# A Compact Low-Power LoRa IoT Sensor Node with Extended Dynamic Range for Channel Measurements
## 1 Introduction  
Wireless sensor networks (WSNs) are at the heart of the ever-developing Internet of Things (IoT). They have received a great deal of attention across a diverse range of research areas such as environmental monitoring, disaster surveillance, smart buildings, smart grids, healthcare, agricultural control, predictive maintenance, transport and asset tracking [1; 2; 3; 4]. Seeing WSN deployment over larger and larger areas, it becomes evident to consider the use of sub-GHz frequency bands for communication in these long-range networks, given the superior propagation characteristics when compared to higher frequency bands. Conveniently, the reduction of the available bandwidth at lower frequencies does not degrade performance since communication links in WSNs are typically very low data-rate connections anyway. Multiple standards for low data-rate sub-GHz communication have been proposed, the most prominent of which are LoRa, SigFox and Dash7 [1; 5; 6; 7; 8]. As Dash7 is promoted to be a medium-range technology [7], for long-range networks, the scope has shifted towards LoRa and SigFox. The adjustable data rate of the LoRa standard, combined with its slightly higher level of global coverage [5; 6] makes for a very promising technology both for applications in WSNs and other long-range, low data-rate connections. LoRa is based on a chirp spread spectrum (CSS) modulation technology. To encode information, this technology uses wideband frequency modulated pulses called chirps to achieve spreading gain, which results in the successful reception of packets at extremely low signal-to-noise ratio (SNR) levels. The LoRa modulation technique was recently described in a rigorous way by [PERSON] [9]. Additionally, the expected performance of LoRa has been discussed in a decent number of other publications [8; 10; 11; 12; 13], all of them praising the potential of LoRa modulation, but some also warning for reduced performance as the number of end-devices grow [8; 12; 13]. To explore the capabilities of LoRa modulation, a suitable radio platform is needed. A commercial LoRa platform frequently used in literature is the SX127X family from Semtech Corp [8; 14; 15; 16; 17; 18]. Unfortunately, as most commercially available LoRa modules are tailored towards applications, they often lack dedicated measurement functions required for research applications. On the other end of the spectrum, lab-grade software radios do offer a lot of functionality, but in addition to being very expensive, they can also be very bulky for certain types of research. In fact, in any type of studies involving mobility or areas that are difficult to reach, both the size and power dependency of research equipment can seriously impede the possible research applications. The middle ground can be found by integrating a commercially available LoRa module into a system with more capabilities to create a compact, low-power wireless sensor node. In this paper, such a node is proposed, designed and tested. For LoRa compatibility, a commercially available LoRa transceiver module--the RN2483 (by Microchip Technology Inc., Chandler, AZ, USA)--is used. Being built around a Semtech SX1276 transceiver (by Semtech, Camarillo, CA, USA), this module offers LoRa modulation for communication in both the 434 MHz and 868 MHz industrial, scientific and medical (ISM) radio bands. The RN2483 also offers channel measurement functions, such as SNR measurement, but due to the fact that LoRa is a proprietary technology, research determining the capabilities of this technology is bound to the capabilities of the most sensitive transceiver available, in this case: the SX1276. In the sensor node proposed in this paper, this is partly circumvented by using stepped attenuators to considerably increase the dynamic range of the measurements. The transceiver module is also certified to the LoRaWAN 1.0 specification, enabling the use of this node within the existing LoRaWAN network infrastructure [19].