共查询到19条相似文献,搜索用时 171 毫秒
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信道接入协议(MAC)是无线数据通信协议的重要组成部分。由于无线信道是一个开放、共享的信道,网络节点在通信过程中存在隐终端和暴露终端问题。基于目前无线通信常用的MAC协议存在的问题,着重分析了基于扩频码的信道接入协议,该协议利用扩频码的正变特性,使得网络中各节点可以同时占用信道而互不干扰,较好地解决了信道争用问题,提高了系统效率。同时指出,在选择MAC协议时,应根据无线网络的拓扑结构及特点灵活选择,以提高网络性能。 相似文献
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基于快速、有效竞争预约接入、无冲突轮询传输的思想和带冲突预防的冲突分解策略,本文提出了适于移动Ad Hoc网络的公平按需多址接入(FODA)协议.该协议在分群结构的基础上,利用公平冲突预防算法预约信道资源获得轮询服务,从而完全消除了载波侦听方式下多跳无线网络业务传输中的隐藏终端和暴露终端问题.另外,公平冲突预防算法解决了节点竞争接入时的冲突问题和不公平现象.最后,仿真结果表明,与带冲突避免的载波侦听多址接入(CSMA/CA)和轮询协议相比,FODA协议可以提供较高的信道吞吐量、较低的平均消息丢弃率和平均消息时延. 相似文献
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在Ad Hoc网络中,采用多跳传输来提高数据传输的质量以及速率。传统的单中继节点已经不能适应迅速增大的数据量以及节点的移动造成的信道衰落情况,所以本文提出了基于智能天线实现多点中继的MAC协议,该协议采用了智能天线实现了菱形握手机制,使数据实现同步传输。其次采用空时编码的协作机制,通过估计源信号来防止中继节点与目的节点信道衰落的情况。最后利用Busy Tones解决了隐藏终端和暴露终端的问题。通过仿真与比较证明MRDMAC协议在数据延时和通过率等各个方面都有很大的优越性。 相似文献
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本文为多跳分布式无线网络(Ad Hoc网络)提出了一种信道多址接入与分布式路由相结合的方案.在该方案中,由扩频码实现多信道系统,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.并且该动态预约方法可以提供用于建立分布式路由机制的网络连通性信息.这种方案打破了信道接入层和网络层的分层概念,并以两者的结合带来了更高的带宽利用率和对网络拓扑变化的更快反应. 相似文献
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基于随机竞争和冲突解决的思想,本文为多跳移动Ad Hoc网络提出了一种分布式服务质量(QoS)保证的多址接入(QMA)协议.该协议中,节点在发送业务分组前利用预报突发进行竞争接入,节点根据业务分组时延情况和最早失效优先原则确定预报突发的长度,所发预报突发能持续到最后的节点优先获得接入.同时,具有实时业务的节点可以按照其优先级在更早的竞争微时隙中开始发送预报突发,而有非实时业务的节点只能在前面竞争微时隙空闲的情况下,才能在后面的微时隙开始发送预报突发,因此发送实时业务的节点可以比发送非实时业务的节点更优先接入信道,从而在移动Ad Hoc网络中实现了对多媒体业务的QoS保证.最后利用OPNET仿真评估了QMA协议的多址性能,并与IEEE 802.11e协议的性能做了比较,结果表明QMA协议可以提供较高的吞吐量和较低的实时业务时延. 相似文献
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In‐Taek Lim 《ETRI Journal》2001,23(2):52-60
In this paper, a medium access control protocol is proposed for integrated voice and data services in wireless local networks. Uplink channels for the proposed protocol are composed of time slots with multiple spreading codes per slot based on slotted code division multiple access (CDMA) systems. The proposed protocol uses spreading code sensing and reservation schemes. This protocol gives higher access priority to delay‐sensitive voice traffic than to data traffic. The voice terminal reserves an available spreading code to transmit multiple voice packets during a talkspurt. On the other hand, the data terminal transmits a packet without making a reservation over one of the available spreading codes that are not used by voice terminals. In this protocol, voice packets do not come into collision with data packets. The numerical results show that this protocol can increase the system capacity for voice service by applying the reservation scheme. The performance for data traffic will decrease in the case of high voice traffic load because of its low access priority. But it shows that the data traffic performance can be increased in proportion to the number of spreading codes. 相似文献
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一种基于有限状态机的新型水声网络多址接入协议的实现 总被引:1,自引:1,他引:0
本文首先提出了一种新型的水声通信网络的多址接入(UAMA)协议.该协议针对水声信道传播时延长的特点,利用扩频码进行多信道预约;通过适当的控制方法,采用与传统的握手协议不同的机制,当发送方发送request_to_send(RTS)后,在选择的业务信道上立刻传输数据,而不必等收到clear_to_send(CTS)后再传输数据,在时间和空间上大大地提高了信道的利用率,因此极大地提高了网络的吞吐量.通过使用OPNET Modeler/Radio仿真器对UAMA协议进行了基于有限状态机(FSM)的建模和设计.仿真结果表明该协议能在水声环境下取得优良的吞吐性能和较低的分组传输时延. 相似文献
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Wei-Ming Yin Ying-Dar Lin 《Communications Letters, IEEE》2001,5(12):494-496
N-ary tree protocols are used for access control on shared channels to resolve collisions among channel users. For exercising a single collision resolution engine (CRE), the throughput and latency of such protocols have been comprehensively studied. This study investigates the same protocols with multiple interleaved CREs in slotted networks. Power, defined as the ratio of throughput over latency, is measured as the criteria to launch or terminate CREs. Analysis results indicate that the appropriate number of CREs to trigger depends on the traffic load and the collision resolution protocol. As the load grows to 0.25, 0.35, 0.5, and 0.8, the optimal number of interleaved CREs becomes 2, 3, 5, and 8, respectively. Moreover, the power of n-ary tree protocol with n determined dynamically outperforms the 3-ary tree protocol by 13% 相似文献
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A protocol design for a mobile radio service supporting half-duplex push-to-talk voice communications over mobile satellite systems is presented. The service enables a closed group of mobile radio users to communicate among themselves, so that a transmission from any user is received by all. A key issue is the efficient utilization of satellite channels. Demand-assignment multiple access (DAMA) is employed to allocate channels only to those user groups in active sessions of conversations. Owing to the unique characteristics of the half-duplex point-to-multipoint group communications, a new DAMA protocol is proposed for this service. Within a channel assigned to a user group, access contentions exacerbated by very long round-trip delay can occur. A signaling protocol is devised to arbitrate access contentions so as to improve the utilization of the assigned channel. The proposed access control protocol offers 65% or 18% improvement in throughput capacity compared to manual carrier-sensed access without and with collision detection, respectively 相似文献
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In mobile communication networks operating in unreliable physical transmission, random access protocol with the collision resolution (CR) scheme is more attractive than the ALOHA family including carrier sense multiple access (CSMA) [IEEE Networks (September 1994) 50–64], due to likely failure on the channel sensing. Being a member of CR family schemes, a protocol known as non-preemptive priority multiple access (NPMA) is utilized in a new high-speed wireless local area network, HIPERLAN, standardized by European Telecommunication Standard Institute (ETSI). A conceptually three-layer CR multiple access protocol generalized from NPMA, supporting single type of traffic, is thus presented and analyzed in this paper. The CR capability of such a protocol (and hence NPMA) is proved to be significant by numerical substantiation that additional collision detection schemes are dispensable; also its throughput/delay performance is excellent when the proportion of the transmission phase to a channel access cycle is large enough (i.e., the winner of contention should transmit all of its packets successively). On the other hand, the simulated performance of NPMA serving integrated traffic is not fully satisfactory, primarily due to its distributed control mode and distinguishing traffic types only by the prioritization process. 相似文献
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本文提出了一种新的、支持数据/话音业务并传的多址接入协议——根据用户数目妥善安排分组传输的多址接入(User-dependent Perfect-scheduling Multiple Access——UPMA)协议,它根据实际需求对上、下行带宽资源实行动态分配.UPMA协议对不同的业务类型赋予不同的优先级,并用轮询方式妥善地安排节点的分组传输;同时,它采用独特的帧结构,使话音业务总是能够得到优先传输.本文还提出了一种高效的竞争接入算法,以保证激活的节点能够快速接入信道.最后,对UPMA协议的性能进行了仿真并与MPRMA协议的性能进行了比较,结果证明UPMA协议有更好的性能. 相似文献
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Enhanced binary exponential backoff algorithm for fair channel access in the ieee 802.11 medium access control protocol 下载免费PDF全文
M. Al‐Hubaishi T. Alahdal R. Alsaqour A. Berqia M. Abdelhaq O. Alsaqour 《International Journal of Communication Systems》2014,27(12):4166-4184
The medium access control protocol determines system throughput in wireless mobile ad hoc networks following the ieee 802.11 standard. Under this standard, asynchronous data transmissions have a defined distributed coordination function that allows stations to contend for channel usage in a distributed manner via the carrier sensing multiple access with collision avoidance protocol. In distributed coordination function, a slotted binary exponential backoff (BEB) algorithm resolves collisions of packets transmitted simultaneously by different stations. The BEB algorithm prevents packet collisions during simultaneous access by randomizing moments at stations attempting to access the wireless channels. However, this randomization does not eliminate packet collisions entirely, leading to reduced system throughput and increased packet delay and drop. In addition, the BEB algorithm results in unfair channel access among stations. In this paper, we propose an enhanced binary exponential backoff algorithm to improve channel access fairness by adjusting the manner of increasing or decreasing the contention window based on the number of the successfully sent frames. We propose several configurations and use the NS2 simulator to analyze network performance. The enhanced binary exponential backoff algorithm improves channel access fairness, significantly increases network throughput capacity, and reduces packet delay and drop. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Using multiple channels in wireless networks improves spatial reuse and reduces collision probability and thus enhances network throughput. Designing a multi-channel MAC protocol is challenging because multi-channel-specific issues such as channel assignment, the multi-channel hidden terminal problem, and the missing receiver problem, must be solved. Most existing multi-channel MAC protocols suffer from either higher hardware cost or poor throughput. Some channel hopping multi-channel protocols achieve pretty good performance in certain situations but fail to adjust their channel hopping mechanisms according to varied traffic loads. In this paper, we propose a load-aware channel hopping MAC protocol (LACH) that solves all the multi-channel-specific problems mentioned above.LACH enables nodes to dynamically adjust their schedules based on their traffic loads. In addition to load awareness, LACH has several other attractive features: (1) Each node is equipped with a single half-duplex transceiver. (2) Each node’s initial hopping sequence is generated by its ID. Knowing the neighbor nodes’ IDs, a node can calculate its neighbors’ initial channel hopping sequences without control packet exchanges. (3) Nodes can be evenly distributed among available channels. Through performance analysis, simulations, and real system implementation, we verify that LACH is a promising protocol suitable for a network with time-varied traffic loads. 相似文献