Analysis, stability and optimization of Aloha-type protocols for multichannel networks

In this paper we propose a protocol appropriate for multiple access in a multichannel environment. All free stations contend in one channel, while the busy stations construct one queue belonging to all retransmission channels for collision resolution. Thus asymmetric access methods, such as pre-selection or sequential selection of retransission channels. A queueing model appropriate for the analysis and performance evaluation of the proposed protocol is derived. Analytic solutions are developed for a system with a finite number of stations using discrete time Markov chains. Numerical results indicate the dependence of normalized performance (normalized throughput and normalized delay) on the number of channels. The cases in which the multichannel system is superior to the single channel protocol are found. The stability of the multichannel system with infinite population is studied. Pakes's Lemma criteria are applied to specify regions in which the multichannel system is stable. The control parameters are the retransmission probabilities. Optimization rules are derived which show that the optimal retransmission probabilities are a function of the number of busy stations.     

Stability and throughput optimization of multichannel slotted non-persistent CSMA protocol

This paper describes two protocols suitable for a multichannel, multiaccess slotted non-persistent CSMA environment for infinite population, analyses their stability and examines their throughput optimization. The common sensing multichannel slotted non-persistent CSMA (CSCSMA) protocol is an extension of the slotted single channel non-persistent CSMA protocol with an appropriate policy for the selection of the channel in which a station (re)transmits. This policy restricts the control information among the stations, and consequently reduces the cost of the station interface. Pakes's Lemma criteria are applied to define sufficient conditions for ergodicity of the Markov chain, which describes the evolution of the busy station population, and to specify regions in which the multichannel system is stable. Control parameters are the retransmission probabilities. Optimization rules are derived which show that the optimal retransmission probabilities may be expressed as a function of the number of busy stations. The separate sensing multichannel slotted non-persistent CSMA protocol (SSCSMA), using a different policy, distinguishes the channels into two groups: the retransmission channel group devoted in collision resolution; and the transmission channel group for the access of free stations. Stability regions are defined using the results for CSCSMA, and rules for optimal allocation of channels among the two groups are derived for improvement of system performance.     

IEEE 802. 11无线局域网中基于最优窗口的退避算法

首先通过把资源分配看成效用最大化的优化模型,说明在IEEE 802. 11无线局域网中各个节点争用信道的退避窗口应当一样,然后通过最小化节点间的冲突概率,得出节点个数与最优退避窗口之间的关系,由此提出一种基于最优共享退避窗口的重传算法。由于各个节点的退避窗口一样,算法有效地解决了I3EI3(I3inary Exponential Back-off)算法的不公平性问题;并且退避窗口根据网络的状况置,吞吐量也得到了较大的提高。仿真试验验证了算法的有效性。     

基于隐藏终端的时隙802.15.4网络吞吐量研究

为了提高802.15.4网络吞吐量性能,设计了一种改进的节点状态转换过程,提出了一种考虑隐藏终端问题和重传的节点接入信道模型,并对模型进行分析计算。基于计算结果和信道状态模型分析,对考虑隐藏终端问题的数据碰撞概率、丢包率和网络吞吐量进行推导。最后研究了数据包到达率、退避指数和隐藏终端对网络吞吐量性能的影响。实验表明,模型较好地描述了节点接入信道过程,能够对网络吞吐量进行精准的动态分析。实验结果表明,与无重传机制的802.15.4网络相比,网络吞吐量增加了83.9%左右。与部分条件休眠的方法比较,网络吞吐量平均增加了13.3%,提出的模型能够有效提升网络吞吐量性能。     

基于HSDPA的增强型分组调度算法研究

从系统吞吐量、用户公平性等方面分析研究了HSDPA系统中支持非实时业务的三种经典分组调度算法RR、Max C/I和PF。针对PF算法重传时延过长问题,提出了一种结合混合自动请求重传HARQ的增强分组调度算法。该算法通过提高重传分组的优先级降低重传时延,有效地避免系统资源的浪费。MATLAB仿真结果表明,该算法在降低单用户重传时延的同时,仍能保证用户间的公平性和系统的吞吐量。     

一种基于链路级功率控制的分簇路由算法

针对非均匀网络环境下链路层的能耗控制问题,提出了一种基于链路级功率控制的分簇路由算法(CLPC算法)。CLPC算法基于最优连通功率成簇,并利用双信道机制和干扰反制策略在网络层解决链路层的冲突重传及信道访问公平性等问题,以期达到提高网络整体性能的目的。最优连通功率机制可以减少网络中节点间的冲突域,降低节点间的竞争强度;双信道机制则通过控制信道和数据信道分别对数据分组和控制分组进行收发,来降低数据传输的冲突概率,提高信道的空间复用率;干扰反制策略通过对具有高发射功率的干扰节点进行反制,来保障低发射功率的节点在共享信道上的公平性。实验仿真结果表明,CLPC算法进一步提高了网络的能量有效性和网络有效吞吐量。     

Properties of Nash solutions of a two-stage nonzero-sum game

This paper contains exact expressions for the complete class of uncountably many globally optimal affine Nasb equilibrium strategies for a two-stage two-person nonzero-sum game problem with quadratic objective functionals and with dynamic information for beth players. Existence conditions for each of these Nash equilibrium solutions are derived and it is shown that a recursive Nash solution is not necessarily globally optimal. Cost-uniqueness property of the derived Nash strategies is investigated and it is proven that the game problem under consideration admits a unique Nash cost pair if and only if it can be made equivalent to either a team problem or a zero-sum game. It is also shown that existence conditions of a globally optimal Nash solution will be independent of the parameters characterizing the nonuniques of the Nash strategies only if the game problem can be made equivalent to a team problem.     

并行多路传输中数据调度算法的研究

针对传统并行多路传输中数据调度算法存在的问题,基于MPTCP协议,提出了带宽预测和前向时延的数据调度算法(data-scheduling algorithm using bandwidth estimation and forward trip-time,DA-BEFT)。该算法充分考虑子流间传输时延差较大的影响,结合性能好的重传选路策略,减轻接收端因数据乱序导致的缓存阻塞,提高整个连接吞吐量。通过仿真实验验证了DA-BEFT在子流时延差变化时能够提高带宽利用率,提高网络的吞吐量。     

Hierarchy sustains partial cooperation and induces a Braess-like paradox in slotted aloha-based networks

This paper studies a hierarchical distributed choice of retransmission probabilities in slotted aloha. In particular, we consider a wireless system composed of one central receiver and several selfish mobile users communicating via the slotted aloha protocol. The set of mobile users is split into two classes: leaders and followers. We then study the induced non-cooperative hierarchical game based on the Stackelberg equilibrium concept. Using a 4D Markovian model, we compute the steady state of the system and derive the average throughput and the expected delay as well. We start by discussing the protocol design and propose a controlled slotted aloha using a virtual controller. The virtual controller can sustain partial cooperation among concurrent mobile users when accessing the channel by making the channel lossy. This leads us to identify a Braess-like paradox in which reducing capacity to the system may improve the performance of all mobile users. We then investigate the impact of hierarchy among mobile users in such a random access protocol and discuss how to distribute leader/follower roles. We show that the global performance of the system is improved compared to standard slotted aloha system. However, slight performances slow-down may be observed for the followers group when the total number of mobile users is relatively small.     

改进的无线Mesh网路由判据算法及其路由协议

为了改善802.11s无线Mesh网传输过程中因重传次数过大而造成的丢包问题,根据实际无线传输中的网络重传次数特性,提出一种基于最大重传次数的空中传播时间改进路由判据算法.同时为了缓解因单根节点造成的网络拥塞,提高实际场景中边缘节点的传输性能,并保证网络中所有节点使用无线信道资源的公平性,基于树的寻径机制从拓扑结构的角度,提出一种改进的多根节点的混合无线Mesh网路由协议(M-HWMP).理论及仿真结果表明,改进的路由判据算法及路由协议优化了无线Mesh网传输不同数据流时的吞吐量、时延特性,并在一定程度上避免了网络拥塞.     

Optimal replicator factor control in wireless sensor networks

For TDMA MAC protocols in wireless sensor networks (WSNs), redundancy and retransmission are two important methods to provide high end-to-end transmission reliability. Since reliable transmissions will lead to more energy consumption, there exists an intrinsic tradeoff between transmission reliability and energy efficiency. For each link, we name the number of its reserved time slots in each MAC superframe as a replicator factor. In the following paper, we propose a reliability-lifetime tradeoff framework (RLTF) for WSNs to study replicator factor control problem. First, for the redundancy TDMA MAC, we formulate replicator factor control problem as convex programming. By the gradient projection method, we develop a fully distributed algorithm to solve the convex programming. Second, for the retransmission TDMA MAC, we set the retransmission upper bound for each link according to the optimal replicator factors under the redundancy MAC and compute the total communication overhead for the retransmission MAC. Finally, we compare the communication overhead of these two MAC protocols under different channel conditions.     

无线网络中基于网络编码的重传机制

鉴于目前网络编码在单跳无线网络重传中的应用研究都是基于单发-多收场景的局限性,提出一种应用于多发-多收无线网络中的重传机制NCWRM。该重传机制中,网络节点既可以是发送方也可以是接收方,节点发送的数据包在直传和第一次重传中都失败后,第二次重传时广播发送由多个丢失数据包编码组合得到的编码包。多个接收方通过解码编码包得到丢失的数据包,从而实现一次重传获得多个丢失的数据包,可以有效提高重传效率。理论分析和仿真结果表明,NCWRM算法能够明显提高系统的饱和吞吐量,同时减小开销及丢包率。     

一种CDMA2000链路层自适应重传算法

TCP协议应用在3G无线网络中时，其传输性能受到了无线网络物理层帧差错率的严重影响。链路层重传技术可以大大改善TCP数据传输性能因无线信道误码率大而下降的情况。主要研究了CDMA2000中链路层重传技术对无线TCP数据传输的影响，并结合TCP层重传超时机制，提出了一种新的自适应链路层重传算法，提高了TCP在无线链路的数据传输性能。最后对该算法进行仿真，验证了此算法可以显著提高TCP吞吐率。     

Improving fairness in IEEE 802.11 networks using MAC layer opportunistic retransmission

This paper introduces DAFMAC (Decode And Forward MAC), a scalable opportunistic cooperative retransmission enhancement for the IEEE 802.11 MAC protocol which operates without the need for additional explicit control signalling. Distributed opportunistic retransmission algorithms rely on selecting a single suitable relay without direct arbitration between nodes. Simulations show that DAFMAC offers a significant improvement in fairness for both throughput and jitter, giving multiple parallel data flows a more equal opportunity to utilise the channel. DAFMAC cooperative retransmissions are shown to reduce node energy consumption for a given throughput. Further, the DAFMAC relay selection algorithm is shown to scale very well in terms of complexity and memory requirements in comparison to other cooperative retransmission schemes.     

Design and experimental testing of an optimization-based flow control algorithm for Energy Harvesting Wireless Sensor Networks

In this paper a distributed flow control law is proposed to maximize throughput and to minimize energy consumption in Energy Harvesting Wireless Sensor Networks (EH-WSNs). We preliminary recast the control problem in terms of primal–dual optimization one taking into account the bandwidth and energy autonomy node constraint. Then, we devise a distributed flow rate control implemented at each node that allows the overall network to converge to the optimal solution of the original problem. The closed loop EH-WSN stability and convergence to the optimal equilibrium are proven. The effectiveness of the proposed control law in terms of throughput and network lifetime performance is experimentally validated by a small representative EH-WSN. The experimental results are in a good agreement with the theoretical ones.     

基于SCTP-CMT的改进重传策略

传输层多宿的端到端并行多路径传输(CMT)相比于SCTP能够同时选择多条路径进行数据块的传输。针对CMT的五种重传策略只能够选择多条路径中的一条进行数据块重传的不足,提出了一种改进的数据块重传策略,该策略综合考虑了SSTHRESH、LOSSRATE和CWND对传输路径性能的影响。仿真实验表明,改进策略能进一步减轻由于接收缓冲区拥塞而造成的端到端吞吐量下降的程度。     

混合ARQ机制的性能分析

高速无线数据服务的需求的增长,要求下一代无线网络显著提高其吞吐量。文章研究了自动重发请求(ARQ)机制,来满足这些新的要求。针对基于速率兼容纠错码的速率自适应I类混合ARQ机制和增量冗余重传II类混合ARQ机制,提出了一种系统框架,并对其在无线瑞利衰落信道上的性能进行了分析。数值结果表明,增量冗余重传(IRR)II类HARQ机制与速率自适应(RA)I类HARQ机制相比,有较高的吞吐量,而RAI类HARQ机制的延迟较小。     

基于卫星网络的TCP拥塞控制算法

分析卫星网络的特点和现有慢启动算法的不足,提出一种使拥塞窗口平滑增长的慢启动算法。引入门限因子和粒度因子实现拥塞窗口指数增长和线性增长阶段之间的平缓过渡。仿真结果表明,该算法改善了TCP建立连接或超时重传阶段拥塞控制的性能,提高了卫星通信网络的吞吐量。     

基于IEEE802.11的无线Ad Hoc网络的接入性能研究及算法改进

在研究IEEE802.11标准的基础上,查阅了Ad Hoc网络信道接入的相关资料,分析了IEEE 802.11信道接入协议的优缺点,提出了对IEEE 802.11DCF工作模式的改进建议,以提高整个系统的性能.本文所作的主要工作包括以下几个方面:1.对IEEE802.11所采用的BEB退避机制,在分析了其缺点的基础上,参照了相关的改进算法,如MILD、LMILD、EIED等,提出了基于信道状况,根据信道忙闲程度的不同来设定相应的竟争窗口的退避机制,缓解了信道接入时发生的不公平性,提高了系统吞吐量.2.对DCF的工作机制进行了改动,在延迟阶段对信道进行探测,以避免出现错误的阻塞,同时,根据节点收发RTS/CTS的情况,探测信道的状况,来确定是否可以并行传送数据,以提高吞吐量.3.对原有的IEEE8 02.11中RTS/CTS和DATA报文的重传门限进行了改进,引入了一种自适应机制来进行门限值得设定,以减少报文被丢弃的可能性,从而达到减少触发TCP拥塞控制机制可能性的目的,从而提高系统的吞吐量.4.使用网络仿真器NS2对相关的改进进行了模拟仿真,仿真结果表明,与原有的接入方案相比,改进后的方案在网络性能方面有所提高.本文针对IEEE802.11的缺陷,提出了一些改进,为Ad Hoc网络的研究,提供了一些参考,具有一定的参考价值和借鉴意义.     

功率受限和自动重传请求条件下系统吞吐量最大化的研究

本文研究了具有ARQ功能的基于衰落信道和数据链路层缓冲区队列状态的资源最优分配问题，目标是通过自适应调整功率分配和调制方式，在系统平均功率的限制下，使系统的吞吐量达到最大。在这个系统中并不限制ARQ的重发次数，所以最大化系统的吞吐量等效于使链路层的缓冲区溢出的数据包最小。本文把这样一个优化问题构造为马尔可夫决策过程，并提出了用动态规划解决该问题的方法。出于实用性的考虑，本文还提出了一种简单的次优资源分配方法，仿真结果显示这种方法与最优的调度方法性能非常接近。