As sub-GHz wireless Internet of Things (IoT) sensor networks set the stage for long-range, low-data-rate communication, wireless technologies such as LoRa and SigFox receive a lot of attention. They aim to offer a reliable means of communication for an extensive amount of monitoring and management applications. Recently, several studies have been conducted on their performance, but none of these feature a high dynamic range in terms of channel measurement. In this contribution an autonomous, low-power, LoRa-compatible wireless sensor node is presented. The main uses for this node are situated in LoRa channel characterization and link performance analysis. By applying stepped attenuators controlled by a dynamic attenuation adjustment algorithm, this node provides a dynamic range that is significantly larger than what is provided by commercially available LoRa modules. The node was calibrated in order to obtain accurate measurements of the received signal power in dBm. In this paper, both the hardware design as well as some verification measurements are discussed, unveiling various LoRa-related research applications and opportunities.

The LoRa standard is currently widely employed for low-power long-range wireless sensor networks at sub-GHz frequency bands. The longer wavelengths associated with sub-GHz technology provide excellent radiowave propagation characteristics, yielding much larger coverage compared to higher frequency bands. In the case of wearable sensors, the 868 MHz band can be covered by textile substrate-integrated-waveguide antennas of a convenient size. In body-centric communication systems, front-to-back diversity is an important asset to mitigate the shadowing of the antennas by the presence of the human body. This paper describes a diversity textile-antenna-based LoRa platform with integrated transceivers. Outdoor measurement campaigns are conducted to assess the performance of the wearable LoRa nodes with front-to-back diversity in an urban radio propagation environment at walking and cycling speeds. These experiments prove that large ranges of 1.5 km can easily and reliably be achieved for off-body LoRa communication links. The results demonstrate a significant performance improvement in terms of packet loss in NLoS situations when comparing single-receiver performance to different spacial receiver diversity applications. Additionally, link budget increases up to 5.5 dB are seen, owing to the realized diversity gain.

When deploying wireless sensor networks in smart buildings, low-power, long-range communication technologies such as LoRa may offer a reliable, low data-rate alternative to existing wireless technologies. For this contribution, custombuilt LoRa nodes were used to measure LoRa propagation characteristics for both the 434 MHz and 868 MHz ISMbands. These measurements show that the presence of people has a negative impact on the quality of the LoRa link and confirm the superiority of the 434 MHz band for indoor LoRa communication.

The relentless expansion of the Internet of Things is fueled by constant innovations in low-power wide-area network technologies. Industry forerunners such as LoRa, SigFox and NB-IoT continuously seek to achieve larger communication ranges while consuming as little energy as possible. These efforts, in turn, facilitate vast performance increases in a wide range of related application areas, such as body-centric communication. For example, recently, LoRa modules have been integrated onto wearable textile antennas, thereby greatly extending the range of the body-centric networks. However, as the resulting communication links need to accommodate mobile users, many nodes will regularly be communicating using suboptimal LoRa modulation parameters as these users move around. Adaptive LoRa modulation aims to solve this by optimizing these parameters in realtime, based on the location of the user and the actual performance of the wireless link. In this contribution, the optimal settings for one of the key LoRa modulation parameters, the spreading factor, are experimentally determined. More specifically, it is shown that only a very limited number of spreading factor options should be used in an adaptive LoRa modulation scheme. The results also yield insight into more general LoRa communication aspects by analyzing packet reception and channel throughput data gathered in an urban environment.

When aiming for the wider deployment of low-power sensor networks, the use of sub-GHz frequency bands shows a lot of promise in terms of robustness and minimal power consumption. Yet, when deploying such sensor networks over larger areas, the link quality can be impacted by a host of factors. Therefore, this contribution demonstrates the performance of several links in a real-world, research-oriented sensor network deployed in a (sub)urban environment. Several link characteristics are presented and analysed, exposing frequent signal deterioration and, more rarely, signal strength enhancement along certain long-distance wireless links. A connection is made between received power levels and seasonal weather changes and events. The irregular link performance presented in this paper is found to be genuinely disruptive when pushing sensor-networks to their limits in terms of range and power use. This work aims to give an indication of the severity of these effects in order to enable the design of truly reliable sensor networks.

Nowadays, wireless sensor networks at sub-GHz frequencies are becoming more and more ubiquitous, owing to their impressive link budget. One of the most widespread standards is LoRa, employing Chirp Spread Spectrum modulation to achieve a relatively high data rate at low transmit powers. The latter is ideal for body-centric communication, but the challenge for wearable devices consists in keeping the antenna dimensions sufficiently small. By exploiting substrate-integrated-waveguide technology, a compact wearable 868 MHz LoRa sensor node has been successfully integrated onto a compact textile antenna platform. The wearable LoRa unit operates in a fully autonomous manner, including an integrated battery, transceiver, microprocessor and memory. This paper documents the construction and the radiation patterns of the wearable node, autonomously deployed on the human body and measured in an anechoic chamber. The measurements were performed without any cables attached to the wearable node and, hence, accurately characterize realistic off-body propagation at sub-GHz frequencies. Finally, a body-to-body wireless link is measured between two persons equipped with wearable nodes in the anechoic chamber, considering different body orientations.

This contribution examines the performance of LoRa in an indoor, body-centric IoT context. This was achieved by deploying custom-made wearable LoRa nodes, featuring a textile substrate-integrated-waveguide antenna, on the chests of test persons who walked around in a modern office environment, logging the strength of the link between them. Both the influence of the test person's bodies as well as the challenging environment, which includes large masses of reinforced concrete, are investigated. The measured channel characterization data illustrate the excellent performance achieved by combining the building penetration qualities of signals at sub-GHz frequencies and the high link budget of the LoRa modulation standard.

In recent years, LoRa has been deployed in countless Internet of Things (IoT) applications across the globe. However, as LoRa is a proprietary technology, research into its physicallayer performance has been challenging. Implementing LoRa on software defined radio (SDR) platforms yields valuable insight into the physical layer of the LoRa standard and paves the way for improvements in packet reception capabilities for LoRa receivers. This paper presents an independently developed packet reception algorithm, which drastically improves the physical performance of LoRa communication links. The advanced signal presence detection, synchronization and symbol detection strategies are shown to significantly increase packet reception ratios in extremely adverse noise conditions. Multiple algorithm variations are presented and compared in terms of bit error rate (BER) performance and computational cost. In comparison to a theoretical system with perfect channel state information, the simulated bit error rate performance of the best performing algorithm only requires an increase of 1.6 dB in signal-tonoise ratio (SNR) to exhibit the same performance. Finally, SDR implementations of the algorithms exhibit average SNR performance gains up to 4.7 dB when compared to commercially available hardware.