IEEE802.16中竞争时隙的动态分配算法

文章通过对IEEE802.16中竞争方式的请求与分配关系进行分析,提出了一种竞争时隙的动态分配方法.与固定分配方式相比,该分配方法可有效提高上行带宽的使用效率,并减小竞争请求引入的时延.仿真结果表明,在各种负载条件下,该分配算法都能较高效地使用系统的上行带宽.     

一种公平的EPON动态带宽分配算法

提出一种EPON上行链路动态带宽分配算法一周期比例DBA。ONU基于多门限周期地上报带宽请求，OLT根据ONU的带宽请求及其合约带宽进行动态带宽分配。当多个ONU竞争系统带宽时，OLT按照ONU合约带宽的比例进行带宽分配。仿真结果表明：周期比例DBA算法在实现高带宽利用率的同时又具有良好的公平性。     

基于动态最大传输窗口的带宽分配算法研究

数据业务和话音业务是未来网络中两个重要业务.作为下一代宽带接入的有效解决方案,以太网无源光网络(EPON)为用户提供了业务接口.对EPON中的上行带宽分配算法进行了分析研究,并提出一种基于动态最大传输窗口 DMTW 的 EPON 上行带宽分配算法.在本算法中根据业务和用户的优先级动态调整最大的传输窗口,合理分配上行带宽的资源,提高信道利用率和QoS,降低了传输时延.最后通过软件进行仿真,验证了算法的有效性.     

P2P流媒体网络中基于博弈理论的带宽请求分配策略

基于对等网(P2P)技术的视频流媒体系统以其较低的服务器开销和良好的可扩展性被广泛应用。但由于在这类系统中普遍存在节点的资源及视频播放位置的异构性,使得节点负载不均衡的问题极易发生,进而严重影响到节点的视频播放质量。该文重点研究面向节点负载均衡的节点带宽请求分配策略,将服务请求节点竞争服务提供节点带宽的行为建模为一个非协作博弈,通过寻求该博弈问题的 Nash 均衡解的方法确定优化的带宽请求分配(GBRA)策略。通过和典型的带宽请求分配策略进行实验对比,数值结果表明该文提出的GBRA 策略能有效改善P2P流媒体网络节点负载不均的问题并降低节点获取所需视频数据的平均延迟。     

一种IEEE 802.16中快速有效的冲突解决算法

IEEE 802.16宽带无线接入系统在其上行媒体接入控制层采用时,分复用和资源竞争与预留的方式进行接入,各用户站(SS)之间存在着竞争与冲突,这将导致系统性能下降。该文针对SS在碰撞以后的冲突解决过程提出了一种快速有效的冲突解决算法动态退避控制(Dynamical Backoff Control,DBC)算法。在该算法中,基站(BS)通过预测下一个上行帧中将会出现的带宽请求报文数,动态地控制SS的退避范围,以增大每帧中成功发送的带宽请求报文数,从而提高MAC层的数据吞吐,降低SS的平均接入延迟。利用OPNET对DBC和二进制指数退避两种算法进行了仿真。仿真结果显示DBC算法对系统性能有一定的改善和提高。     

谐振式无线输电系统线圈参数优化

为优化同轴同心型无线电能传输系统的线圈尺寸，提高最大传输效率，文中基于等效电路理论建模，通过电感、互感表达式推导耦合系数、最大传输效率关于线圈尺寸参数的关系式，运用仿真分析线圈长度、线圈直径和传输距离对耦合系数的影响规律，进一步优化传输系统的最大传输效率，并通过多物理场仿真不同线圈尺寸的磁场分布特征。最后选定线圈尺寸进行实验测试，并与理论、仿真数据进行对比。结果表明，所提方法的最大传输效率的理论值、仿真值与实测值基本吻合。     

GPON系统中基于QoS的动态带宽分配算法的研究

为了实现吉比特无源光网络(GPON)带宽分配的公平性,降低网络的丢包率及传输延时,研究了GPON系统传输汇聚层的帧结构及带宽分配的实现方法,提出了一种新的动态带宽分配(DBA)算法--基于QoS的二层动态带宽分配算法.性能分析与对比表明,这种算法对不同用户和不同等级的业务都具有很好的公平性,并可以降低低等级业务的传输延时.     

一种保证QoS的10G-EPON动态带宽分配算法

随着高清IPTV、在线游戏等业务的发展,用户对于带宽的需求日益增加,10G-EPON技术应运而生。与传统的EPON系统一样,10G-EPON系统的动态带宽分配问题仍然十分关键。带宽分配方式的选择对于如何避免传输冲突,提高系统的带宽利用率且保障服务质量都非常重要。在已有算法的基础之上,提出一种改进型动态带宽分配算法。该算法重点确保高优先级业务的服务要求,在一定程度上体现了不同等级ONU之间的公平性,提高了上行带宽利用率。     

EPON MAC控制层实现动态带宽分配策略的研究

针对EPON系统上行链路多个ONU共享带宽的拓扑结构，本文分析了制定带宽分配策略所需考虑的基本因素，在此基础上提出了一种新的动态带宽分配方案，通过动态请求分配机制，实现上链路的高效利用，最后，通过建模仿真，分析了该方案的时延及丢包率特性。     

HDTV SoC平台中存储器控制及其VLSI优化

在分析视频解码标准硬件实现要求的基础上，提出了SoC系统结构和SDRAM接口控制器的设计策略，包括冲突调度和面向提升带宽利用率的优化设计。并配置了一个二级请求缓冲池，配合固定优先级策略，解决了共享设备总线冲突问题；提出bank交叠方法隐藏读写等待时间，以达到提高带宽利用率的目的；另外，还用合并空闲状态的方法实现硬件可重用。     

Contention resolution with EIED backoff for bandwidth request in IEEE 802.16 networks

In this letter, we suggest contention resolution with exponential increase and exponential decrease (EIED) backoff for bandwidth request in worldwide interoperability for microwave access (WiMAX) networks. In EIED, setting of backoff factor to overcome collision due to contention is very challenging and hence we suggest a method to compute backoff factor with average contention window. Further, to reduce access delay, we estimate the response time based on probability of failure and average contention window. Simulations validate the proposed EIED backoff in terms of contention efficiency, capacity and access delay. The contention efficiency and capacity is improved by 47.50% (for q value of 0.25) and 28.57% (for 25 numbers of transmission opportunity), respectively, when bandwidth request is made with the proposed EIED backoff mechanism.     

Investigation on group based contention bandwidth request in LTE-A networks under high delay spread environment

In this paper, contention bandwidth request has been investigated for long term evolution-advanced (LTE-A) networks under extended typical urban based multipath fading channel that displays high delay spread environment. As the choice of preambles has to provide high detection probability under such environments, at the outset, this paper examines various group based preamble selection mechanisms, namely, Type I, Type II and Type III preamble sets. With suitable type of group based preamble, the challenge during contention bandwidth request is the appropriate choice of contention window during contention resolution. The contention window in this paper is chosen based on the indicators of various failure events, namely, probability of collision due to contention, probability of unavailability of bandwidth, probability of channel error and probability of improper detection of Zadoff–Chu sequences. After suggesting a scheme to account the possible failure events, an analytical model for contention-based bandwidth request has been developed for LTE-A networks. In addition, two backoff mechanisms are proposed to resolve contention among user equipment’s effectively and these mechanisms are compared to the existing techniques, namely, binary exponential backoff and uniform backoff. Further, the contention mechanism has been substantiated for varying depth of channel errors. With Type I grouping, the backoff with optimized contention window improves the efficiency by 13.95 %, reduces the access delay by 18.71 % and decreases the dropping probability by 59.33 % than the existing uniform backoff mechanism.     

Modeling Contention Based Bandwidth Request Scheme for IEEE 802.16 Networks

IEEE 802.16 standard specifies a contention based bandwidth request scheme for best-effort and non-real time polling services in point-to-multipoint (PMP) architecture. In this letter we propose an analytical model for the scheme and study how the performances of bandwidth efficiency and channel access delay change with the contention window size, the number of contending subscriber stations, the number of slots allocated for bandwidth request and data transmission. Simulations validate its high accuracy.     

Investigations on heuristic bandwidth request mechanism with signaling analysis for BWA networks

Best effort services in next generation broadband wireless access (BWA) networks would be more interactive and bandwidth demanding. This attracted a substantial amount of researches to focus on contention bandwidth request mechanisms for best effort services. The contention resolution with code division multiple access (CDMA) based mobile assisted truncated binary exponential backoff (C-MAB) suffers low contention efficiency and high access delay due to the nature of accessing mechanism in worldwide interoperability for microwave access (WiMAX) network that confines the mobile station in estimating the optimum contention window. Further, these performances decrease when transmission failure is modeled with unavailability of bandwidth, collision due to contention, transmission code failure, and channel error. To improve the performances, in this paper, we suggest a contention resolution with CDMA based base station assisted backoff (C-BAB) for orthogonal frequency division multiple access (OFDMA) based WiMAX networks. With C-BAB, the base station computes an optimum contention window by accounting average contention window and probability of failure. With a 2.69% additional overhead at the BS, the proposed C-BAB shows a 32.82% increase in contention efficiency and 24.21% decrease in access delay (25% error rate, q = 0.60 and ranging slot = 64) compared to C-MAB.     

Performance analysis of bandwidth requests under unicast, multicast and broadcast pollings in IEEE 802.16d/e

In the polling mode in IEEE 802.16d/e, one of three modes: unicast, multicast and broadcast pollings, is used to reserve bandwidth for data transmission. In the unicast polling, the BS polls each individual MS to allow to transmit a bandwidth request packet, while in the multicast and broadcast pollings, the truncated binary exponential backoff (TBEB) mechanism is adopted as a contention resolution among mobile stations (MSs) in a multicast or broadcast group. This paper investigates the delay of bandwidth requests in the unicast, multicast and broadcast pollings, by deriving the delay distribution of the unicast polling and the TBEB by means of analytical methods. We consider an error-free channel as well as an error-prone channel with i.i.d. constant packet error rate per frame. Furthermore, we find the utilization of transmission opportunity to see efficiency of the bandwidth in the TBEB. Performance evaluations are provided to show that analytical results are well-matched with simulations. By the numerical results, we can find the optimal parameters such as the initial backoff window size of the TBEB and the number of transmission opportunities (or slots) satisfying quality of service (QoS) requirement on delay and loss, and thus we can determine which scheme is better than others depending on the probability of a request arrival during one frame. Numerical examples address that the TBEB performs better than the unicast polling for light traffic loads and vice versa for heavy traffic loads. Also, it is shown that the multicast polling has better performance than the broadcast polling in the sense of shorter delay, lower loss probability and higher utilization of transmission opportunity.     

Distributed Optimal Contention Window Control for Elastic Traffic in Single-Cell Wireless LANs

This paper presents a theoretical study on distributed contention window control algorithms for achieving arbitrary bandwidth allocation policies and efficient channel utilization. By modeling different bandwidth allocation policies as an optimal contention window assignment problem, the authors design a general and fully distributed contention window control algorithm, called general contention window adaptation (GCA), and prove that it converges to the solution of the contention window assignment problem. By examining the stability of GCA, we identify the optimal stable point that maximizes channel utilization and provide solutions to control the stable point near the optimal point. Due to the generality of GCA, this work provides a theoretical foundation to analyze existing and design new contention window control algorithms.     

Carrier sense multiple access with improvised collision avoidance and short-term fairness

In this paper, we present a simple method to simultaneously enhance collision avoidance efficiency and short-term fairness of a most popular contention based medium access control protocol, carrier sense multiple access with collision avoidance. The key idea here is to adaptively tune the shape of contention slot selection distribution over the temporal contention window during ongoing collision resolution process which, in the legacy scheme, used to be flat throughout. The tuning mechanism is such designed that it not only maximizes the selection likelihood of relatively less collision prone contention slots over the contention window but also compensates the idle delay that the contending stations have suffered in their recent access attempt. Through rigorous numerical and simulation based analysis, the proposed scheme is shown to enhance the performance of a IEEE 802.11 based distributed wireless network in terms of network throughput efficiency and packet transmission delay while allowing individual stations to share the channel fairly even in short time scale.     

Hybrid Unified-Slot Access Protocol for Wireless Body Area Networks

Wireless body area network (WBAN) solution is an emerging new technology to resolve the small area connection issues around human body, especially for the medical applications. Based on the integrated superframe structure of IEEE 802.15.4, a modified medium access control (MAC) protocol, named Hybrid Unified-slot Access (HUA) protocol for WBANs is proposed with focus on the simplicity, dependability and power efficiency. Considering the support to multiple physical layer (PHY) technologies including ultra-wide band (UWB), the slotted ALOHA is employed in the contention access period (CAP) to request the slot allocation. Mini-slot method is designed to enhance the efficiency of the contention. Moreover, sufficient slot allocation in the contention-free period (CFP) makes HUA adaptive to the different traffic including the medical and non-medical applications. Simulation results show that the protocol effectively decreases the probability of collision in a CAP and extends the CFP slots to support more traffic with quality of service (QoS) guarantee.     

A smart exponential‐threshold‐linear backoff mechanism for IEEE 802.11 WLANs

Based on the standardized IEEE 802.11 Distributed Coordination Function (DCF) protocol, this paper proposes a new backoff mechanism, called Smart Exponential‐Threshold‐Linear (SETL) Backoff Mechanism, to enhance the system performance of contention‐based wireless networks. In the IEEE 802.11 DCF scheme, the smaller contention window (CW) will increase the collision probability, but the larger CW will delay the transmission. Hence, in the proposed SETL scheme, a threshold is set to determine the behavior of CW after each transmission. When the CW is smaller than the threshold, the CW of a competing station is exponentially adjusted to lower collision probability. Conversely, if the CW is larger than the threshold, the CW size is tuned linearly to prevent large transmission delay. Through extensive simulations, the results show that the proposed SETL scheme provides a better system throughput and lower collision rate in both light and heavy network loads than the related backoff algorithm schemes, including Binary Exponential Backoff (BEB), Exponential Increase Exponential Decrease (EIED) and Linear Increase Linear Decrease (LILD). Copyright © 2011 John Wiley & Sons, Ltd.     

CSMA/CA‐based medium access control for indoor millimeter wave networks

Millimeter wave (mmWave) communication is a promising technology to support high‐rate (e.g., multi‐Gbps) multimedia applications because of its large available bandwidth. Multipacket reception is one of the important capabilities of mmWave networks to capture a few packets simultaneously. This capability has the potential to improve medium access control layer performance. Because of the severe propagation loss in mmWave band, traditional backoff mechanisms in carrier sensing multiple access/collision avoidance (CSMA/CA) designed for narrowband systems can result not only in unfairness but also in significant throughput reduction. This paper proposes a novel backoff mechanism in CSMA/CA by giving a higher transmission probability to the node with a transmission failure than that with a transmission success, aiming to improve the system throughput. The transmission probability is adjusted by changing the contention window size according to the congestion status of each node and the whole network. The analysis demonstrates the effectiveness of the proposed backoff mechanism on reducing transmission collisions and increasing network throughput. Extensive simulations show that the proposed backoff mechanism can efficiently utilize network resources and significantly improve the network performance on system throughput and fairness. Copyright © 2014 John Wiley & Sons, Ltd.