1.1 3 1.2 BSN CCU 4 2.1 TDMA CSMA/CA 16 3.1 22 3.2 22 3.3 25 3.4 28 3.5 29 3.6 MAC 30 3.7 MAC 30 3.8 MAC ACK. 30 3.9 MAC 31 3.10 MAC CCU, 32 4.1 35 4.1 35 4.2 ECG 37 4.3 38 4.4 39 4.5 40 4.6 ECG, 42 42 4.7 43 4.8 ECG, 44 ON ON
users. Adaptive low-power design [22] proposes a multi-layer hierarchy architecture for BSN thus dividing the BSN into the following layers: A system layer which is a PC or server in hospitals managing the control path and the data path for the BSN by sending commands to the application layer and receiving data. Determining the lowest energy data path is the most important function of this layer. An application layer controlling all the sensor groups by sending commands and receiving data from them. A sensor group layer that includes several sensor nodes. The body area is divided to several sub-areas and each sensor group consists of sensors in one area. A sensor that includes only one sensor node receiving commands from a sensor group and sending the detected data to the sensor group. Hierarchy architecture helps the spread of the BSN to a greater number of sensor nodes with the least changes in higher levels. When both the data source (e.g., BSN) and the destination (e.g., caregiver or physician) are two mobile nodes, an open source framework named SenseFace application [15] is proposed to connect them to each other. The destination is a social network such as fax, email, voicemail, short message (SMS), file attachment, Facebook, YouTube, LinkedIn, tweeter, etc Energy Conservation Energy can be remotely fed to the sensor nodes. Adaptive threshold rectifier (ATR) [9] is a remote method to deliver the energy to several small nodes such as electrocardiograph (ECG). This rectifier wirelessly feeds the sensor node by an adhesive bandage. Energy is delivered remotely by ATR with 54.9% efficiency. This method is not expandable for all nodes due to an extra bandage over each sensor and almost twice as much in extra power expanded. Other energy conservation methods are proposed on PHY and MAC layer. Energy Saving and Harvesting in PHY Application-specific integrated circuit (ASIC) defines three different modes [20]. The first mode is the “active” mode in which nodes communicate with each other through the
transmission rate between 12:00 am to 8:00 am, 8:30 am to 5:00 pm and 5:30 pm to 9:30 pm. Figure 4.2 Transmissions of ECG data The transmission rate of the ECG was 8207 bits per second (bps) in conventional state (Table 4.2). We can calculate the average rate for burst communication state and dynamic transmission state by Equation (3.3) when samples/second,, (Burst communication) and data ratio=5% (Dynamic transmission). Burst communication state shows a minor transmission reduction, as shown in Figure 4.3 between 9:30 pm and 12:00 am. Dynamic transmission state transmission reduction is equal to ECG. Figure 4.3 Transmissions of accelerometer The transmission rate of the accelerometer was 815 bps in conventional mode. We calculated the average rate for communication state and dynamic transmission state by Equation (3.3) when samples/second, , (Burst communication) and data ratio=5% (Dynamic transmission). communication state shows more fluctuation in transmission shape due to data accumulation and flooding, as shown in Figure 4.4 between 9:30 pm and 12:00 am. Dynamic transmission state transmission reduction is similar to ECG.