TCP-H：基于三重判决的TCP拥塞控制

在异构无线网络中存在高误码、切换、信号衰落等链路特性,使传统的TCP拥塞控制机制受到了挑战。在不增加开销的情况下,基于丢包检测、RTT时间和ACK返回速率三重判决,提出了一种新的TCP拥塞控制机制（TCP—H）。仿真结果表明,TCP—H增强了对拥塞和随机差错的区分能力,满足公平性要求,改进的最小RTT计算方法解决了在低延迟向高延迟网络切换的时Vegas,Westwood等算法存在的最小RTT更新问题,有效提高了在异构无鲅网络环埔下TCP的性能．     

LTE-Advanced异构网络控制信道干扰协调技术

为了保证(LTE-Advanced)异构网络控制信道的可靠传输,首先对异构组网后的典型干扰场景进行了详细的分析;然后,针对上述干扰情况提出了2种可行的控制信道干扰协调方案;最后,通过对异构网络进行系统级的仿真建模来评估这2种控制信道干扰协调技术对系统性能的影响。仿真结果表明,提出的控制信道干扰协调技术能够有效提升异构网络系统的整体性能。     

一种透明传输的双向SPI接口的设计与实现

在高速图像/指令扩频无线传输系统中,前向链路主要为遥控指令或者遥控数据(例如航迹),后向链路主要为高速图像数据,无线传输信道为实时双向链路.针对这种前后向链路数据量不对称而又需要实时传输的特点,设计了一种新型的SPI接口,从而较好地解决了此类数据不对称信道中的数据实时双向透明传输的问题.该设计基于FPGA实现,可与绝大多数具有SPI接口的MCU(MPU)主设备进行双向SPI透明传输,而不需要增加任何协议.给出了SPI接口的仿真波形和实现结果,设计完成后经测试证明,该接口完全满足SPI协议串行数据传输的要求,性能可靠.     

TCP over OBS边缘节点重传机制的研究

使用传输控制协议(TCP)的拥塞控制机制在传统互联网技术中是解决问题的很好方法.然而在面对新型的光网络技术OBS网络,简单地采用TCP技术因受到OBS自身特性的影响,性能表现不佳,吞吐量低下.为此,通过对OBS技术和TCP拥塞控制机制深入的研究,提出一种基于OBS边缘节点的ACK重传机制来提升TCP over OBS性能的方法,提高OBS网络吞吐量.     

一种基于IEEE 802.11的多速率自适应MAC协议

提出了一种新颖的基于连续ACK帧统计信息的IEEE 802.11多速率自适应MAC协议EARF(EnhancedARF),其主要思想是:每一个速率有各自的成功阈值——速率升高的门限值,并且该值根据信道状况(用延时因子量化)动态地变化。协议不需对现有的IEEE 802.11标准做任何修改,因此易于通过编写驱动程序实现。仿真表明在大多数信道条件下,该协议性能较现有的基于ACK帧统计的速率自适应协议如ARF,ARF3-10都有较大的提高。     

EPON中一种新型的ONU休眠节能机制研究

为实现以太网无源光网络(EPON)的能源节省,提出了一种新型的基于双向业务流量的光网络单元休眠节能的控制机制。该机制通过扩展多点控制协议,并根据业务汇聚到缓存的容量来进行ONU休眠节能的时隙安排。仿真结果表明,该机制在实现绿色节能的同时可有效保证EPON网络的性能。     

异构分层无线网络中的混合动态流量均衡算法研究

结合信道借用和流量转移技术提出了一种混合动态流量均衡算法。使用该算法热点小区可以向紧凑模式中的同类型轻负载小区借用信道，同时还可以按一定条件将呼叫转移到与热点小区重叠覆盖的异构轻负载小区中，每个流量周期借用的信道数和转移的呼叫数将根据热点小区的剩余可用信道数和新呼叫到达率来计算。仿真结果表明，该流量均衡算法能够显著降低热点小区系统和整个异构系统的新呼叫阻塞概率、切换呼叫掉线率，而且整个异构系统的利用率也得到了相应提高。     

基于网络编码的无线网络分布式协作通信机制

 本文提出了一种基于无线网络编码的协作通信机制NCCC.无线网络编码能够在取得合作分集的性能增益的同时,降低网络中断概率.分布式中继节点选择算法是NCCC机制的核心,该算法根据即时信道状态,选择执行网络编码操作的最优中继节点.理论和仿真结果证明, NCCC机制可以提高无线网络双向多信源多信宿传输的性能和鲁棒性.     

不对称速率传输中网络编码与信道编码的联合设计

本文针对双向中继信道中不对称速率传输的情况进行了研究。在实际双向中继信道的通信传输中,由于信道质量,发射功率,业务需求等条件的不对称,双向信道的传输速率往往也是不对称的。本文提出了一种称为子集编码的方案,将调制、物理层网络编码、信道编码联合起来设计,使得较差信道的信道编码码字为较好信道的子集,这样中继节点可以利用信道编码的线性性质对接收到的叠加信号直接进行译码,从而使译码复杂度降低50%;同时,较好信道使用高阶调制,较差信道使用低阶调制,利用较好信道提高了系统的传输速率。仿真结果表明,与对称速率传输相比,本文提出的方案在提高系统有效性的同时,又保证了系统的可靠性。      

不对称速率双向中继传输策略研究

在实际双向中继信道的通信传输中,由于信道质量,发射功率,业务需求等条件的不对称,双向信道的传输速率往往也是不对称的。该文针对双向中继信道中不对称速率传输的情况进行了研究,基于物理层网络编码,提出两种不对称传输的方案。第1种方案采用级联信道编码;第2种方案采用子集编码和子集调制。这样设计使得中继节点对接收到的叠加信号只需一次译码就可以直接解出信息比特的异或,从而降低了译码复杂度。仿真结果表明,结合信道编码的不对称传输设计,在提高系统有效性的同时,进一步降低了误比特率,保证了系统的可靠性。     

Improving TCP/IP Performance over Third-Generation Wireless Networks

As third-generation (3G) wireless networks with high data rate get widely deployed, optimizing the transmission control protocol (TCP) performance over these networks would have a broad and significant impact on data application performance. In this paper, we make two main contributions. First, one of the biggest challenges in optimizing the TCP performance over the 3G wireless networks is adapting to the significant delay and rate variations over the wireless channel. We present window regulator algorithms that use the receiver window field in the acknowledgment (ACK) packets to convey the instantaneous wireless channel conditions to the TCP source and an ACK buffer to absorb the channel variations, thereby maximizing long-lived TCP performance. It improves the performance of TCP selective ACK (SACK) by up to 100 percent over a simple drop-tail policy, with small buffer sizes at the congested router. Second, we present a wireless channel and TCP-aware scheduling and buffer sharing algorithm that reduces the latency of short flows while still exploiting user diversity for a wide range of user and traffic mix.     

An Adaptive Delayed Acknowledgment Strategy to Improve TCP Performance in Multi-hop Wireless Networks

In multi-hop wireless networks, transmission control protocol (TCP) suffers from performance deterioration due to poor wireless channel characteristics. Earlier studies have shown that the small TCP acknowledgments consume as much wireless resources as the long TCP data packets. Moreover, generating an acknowledgment (ACK) for each incoming data packet reduces the performance of TCP. The main factor affecting TCP performance in multi-hop wireless networks is the contention and collision between ACK and data packets that share the same path. Thus, lowering the number of ACKs using the delayed acknowledgment option defined in IETF RFC 1122 will improve TCP performance. However, large cumulative ACKs will induce packet loss due to retransmission time-out at the sender side of TCP. Motivated by this understanding, we propose a new TCP receiver with an adaptive delayed ACK strategy to improve TCP performance in multi-hop wireless networks. Extensive simulations have been done to prove and evaluate our strategy over different topologies. The simulation results demonstrate that our strategy can improve TCP performance significantly.     

A buffer management algorithm for improving up/down transmission congestion protocol fairness in IEEE 802.11 wireless local area networks

The fair allocation of the resources is an important issue in wireless local area network (WLAN) because all wireless nodes compete for the same wireless radio channel. When uplink and downlink transmission congestion protocol (TCP) flows coexist in WLAN, the network service is biased toward the uplink TCP flows, and the downlink TCP flows tend to starve. In this article, we investigate the special up/down TCP unfairness problem and point out that the direct cause is the uplink acknowledgement (ACK) packets occupy most buffer space of access point. We thus propose a buffer management algorithm to ensure the fairness among uplink and downlink TCP flows. In order to limit the greedy behavior of ACK packets, the proposed algorithm adjusts the maximum size of buffer allocated for the ACK packets. Analysis and simulation results show that the proposed solution not only provides the fairness but also achieves 10–20% lower queue delay and higher network goodput than the other solutions. Copyright © 2012 John Wiley & Sons, Ltd.     

非对称无线网络中增强TCP性能的方法

针对非对称无线网络中,源节点和目的节点之间可能存在多条通信路径,通过计算反向路径带宽和平均吞吐量的关系,提出了将TCP数据报文段和确认报文段（ACK）的传输路径分离的方法。把路径的带宽作为判断标准,选择带宽大的那条路径返回ACK信号。仿真证明了提出的方法可以更加有效地提高TCP吞吐量,增强TCP的性能。     

DTPA: A Reliable Datagram Transport Protocol over Ad Hoc Networks

As a prevalent reliable transport protocol in the Internet, TCP uses two key functions: AIMD (Additive Increase Multiplicative Decrease) congestion control and cumulative ACK technique to guarantee delivery. However, with these two functions, TCP becomes lowly efficient in ad hoc networks that have a much lower BDP and frequent packet losses due to various reasons, since TCP adjusts its transmission window based on packet losses. In this paper, we present that, provided that the BDP is very small, any AIMD-style congestion control is costly and hence not necessary for ad hoc networks. On the contrary, a technique to guarantee reliable transmission and to recover packet losses plays a more critical role in the design of a transport protocol over ad hoc networks. With this basis, we propose a novel and effective datagram-oriented end-to-end reliable transport protocol for ad hoc networks, which we call DTPA. The proposed scheme incorporates a fixed-size window based flow control and a cumulative bit-vector based selective ACK strategy. A mathematical model is developed to evaluate the performance of DTPA and to determine the optimum transmission window used in DTPA. The protocol is verified using GloMoSim. The simulation results show that our proposal substantially improves the network performance.     

A Smart TCP Acknowledgment Approach for Multihop Wireless Networks

Reliable data transfer is one of the most difficult tasks to be accomplished in multihop wireless networks. Traditional transport protocols like TCP face severe performance degradation over multihop networks given the noisy nature of wireless media as well as unstable connectivity conditions in place. The success of TCP in wired networks motivates its extension to wireless networks. A crucial challenge faced by TCP over these networks is how to operate smoothly with the 802.11 wireless MAC protocol which also implements a retransmission mechanism at link level in addition to short RTS/CTS control frames for avoiding collisions. These features render TCP acknowledgments (ACK) transmission quite costly. Data and ACK packets cause similar medium access overheads despite the much smaller size of the ACKs. In this paper, we further evaluate our dynamic adaptive strategy for reducing ACK-induced overhead and consequent collisions. Our approach resembles the sender side's congestion control. The receiver is self-adaptive by delaying more ACKs under nonconstrained channels and less otherwise. This improves not only throughput but also power consumption. Simulation evaluations exhibit significant improvement in several scenarios     

Analysis and improvement of TCP performance in opportunistic networks

Opportunistic networks have attracted attention due to their inherent characteristics, such as long latency, low data rate, and intermittent connectivity. Extensive research has been conducted on opportunistic networks, including the architecture, and routing. However, few in the literature report the performance of TCP in opportunistic networks, especially in the case of Epidemic Routing. In this paper, we first evaluate the performance of TCP in opportunistic networks with Epidemic Routing. Our results show that the Epidemic Routing in opportunistic networks degrades the performance of TCP because multicopy data packets cause duplicate ACKs, and in turn reduce the transmission rate of TCP. Then an enhanced algorithm for TCP, named A-TCP/Reno is proposed to solve the above problem. A-TCP/Reno avoids the duplicate ACK problem caused by Epidemic Routing. The simulation results show that A-TCP/Reno outperforms the TCP/Reno in opportunistic networks with Epidemic Routing protocol.     

Adaptive downlink and uplink channel split ratio determination for TCP-based best effort traffic in TDD-based WiMAX networks

In this paper, we study the determination of downlink (DL) and uplink (UL) channel split ratio for Time Division Duplex (TDD)-based IEEE 802.16 (WiMAX) wireless networks. In a TDD system, uplink and downlink transmissions share the same frequency at different time intervals. The TDD framing in WiMAX is adaptive in the sense that the downlink to uplink bandwidth ratio may vary with time. In this work, we focus on TCP based traffic and explore the impact of improper bandwidth allocation to DL and UL channels on the performance of TCP. We then propose an Adaptive Split Ratio (ASR) scheme which adjusts the bandwidth ratio of DL to UL adaptively according to the current traffic profile, wireless interference, and transport layer parameters, so as to maximize the aggregate throughput of TCP based traffic. Our scheme can also cooperate with the Base Station (BS) scheduler to throttle the TCP source when acknowledgements (ACKs) are transmitted infrequently. The performance of the proposed ASR scheme is validated via ns^-2 simulations. The results show that our scheme outperforms static allocation (such as the default value specified in the WiMAX standard and other possible settings in existing access networks) in terms of higher aggregate throughput and better adaptivity to network dynamics.     

Performance evaluation of TCP algorithms in multi‐hop wireless packet networks

Wireless packet ad hoc networks are characterized by multi‐hop wireless connectivity and limited bandwidth competed among neighboring nodes. In this paper, we investigate and evaluate the performance of several prevalent TCP algorithms in this kind of network over the wireless LAN standard IEEE 802.11 MAC layer. After extensively comparing the existing TCP versions (including Tahoe, Reno, New Reno, Sack and Vegas) in simulations, we show that, in most cases, the Vegas version works best. We reveal the reason why other TCP versions perform worse than Vegas and show a method to avoid this by tuning a TCP parameter— maximum window size. Furthermore, we investigate the performance of these TCP algorithms when they run with the delayed acknowledgment (DA) option defined in IETF RFC 1122, which allows the TCP receiver to transmit an ACK for every two incoming packets. We show that the TCP connection can gain 15 to 32 per cent good‐put improvement by using the DA option. For all the TCP versions investigated in this work, the simulation results show that with the maximum window size set at approximately 4, TCP connections perform best and then all these TCP variants differ little in performance. Copyright © 2001 John Wiley & Sons, Ltd.