Technical University of Braunschweig Body Sensor Network
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Saadaoui and Wolf describe a system for health monitoring of elderly people with cardiac arrhythmia. The Body Network Sensor System consists of a pulse oximeter sensor which monitors the blood oxygen saturation (SpO2) and heart rate (HR) and an Electrocardiogram sensor (ECG) for monitoring heart activity. They are concerned with transmission of both routine and emergency vital signs and propose a solution that can fit both indoor and outdoor environments. While it is mainly deployed at home, the system remains operational if the elderly leaves his/her home. In the home both routine and emergency vital signs are transmitted over a Wireless LAN network. In outdoor environments, only emergency vital signs measurements are transmitted over a GPRS network. Routine vital signs are stored locally and uploaded when the person gets back home. This choice minimizes communication costs over the GPRS network.
The system uses IEEE 802.15.4 as the cimmunications protocol. In most cases the sampling frequency of the physiological signals is configurable. The ECG signal is sampled at a rate of 500 samples per second with a sample size of 16 bits. The oxygenation as well as the heart rate are sampled at a rate of 1 sample per second with a sample size of 16 bits. The application data traffic is 500*16+1*16+1*16=8032bits/s. The coverage area varies from the body area (<1m), personal area (<10m), local area (<100m) to wide area (>100m). Since the healthcare application communicating devices are in close proximity to each other, IEEE 802.15.4 is an appropriate choice for communication in the personal area while the IEEE 802.11b covers the local area and GPRS covers the wide area.
Results - Simulations of the proposed architecture show that the acknowledged data service of the IEEE 802.15.4 performs particularly well offering a packet delivery fraction greater than 97% for all transmission power values. Reducing the transmission power does not really save energy. This can be achieved by a proper power management scheme. Simulation and design is ongoing and scalability is being investigated.
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