【作者】 李旭；

【导师】 卫国；

【作者基本信息】 中国科学技术大学 ， 信息与通信工程， 2015， 博士

【摘要】 在有蜂窝网覆盖,但是无法满足骤然增加的通信需求的场所,如大型集会场所等；在没有蜂窝网覆盖,但是存在通信需求的场所,如存在通信需求的地下环境或者偏远地区等；在蜂窝网基础设施被摧毁,但是存在通信需求的场所,如地震或者海啸的灾后现场等,应急通信系统综合利用各种通信资源,提供暂时性的无线覆盖和满足需要的通信手段。本文针对实际的应用场景,讨论基于中继网络的应急通信系统,研究中继网络部署相关问题。将中继节点部署在最优位置最优化系统性能,或者在系统性能约束下部署最少的中继节点以降低系统成本。主要的研究内容和贡献如下：针对矿难或者隧道事故等应用场景,采用沿途部署便携式中继节点的方式建立一维中继网络。本文系统地研究了收发端距离已知时,最优的中继部署与资源配置最小化中断概率或者最大化传输速率。收发端距离未知时,中断概率或者传输速率约束下,最优的中继部署与资源配置最大化传输距离。当中断概率作为系统性能指标时,只需要优化中继部署,优化问题为凸问题。采用凸优化理论可以得到全局最优解。当传输速率作为系统性能指标时,需要联合优化中继部署与资源配置,优化问题为非凸问题。分析了链路分配总资源与链路距离一阶导数的非负性质和凸性质,并利用这些性质设计低复杂度的求解算法,可以得到全局最优解。针对火灾或者抓捕等应用场景,采用部署基站和移动中继节点的方式建立二维移动中继网络。本文系统地研究了最优的基站部署、中继部署与资源配置问题。在基站部署方面,最优的基站部署最大化目标区域内的最小信噪比。基站可以部署在目标区域内外的任意位置时的优化问题为凸问题。基站只能够部署在目标区域边上或者外面时的优化问题为非凸问题。对于两个优化问题,采用几何分析的方法,给出低复杂度的求解算法,得到全局最优解。在中继部署与资源配置方面,最优的中继部署与资源配置最小化所有用户中的最大中断概率,或者最大化所有用户中的最小传输速率。当中断概率作为系统性能指标时,只需要优化中继部署。优化问题为非凸问题。采用低复杂度的贪婪算法获得次优解,并与穷搜索算法得到的全局最优解进行比较。通过仿真可得两者的所有用户中的最大中断概率基本重合。当传输速率作为为系统性能指标时,需要联合优化中继部署与资源配置。优化问题为非凸问题。由于每个用户只会选择资源效率最高的一条链路。集中式算法遍历用户的链路选择,得到全局最优解,复杂度较高。分布式算法基于用户分类,交替迭代得到次优解,复杂度较低。通过仿真可得两者的所有用户中的最小传输速率基本重合。针对地震或者海啸等应用场景,采用部署基站和随机中继节点的方式建立二维随机中继网络。针对中继部署的随机性、位置不可控的特征,本文系统地研究了中继密度和路径选择问题。在中继密度方面,用户与最近的中继节点通信。采用随机几何工具分析用户成功发送一个数据包至最近的中继节点,和用户从最近的中继节点成功接收一个数据包的时延。并进一步分析不同的调制编码方式对时延的影响。在给定时延需求的情况下,给出低复杂度的求解算法得到最小的中继密度。在路径选择方面,为每个中继节点与基站间建立中继链路。考虑实时业务,时延较大的数据包不具有实际价值。在限制每跳链路的重传次数上界的情况下,分析每个设备的最优发送功率,端到端成功传输一个数据包的能耗与剩余能量的比值。然后根据网络特点,以最小化能耗与剩余能量的比值为准则,改进OLSR协议,采用Dijkstra算法,实现分布式且低复杂度的路径选择。更多还原

【Abstract】 Even with today’s seemingly ubiquitous wireless access, the cellular networks may not be sufficient to support the elevated traffic at incident or disaster areas. Many areas and corners are not fully covered by cellular networks, such as the basement level of large buildings and remote unpopulated areas. The existing cellular infrastructure may also be knocked out of service for periods of times in areas hit by disasters. This is a great threaten to the public safety, and a Public Safety Broadband Networks should be established to provide temporary wireless coverage for saving life and property.This dissertation takes relays as a means of establishing the Public Safety Broad-band Networks. Models, analytical results, and algorithms are proposed to study the optimal relays deployment problem, where the relays are deployed at the optimal place for optimizing the quality of service (QoS) or minimizing the number of relays subject to the QoS requirement. The main results are summarized as follows:For the scenes of mine and tunnel accidents, it is proposed that relays are deployed to establish a one-dimensional relays networks. With the location information of the base station and the user, the optimal relays deployment and resources allocation opti-mizes the QoS. Without the location information of the base station and the user, the optimal relays deployment and resources allocation maximizes the reach of the cover-age subject to the QoS requirement. When the QoS metric is the outage probability, only the relays deployment should be optimized. The optimization problems are con-vex, which could be efficiently solved by convex optimization theory. When the QoS metric is the data rate, the relays deployment and resources should be jointly optimized. The optimization problems are non-convex. After analyzing the resources allocated to each hop with respect to the hop distance, an efficient algorithm is proposed to solve the optimization problems. The proposed algorithms achieves the global optimal solutions with low complexity.For the scenes of fire accident and arrest event, it is proposed that a base station and multiple mobile relays are placed to establish a two-dimensional mobile relays net-works. The optimal base station deployment maximizes the minimum signal-to-noise-ratio (SNR) over the target area. Without placement restriction, the base station could be deployed anywhere, where the optimization problem is convex. With placement restriction, the base station could be deployed on the boundary or outside the target area, where the optimization problem is non-convex. Based on geometric analysis, ef-ficient algorithms are proposed to compute the global optimal solutions. The optimal relays deployment and resources allocation minimizes the maximum outage probabil-ity or maximizes the minimum data rate of multiple users. When the QoS metric is the outage probability, only the relays deployment should be optimized. The optimization problem is non-convex. A greedy algorithm is proposed to compute one local optimal solutions, whose system performance almost overlaps that of the global optimal solu-tions obtained by exhaustive searching method. And the complexity of the proposed greedy algorithm is much lower than that of the exhaustive searching method. When the QoS metric is the data rate, the relays deployment and resources should be jointly optimized. The optimization problem is non-convex. Each user will only choose the link with the highest resource efficiency. A centralized algorithm is proposed, which traverses the link selections to obtain the global optimal solutions. Another distributed algorithm is proposed based on users classification, which obtain one local optimal so-lutions. The system performance of the two proposed algorithms are almost the same, but the complexity of the distributed algorithm is much lower than that of the centralized one.For the scenes of earthquake and tsunami disasters, it is proposed that a base station and multiple randomly distributed relays are deployed to establish a two-dimensional randomly distributed relays networks. Relays and users are randomly distributed. The minimum number of relays is studied to minimize the system cost subject to the rescue delay requirement. The rescue delay is defined as the delay for the typical user transmit-ting or receiving one packet to or from its nearest relay. Stochastic geometry is utilized to analyze the rescue delay, while taking the modulation and coding schemes into con-sideration. The routing scheme is studied to establish the relay links between the base station and each relay. With the limitation of retransmission count of each hop, the op-timal routing optimizes the transmit power of each hop and minimizes the end-to-end energy consumption to energy residual ratio. Advanced optimized link state routing (OLSR) protocol is proposed and Dijkstra algorithm is utilized to select the optimal routing, which reduces the system complexity.All the proposed models, analytical results, and algorithms are the significant guid-ance to the design of relays assisted Public Safety Broadband Networks.更多还原