Abstract
The age of the Internet of Things (IoT) and smart cities calls for low-power wireless communication networks, for which the Long-Range (LoRa) is a rising star. Efficient network engineering requires the accurate prediction of the Received Signal Strength Indicator (RSSI) spatial distribution. However, the most commonly used models either lack the physical accurateness, resolution, or versatility for cityscape real-world building distribution-based RSSI predictions. For this purpose, we apply the 2D electric field wave-propagation Oscillator Finite-Difference Time-Domain (O-FDTD) method, using the complex dielectric permittivity to model reflection and absorption effects by concrete walls and the receiver sensitivity as the threshold to obtain a simulated coverage area in a 600 × 600 m2 square. Further, we report a simple and low-cost method to experimentally determine the signal coverage area based on mapping communication response-time delays. The simulations show a strong building influence on the RSSI, compared against the Free-Space Path (FSPL) model. We obtain a spatial overlap of 84% between the O-FDTD simulated and experimental signal coverage maps. Our proof-of-concept approach is thoroughly discussed compared to previous works, outlining error sources and possible future improvements. O-FDTD is demonstrated to be most promising for both indoors and outdoors applications and presents a powerful tool for IoT and smart city planners.
Highlights
We considered a 600 × 600 m2 map surrounded by 0.60 m margins used for the perfectly matched layers (PML) boundary conditions required by the Oscillator Finite-Difference Time-Domain (O-Finite-Difference Time-Domain (FDTD)) algorithm and exported the final map as a bitmap *.png file
We quantified the differences between O-FDTD simulated and experimental signal coverage maps (Section 4.4)
The LoRa mid-range radiofrequency communication coverage area was spatially mapped in an urban environment and observed to be highly dependent on the building arrangement of the city
Summary
The age of smart devices has arrived. With the increasingly powerful paradigm of the Internet of Things (IoT), smart city environments have become a pressing need for wireless technologies that enable efficient communication between distant objects [1,2]. Long Range (LoRa) [3] technology stands out for its combined low-power requirements and long-range coverage compared to other IoT communication protocols such as Bluetooth, Wi-Fi, ZigBee, or GSM. Such features are owed to its chirped spread spectrum and large bandwidth, making it less prone to interference and distance-fading. Examples of previous works deploying LoRa include monitoring systems for energy [4], environmental [5], and road condition monitoring [6], and flood prevention [7], among many other applications [8,9]
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