Analytical modeling of Transmission Control Protocol NewReno using Generalized Stochastic Petri Nets

This paper presents a novel analytical model of Transmission Control Protocol (TCP) using a generalized stochastic Petri net (GSPN). Extensive simulation work has been done for the performance evaluation of TCP NewReno protocol. In view of the limitations of the simulation technique, we present an analytical approach using GSPN. A GSPN is a useful mathematical tool that solves continuous time Markov chains for complex systems and evaluates the stationary behavior. In this paper, we analyze the slow‐but‐steady variant of TCP NewReno. The model captures the behavioral aspects of the slow start and the congestion avoidance phase together with the fast retransmit and recovery capabilities of TCP NewReno. Performance metrics such as throughput, goodput, and task completion time of the system are obtained. The effect of variation in the model parameters on the performance is studied. The results are validated using the network simulator, and their accuracy is verified by evaluating the confidence interval. The performance of the proposed model is compared with that of TCP Reno. The performance of the proposed model is also compared with one of the previous models. The numerical illustrations and comparison of the proposed technique with simulation validates the accuracy, efficiency, and competence of the GSPN technique. While GSPN modeling for TCP is investigated in depth for the TCP NewReno and TCP Reno variant in this paper, other protocols could be also analyzed similarly. Copyright © 2013 John Wiley & Sons, Ltd.     

Goodput and throughput comparison of single‐hop and multi‐hop routing for IEEE 802.11 DCF‐based wireless networks under hidden terminal existence

We investigate how multi‐hop routing affects the goodput and throughput performances of IEEE 802.11 distributed coordination function‐based wireless networks compared with direct transmission (single hopping), when medium access control dynamics such as carrier sensing, collisions, retransmissions, and exponential backoff are taken into account under hidden terminal presence. We propose a semi‐Markov chain‐based goodput and throughput model for IEEE 802.11‐based wireless networks, which works accurately with both multi‐hopping and single hopping for different network topologies and over a large range of traffic loads. Results show that, under light traffic, there is little benefit of parallel transmissions and both single‐hop and multi‐hop routing achieve the same end‐to‐end goodput. Under moderate traffic, concurrent transmissions are favorable as multi‐hopping improves the goodput up to 730% with respect to single hopping for dense networks. At heavy traffic, multi‐hopping becomes unstable because of increased packet collisions and network congestion, and single‐hopping achieves higher network layer goodput compared with multi‐hop routing. As for the link layer throughput is concerned, multi‐hopping increases throughput 75 times for large networks, whereas single hopping may become advantageous for small networks. The results point out that the end‐to‐end goodput can be improved by adaptively switching between single hopping and multi‐hopping according to the traffic load and topology. Copyright © 2015 John Wiley & Sons, Ltd.     

Degree distribution optimization for LT codes and its application in link maintenance of cognitive radio

The degree distribution has a great influence on the performance of Luby transform (LT) codes.Based on the link maintain model of cognitive radio system,the novel degree distribution of LT codes was obtained by using the THOA (two-layer hierarchical optimization algorithm) to combine the IPD (improved poisson distribution) which achieved high decoding success rate with low overhead and the robust soliton distribution (RSD) which achieved high decoding success rate with high overhead.Simulation results show that the proposed method with application to link maintenance in cognitive radio system can improve the reliability and efficiency of secondary communication.     

低复杂度的OFDM系统有效吞吐量最大化算法

针对OFDM系统有效吞吐量最大化问题,提出了一种低复杂度的资源分配算法LCGM.该算法的子载波采用统一的编码调制方式,以等误比特率的方式分配功率,并在此条件下将有效吞吐量最大化问题进行简化.利用有效吞吐量函数在平坦衰落信道和频率选择性衰落信道下为单峰函数这一特点,通过引入一种新的等效信道增益,采用二分法确定数据占用的子载波集合.仿真结果表明,LCGM算法以较低的复杂度获得了与高复杂度算法相当的有效吞吐量,在性能和复杂度之间取得了较好的折中.     

基于goodput优化的OFDMA系统资源分配算法

资源分配是OFDMA系统资源调度中的一个重要研究问题。针对OFDMA下行链路信道知识获取的现实误差问题,提出了一种基于实际吞吐量优化的资源分配算法。重点研究了功率和数据率在用户之间的分配问题,以往的很多分配算法通常是假设下行链路发射端具有理想信道信息,这与实际状况不符,同时根据部分信道信息得到的速率分配不被真实的信道支持,会造成传输的中断事件。算法考虑了信道估计的误差问题,将实际吞吐量goodput作为分配算法优化的依据。仿真结果表明,该算法获得了较好的多用户分集增益和实际吞吐量性能。     

Physical and Medium Access Control criteria for the optimal Medium Access Control protocol data unit size in Automatic Repeat Request‐enabled connections in IEEE 802.16e/ WiMAX systems

In this paper, we address an aspect of the mutual influence between the physical (PHY) layer budding blocks (forward error correction (FEC) blocks) and the medium access control (MAC) level allocations in the uplink and downlink of IEEE 802.16e/WiMAX systems. In these systems, it is possible to transmit MAC level frames, denoted MAC protocol data units (PDUs), such that a PDU contains an integral number of fixed size data blocks. We compute the optimal size of a PDU according to two criteria, one related to the PHY layer and one related to the MAC layer. In relation to the PHY layer, the criterion maximizes the average number of data bits that are transmitted in a PHY slot. In relation to the MAC layer, the criterion maximizes the goodput of the PDU. The goodput depends on the success probability of the PDU, which in turn depends on the FEC blocks over which the PDU is allocated. We then compare the maximal PDU goodputs in different sizes of the FEC blocks and the data blocks. The main outcome is that the PDU goodput is sensitive in those cases in which data blocks are very large. We also give guidelines on how to choose the best modulation/coding scheme to use in a scenario where the signal‐to‐noise ratio can change significantly during transmissions, to maximize the PDU goodput. Finally, we compare between the two criteria. Copyright © 2013 John Wiley & Sons, Ltd.     

一种按需分配的多路径传输分组调度算法

利用多路径传输协议,多宿主主机可以通过多条路径并行传输数据,从而有效提高系统的吞吐率和鲁棒性.但是由于不同路径在带宽、延迟和丢包率等方面存在差异,接收端必须缓存大量乱序到达的分组.数学分析表明,减少接收端的缓存开销有两条途径:一是最小化每条路径的发送队列中积压分组的数量,二是降低分组发送速率.由前者,提出依据每条路径的空闲发送窗口大小进行分组调度的算法SOD(Scheduling On Demand);由后者,提出利用窗口通告机制限制分组发送速率的流控方法.模拟实验结果表明:与现有算法相比,SOD的缓存开销最小;在接收端进行流控限制的情况下,SOD的吞吐率最大,并且在不同实验场景中性能表现稳定.     

OFDM系统用户上行有效吞吐量最大化算法

为了最大化OFDM系统用户上行链路的有效吞吐量,提出了一种新的用户上行资源分配策略.与传统策略相比,该策略通过引入自适应的子载波分段数和数据包OFDM符号数,增加了设计自由度.为降低计算复杂度,有效吞吐最最大化问题被分解为2个较简单的子问题,即用户有效资源分配和数据包参数设置.针对这2个子问题,分别通过分析目标函数的单...     

一种基于Intserv over Diffserv的QoS模型映射机制的设计

介绍了一种端到端的QoS架构模型：Intserv over Diffserv,研究了它的映射机制,构造了一种映射函数和网络配置,然后以服务流的吞吐量、路由器中的队列长度和分组的丢包率作为衡量参数,通过具体的仿真评估了此模型中的IntServ服务通过Diffserv区时所能获得的QoS。     

认知无线电网络用户合作机会接入方案的研究

认知无线电技术可以用来解决随着无线通信的迅速发展而突显出来的频谱实际利用率不高的问题,并缓解频谱分配紧张的局面.本文所关注的是多个认知无线电用户(SU)的机会频谱接入问题.分布式认知无线电网络中,为避免和授权用户(PU)发生冲突,通常采用周期性感知方法,这将使吞吐量降低.本文提出了一种认知无线电用户间高效的合作方案.文中分析了用户合作的最好和最坏两种情况下系统吞吐量的解析解.通过仿真验证了理论结果,并比较分析几种方案下每个用户和系统吞吐量随用户数量的变化,得出了用户间有效的合作可以提高各自以及整个系统的吞吐量的结论.