# LoRa Mobile-To-Base-Station Channel Characterization in the Antarctic
## 2 Materials and Methods  
The measurement campaign is based on a setup employing a fixed LoRa transceiver with directional antennas at the base station and a mobile transceiver equipped with two omnidirectional antennas deployed on a moving \(4\times 4\) vehicle. The snowmobile is a Toyota Hilux equipped with tracks, resulting in an antenna height of 210 cm above ground level.  
We study a unidirectional channel where the mobile transmits sensor data to the base station at minimal transmit power. The knowledge obtained about such a wireless channel will help scientists to optimally deploy fixed wireless sensor nodes that monitor the Antarctic environment. Current sensor systems--such as the one shown in Figure 1--typically measure meteorologic conditions such as wind velocity and direction, temperature, light intensity, air pressure, and relative humidity, parameters related to snow drift such as snow particle size and speed at 50 cm above ground level, seismic activity such as ground vibration, and the Earth's magnetic field. For such setups, autonomy of the remote wireless sensor system must be maximized by minimizing the energy spent on wireless communication. Besides this constraint, the channel characterization was performed without any initial link requirements for data rate in mind. LoRa technology was experimentally tested to determine its operational range, assuming that the data rate could be very low. There is no acknowledgementrequired or used for the transmissions under study. Transmissions with increasing packet sequence numbers were employed to verify the effective reception of the packets, including validation of the signal-to-noise ratio (SNR) in the chip's SNR register (if no packet is received, the SNR register is not updated). The directive Yagi-Uda base station antenna only serves to receive sensor data which were transmitted unidirectionally, without acknowledgement, feedback, or adaptive communication to limit energy consumption as much as possible.  
Other wireless sensor network technologies could realize the link, but they have some disadvantages compared to LoRa. The following list includes potentially suitable technologies for sub-GHz industrial, scientific and medical (ISM) bands:  
* Sigfox
* LTE-M  
Sigfox was not chosen due to extreme limitations in payload length, very low data rate, and severe restrictions on the packet rate. Moreover, the ultra-low bandwidth makes the system very sensitive to Doppler shifts. An LTE-M network is currently being rolled out in the US by Verizon. This is a totally new technology, which is still in its infancy.  
At both ends of the link, the hardware used for this measurement is the Microchip Technology DM164138 development board [12]. The board relies on a Microchip RN2483 chip. It is capable of transmitting and receiving LoRa signals at 434 and 868 MHz with an output power of 14 dBm and a specified input sensitivity of \(-148\) dBm.  
During our measurements, the mobile transceiver is transmitting a packet every five seconds, alternating between both bands. The packets contain sequence numbers, which are registered by the base station transceiver, recording the sequence numbers with the signal-to-noise ratio (SNR) as determined by the RN2483 chip.  
The data collected at the transmit side (mobile user) are:  
* Time stamp
* GPS coordinates (accuracy \(\pm 15\) m (50 ft), during 95% of the time)
* GPS altitude (accuracy \(\pm 23\) m (75 ft), during 95% of the time)  
Figure 1: Mobile, carrying out the channel characterization experiments at one of the fixed wireless sensor nodes, monitoring meteorological conditions in the Antarctic.  
The data collected at the receiver side (base station) are:  
* Time stamp
* Sequence number read from the packet
* Band in which this packet was received (434 MHz or 868 MHz)
* Measured SNR for the received packet