Fault Tolerant FPGAs:where to spend the effort?

\u3cp\u3eStatic Random-Access Memory-based (SRAM-based) Field-Programmable Gate Arrays (FPGAs) are widely used in reallife applications, such as autonomous driving, high tech systems, and in space, where high dependability is a mandatory requirement. Since FPGA designs are stored in the Configuration Memory (CM) in SRAM-based FPGAs, they are very sensitive to Single Event Upsets (SEUs). Thus, adapting FPGA designs to make them more Fault Tolerant (FT) is extremely important. FT techniques introduce additional penalties in system parameters, like area, power consumption and performance. In order to tradeoff between the overhead introduced by FT techniques and system robustness, an accurate estimation of CM vulnerability to SEUs is needed. Many intrinsic error tolerant applications can tolerate in-exact output values to some degree. This paper shows how to exploit this property in making much cheaper FT FPGA designs with less overhead. For instance, our method can remove 51% of the area overhead for less than 0.048% output degradation, when considering a 32-bit FT adder FPGA design by applying Triple Modular Redundancy. We verify our results on various FPGA designs using a ZedBoard.\u3c/p\u3

Scatter scrubbing:a method to reduce SEU repair time in FPGA configuration memory

\u3cp\u3eSRAM-based FPGAs are widely used in many critical systems in which dependability is an essential factor. However, SRAM-based FPGAs are sensitive to Single Event Upsets (SEUs), especially when they are used in space. Scrubbing is an effective technique to protect FPGA Configuration Memory (CM) against SEUs. One major hurdle in read-back scrubbing techniques is that they suffer from long Mean Time To Repair (MTTR). In this paper, we propose scatter scrubbing, a new method that reduces MTTR by exploiting the locality of SEUs sensitive bits in CM. It is based on 1) splitting FPGA CM into several partitions based on how critical the CM bits are for proper operation of the FPGA circuit, and 2) deriving a smart schedule for scrubbing the partitions. Finding an optimal partition and scheduling has non-polynomial complexity; therefore we rely on clever heuristics, especially for the first step. However, for small designs, we developed an accelerated brute-force method giving the optimal solution, which we can use as a reference. The experimental results show, for real FPGA designs, up to 64% reduction in MTTR compared to state-of-the-art techniques.\u3c/p\u3

Determining the necessity of fault tolerance techniques in FPGA devices for space missions

\u3cp\u3eFunctionality of electronic components in space is strongly influenced by the impact of radiation induced errors which may interfere with the proper operation of the equipment. In space missions, FPGA implementations are generally protected using computationally expensive radiation-error mitigation techniques such as error co rrecting codes (ECC) and triple modular redundancy (TMR). For high-performance systems, such fault tolerance techniques can prove problematic due to both the added computational requirements and their resulting power overhead. As such it is important to make a proper assessment of the expected error rates to make a proper selection of mitigation techniques. This paper provides an extensive overview of the techniques used for determining the necessity of such mitigation techniques in space missions and other situations where a large radiation dose will be encountered. Given the presented study and radiation analysis, in this paper an experimental example is presented in the form of a case study on the Digital Receiver System (DRS) in the Netherlands–China Low-frequency Explorer (NCLE) mission, which is implemented using a Xilinx Kintex-7 SRAM FPGA. Fault rates are estimated for a five-year mission to the second Earth-Moon Lagrange point (L2) and the chosen fault mitigation strategy as implemented in NCLE–DRS is presented. The effect of potential upsets on the functionality of DRS has been taken into account in order to make error estimations more precise. Thus, two test-benches are developed and presented to experimentally evaluate the effect of upsets in FPGA configuration memory and the data on the DRS final outputs. The approach provided in this paper should generalize well to other space missions, as long as a general estimate of the expected radiation environment is available.\u3c/p\u3

A generic methodology to compute design sensitivity to SEU in SRAM-Based FPGA

\u3cp\u3eRecently, SRAM-based FPGAs are widely used in aeronautic and space systems. As the adverse effects of radiations in space are much higher than in the Earth, developing fault tolerant techniques play crucial roles for the use of electronics in space. However, fault tolerance techniques might introduce additional penalties in area, power, performance and design time. In order to compromise between the overhead introduced by these techniques and system fault tolerance, a generic methodology for calculating design sensitivity to Single-Event Upset (SEU) is proposed in this paper. Separate schema and test-bench for evaluating effects of SEU in various types of FPGA memory are proposed in which both the raw device error rate and the vulnerability characteristic of the specific application mapped on the device are taken into account. Experimental results show that using our model in order to selectively add Triple Modular Redundancy (TMR) improve the design robustness only 18% less than full TMR while roughly introduces 69% less redundancy compared to full TMR for Fast Fourier Transform (FFT).\u3c/p\u3

Optimized multiobjective H∞ control applied to inverted pendulum

\u3cp\u3eThis paper introduces several practical aspects of designing multiobjective problems such as H∞ controllers. We present a procedure to obtain a controller with two degree of freedom (DOF). First we stabilize the nominal system by a conventional controller like LQR. We use genetic algorithm to optimize LQR controller, too. This part of our controller leads to low cost of control input effort, and then we enforce other objectives in the framework of LMI optimization. This procedure leads to less energy consumption in comparison with using LMI methods alone. We design and implement this approach in an inverted pendulum as one of the most commonly nonlinear studied systems in the control area and can be considered as a benchmark for evaluating controlling methodologies.\u3c/p\u3

Basic radio interferometry for future lunar missions

\u3cp\u3eIn light of presently considered lunar missions, we investigate the feasibility of the basic radio interferometry (RIF) for lunar missions. We discuss the deployment of two-element radio interferometer on the Moon surface. With the first antenna element is envisaged to be placed on the lunar lander, the second antenna element is either ejected from the lander onto the lunar surface or is placed on a rover. Such an experiment will examine the radio communication on the Moon surface and will test the basic RIF requirements such as phase stability in the lunar environment. This is a necessary step for development of future large arrays on the Moon. In addition, this first ever in-situ lunar RIF would provide a unique degree-resolution of a radio sky map at lower frequencies, which are not accessible from the Earth. The expected results such as the spectral flux density and the spatial resolution of the radio sky map will be presented for lunar lander-rover experiment. As an extended scenario, the RIF using the multiple antennas onboard the lunar/(Earth's) orbiter satellites are introduced.\u3c/p\u3

Antenna design and implementation for the future space Ultra-Long wavelength radio telescope

\u3cp\u3eIn radio astronomy, the Ultra-Long Wavelengths (ULW) regime of longer than 10 m (frequencies below 30 MHz), remains the last virtually unexplored window of the celestial electromagnetic spectrum. The strength of the science case for extending radio astronomy into the ULW window is growing. However, the opaqueness of the Earth’s ionosphere makes ULW observations by ground-based facilities practically impossible. Furthermore, the ULW spectrum is full of anthropogenic radio frequency interference (RFI). The only radical solution for both problems is in placing an ULW astronomy facility in space. We present a concept of a key element of a space-borne ULW array facility, an antenna that addresses radio astronomical specifications. A tripole–type antenna and amplifier are analysed as a solution for ULW implementation. A receiver system with a low power dissipation is discussed as well. The active antenna is optimized to operate at the noise level defined by the celestial emission in the frequency band 1 − 30 MHz. Field experiments with a prototype tripole antenna enabled estimates of the system noise temperature. They indicated that the proposed concept meets the requirements of a space-borne ULW array facility.\u3c/p\u3

REXUS-25 rocket flight of a CubeSat cosmic-ray detector

\u3cp\u3eIn recent years CubeSats have been revolutionizing research in space, enabling low-budget, small-scale, and fast-development of projects. The Rocket Experiments for University Students (REXUS) program provides students from higher education opportunities to perform their scientific and technological experiments on a sounding rocket launching to space. A compact cosmic-ray detector, build to CubeSat specifications, has been designed to detect light produced in a scintillating material when cosmic rays pass through. At only 1 dm \u3csup\u3e3\u3c/sup\u3e in size and operating on only 1 Watt, this REXUS payload as part of the Payload for Radiation measurement and Radio-interferometry in Rockets (PR3), has measured the charged-particle rate going up in the atmosphere and into space. Besides providing a chance for students to work on reproducing the historical discoveries of Hess, Pfotzer, Regener, Van Allen, and others in the last century, it has also been an outreach opportunity to engage the general public with astroparticle physics. But above all, it is a proof of concept for compact cosmic-ray detectors in orbit. Where the worldwide network of neutron detectors is able to monitor the cosmic-ray flux at ground level, and detectors on the ground and in space detect cosmic rays locally, global near-real-time coverage of cosmic-ray flux above the atmosphere is only feasible with an ensemble of small and cheap detectors like the one presented here. Details on the detector design and performance, and the results from the rocket flight will be presented. \u3c/p\u3