# A New LoRa-like Transceiver Suited for LEO Satellite Communications +
###### Abstract  
LoRa is based on the chirp spread spectrum (CSS) modulation, which has been developed for low power and long-range wireless Internet of Things (IoT) communications. The structure of LoRa signals makes their decoding performance extremely sensitive to synchronization errors. To alleviate this constraint, we propose a modification of the LoRa physical layer, which we refer to as differential CSS (DCSS), associated with an original synchronization algorithm. Based on this modification, we are able to demodulate the received signals without performing a complete frequency synchronization and by tolerating some timing synchronization errors. Hence, our receiver can handle ultra narrow band LoRa-like signals since it has no limitation on the maximum carrier frequency offset, as is actually the case in the deployed LoRa receivers. In addition, in the presence of the Doppler shift varying along the packet duration, DCSS shows better performance than CSS, which makes our proposed receiver a good candidate for communication with a low-Earth orbit (LEO) satellite. D 20222221830 20  
services for places where there are no terrestrial networks. Currently, several works attempt to implement IoT communications with geostationary (GEO) satellites, such the work in [6], using the NB-IoT technology, and especially with LEO satellites. Indeed, several industrial and academic works have recently proposed deploying popular LPWANs in LEO satellite communications, such as nano-satellites lunched by Eutelsat to serve Sigfox's generic IoT applications [7]. However, such communications lead to an increase in the complexity of the synchronization process, typically caused by the Doppler effects related to the satellite movements. Satellite IoT entail higher interference levels compared to ground-based IoT, due to the fields of view of LEO satellites, which allow connecting a huge number of end-nodes using several technologies, especially when considering ISM unlicensed bands. This issue is aggravated by uncoordinated access to the radio channel of the majority of LPWANs. We dealt with this problem in several of our previous works, in the case of LoRa communications. For instance, in [8], we provided an approach to \"deal\" the same-technology destructive collisions in LoRa. This method allows one to considerably enhance the throughput of LoRa-based networks since it makes it possible to decode up to four LoRa-like signals in a destructive collision. However, even with the huge number of devices that could be connected to a LEO satellite, more sophisticated methods should be implemented. We quantified in [9] the impact of an ultra narrow band interference of LoRa-like communications in ISM bands. Given this massive connectivity, the use of ALOHA-based random access protocols, as in the case of ground-based LPWANs, is a challenging task. Indeed, in the IoT communication with LEO satellites, the satellite needs to serve many terminals at the same time; thus, the probability of a packet collision is very important in such scenarios. Hence, an optimization of ALOHA could be implemented to reduce the number of lost or re-transmitted packets in such a context. For instance, the authors in [10] propose combining ALOHA with time division multiple access (TDMA) in order to reduce the probability of packet collision. However, this approach needs further synchronization processes between the satellite and end-devices, which would increase their energy consumption. It should also mention the potential use of enhanced spread-spectrum ALOHA [11] and Asynchronous contention resolution diversity ALOHA [12] for LEO satellite IoT, in order to reduce the probability of packet loss. In this paper, we focus only on synchronization issues when considering LEO satellite communications using LoRa-like signals. When LoRa communication is considered, the transmitted symbols are estimated in the frequency domain using fast Fourier transform (FFT) processing [13; 14]. As a consequence:  
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