Body-worn channel characterization unit for the 868 MHz band

With the development of the Internet of Things, wireless sensor networks are constantly being deployed over larger and larger areas. Compared to higher radio frequencies, sub-GHz frequency bands possess superior radio propagation properties for long-range wireless connections. However, as frequency decreases, efficient antennas become larger. The highest sub-GHz band at 868 MHz enables good radio propagation and provides the possibility to design efficient body-worn antennas by means of substrate-integrated waveguide technology. A number of standards, such as LoRa, Sigfox and Dash7 can be employed for communication in this band. Commercial transceivers for these standards often do not allow accurate measurement of the received signal strength. For off-body radio propagation research, a wearable measurement node for 868 MHz is proposed, exploiting an accurate logarithmic power detector. A prototype of the node was implemented and tested, yielding accurate channel measurements for this band. Recorded signal levels are documented in an indoor environment for Line of Sight as well as Non Line of Sight propagation paths. Different features caused by various radio propagation phenomena are clearly visible in the measurement results and illustrate the correct operation of the system.