On-Board Multi-Core Fault-Tolerant SAR Imaging Architecture Helena Cruz helena.cruz@tecnico.ulisboa.pt Instituto Superior T ´ ecnico, Universidade de Lisboa November 2018 Abstract Nowadays, there is an increasing need for satellites, drones and UAVs to have lightweight, small, au- tonomous, portable, battery-powered systems able to generate SAR images on-board and broadcasting them to Earth, avoiding the time-consuming processing data at the receivers. SAR is a form of radar used to generate images of Earth, mounted on moving platforms, such as satellites, drones or airplanes and is used to monitor the surface of the Earth for geology, agriculture, oceanography, glaciology, forestry and natural disasters. Backprojection is an algorithm for SAR image generation capable of generating high quality images, however, it is one of the most computationally intensive. Space is a harsh environment, due to the radiation, which causes temporary or permanent errors on computing systems, thus, there is a need to mitigate its impact on the devices implementing fault tolerance mechanisms to detect and correct errors. In this research work, an on-board multi-core embedded architecture was developed for SAR imaging systems, implementing two fault tolerance mechanisms: lockstep and reduced-precision redundancy. This architecture aims to protect the Backprojection algorithm, using a software-only ap- proach, generating acceptable SAR images in a space environment. The solution was implemented on a Xilinx SoC device with a dual-core processor. For error rates similar to the ones measured in a space environment, the present work produced images with less 0.65dB on average at the expense of a time overhead up to 33%. Notwithstanding, the Backprojection algorithm executed up to 1.58 times faster than its single-core version algorithm, without fault tolerance mechanisms. Keywords: Synthetic-Aperture Radar (SAR), Backprojection Algorithm, Multi-Core Fault Tolerance, Software Fault Tolerance 1. Introduction Space is a harsh environment for electronic com- ponents used in circuits and systems. Therefore, systems designed for spacecrafts or satellites must be highly reliable and be able to tolerate the levels of radiation present in space. The main sources of radiation in space are high-energy cosmic ray protons and heavy ions, protons and heavy ions from solar flares, heavy ions trapped in the mag- netosphere and protons and electrons trapped in the Van Allen belts [3]. These are capable of dete- riorating the electronic systems and provoking bit- flips, leading to failures in electronic systems [15]. Fault tolerance mechanisms are used to increase the reliability of these systems. Synthetic-Aperture Radar (SAR) is a form of radar which is usually mounted on moving plat- forms such as satellites, aircrafts and drones and is used to generate 2D and 3D images of Earth. SAR operates through clouds, smoke and rain and does not require a light source, making it a very at- tractive method to monitor the Earth, in particular, the melting of polar ice-caps, sea level rise, wind patterns, erosion, drought prediction, precipitation, landslide areas, oilspills, deforestation, fires, natu- ral disasters such as hurricanes, volcano eruptions and earthquakes. There is a need for satellites, drones and Unmanned Aerial Vehicles (UAVs) to have a lightweight, small, autonomous, portable, battery-powered system able to generate SAR im- ages on-board and broadcasting them to Earth, avoiding processing data on the receivers. This paper describes an architecture for SAR imaging capable of tolerating faults resulting from radiation in a space environment. This architecture uses the Backprojection Algorithm to generate im- ages and is implemented and tested on a System- on-Chip (SoC) device [21]. 2. Background This section introduces SAR, the Backprojection algorithm and fault tolerance mechanisms. 2.1. Synthetic-Aperture Radar (SAR) Synthetic-Aperture Radar is a form of radar used to generate 2D and 3D high resolution images of 1