基于双忙音的无冲突多址接入协议

在Ad Hoc网络中,隐终端和暴露终端的存在严重影响了网络的通信能力.文中详细讨论了隐终端和暴露终端问题.在此基础上,介绍一种新的可完全避免分组冲突的MAC层协议--双忙音多址接入(DBTMA)协议.该协议采用RTS/CTS对话机制来预约信道,通过引入两个窄带带外忙音信号来避免分组间冲突,彻底解决了隐终端和暴露终端问题,提高了网络的吞吐量.     

双忙音多址接入-Ad Hoc网络中的多址接入控制机制的研究

在Ad Hoc网络中,隐藏终端和暴露终端的存在,严重影响了网络的通信能力。但是通常只采用RTS／CTS对话的MAC层机制不能完全解决隐藏终端和暴露终端的影响,正如单纯的分组侦听的MAC机制在全连通的网络中并不安全一样。为了解决这些问题,介绍一种新的MAC层协议——双忙音多址接入(DBTMA)机制。他的运行借助2个窄带带外忙音。通过使用RTS分组和接收端的接收忙音完全解决了隐藏终端的影响,接收端的CTS分组和接收忙音解决了暴露终端的影响。发送端建立的忙音保护了RTS分组,提高了接收RTS成功的概率,因此也就提高了吞吐量。     

基于双忙音的多址接入协议的研究

在Ad Hoc网络中．隐藏终端和暴露终端的存在严重影响了网络的通信能力。双忙音多址接入（DBTMA）协议是采用RTS／CTS对话机制来预约信道，通过引入两个窄带带外忙音信号来避免分组间冲突，解决了隐藏终端和暴露终端问题。本文在两个方面进一步对DBTMA进行改进：第一，使用一个控制分组RTS来预约信道，通过目的节点所发接收忙音来响应RTS分组；第二，采用时隙ALOHA协议对RTS分组进行传输，通过改进，提高了控制分组成功传输的概率，经仿真研究分析表明，提高了网络的吞吐量，增强了网络性能。     

A Highly Reusable Code Assignment Approach with Modified Busy Tone Signaling for CDMA-Based Ad Hoc Networks

Medium access control (MAC) protocol is among the most active topics of research in ad hoc networks. With the CDMA-based MAC protocol the code allocation plays an important role and has significant impact on the protocol performance. In this paper, we propose a distributed CDMA code assignment protocol for the mobile ad hoc networks (MANETs). The protocol is mainly composed of (1) a modified busy tone signaling mechanism that protects on-going data transmission as well as distributes code usage information, and (2) a set of specially designed code selection rules that work by taking into consideration whether relevant nodes are in the transmitting or receiving state. By combining the two proposed schemes with the conventional request-to-send (RTS)/clear-to-send (CTS) dialogue and power control mechanism, our protocol is able to increase CDMA code reusability. The simulation results indicate that the proposed protocol indeed performs better than the static and dynamic code assignment methods (either with or without power control) in terms of successful transmission rate and successful code assignment rate. And instead of sending continuously, the proposed modified busy tone mechanism only issues busy tone signal in randomly selected cycles, which may save battery energy as compared to conventional busy tone implementations. Moreover, the proposed code selection rules and the modified busy tone signaling may also be integrated into existing MAC protocols, either separately or in combination.     

基于多信道预约可冲突避免的多址接入协议

本文为多跳分布多无线网络提出了一套灵活而有效的自适应获取冲突避免（AACA）的多址接入协议。在该协议中，各节点竞争公共信道，利用RTS/CTS对话形式来预约各业务信道，成功预约后的分组传输不会受到其他节点的干扰。它使用任意确定数目信道，以异步方式工作，并且使得各节点利用半双工无线电台就可以灵活、简便地实现资源预约。分析和比较结果说明，所提出的多信道预约协议可以有效地解决隐藏终端、暴露终端以及侵入终端的问题。     

Can multiple subchannels improve the delay performance of RTS/CTS-based MAC schemes?

We analyze the delay performance of RTS/CTS-based (Request-To-Send/Clear-To-Send) multi-channel MAC (Medium Access Control) schemes for wireless networks. These schemes usually employ multiple data subchannels for data transmission and one control subchannel to send the RTS/CTS dialogue for channel reservation. Through theoretical analysis and simulations, we show that, in fully-connected networks, such multi-channel MAC schemes suffer longer delays than the corresponding single channel MAC scheme, that puts the RTS/CTS dialogue on the same channel as data packet transmissions. This conclusion holds even when data packets have different priorities and higher priority traffic is sent ahead of lower priority traffic.     

Collision reduction mechanism for masked node problem in ad hoc networks

IEEE 802.11 MAC uses RTS/CTS mechanism to avoid DATA packet collisions. RTS/CTS mechanism has been introduced to solve the problems of carrier sense multiple access (CSMA) in ad hoc networks such as hidden/exposed node problem. However, it creates a new problem called masked node problem. In this paper, a collision reduction mechanism named RTS/CTS/TTM with resume is introduced. This mechanism aims to minimize the probability of DATA packet collisions due to the masked nodes in an ad hoc network. We develop a new control packet called time-to-mask (TTM), which contains the time that the node will be masked. The proposed mechanism has been evaluated with a mathematical analysis and a simulation on a small IEEE 802.11 ad hoc network. The numerical results indicate that the RTS/CTS/TTM with resume reduces the probability of DATA packet collision.     

POWMAC: a single-channel power-control protocol for throughput enhancement in wireless ad hoc networks

Transmission power control (TPC) has great potential to increase the throughput of a mobile ad hoc network (MANET). Existing TPC schemes achieve this goal by using additional hardware (e.g., multiple transceivers), by compromising the collision avoidance property of the channel access scheme, by making impractical assumptions on the operation of the medium access control (MAC) protocol, or by overlooking the protection of link-layer acknowledgment packets. In this paper, we present a novel power controlled MAC protocol called POWMAC, which enjoys the same single-channel, single-transceiver design of the IEEE 802.11 ad hoc MAC protocol but which achieves a significant throughput improvement over the 802.11 protocol. Instead of alternating between the transmission of control (RTS/CTS) and data packets, as done in the 802.11 scheme, POWMAC uses an access window (AW) to allow for a series of request-to-send/clear-to-send (RTS/CTS) exchanges to take place before several concurrent data packet transmissions can commence. The length of the AW is dynamically adjusted based on localized information to allow for multiple interference-limited concurrent transmissions to take place in the same vicinity of a receiving terminal. Collision avoidance information is inserted into the CTS packet and is used to bound/ the transmission power of potentially interfering terminals in the vicinity of the receiver, rather than silencing such terminals. Simulation results are used to demonstrate the significant throughput and energy gains that can be obtained under the POWMAC protocol.     

Intelligent medium access for mobile ad hoc networks with busytones and power control

In mobile ad hoc networks (MANETs), one essential issue is how to increase channel utilization while avoiding the hidden-terminal and the exposed-terminal problems. Several MAC protocols, such as RTS/CTS-based and busy-tone-based schemes, have been proposed to alleviate these problems. In this paper, we explore the possibility of combining the concept of power control with the RTS/CTS-based and busy-tone-based protocols to further increase channel utilization. A sender will use an appropriate power level to transmit its packets so as to increase the possibility of channel reuse. The possibility of using discrete, instead of continuous, power levels is also discussed. Through analyses and simulations, we demonstrate the advantage of our new MAC protocol. This, together with the extra benefits such as saving battery energy and reducing cochannel interference, does show a promising direction to enhance the performance of MANETs     

The slow start power controlled MAC protocol for mobile ad hoc networks and its performance analysis

We propose and evaluate the performance of a new MAC-layer protocol for mobile ad hoc networks, called the Slow Start Power Controlled (abbreviated SSPC) protocol. SSPC improves on IEEE 802.11 by using power control for the RTS/CTS and DATA frame transmissions, so as to reduce energy consumption and increase network throughput and lifetime. In our scheme the transmission power used for the RTS frames is not constant, but follows a slow start principle. The CTS frames, which are sent at maximum transmission power, prevent the neighbouring nodes from transmitting their DATA frames at power levels higher than a computed threshold, while allowing them to transmit at power levels less than that threshold. Reduced energy consumption is achieved by adjusting the node transmission power to the minimum required value for reliable reception at the receiving node, while increase in network throughput is achieved by allowing more transmissions to take place simultaneously. The slow start principle used for calculating the appropriate DATA frames transmission power and the possibility of more simultaneous collision-free transmissions differentiate the SSPC protocol from the other MAC solutions proposed for IEEE 802.11. Simulation results indicate that the SSPC protocol achieves a significant reduction in power consumption, average packet delay and frequency of RTS frame collisions, and a significant increase in network throughput and received-to-sent packets ratio compared to IEEE 802.11 protocol.     

Analyzing split channel medium access control schemes

In this work, we analyze and evaluate the maximum achievable throughput of split-channel MAC schemes that are based on the RTS/CTS (ready-to-send/clear-to-send) dialogue and that rely on pure ALOHA or on p-persistent carrier sensing multiple access (CSMA) contention resolution techniques. Our results show that, when radio propagation delays are negligible and when the pure ALOHA mechanism is used, then for a network with relatively large number of nodes, the maximum achievable throughput of the split-channel MAC schemes is lower than that of the corresponding single-channel MAC schemes. When the split-channel MAC schemes employ the p-persistent CSMA mechanism, then they out-perform the corresponding single-channel schemes when the maximum end-to-end propagation delays are at least 25% of the transmission time of the control packets on the single shared channel.     

Analytical modeling of MAC protocol in ad hoc networks

In ad hoc networks, CSMA/CA is a widely used MAC layer protocol. There has been considerable work on the performance evaluation of this protocol. But most work is confined to saturation performance of single‐hop ad hoc networks. In this paper, we employ a linear feedback model to evaluate the performance for CSMA/CA according to the Poisson distributed traffic in both single‐hop and multi‐hop ad hoc networks. To the best of our knowledge, this is the first attempt to analytically evaluate the performance for CSMA/CA protocol under a general assumption about the traffic. This paper also gives analytical results, showing the impact of RTS/CTS. Although RTS/CTS do add the overhead to the system, they become essential when either the hidden terminal problem is dominant, or the traffic is heavy, or the packet length is very large. This paper also shows that the performance degrades dramatically in multi‐hop ad hoc networks when the number of competing nodes increases, which implies that the scalability is still a major problem in ad hoc networks. To validate our analytical results, we have done extensive simulations, and it is observed that the simulation results match the analytical results very well. Copyright © 2006 John Wiley & Sons, Ltd.     

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 …     

Power-controlled medium access for ad hoc networks with directional antennas

Directional antennas have the potential to significantly improve the throughput of a wireless ad hoc network. At the same time, energy consumption can be considerably reduced if the network implements per-packet transmission power control. Typical MAC protocols for ad hoc networks (e.g., the IEEE 802.11 Ad Hoc mode) were designed for wireless devices with omnidirectional antennas. When used with directional antennas, such protocols suffer from several medium access problems, including interference from minor lobes and hidden-terminal problems, which prevent full exploitation of the potential of directional antennas. In this paper, we propose a power-controlled MAC protocol for directional antennas that ameliorates these problems. Our protocol allows for dynamic adjustment of the transmission power for both data and clear-to-send (CTS) packets to optimize energy consumption. It provides a mechanism for permitting interference-limited concurrent transmissions and choosing the appropriate tradeoff between throughput and energy consumption. The protocol enables nodes to implement load control in a distributed manner, whereby the total interference in the neighborhood of a receiver is upper-bounded. Simulation results demonstrate that the combined gain from concurrent transmissions using directional antennas and power control results in significant improvement in network throughput and considerable reduction in energy consumption.     

A multiple access collision avoidance protocol for multicast services in mobile ad hoc networks

In order to improve cross-layer optimization, we propose a multiple access collision avoidance protocol that combines RTS/CTS with scheduling algorithms to support the multicast routing protocol. We avoid collision by including additional information in the RTS. The proposed scheme, together with extra benefits, such as power saving, reliable data transmission and higher channel utilization compared with CSMA or multiple unicast, enables the support of multicast services in mobile ad hoc networks.     

Effectiveness of RTS/CTS handshake in IEEE 802.11 based ad hoc networks

IEEE 802.11 MAC mainly relies on two techniques to combat interference: physical carrier sensing and RTS/CTS handshake (also known as “virtual carrier sensing”). Ideally, the RTS/CTS handshake can eliminate most interference. However, the effectiveness of RTS/CTS handshake is based on the assumption that hidden nodes are within transmission range of receivers. In this paper, we prove using analytic models that in ad hoc networks, such an assumption cannot hold due to the fact that power needed for interrupting a packet reception is much lower than that of delivering a packet successfully. Thus, the “virtual carrier sensing” implemented by RTS/CTS handshake cannot prevent all interference as we expect in theory. Physical carrier sensing can complement this in some degree. However, since interference happens at receivers, while physical carrier sensing is detecting transmitters (the same problem causing the hidden terminal situation), physical carrier sensing cannot help much, unless a very large carrier sensing range is adopted, which is limited by the antenna sensitivity. In this paper, we investigate how effective is the RTS/CTS handshake in terms of reducing interference. We show that in some situations, the interference range is much larger than transmission range, where RTS/CTS cannot function well. Two independent solutions are proposed in this paper. One is a simple enhancement to the IEEE 802.11 MAC protocol. The other is to utilize directional antennas. Simulation results verify that the proposed schemes indeed can help IEEE 802.11 resolve most interference caused by large interference range.     

A distributed transmission power control protocol for mobile ad hoc networks

In this paper, we propose a comprehensive solution for power control in mobile ad hoc networks (MANETs). Our solution emphasizes the interplay between the MAC and network layers, whereby the MAC layer indirectly influences the selection of the next-hop by properly adjusting the power of route request packets. This is done while maintaining network connectivity. Channel-gain information obtained mainly from overheard RTS and CTS packets is used to dynamically construct the network topology. Unlike the IEEE 802.11 approach and previously proposed schemes, ours does not use the RTS/CTS packets to silence the neighboring nodes. Instead, collision avoidance information is inserted in the CTS packets and sent over an out-of-band control channel. This information is used to dynamically bound the transmission power of potentially interfering nodes in the vicinity of a receiver. By properly estimating the required transmission power for data packets, our protocol allows for interference-limited simultaneous transmissions to take place in the neighborhood of a receiving node. Simulation results indicate that, compared to the IEEE 802.11 approach, the proposed protocol achieves a significant increase in the channel utilization and end-to-end network throughput and a significant decrease in the total energy consumption.     

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…     

Mobility impact in IEEE 802.11p infrastructureless vehicular networks

Vehicular ad hoc networks (VANETs) are an extreme case of mobile ad hoc networks (MANETs). High speed and frequent network topology changes are the main characteristics of vehicular networks. These characteristics lead to special issues and challenges in the network design, especially at the medium access control (MAC) layer. In this paper, we provide a comprehensive evaluation of mobility impact on the IEEE 802.11p MAC performance. The study evaluates basic performance metrics such as packet delivery ratio, throughput, and delay. An unfairness problem due to the relative speed is identified for both broadcast and unicast scenarios. We propose two dynamic contention window mechanisms to alleviate network performance degradation due to high mobility. The first scheme provides dynamic level of service priority via adaptation to the number of neighboring nodes, while the second scheme provides service priority based on node relative speed. Extensive simulation results demonstrate a significant impact of mobility on the IEEE 802.11p MAC performance, the unfairness problem in the vehicle-to-vehicle (V2V) communications, and the effectiveness of the proposed MAC schemes.     

配电网故障定位中通信系统协议设置

采用无线自组织网络实现配电网故障检测。通过在配电网上安装无线节点,架构无线网络实现对配电网实时在线监测。文中主要利用NS2软件对无线自组织网络的协议进行了仿真分析,目的是选择适用于该系统的协议,以提高系统的性能。对DSDV、DSR、AODV的3种协议在节点数和停留时间不同情况下的端到端延时、分组投递率进行了比较,并且对基本接入机制和RTS/CTS机制下的吞吐量进行了比较,最终选择AODV协议并设置帧长门限值。