Reliable real-time communication for coach-assisted feedback systems in swimmingKos, Anton (Avtor) Hernández Casillas, Andrea (Avtor) Tomažič, Sašo (Avtor) Umek, Anton (Avtor) biofeedback systemblock selective repeat protocolcyclically interrupted channelrealtime communicationswimmingwearable devicewireless sensor deviceWireless communication in aquatic environments faces major challenges as the radio channel is temporarily unavailable due to submersion and the movement of swimmers. These interruptions can lead to sudden and prolonged packet loss, making real-time biofeedback difficult to achieve with standard communication protocols. This paper presents a real-time swimmer monitoring system built around a novel Block Selective Repeat (BSR) communication protocol specifically designed for environments with cyclic channel interruptions. BSR extends the traditional selective repeat model by introducing dynamic packet composition, cumulative acknowledgements with loss indicators and buffered retransmission. These features enable efficient and reliable transmission of sensor data, even when the connection is temporarily interrupted. The system was implemented using low-cost, commercially available Wi-Fi enabled microcontrollers and tested under real swimming conditions in four swimming styles. Experimental results show that BSR achieves 100% data recovery, with consistent low-latency performance across all swimming styles, including high-loss scenarios such as breaststroke and butterfly. The protocol also preserves the temporal structure of the movement data, enabling accurate recognition of movement patterns for real-time coaching and performance analysis. These findings demonstrate the suitability of BSR for biofeedback systems in swimming and other applications where intermittent wireless connectivity is a constraint.20252025-10-08 08:49:31Članek v reviji174652sl