This paper describes an unobtrusive IEEE 802.15.4-based wireless Body Sensor Network (BSN) that enables continuous cuff-less blood pressure monitoring, opening up new perspectives for hypertension diagnosis and treatment, cardio-vascular event detection, and stress monitoring. We estimate the arterial blood pressure based on the Pulse Arrival Time (PAT), which is measured with a waist electrocardiogram (ECG) and an ear photo-plethysmogram (PPG). The PAT measurement requires the synchronization of the wireless sensors' clocks. This is achieved with the Flooding Time Synchronization Protocol (FTSP). The evaluation of both the implemented time synchronization and the robustness of the wireless data transmission yielded promising results. Future work will include the study of packet collisions in synchronized IEEE 802.15.4 networks, the enhancement of the BSN with additional context-providing sensors (e.g. accelerometer, magnetometer, thermistor), and the integration of the blood pressure estimation algorithm in a wireless sensor unit.
