# ICARUS--Very Low Power Satellite-Based IoT
###### Abstract  
The ICARUS (International Cooperation for Animal Research Using Space) satellite IoT system was launched in 2020 to observe the life of animals on Earth: their migratory routes, living conditions, and causes of death. These findings will aid species conservation, protect ecosystem services by animals, measure weather and climate, and help forecast the spread of infectious zoonotic diseases and possibly natural disasters. The aim of this article is to explain the system design of ICARUS. Essential components are \"wearables for wildlife\", miniature on-animal sensors, quantifying the health of animals and the surrounding environment on the move, and transmitting artificially intelligent summaries of these data globally. We introduce a new class of Internet-of-things (IoT) waveforms--the random-access, very-low-power, wide-area networks (RA-vLPWANs) which enable uncoordinated multiple access at very-low-signal power and low-signal-to-noise ratios. RA-vLPWANs used in ICARUS solve the problems hampering conventional low-power wide area network (LPWAN) IoT systems when applied to space communications. Prominent LPWANs are LoRA, SigFox, MIOTY, ESSA, NB-IoT (5G), or SCADA. Hardware and antenna aspects in the ground and the space segment are given to explain practical system constraints. satellite IoT; very-low-power signaling; CDMA; random access 2022222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222199 August2222222222222222222222222222222222222222  
described in [4; 5], which exhibits comparable RA-vLPWAN attributes as the ICARUS signaling concept but was made for geostationary satellite communications. Both ICARUS and UCSS are explicitly made to tackle the problems of conventional IoT systems when applied to space communications. These conventional IoT systems are namely LoRA [6], SigFox, MIOTY, ESSA, NB-IoT (5G), and SCADA networks [4; 5], which constitute the group of low-power, wide-area networks (LPWANs). Conventional LPWAN systems are made for data rates between some 100 bit/s up to several kbit/s as depicted in Figure 1. [PERSON] et al. have shown in [4; 5] that other than the newly introduced RA-vLPWAN class, LPWANs cannot be scaled down to lower data rates or to a signal-to-noise ratio as low as expected in space communications for the following reasons:  
* LPWAN systems need a minimum data rate of approximately 1 kbit/s to establish stable time and frequency synchronization. These systems are not made for establishing a stable signal synchronization for SNR \(<-20\) dB and high random Doppler shifts. * Efficiency: All the conventional LPWAN systems use fixed preamble/pilot signal sequences for synchronization. At a very-low-data rate, the spectral efficiency gets prohibitively low since the ratio between pilot and payload data gets worse. * Some of the well-established IoT systems, such as LoRA, do not support uncoordinated random-access schemes where all tags start transmission at arbitrarily chosen time instants. As a consequence, the number of supported users per satellite beam is very limited and can be, in a worst case, as low as one. * By design, LPWAN systems, such as NB-IoT, typically are not resilient against huge random Doppler shifts since they are made for terrestrial mobile communications. Motivated by initial channel measurements in 2015 [7], ICARUS has been the first waveform ever since to introduce the RA-vLPWAN class of IoT systems, tackling all problems of conventional IoT systems when applied to space applications. ICARUS uses uncoordinated random access and allows stable time and frequency synchronization even in low SNR, at low-data rates, and high-Doppler shifts. The ICARUS system is often compared to the ARGOS satellite-based object-tracking system [8]. However, ARGOS requires a higher UL-signal power and does not provide a backward channel to adjust/trigger specific tag behavior.