【作者】 李蓥；

【导师】 李明禄；

【作者基本信息】 上海交通大学 ， 计算机应用技术， 2007， 博士

【摘要】 无线自组织网中由于通信的多跳性,造成节点间的干扰加剧,网络的吞吐量较低,提高网络的吞吐量成为无线自组织网MAC层协议研究的重点之一。在无线自组织网MAC协议的发展上,由简单的单信道协议,发展到多信道协议,又发展到基于有向天线的协议,这一系列的发展都体现了人们希望提高无线自组织网吞吐量的迫切需求。但是当前大量的协议仍然基于简单的干扰模型,未能适应于干扰范围的动态变化,也无法从根本上解决RTS/CTS握手机制中的隐终端和暴露终端问题。而且随着新的技术的引入,在增加了系统容量的情况下,又引入了新的MAC层协议设计的问题。针对这些新的问题,本文进行了分析研究,主要涉及了当前无线自组织网中IEEE 802.11 MAC协议的改进、多信道MAC协议的研究以及基于有向天线的有向MAC协议的研究三个方面。本文的创新性研究工作主要有以下几个方面:(1)提出了同时解决隐终端和暴露终端问题的无线自组织网MAC协议。IEEE 802.11MAC协议没有根据干扰范围的动态变化的特性来设计,无法解决隐终端和暴露终端问题。虽然当前有众多的研究致力于解决这两个问题,但是一般只是从一个方面进行研究,往往解决了隐终端问题的协议,可能会降低系统的空间复用;而解决了暴露终端问题的协议,可能会引入更多的隐终端。本文提出了通过忙音的频率来表示接收端当前的干扰情况,通过在忙音中编码当前节点的干扰情况,潜在的发送端可以根据这个信息来判断自己的发送会不会干扰到其他节点的接收,从而同时解决了隐终端和暴露终端问题。(2)分析了多信道协议中存在的“聋”(Deafness)问题,以及基于IEEE 802.11DCF机制的多信道协议中的新的隐终端问题。并且设计了新的协议,用来同时解决多信道协议在信道预留、分配上存在的隐终端和暴露终端问题。在对简单的多信道协议进行分析的基础上,研究了在多信道协议中存在的一类新问题:“聋”问题。当目标节点处于“聋”状态下时,发送节点将会不停的重发RTS。这样不但造成了发送节点自身的延迟,而且同时还造成别的节点和发送节点间通信的推迟。这个现象可能在整个网络中传播,造成网络吞吐量的下降。同时,现有的基于RTS/CTS握手的多信道预留、选择机制仍然无法解决隐终端问题,从而造成信道选择错误。针对这些问题,本文提出了一个基于忙音的可感知干扰的多信道协议,可以同时解决多信道协议在信道预留、分配上存在的隐终端和暴露终端问题,从而提高了无线自组织网的吞吐量。(3)提出了一个可以完全解决有向MAC协议中的“聋”问题的协议,该协议同时也可以解决隐终端和暴露终端问题。有向天线的使用可以减少节点间的干扰,增加空间复用。但是其引起的“聋”问题造成发送端不停的重发RTS,使得网络的整体性能下降,成为影响网络吞吐量的重要因素。当前现有的协议只能减缓“聋”问题,并不能彻底解决。本文通过设计新的有向MAC协议,使用两对忙音脉冲协同工作,不但完全解决了有向MAC协议中的“聋”问题,而且可以同时解决隐终端和暴露终端问题,使得有向MAC协议的吞吐量有了进一步的提高。更多还原

【Abstract】 To improve the throughput of wireless Ad hoc network becomes one of important research areas in the design of MAC protocols due to the serious interference in multi-hop transmission. But currently, most of MAC protocols use simplified interference mode, which does not consider the interference range is changing dynamically in the real world. Thus these protocols cannot solve the hidden/exposed terminal problems existing in RTS/CTS handshake mechanism. Meanwhile, with the usage of new technologies, new issues are brought into the design of MAC protocols. The earlier MAC protocols use single channel. In order to increase the throughput, multi-channel and directional antenna technologies have been used in wireless communication.The purpose of this study is to solve these problems, including 1) improving the performance of Ad hoc MAC protocol 2) designing a new multi-channel MAC protocol and 3) designing a new directional MAC protocols using directional antenna. Major contributions and the originalities of this dissertation are as follows:(1) A novel MAC protocol is proposed, which can solve the hidden and exposed terminal problem simultaneously.IEEE 802.11 MAC protocol can not solve the hidden and exposed terminal problems because it regards the transmission range and the interference range as same while the interference range is actually a dynamic value. Many protocols have been proposed to solve these problems. But most of these protocols only focus on one aspect of the interference problem, hence, an interference-aware busy tone based MAC protocol (IABT) is proposed to improve the throughput of the network. Encoding the interference information in the frequency, a busy tone will reserve the space necessary for the ongoing transmission. IABT protocol can solve both the hidden and exposed terminal problem simultaneously.(2) A new deafness problem in simple multi-channel MAC protocol and a new type of hidden terminal problem when using RTS/CTS handshake to reserve the channel are put forward and figured out; A novel mutli-channel MAC protocol is proposed to avoid the deafness problem,hidden and exposed terminal problems simultaneously.The deafness problem will cause the sender sends the RTS repeatedly while the receiver is busy. The consequences of the deafness problem can propagate throughout the entire Ad hoc network and cause low performance and unfairness. Meanwhile the RTS/CTS based handshake cannot solve the hidden terminal problem, which would cause channel selection error in multi-channnel protocol. Currently, most of multi-channel protocols do not deal with the difference between the transmission range and interference range. To solve these problems, a new tone-based multi-channel MAC protocol is proposed, which can improve the throughput of the network.(3) A tone based MAC protocol using directional antennas is proposed to solve the deafness problem, hidden terminal and exposed terminal problems simultaneously.Directional transmission can reduce the interference, increasing the transmission range and the spatial reuse. But it also brings deafness problem in directional MAC protocol, which would lead to the situation that the sender continually backs off, resending RTS. Some protocols can alleviate the deafness problem, but cannot solve it completely. By using two pairs of flip-flop tones, a new directional MAC protocols is proposed to solve the deafness problem, hidden terminal and exposed terminal problems simultaneously, which would greatly increase the throughput of the Ad hoc network using directional antenna.更多还原