Energy Profiling of Secure MQTT over WiFi on ESP32-Based IoT Devices

This paper investigates the energy impact of Transport Layer Security (TLS) protocol on an ESP32-based IoT system for ambient intelligence applications. The prototype integrates inertial and electrocardiogram (ECG) sensors and transmits data over WiFi using MQTT, with and without TLS. Current consumption is profiled using an INA219 sensor under varying payload sizes (158 to 4096 bytes) and transmission intervals (1 to 600 seconds). Results show that TLS introduces negligible overhead (below 2%) on average current consumption, even under frequent transmissions and large payloads. Transmission interval remains the dominant factor shaping energy consumption. Deep Sleep mode significantly extends battery life, yielding up to 75% reduction in average current for low-duty-cycle settings. The findings provide guidance for designing secure, energy-efficient IoT systems in constrained environments.