Dynamic Ambient RF Energy Density Measurements of Montreal for Battery-Free IoT Sensor Network Planning

This work summarizes an outdoor dynamic measurement of ambient radiofrequency (RF) power density in the core areas of Montreal city, which can eventually be exploited for possible battery-free Internet of Things (IoT) sensor network planning. The measurement covers a frequency range of 400-2700 MHz. The power density along major streets, roads, and highways is captured and analyzed, which differs from previous stationary measurements. Results indicate that cellular communication bands (GSM/LTE850 and LTE700) are the best choice for RF energy recycling in downtown (populated) areas. The largest average power levels of GSM/LTE850 and LTE700 bands are -35.50 and -36.95 dBm, respectively. In contrast, in suburban areas where cellular communication signals are generally weak, the digital television band with a peak level of -47.68 dBm presents the largest among all frequency bands. Moreover, one separate measurement at a fixed location is conducted on a typical workday to study the effects of foot traffic on ambient RF power density. Results illustrate that no obvious fluctuations are detected during this daytime measurement. For example, both average power levels of GSM/LTE850 and LTE700 remain at a relatively stable level of -25 dBm throughout the measurement. With the advance of far-field wireless power transfer and backscattering techniques, ambient RF power-enabled battery-free IoT sensors are feasible and will contribute to the planning and implementation of a smarter and greener city.