移动Ad Hoc网络中应用智能天线的多址协议及其性能分析

对智能天线在移动Ad Hoc网络(MANET)中的应用进行研究．提出了自适应波束形成CSMA／CA(ABF—CSMA／CA)协议．该协议利用RTS／CTS对话实现信道预约；在RTs与CTS分组中设置了训练序列，收发节点的智能天线基于训练序列进行自适应波束形成以传输数据分组与ACK．提出改进的“虚拟载波监测”机制进行冲突避免(CA)．每个节点中设置两类网络分配矢量(NAV)，用一个oNAV记录邻节点以全向模式占用信道的时间，用多个bNAV分别记录各邻节点以波束形成模式传输分组的时间．推导了信道利用率的近似计算公式并进行了仿真，考察了节点传输距离、训练序列长度及天线模式切换时间对网络性能的影响．结果表明，ABF-CSMA／CA协议与智能天线的结合能有效实现信道的空分复用(SDMA)，显著提高整个网络的信道利用率．

Multiple Access Protocol for Mobile Ad Hoc Network with Smart Antennas

The approach to employ smart antennas in mobile ad hoc network (MANET) nodes is presented, and an adaptive beamforming CSMA/CA protocol (ABF-CSMA/CA) is proposed. In ABF-CSMA/CA, RTS/CTS dialogue is used to distribute channel reservation information. Training sequences are placed in RTS and CTS packets, so the temporal reference beamforming (TRB) can be performed by the source node and the destination node. An improved virtual carrier-sense mechanism is also proposed to enhance collision avoidance (CA) and obtain efficient space division multiple access (SDMA). In this scheme, every node has two kinds of network allocation vector (NAV). An oNAV maintains the interval of ongoing transmission of neighbors whose smart antennas operate in omnidirectional mode, and multiple bNAVs maintain those intervals of neighbors whose smart antennas operate in beamforming mode. Theoretical analysis of channel utilization is presented. Results show that ABF-CSMA/CA protocol combining with smart antennas can provide higher channel utilization.