ITR: A Cross-layer PHY/MAC Solution for Ad-hoc Networks with Multiple-element Arrays

Ad-hoc无线网络缺乏传统无线网络的基础设施;例如，它们没有基站或交换中心。ad-hoc网络中的每个节点都可以充当其他节点的转发器或路由器。 虽然ad-hoc网络主要被设想用于军事和紧急救援应用，但是最近，这样的网络在常规无线分组数据环境中找到应用，因为它们提供了方便的部署、改进的覆盖、减少的能量消耗以及比传统基础设施网络更高的网络容量。 随着ad hoc网络应用的扩展，多输入多输出（MIMO）链路由于其在没有干扰的情况下可以支持极高的数据速率而引起了极大的兴趣。 MIMO链路在发射机处具有多个天线并且在接收机处具有多个天线。 多个发射天线用于在相同信道中发射多个并行数据流;对多个接收器天线的输出的信号处理分离并行流。 在存在干扰的情况下，已知要求发射机具有信道状态信息（CSI）的闭环MIMO（CL-MIMO）显著优于不使用CSI的开环MIMO。本项目研究如何MIMO可以在ad-hoc无线网络中使用，以增加其吞吐量。 作者之前的工作表明，通过允许一些CL-MIMO链路相互干扰，换句话说，通过允许CL-MIMO链路的空分多址（SDMA），网络吞吐量可以增加高达70%。控制流的数量是解决这个问题的关键，因为使得MIMO链路能够承载如此高的数据速率的相同并行流特征也使得来自MIMO发射机的干扰对非预期接收机尤其降级。 这种复杂的天线技术需要在网络协议栈的不同层进行适当的开发。作者以前的工作表明，现有的多址接入控制（MAC）协议，如IEEE标准802.11的MAC，是无法达到最大吞吐量可能与SDMA和CL-MIMO链路。这个项目的主要目标是确定一个跨层的物理层/媒体接入控制的解决方案，为ad-hoc网络与MIMO链路。 “跨层”意味着在物理层和MAC层之间共享的信息量超过传统的信息量。 例如，接收机可以在PHY层估计它可以容忍多少更多的流（期望的或干扰的）而不被淹没。 然后，MAC协议可以使用该信息来允许或不允许在该区域中发送附加的同信道流。 具体的物理层研究活动包括研究（i）联合链路自适应过程的动态，包括分组的拥塞的影响和MAC协议施加的约束，（ii）发射机的各种学习机会以加速收敛，（iii）非线性接收机处理器算法如何影响流控制，（iv）现实信道模型，以及（v）备选联合优化算法。 此外，该项目中的MAC层研究活动集中在（i）制定具有CL-MIMO链路的ad-hoc网络中的介质访问控制问题，并确定关键优化考虑因素，（ii）设计和开发介质访问控制算法和方案，以帮助实现流控制的好处，解决目标环境中的缺点，结合关键优化考虑因素，并且在其操作中使用由PHY层提供的独特灵活性，（iii）将所得到的MAC协议成型为在实际的和可部署的协议框架内操作，以及（iv）通过原型实现来开发算法，

Ad-hoc wireless networks lack the infrastructure of traditional wireless networks; for example, they have no base stations or switching centers. Every node in an ad-hoc network can act as a forwarder or router to the other nodes. While ad-hoc networks were conceived primarily for military and emergency relief applications, more recently, such networks are finding applications in regular wireless packet data environments because they offer convenient deployment, improved coverage, reduced energy consumption, and higher network capacity than traditional infrastructure networks. Concurrent with the expansion of ad hoc network applications, multiple-input multiple-output (MIMO) links have drawn tremendous interest for the extremely high data rates they can support in the absence of interference. A MIMO link has multiple antennas at the transmitter and multiple antennas at the receiver. The multiple transmit antennas are used to transmit multiple parallel streams of data in the same channel; signal processing on the outputs of the multiple receiver antennas separates the parallel streams. In the presence of interference, closed-loop MIMO (CL-MIMO), which requires that the transmitter have channel state information (CSI), is known to significantly outperform open-loop MIMO, which does not use CSI. This project investigates how MIMO can be used in ad-hoc wireless networks to increase their throughput. Previous work by the authors has shown that network throughput can be increased by up to 70% by allowing some CL-MIMO links to interfere with each other, in other words, by allowing space-division multiple access (SDMA) for CL-MIMO links. Control of the number of streams is the key to this problem, because the same parallel stream feature that enables a MIMO link to carry such high data rates also makes interference coming from a MIMO transmitter especially degrading to an unintended receiver. Such sophisticated antenna technology necessitates appropriate developments at the different layers of the network protocol stack. Previous work by the authors has shown that existing multiple access control (MAC) protocols, such as the MAC for the IEEE Standard 802.11, are incapable of attaining the maximum throughputs possible with SDMA and CL-MIMO links. The main objective of this project is to determine a cross-layer physical-layer/medium-access-control solution for ad-hoc networks with MIMO links. "Cross-layer" means that more than the traditional amount of information is shared between the physical and MAC layers. For example, a receiver can estimate, at the PHY layer, how many more streams (either desired or interfering) it can tolerate without being overwhelmed. This information can then be used by the MAC protocol to allow or disallow additional co-channel streams to be transmitted in the area. Specific physical layer research activities include study of (i) the dynamics of the joint-link adaptive process, including the effects of asynchrony of packets and the constraints imposed by the MAC protocol, (ii) various learning opportunities for the transmitter in order to speed convergence, (iii) how nonlinear receiver processor algorithms effect stream control, (iv) realistic channel models, and (v) alternative joint optimization algorithms. Also, the MAC layer research activities in this project are focused on (i) formulation of the medium access control problem in ad-hoc networks with CL-MIMO links, and identification of the key optimization considerations, (ii) design and development of medium access control algorithms and schemes that help achieve the benefits of stream-control, address its drawbacks in the target environment, incorporate the key optimization considerations, and use the unique flexibility offered by the PHY layer in its operation, (iii) molding the resulting MAC protocol to operate within practical and deployable protocol frameworks, and (iv) the development of algorithms through a prototype implementation that