks, we develop a useful mathematical model. Both models have been evaluated through simulations and simulation results show good agreement with the analytical results.     

时分双工方式下的F-PRMA协议及其性能分析

本文提出了一个适合微蜂窝移动通信的时分双工方式下的分组预约多址协议－Ｆ－ＰＲＭＡ（Ｆｒａｍｅ－ｂａｓｅｄＰａｃｋｅｔＲｅｓｅｒｖａｉｔｏｎＭｕｌｔｉｐｌｅＡｃｃｅｓｓ）利用马尔夫过程理论为Ｆ－ＰＲＭＡ协议系统建立了三状态简化模型，应用Ｔａｓａｋａ提出的平衡点分析方法（ＥＰＡ）对该协议进行了性能分析，推导出分组丢弃概率和系统吞吐率等重要性能参数的解析式，通过数值分析和系统仿真全面考察了允许概率Ｐ帧长     

The SRUC Protocol for Satellite Packet Communication--A Performance Analysis

SRUC is an adaptive multiple access protocol which combines the slotted ALOHA protocol and a reservation protocol; it switches from one to the other according to the state of the channel. This paper studies SRUC with a go-back-NARQ scheme (SRUC/GBN) in a satellite communication environment to improve the performance over SRUC with a stop-and-wait ARQ scheme (SRUC/SAW) previously studied. The performance of SRUC/GBN is analyzed in this paper, it is assumed that each user handles one message at a time and that the number of packets in a message is geometrically distributed. An approximate Markovian model for SRUC/GBN is developed which has a multidimensional state vector. The model is analyzed by the technique of equilibrium point analysis. The throughput and average message delay performance is derived. Numerical results from both analysis and simulation are given. The performance of SRUC/GBN is also compared with that of SRUC/SAW and other multiple access protocols.     

Performance analysis of Markov modulated 1-persistent CSMA/CA protocols with exponential backoff scheduling

This paper proposes a Markovian model of 1-persistent CSMA/CA protocols with K-Exponential backoff scheduling algorithm. The input buffer of each access node is modeled as a Geo/G/1 queue, and the service time distribution of each individual head-of-line packet is derived from the Markov chain of the underlying scheduling algorithm. From the queueing model, we derive the characteristic equation of network throughput and obtain the stable throughput and bounded delay regions with respect to the retransmission factor. Our results show that the stable throughput region of the exponential backoff scheme exists even for an infinite population. Moreover, we find that the bounded delay region of exponential backoff is only a sub-set of its stable throughput region due to the large variance of the service time of input packets caused by the capture effect. All analytical results presented in this paper are verified by simulations.