【作者】 王磊；

【导师】 仲伟志；

【作者基本信息】 南京航空航天大学 ， 通信与信息系统， 2020， 硕士

【摘要】 随着无人机业务的不断扩展,通信技术的不断进步,利用无人机搭载通信设备作为空中基站对目标区域进行波束覆盖受到越来越多研究者的关注。研究表明,利用混合波束成形的大规模阵列天线技术能够有效地缓解毫米波较高的传播损耗问题。但是传统的基站波束覆盖会遇到波束形状较窄,对目标区域覆盖不均匀,在区域边缘通信质量不佳等问题,另外,以往的混合波束预编码算法计算复杂度较高,在实际系统中往往需要较多的射频链,增加了系统的开销。针对这些问题,本文在不同场景下采用不同的混合波束预编码方法,提高系统通信容量和覆盖效果的同时,减少系统硬件的开销。本文的主要研究内容如下:(1)针对毫米波信道的稀疏特性,本文将理想混合预编码向量实现问题转化为稀疏矩阵的重构问题,并探究了正交匹配追踪算法、梯度追踪算法和基于动态字典学习的正交匹配追踪算法,然后在上述算法的基础上,提出了改进的梯度追踪算法,并采用该改进跟踪算法对理想预编码向量进行迭代运算。仿真表明,本文提出的改进GP算法的迭代效率和迭代时间综合性能最优。(2)针对单区域覆盖场景下波束覆盖不均匀这一问题,本文首先对覆盖区域进行分块量化,然后以区域内平均通信容量最大化为目标,利用基于二维傅里叶逆变换的改进方法对波束进行优化设计。仿真表明该方法能够有效地提高通信速率并且提升了通信边缘区域的覆盖效果。(3)针对多区域覆盖场景下系统复杂度较高这一问题,本文首先从多波束混合成形系统结构出发,分别对数字预编码器和射频移相预编码器进行设计,而后在移相器分辨率限制的条件下对预编码器进行优化设计。最后仿真实验表明,相较于传统方法,本文采用的波束优化设计方法能有效地减少射频链的使用,提高多波束通信速率总和的同时降低系统硬件开销和复杂度。更多还原

【Abstract】 With the continuous expansion of unmanned aerial vehicle business and the continuous progress of communication technology,the use of unmanned aerial vehicle equipped with communication equipment as air base stations to cover the target area with beams has attracted more and more researchers’ attention.Studies have shown that large-scale array antenna technology using hybrid beamforming can effectively alleviate the problem of higher propagation loss of millimeter waves.However,traditional base station beam coverage will encounter problems such as narrow beam shapes,uneven coverage of the target area,and poor communication quality at the edge of the area.In addition,the previous hybrid beam precoding algorithms have high computational complexity.In actual systems,more RF chains are often required,which increases system overhead.To address these issues,this article uses different hybrid beam precoding methods in different scenarios to improve system communication capacity and coverage while reducing system hardware overhead.The main research contents of this article are as follows:(1)In view of the sparse characteristics of millimeter-wave channels,this paper converts the realization of ideal mixed precoding vectors into reconstruction of sparse matrices,and explores orthogonal matching pursuit algorithms,gradient pursuit algorithms,and orthogonal matching pursuit algorithm based on dynamic dictionary learning,then based on the above algorithm,an improved gradient pursuit algorithm is proposed,and the improved pursuit algorithm is used to iteratively calculate the ideal precoding vector.Simulations show that the iterative efficiency and iteration time of the improved GP algorithm proposed in this paper are optimal.(2)In order to solve the problem of uneven beam coverage in a single-area coverage scenario,this article first quantizes the coverage area,and then aims to maximize the average communication capacity in the area,using an improvement based on the inverse two-dimensional Fourier transform methods optimize the beam design to get the actual beam.Simulations show that this method can effectively improve the communication rate and improve the coverage effect of the communication edge area.(3)In order to solve the problem of high system complexity in a multi-area coverage scenario,Based on the structure of the multi-beam hybrid forming system,this paper first designs digital precoders and RF phase-shifted precoders,and then optimizes the precoders under the condition that the phaser resolution is limited.Finally,simulation experiments show that compared with the traditional method,the beam optimization design method used in this paper can effectively reduce the use of the RF chain,improve the sum of multi-beam communication rates,and reduce system hardware overhead and complexity.更多还原