Experimental Analysis of Sub-GHz RF Communication for in-Water Wearables in Swimming Applications

This paper investigates the experimental evaluation of sub-GHz radio frequency (RF) communication systems for wearable devices used in swimming applications. Specifically, we analyze the feasibility and performance of two frequency bands, 169 MHz and 434 MHz, in supporting near real-time data transmission from in-water sensors to above-water receivers. A series of controlled experiments were conducted in an Olympic-size swimming pool, with the transmitter placed at various depths and distances. We measured key communication metrics, including Received Signal Strength Indicator (RSSI) and packet loss, across three different antenna placement scenarios: on the water surface, under the water surface, and submerged at 10 cm depth. Both frequencies were tested using evaluation boards with comparable antenna setups and power configurations. The results show that the 169 MHz band consistently provides stronger signal performance and better range, while the 434 MHz band offers acceptable performance under specific configurations with lower power consumption. Our findings highlight the potential of sub-GHz RF technologies for enabling reliable in-water communication in wearable swimmer monitoring systems for real-time aquatic telemetry for sports and health applications.