Collaborative Research: Wideband Multi-Beam Antenna Arrays: Low-Complexity Algorithms and Analog-CMOS Implementations

联邦通信委员会认识到无线行业需要探索28-95 GHz毫米波（mm波）频带，其中更宽的带宽可用，并且未来的分配可能达到100 GHz以上。毫米波带宽的爆炸式增长为5G无线系统开辟了应用，涵盖通信、定位、成像和雷达。该项目解决了在毫米波频率下产生多个并行无线电“波束”的基本科学和工程挑战。无线电波束是指一种定向信道，它为无线通信和遥感建立点对点联系。形成大量高带宽无线电波束的能力将极大地提高下一代无线系统的性能。例如，多波束对于实现无线应用爆炸性增长所需的容量、数据速率和地理渗透的数量级增加至关重要。此外，它们对于发射器和接收器都很重要。 该项目将利用空间傅里叶变换和薄光学透镜之间的类比来获得多个宽带光束。与文献中基于透镜天线的方法不同，该项目将使用平面孔径天线与模拟集成电路结合，以产生许多受功率和尺寸限制的宽带毫米波波束。所提出的高度集成的方法对于包括5G智能设备、物联网、移动的机器人和无人驾驶飞行器的移动的应用以及专注于毫米波的其他新兴应用具有吸引力。除了科学研究外，该项目还将确保少数民族学生和女生都能得到数学、通信以及微波电路和系统方面的职业指导。将为教学阵列信号处理、微波集成电路（IC）设计和超高速模拟信号处理开发教育材料。首席研究员（PI）Madanayake和Mandal将组织一个小型会议，以加强俄亥俄州东北部附近大学的微波和毫米波研究活动。PI Madanayake将与co-PI合作，指导代表性不足的学生从事科学，技术，工程和数学（STEM）职业。 提案团队在促进跨越电气工程和数学领域的STEM主题方面具有独特的地位。该项目将导致教育更广泛的社会对跨学科合作的重要性。此外，该团队将努力展示学习更深入的数学主题对技术和工程事业成功的重要性。由于其信号流图的潜在复杂性，多波束阵列接收器很难以IC形式实现。在这项工作中，数学方法的基础上的理论，i）稀疏分解的结构复杂的矩阵，和ii）近似变换提出了解决这个问题。由此产生的矩阵实现多GHz带宽使用模拟IC。其中的智力贡献是有效的宽带波束形成器的延迟范德蒙矩阵（DVM）的稀疏分解的基础上的发展。该DVM算法解决了长期存在的“波束偏斜”问题，即，波束方向随输入频率而改变，使得真正的宽带操作不可能。另一个是推导具有特定性质的近似离散傅立叶变换（DFT）的变换矩阵。这种近似变换不受精确DFT的已知计算复杂度界限的影响，并且基于近似DFT的多波束形成器实际上可以使用电流模式模拟IC来有效地实现。最后，精密电路设计，数字校准，内置自测试，和其他方法将探索有效地实现模拟IC形式的多波束形成网络。

The Federal Communications Commission recognizes the need for the wireless industry to explore the 28-95 GHz millimeter-wave (mm-wave) bands where wider bandwidth is available, and future allocations may reach above 100 GHz. This explosion of mm-wave bandwidth opens up applications in 5G wireless systems spanning communications, localization, imaging, and radar. This project addresses fundamental scientific and engineering challenges in generating multiple parallel radio "beams" at mm-wave frequencies. A radio beam refers to a directional channel that establishes point-to-point contact for wireless communications and remote sensing. The ability to form a large number of such radio beams with high bandwidths will tremendously improve the performance for next-generation wireless systems. For example, multiple beams are essential for achieving the orders-of-magnitude increases in capacity, data rate, and geographical penetration required by the explosive growth in wireless applications. Moreover, they are important for both transmitters and receivers. The project will draw on an analogy between the spatial Fourier transform and a thin optical lens to obtain multiple wideband beams. Unlike lens-antenna-based approaches in the literature, this project will use a planar aperture antenna in conjunction with analog integrated circuits to generate many wideband mm-wave beams subject to power and size constraints. The proposed highly integrated approach is attractive for mobile applications including 5G smart devices, the internet of things, mobile robotics, and unmanned aerial vehicles, and other emerging applications focused on mm-waves. In addition to scientific research, the project will ensure that both minority students and female students will be mentored towards careers in mathematics, communications, as well as microwave circuits and systems. Educational materials will be developed for teaching array signal processing, microwave integrated circuit (IC) design, and ultra-high-speed analog signal processing. Principal Investigators (PIs) Madanayake and Mandal will organize a mini-conference to enhance microwave and mm-wave research activities at nearby universities in northeast Ohio. PI Madanayake will collaborate with co-PIs towards mentoring underrepresented students towards careers in Science, Technology, Engineering, and Math (STEM). The proposal team is uniquely placed to promote STEM topics spanning both electrical engineering and mathematics domains. The project will lead to education of the wider community on the importance of cross-disciplinary collaboration. Further, the team will strive to show the importance of learning deeper math topics towards success in technology and engineering careers.A multi-beam array receiver is deeply difficult to realize in IC form due to the underlying complexity of its signal flow graph. In this work, mathematical methods based on the theories of i) sparse factorization of structured complex matrices, and ii) approximate transforms are proposed to solve this problem. The resulting matrices are realized with multi-GHz bandwidths using analog ICs. One of the intellectual contributions is the development of efficient wideband beamformers based on sparse factorizations of delay Vandermonde matrices (DVM). This DVM algorithm solves the longstanding "beam squint" problem, i.e., the fact that the beam direction changes with input frequency, making true wideband operation impossible. Another is the derivation of transform matrices with specified properties that approximate the discrete Fourier transform (DFT). Such approximate transforms are not subjected to the known computational complexity bounds of the exact DFT, and approximate-DFT-based multi-beamformers can in fact be efficiently implemented using current-mode analog ICs. Finally, precision circuit design, digital calibration, built-in self-test, and other methods will be explored for efficiently realizing the proposed multi-beamforming networks in analog IC form.