## 3 Telemetry System Architecture for Physiological Data Collection  
Mobility-aware healthcare systems are created as a synergy of emerging mobile computing, wireless medical sensors, and wireless communications and networks technologies. Figure 1 outlines the proposed telemetry transmission system where multiple physiological signals (such as ECG, EEG and GSR) are monitored using sensors and their state integrated using a low-power DSP based personal server. The whole system is integrated into hierarchically organised functional components. The medical centre base station (MBS) is a data aggregator and can be used to: Request updates from a patient, Receive regular (scheduled) updates from a patient, Report on alarms and adverse events and Store data. The patient wears one or more wireless medical sensors with networking capability for physiological data collection. The sensor nodes measure and transmit patient vital sign information (e.g., the heart rate and blood oxygenation) to the local base station. Individual sensors would cover only limited range (in the order of ten feet) and therefore require very low power consumption for communication. Also, the sensors are so small that they will not affect the appearance and function of the patients in which they are embedded. Also, monitoring is carried out actively but unobtrusively without the patient or the people close by being aware of it. Moreover, the medical sensors make possible the combined processing of spatially and temporally gathered physiological information from different parts of the patient body and the external communication for mobile health care. Figure 1: A medical telemetry system architecture for physiological data collection. The medical sensors are connected to a GSM-compatible self-powered and wearable patient mobile personal gateway (PG) with the Internet access. The medical sensors will transmit data to PG which will subsequently transmit the combined data to a record server connected to a hospital network. PGs provide enough processing power for real-time data processing and analysis as well as reduced power consumption is achieved by employing mobile gateways. Individual sensors communicate with a PG using Bluetooth [12] or ZigBee [20]. The PG receives data from the sensors, logs this data to local memory, and then sends data using SMS over the network to a remote receiver. Standard SMS (and thus GSM network functionality) is used as the data carrier medium. Through the GSM network (or descendant networks such as 3G), the PG connects to the network, creates standard SMS message packets containing the encoded protocol, and sends data to the remote base station at the medical centre. Although WBAN based on a low cost wireless sensor network technology could greatly benefit patient monitoring systems in residential environments [14], the mesh networks do not require a fixed wired infrastructure, the cost of using a mesh network consisting of wireless sensors is lesser than that of using a Wi-Fi based system. The system supports both scheduled transmission and polled requests from a remote base station at the medical centre. Alternatively, a message may be triggered by an adverse event which the base station is configured to look for. As it is impossible for a controller at hospital or relatives to make any sense or analyse a constant flow of patient data, the data should be forwarded to the hospital to be analysed only in critical cases, for example when the data diverge from the patient's history. For example, a heart rate outside the normal adult range of 50-140 beats per minute may trigger an alarm message. The patient or doctor or both could formulate triggers that cause even more data to be collected, additional sensors to be enabled, or medical personnel to be contacted. At the medical centre, the system will understand protocol messages and should be able to both read and write them. The medical centre base station may issue requests to remote patient stations and perform a number of operations with the data it receives.