【作者】 崔苗；

【导师】 尹俊勋；

【作者基本信息】 华南理工大学 ， 电路与系统， 2009， 博士

【摘要】 战术通信环境是移动Ad Hoc网络的一种很重要的应用场景。未来战争的形式以网络化、信息化为主。网络化使通信系统的规模迅速扩大,节点之间传输的信息量也飞速增长,使其对带宽的需求及宽带的重要性提到了一个新的高度。移动Ad Hoc网络是一个复杂的系统,所涉及的研究内容非常广泛,目前仍存在一些需要彻底研究的问题,而新的应用也对它的研究和发展不断提出新的挑战。这些问题影响到网络设计的各个方面,比如物理层、MAC层、网络层、QoS管理、网络安全等。本文主要在其物理层的OFDM技术、MAC层的多址接入技术和支持有向天线的MAC技术等方面进行了研究,并取得了以下一些研究成果:1)在分析了无线移动战术信道和OFDM系统关键技术基础上,设计宽带OFDM通信系统,提出了一种自适应频域迭代信道估计算法,这种迭代方法准确估计了每个OFDM符号经历的快速变换的信道状态,相比其他方法,所提方案能够解决系统对抗信道快速时变特性面临的问题,并达到降低运算复杂度和提高频谱效率的目的。考虑到战术通信特点以及系统硬件平台的可行性,又提出简单可行的同步和峰均比降低方案。OFDM系统的编码调制、信道估计、同步技术、峰均比抑制等关键技术的仿真结果均表明本文提出的算法较好的解决了快速时变信道下OFDM系统面临的关键难点。最后通过硬件验证平台检测结果来看,所采用的技术和算法在多径快速时变信道环境下都是可行的。2)在SUI信道以及ITU信道基础上,研究自适应MIMO-OFDM系统在战术通信环境下的性能。分别就不同地形环境下的系统性能、天线相关性对系统容量的影响以及一定频谱利用率下系统的性能进行了仿真。静止状态下仿真结果表明:在能提供更多分集增益的地形中,其系统误码性能较好;在有较多障碍物的地形中,其系统容量与误码性能较好。仿真说明了天线相关性对系统容量的影响,仿真又给出了一定频谱利用率条件下系统误码性能。3)对IEEE 802.11DCF接入方式进行了深入的研究。提出了针对退避时间服从指数分布的BEEB算法,并将采用BEEB算法的节点称为积极节点。同标准的IEEE 802.11协议BEB算法相比,BEEB算法保持了原有算法的简单性、无开销性、完全分布性。理论分析和仿真结果表明:BEEB算法能够减少信道空闲等待时间,缩短信道接入时间,在加速信道竞争的过程中,减少数据包重传次数和网络时延,在提高网络吞吐量和信道利用率具有很明显的优势。4)分析了支持有向天线应用的Ad Hoc网络特点及MAC层所面临的问题,如队列头阻塞(Head of Line Blocking,HOL)问题、隐藏及暴露终端等问题。提出了一种基于有向网络分配矢量包调度的多址接入协议(Directional Network Allocation Vector-based Packets Scheduling for MAC Protocol,DBPS)。协议充分考虑到有向天线应用中存在的隐藏终端问题和队列头阻塞问题,利用DNAV作为包调度的策略,划分节点周边区域,剔除不可用区域,在可用区域范围内选择理想的目的数据包进行发送。仿真结果证明,DBPS协议能有效支持有向天线在移动Ad Hoc网络中的应用,具有较高的信道利用率,且降低了节点的接入时延和控制分组的碰撞概率,较好地解决HOL问题。5)在第五章研究基础上,采用了波束标记、计时器等措施对其路由发现和路由维护机制进行了优化,设计了EDRP协议。考虑到负载平衡和网络生存寿命因素,采用延迟转发路由请求分组的策略,使获取的路由是负载最轻的路径,提出了支持有向天线应用的战术移动Ad Hoc网络有向负载均衡路由协议LEDRP。LEDRP协议在路由发现过程中充分使用了源和目的节点间的总路径信息,可以使路由请求分组在最短时间内到达目的节点,选择一条负载最轻的路径,从而以最快速度将数据分组发送出去,协议采用了局部路由维护机制,能快速修复因节点移动而导致的链路断路,因而能更好的适应拓扑结构的快速变化。仿真结果表明,LEDRP协议充分发挥了有向天线的特性,同时路径选择时利用了源和目的节点间总路径信息,综合考虑路径跳数、节点负载和中间节点的负载等因素,避免负载过重的节点被选择到路径中,使网络中的业务均衡分配,提高网络的性能特别是当网络很拥塞时,性能更优越。虽然LEDRP协议在负载较轻时的延时会有所增加,但相对于在网络开销和分组发送成功率的提高,且这种轻微的时延增加是可以接受的。更多还原

【Abstract】 Tactical communication is one of the most primary application backgrounds for Mobile Ad Hoc Networks. Future war is composed mainly of Networks and Information, which rapidly expand scale of communication system and information transmitted between nodes. High bandwidth is useful because it supports increased capacity, high volume data exchange, short delays, and high assurance of connectivity. Bandwidth has become increasingly critical.Mobile Ad Hoc Networks is a complex system and the research work in this dissertation carries a deep study on new techniques of Mobile Ad Hoc Networks that will continue to increase available bandwidth. There are still some key technologies need to be solved to make the MANET’s work efficiently, all of the above problems are reflected in the following aspects in network designing, including physical layer, Media Access Control (MAC) layer, network layer, application layer, QoS management, network security, etc. In this dissertation, we focus mostly on the OFDM technology in physical layer, scheduling technology and directional antenna in MAC layer, and the main contributions are listed as the following:1)A full OFDM system, based on the study of wireless tactical channel and key technology of OFDM, is designed and realized. The paper Propose improved channel estimation and tracking algorithm for tactical OFDM system in frequency domain. The results of both theoretical analysis and simulation show that the proposed algorithm possesses all impressive performance with less system overhead and lower computation burden than conventional algorithms.Considered the characteristic of tactical communication and the feasibility of system hardware, the paper proposes synchronization and PAPR reduction scheme with low complexity. Simulation including code and modulation, channel estimation, synchronization and PAPR show that all of the schemes are well solved the difficulties. The hardware platform demonstrates that the proposed method performs well at typical mid-wave and short-wave broadcasting channel and it is easy to implement.2) Based on SUI channel and ITU channel model, the paper studies the performance of adaptive MIMO-OFDM system under tactical communication environment. The simulations include system performance under different terrain, influence of antenna correlation on system capacity and system performance under spectrum efficiency. Simulation results under static state show that the bit error performance of system which provides more diversity gain is much better. And the performance of system under complex terrain is much better.3) To improve the channel throughput of IEEE 802.11 protocol with the Binary Exponential Back-off algorithm (BEB), we propose a novel BEEB algorithm (Binary Exponential Exponential Backoff),which the Back-off time obeys the exponential distribution and the idea of active nodes. BEEB algorithm has the following characteristics: simplicity, integrability, complete distribution. The BEEB algorithm can effectively improve the default that nodes choose long defer time and access the channel slowly, and can shorten the idle time and decrease the time to acquire the channel by accelerating the collision process. Results show that the BEEB algorithm can decrease the collision times, provide higher channel utilization and a lower network load compared with IEEE 802.11 DCF protocols.4) For directional antennas application in Mobile Ad Hoc Networks, a novel Directional Network Allocation Vector-based Packets Scheduling (DBPS) algorithm is proposed. The algorithm divides the surrounding region of the node using the DNAV parameters, and secondly eliminates the region that is not available, and lastly chooses the ideal destination node to send the packet. The DBPS scheme can enable a higher throughput while effectively solving the HOL blocking problem. The computer simulation and performance analysis give farther proof that the DBPS algorithm is effective and reasonable.5) Based on the Chapter 5, the article designed the EDRP routing protocol, which is support the directional antenna. The direction of antenna for mobile Ad Hoc networks generated velocity switch, radio, overhead and other issues, using the beam mark, timer, and improved routing maintenance to reduce the impact of such means. At the same time, the paper takes into account not only the direction of the antenna, but also taking into account the mobile Ad Hoc networks are two important factors-the survival of life of the network and network load balancing, and improve the routing strategies of the EDRP protocol, and the use of a delay in forwarding the request routing strategy, and give the direction of an antenna in support of the load-aware mobile Ad Hoc network routing protocol (LEDSR). LEDSR protocol considers total path information between source node and destination node as the primary route selection metric while discovering and maintaining route, the network load is balanced by avoiding the congestion path.更多还原