无线Ad Hoc网络MAC层速率自适应技术研究

目前的IEEE802.11标准虽然在物理层提供了对多速率的支持,但是在MAC（媒体接入控制,Media Access Control）层却没有规定速率自适应的方法。研究了无线Ad Hoc网络（自组织网）中的速率自适应技术,针对RBAR协议存在的不足提出了一种改进的MAC层速率自适应协议,该协议实现简单,与标准的兼容性好,对信道的变化适应能力更强。仿真结果表明,该协议比RBAR协议具有更好的性能。     

Ad Hoc网络基于TCP吞吐量的速率自适应技术

目前的IEEE 802.11标准在物理层支持多速率传输,但在媒体接入控制(MAC,Media AccessControl)层却没有相应的速率自适应方法。针对目前Ad Hoc网络自适应速率控制方法的不足和在无线通信环境下TCP性能会大幅度恶化,提出了一种改进的MAC层速率自适应协议,该协议实现简单,与传统标准兼容性好,在提高TCP吞吐量的基础上能适应快速变化的无线信道,且能实现分段数据包的速率自适应传输。仿真结果表明,该协议比RBAR协议有更好的吞吐量。     

自适应速率需求的无线Ad hoc网络MAC协议

在802.11的基础上,从服务质量(QoS)中的速率需求角度出发,采取了跨层设计的方法,把应用层对数据传输速率的需求直接同MAC层中对无线信道的随机接入过程相结合,提出了一种自适应速率需求的Ad hoc无线网络MAC协议(Rate-requirement Aware Adaptive MAC Protocol,RAA-MAC).模拟实验的结果显示,与802.11协议相比,RAA-MAC在网络吞吐量、数据包延迟等性能上有较大提高.     

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。     

基于IEEE 802.11高速无线局域网的速率自适应MAC协议研究

目前的IEEE 802.11标准在物理层提供了对多种发送速率的支持,然而在MAC层却没有规定速率自适应的方法。该文研究了高速IEEE 802.11 无线局域网中的速率自适应方案。首先,提出了EACK协议,EACK使用基本速率发送MAC头,并在ACK帧中携带信道信息,因而能够较快速地响应信道的变化,同时具有少的开销;其次,在EACK基础上,提出了一种恒定发送时间(CEACK)的策略,CEACK能够克服传统IEEE 802.11 DCF MAC协议的理论吞吐量上限,并且具有更好的时间公平性能,能够应用于高速的无线局域网。     

面向QoS的UWB分布式MAC协议设计

提出了一种在分布式UWB网络结构中提供QoS服务的MAC协议.该MAC协议能够自适应地协调功耗与速率,设计过程分为资源分配和多路接入两方面.仿真结果表明,通过与功率控制机制及速率控制机制的比较.提出的协议在功率消耗,网络吞吐量及延时方面都有较好的改善.     

基于TDD-CDMA的集成可变速率多媒体业务传输的MAC协议

文章给出了一种应用于移动多媒体通信的无线媒体接入控制(MAC)协议.该MAC协议采用混合TDMA/CDMA结构,以提高资源利用率;采用多码并行传榆提供可变速率,以支持集成多媒体业务.系统仿真表明,该协议具有较高的码利用率和良好的灵活性,适用于可变速率多媒体业务集成传输.     

太赫兹网络中基于中继协作转发的高效双信道MAC协议

针对现有多输入多输出(Multiple-Input Multiple-Output, MIMO)太赫兹通信网络双信道MAC协议存在波束重叠干扰和冗余控制开销等问题,提出了一种太赫兹网络中基于中继协作转发的双信道MAC协议(High Efficiency Dual channel MAC Protocol Based on Relay Cooperative Forwarding in Terahertz Networks, HE-RCFMAC)。HE-RCFMAC协议包含动态帧聚合、基于位置信息自适应协作转发和精简RTS(Request To Send)/CTS(Clear To Send)帧三种机制。经三种机制处理后,可有效提升信道利用率,同时减小控制开销,提高数据传输成功率和整体网络吞吐量。仿真结果表明,所提协议与现有的MIMO太赫兹双信道MAC协议相比,MAC层吞吐量、数据传输成功率和信道利用率分别提升了12.82%、12.28%和8.73%,证明了所提协议的有效性。     

基于TMS320C66x的TD-LTE-A系统MAC层下行载波聚合设计与实现

提出了一种基于TMS320C66x多核DSP的LTE-A系统MAC层下行载波聚合的实现方法,在3GPP发布的LTE-Advanced协议的基础上,将MAC层实体按服务小区类型拆分为多个MAC子实体,每个MAC子实体独自占用一个DSP核,最终达到载波聚合的效果;针对上述方案提出了一种自适应动态反馈算法,该算法能够均衡MAC子实体间的数据传输延时和缓存区大小,通过对自适应动态反馈算法的仿真和结果分析,给出了适合2个服务小区下行载波聚合的参数建议值,并在终端测试仪表中将该方案进行了验证和应用。     

自适应传输速率MAC层协议的探讨

随着无线通信技术的发展和器件性能的提高,无线网络有能力支持更高的数据传输速率.随之而来的问题是如何提高网络的性能,即根据无线信道的状况而自适应地改变传输参数.文中讨论了媒体访问控制(MAC)层协议上多跳无线网络自适应传输速率的技术方案.该方案运用自适应调制和编码技术,可以最大限度地利用信道的容量,根据不同终端报告的信道情况提供个性的调制与编码选择;对位置较好的用户提供高速率的数据服务,增加系统的吞吐率;并且由于信道的自适应是通过改变调制和编码的方式,而不是像功率控制那样改变发射功率,因此系统中干扰变化很小.     

Ad hoc网络中DCF公平性分析与改进

在考虑节点的物理载波检测范围大于通信范围的情况下,该文分析了多跳Adhoc网络中物理载波检测机制对IEEE 802.11DCF协议公平性的影响。针对载波干扰给IEEE802.11DCF协议带来的严重不公平问题,提出了一种基于冲突和干扰感知的退避(CIAB)算法。仿真证明,该算法能有效地改善IEEE802.11DCF协议的公平性,并且没有引起网络吞吐量的严重下降。     

一种自组网功率控制算法及分析

无线自组网中的移动节点大多依靠电池提供能量,因此能量是影响无线自组网性能的一个很大的瓶颈,作为事实上的无线自组网媒体接入协议,802.11并没有动态调整传输功率的能力,大大限制了网络的生存时间。采用功率控制可以提高节点的功率使用效率,减少相邻节点间的干扰,改善网络的性能。在802.11基础上提出一种基于信噪比的动态传输功率控制算法。通过进行计算机仿真,与802.11协议相比,在保持吞吐量性能的前提下,大大减少了节点的功率消耗,提高了节点的能量利用率。     

一种新的基于跨层的Ad Hoc网络的MAC协议设计

为了提高Ad Hoc网络的性能,提出一种新的基于跨层的MAC协议,它能自适应的选择802.11b物理层规范中的两种不同的物理层数据单元格式进行传输。由于具有短导频的物理层数据单元格式比具有长导频的物理层数据格式占用更少的信道时间,基于跨层的MAC协议在一定条件下,采用具有短导频的物理层数据单元进行传输以减少物理层的开销,提高网络性能。其基本思想是如果需要通信的两个节点都支持具有短导频的物理层数据格式,则采用具有短导频的物理层数据格式进行传输,否则,采用具有长导频的物理层数据格式进行传输。同时提出一种自适应的网络分配向量计算算法,该算法能够根据MAC数据包的持续时间值判断节点是否支持具有短导频的物理层数据格式,不需要修改802.11b的帧格式。通过NS仿真证明,基于跨层的MAC协议能够提高网络的性能,如端到端的时延、吞吐量和传包率。     

无线多跳Ad hoc网络中MAC机制的公平性与网络容量利用率

高效、公平的MAC协议是目前无线多跳Ad hoc网络研究的关键问题之一。该文在给出一种新的无线多跳Ad hoc网络的网络模型前提下,定义了MAC协议公平性、网络容量利用率两个性能参数。给出了一种能在竞争节点间公平共享无线信道并充分利用网络容量的MAC协议(FMAC),仿真比较了FMAC和IEEE 802.11 DCF的公平性和网络容量利用率。结果表明FMAC能在充分利用网络容量的前提下,实现无线信道在竞争节点间的公平共享。     

A cross-layer scheme for medium access control with QoS guaranteeing for Ad hoc networks

1 Introduction medium access control (MAC) protocols play a crucial role in determining the performance of Ad hoc networks. However, the design of MAC protocols for Ad hoc networks has traditionally been separated from that of the physical layer. In most …     

A Novel Medium Access Control for Ad hoc Networks Based on OFDM System

1IntroductionIn Ad hoc networks , the nodes share the wirelesschannel under the control of media access control proto-col . Currently,there are two types of MAC protocolsproposedfor Ad hoc networks . The first is hand-shak-ing protocol such as IEEE 802 .11 MAC protocol[1 ~4]and MACAW[5], which controls the access procedureby exchanging the control packets among the activenodes . The secondis busy-tone protocol that introducesadditional busy tone signal to control the medium ac-cess . S…     

Design and performance of an enhanced IEEE 802.11 MAC protocol for multihop coverage extension

Ad hoc communication is gaining popularity, not only for pure ad hoc communication networks but also as a viable solution for coverage extension in wireless networks. Especially for upcoming WLAN hotspots, this is an interesting option to decrease installation costs. In this article we introduce a new MAC protocol that needs only marginal changes to the standard and enables efficient multihop networking. We advocate the use of multiple IEEE 802.11 channels, where one channel is reserved as a common signalling channel for the task of assigning the others (data channels) among wireless terminals. The proposed MAC protocols are based on a four-way handshake over the common signalling channel, while data transmission occurs on a dedicated channel. We propose a further optimization applying multiple wireless network interface cards. This improvement in performance comes at the price of a slightly more complex hardware. Two different simulation models are implemented to investigate our approach. The first model investigates the MAC protocol and its improvements, while the second model analyzes the multihop performance in terms of delivery ratio and transmission delay. BY means of numerous simulations we present the performance of our MAC approach in comparison with two standard approaches in terms of bandwidth, packet delivery, and transmission delay. For our performance evaluation we apply the IEEE 802.11a technology, but we note that our approach can also be used for IEEE 802.11b.     

Does the IEEE 802.11 MAC protocol work well in multihop wireless adhoc networks?

The IEEE 802.11 MAC protocol is the standard for wireless LANs; it is widely used in testbeds and simulations for wireless multihop ad hoc networks. However, this protocol was not designed for multihop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multihop connectivity is one of the most prominent features. In this article we focus on the following question: can the IEEE 802.11 MAC protocol function well in multihop networks? By presenting several serious problems encountered in an IEEE 802.11-based multihop network and revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multihop ad hoc networks. We thus doubt whether the WaveLAN-based system is workable as a mobile ad hoc testbed     

A hybrid multi-channel MAC protocol for wireless ad hoc networks

In a regular wireless ad hoc network, the Medium Access Control (MAC) protocol coordinates channel access among nodes, and the throughput of the network is limited by the bandwidth of a single channel. The multi-channel MAC protocols can exploit multiple channels to achieve high network throughput by enabling more concurrent transmissions. In this paper, we propose a hybrid and adaptive protocol, called H-MMAC, which utilizes multi-channel resources more efficiently than other multi-channel MAC protocols. The main idea is to adopt the IEEE 802.11 Power Saving Mechanism and to allow nodes to transmit data packets while other nodes try to negotiate the data channel during the Ad hoc Traffic Indication Message window based on the network traffic load. The analytical and simulation results show that the proposed H-MMAC protocol improves the network performance significantly in terms of the aggregate throughput, average delay, fairness and energy efficiency.     

A Load-Balancing and Push-Out Scheme for Supporting QoS in MANETs

Currently, mobile ad hoc networks (MANETs) lack load-balancing capabilities, and thus, they fail to provide good performance especially in the case of a large volume of traffic. Ad hoc networks lack also service differentiation. However, in these wireless environments, where channel conditions are variable and bandwidth is scarce, the differentiated services developed for the Internet are suboptimal without lower layers' support. The IEEE 802.11 standard for Wireless LANs is the most widely used WLAN standard today. It has a mode of operation that can be used to provide service differentiation, but it has been shown to perform badly. In this paper, we present a simple but very effective method for support Quality of Service, by the use of load-balancing and push-out scheme. This approach offers to the mobile node: the ability to alleviate congestion by traffic distribution of excessive load, and to support priority of packets in the single MAC buffer. We evaluate the performance of our algorithm and compare it with the original IEEE 802.11b protocol. Simulation results show that this new approach reduces packet loss rate and increases throughput as well as provides service differentiation in the MAC layer.