SWIFT-SAT: Unlimited Radio Interferometry: A Hardware-Algorithm Co-Design Approach to RAS-Satellite Coexistence

射电天文学改变了人们对宇宙的看法，为星系、恒星和其他宇宙事件的性质和行为提供了有价值的见解。射电天文学服务(RAS)的一项基本要求是获得没有来自其他来源的射频干扰(RFI)的频谱。RFI可以遮挡微弱的天文物体，产生虚假信号，降低射电望远镜的灵敏度，并导致严重的数据损失和带宽限制。传统上，RAS在与世隔绝的地区运作，利用周围的地形将其与人口稠密的地区隔离，或者在无线电静默区内对人类产生的RFI执行严格的规定。虽然这些措施在减轻地面射频干扰方面是有效的，例如电视台/无线电台、移动电话和WiFi网络，但它们无法保护RAS免受来自空间卫星的射频干扰。随着越来越多的巨型星座卫星被SpaceX等公司发射到太空，卫星RFI对RAS构成了严重威胁。一方面，卫星运营商必须合作，避免照亮地面RAS接收器，并将RFI降至最低。另一方面，民航处将必须加强其在强大的、不可避免的RFI中运作的能力。通过利用一种新颖的模抽样方法，该项目旨在开发尖端电路设计和信号处理算法，以增强射电望远镜对抗RFI的弹性。它在优化RAS数据的收集和处理方面具有巨大的潜力，同时也促进了无线电频谱中卫星通信和科学研究的共存。该项目的主要目标是在存在地理上无法避免的卫星发射机产生的强烈射频干扰的情况下，加强射电天文服务的业务能力。要对RAS系统进行电子化保护，关键的一步是确保RAS接收机的线性度。接收器中的非线性或饱和会产生互调产物，可能会抹去整个观测频段。使用高动态范围(HDR)低噪声放大器和用于放大和数字化的高分辨率模数转换器(ADC)等传统技术来增强RAS接收器的线性度是昂贵的。这是因为这样的增强可能导致RAS数据的雪崩，而RAS数据以其非常大的大而闻名。所提出的研究采用基于模抽样的方法来对射频干扰进行稳健的无线电干涉测量。具体地说，模数采样在使用常规分辨率ADC进行采样之前将超出范围的输入信号折叠到动态范围内。这允许从低动态范围(LDR)测量中恢复HDR信息。在模抽样方法的基础上，拟议的研究包括三个方面：(1)稳健和超分辨率无线电干涉测量的信号处理框架，使接收器能够在不受固定动态范围限制的情况下运行；(2)可扩展的模数ADC设计，用于在RFI存在的情况下展示无限的干涉能力；以及(3)结合模数ADC进行全面测试和评估的实验。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Radio astronomy has transformed the perception of the universe, providing valuable insights into the properties and behaviors of galaxies, stars, and other cosmic events. An essential requirement of radio astronomy service (RAS) is access to a spectrum devoid of radio frequency interference (RFI) from other sources. RFI can obscure faint astronomical objects, create false signals, reduce the sensitivity of radio telescopes, and lead to significant loss of data and bandwidth limitation. Traditionally, RAS operates in secluded regions, using the surrounding terrain to shield it from populated areas, or inside a radio quiet zone that enforces strict regulations on human-generated RFI. While these measures are effective in mitigating terrestrial RFI, such as TV/radio stations, mobile phones, and WiFi networks, they are unable to protect RAS against RFI originating from satellites in space. With an increasing number of mega-constellation satellites being launched into space by companies like SpaceX, satellite RFI presents a grave threat to RAS. On the one hand, it is imperative for satellite operators to cooperate, avoiding illuminating ground RAS receivers and minimizing the RFI. On the other, the RAS will have to strengthen its ability to operate amidst strong unavoidable RFI. By leveraging a novel modulo sampling approach, this project aims to develop cutting-edge circuit designs and signal processing algorithms that will bolster the resilience of radio telescopes against RFI. It holds great potential for optimizing the collection and processing of RAS data, while also fostering the coexistence of satellite communications and scientific research in the radio spectrum. The primary goal of this project is to enhance the operational capabilities of radio astronomy service (RAS) in the presence of strong radio frequency interference (RFI) arising from satellite transmitters that cannot be avoided geographically. To protect RAS systems electronically, a crucial step is to ensure the linearity of RAS receivers. Nonlinearity or saturation in receivers generates intermodulation products that can wipe out the entire observing band. It is costly to use conventional technologies, e.g., high-dynamic range (HDR) low-noise amplifiers and high-resolution analog-to-digital converters (ADCs) for amplification and digitization, to enhance the linearity of RAS receivers. This is because such enhancements can result in an avalanche of RAS data, which is known for its very large size. The proposed research takes a modulo sampling-based approach to operate radio interferometry robustly against RFI. Specifically, modulo sampling folds the out-of-range input signal to within the dynamic range before taking samples using a regular-resolution ADC. This allows the recovery of HDR information from low-dynamic range (LDR) measurements. Building on the modulo sampling approach, the proposed research encompasses three thrusts: (1) a signal processing framework for robust and super-resolution radio interferometry, which enables the receiver to operate without being limited by a fixed dynamic range; (2) scalable modulo ADC design for demonstration of unlimited interferometry capability in the presence of RFI; and (3) experimentation incorporating the modulo ADCs for comprehensive testing and evaluation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.