# LoRa Mobile-To-Base-Station Channel Characterization in the Antarctic
## 1 Introduction  
Nowadays, low-power long-range networks are gaining interest in the context of the Internet of Things (IoT). Such networks are also very suitable for wireless communication with scientific measurement nodes in remote areas. In case of measurement setups in polar regions, systems need to operate at very low power. The increased scientific interest in live meteorological and seismic data in and around the Antarctic has given a boost to the research of very low power transmissions in extreme climate conditions. In this paper, we study the channel conditions experienced by a communication system that monitors scientific experiments within a radius of 30 km around the Belgian Princess Elisabeth Antarctic Station [1]. The sensor nodes need to operate on battery power for at least a full year, as solar panels cannot be used during the long and dark winter. Snow accumulation on solar panels is also problematic. Solutions that need maintenance more than once a year are not feasible due to the difficulty and cost related to visiting scientific setups in the Antarctic. For instruments near the station, omnidirectional antennas and commonly used modulation techniques perform well. This paper concentrates on scientific experiments deployed at a distance in the order of 20 to 30 km from the station. For these distances, modulation techniques with a larger link budget are preferred. For fixed scientific setups, the deployment of directional receive antennas delivers an obvious benefit. However, this setup is also advantageous for mobile applications, as the trajectory to the destination is likely to be along a straight line because of the absence of roads. The Antarctic may seem endless and flat, but for the region (Queen Maud Land) where this research is being performed, measurements show that for expeditions north of the Princess Elisabethbase at distances of less than 10 km, the slope of the ice already causes an absence of Line-of-Sight (LoS) conditions. For expeditions to the south, mountain tops are preventing this straight-line trajectory, making wireless data transmission very difficult but not impossible, as experimentally observed. Another important aspect is the total absence of other transmitters in the area, causing the frequency band to be exceptionally free of interference. This is also reflected in the absence of spectrum regulations for the Antarctic region. In this paper, channel measurements are presented for wireless mobile-to-base-station links in the Antarctic. The results provide valuable insights to scientists planning the deployment of fixed point-to-point wireless links from their sensors to a base station. In such a scenario, the communication channel is unidirectional, with the aim of wirelessly transmitting sensor data from the sensor to the base station at minimal power. Sub-GHz frequencies may still provide a long communication range in such operating conditions. The wireless communication system relies on LoRa technology [2], whose chirp spread spectrum (CSS) modulation provides a large link budget. CSS modulation yields spreading gain, accurate channel estimation, and suppression of delayed multipath components. Transmissions are performed at 434 and 868 MHz, such that propagation characteristics at these frequencies can be compared. The received signal levels are recorded as a function of distance to the base station. Terrain elevation is also taken into account. Although many channel measurements and models [3] are documented for rural and urban environments in the 700-900 MHz frequency range, only a scarce number of publications about LoRa channel characteristics exist at the moment, as this is a relatively new technology. Measurements for fixed setups over a 700-m range in a suburban environment are described in [4]. The authors of [5] have performed outdoor measurements to determine the link budget for a range up to 8 km. Therefore, they have employed LoRa hardware by the Semtech corporation, similar to the hardware applied in this manuscript.