# Validation of Wired and Wireless Interconnected Body Sensor Networks
## 3 Proposed Energy Efficient Data Transfer in Wireless DigiAID  
Network topology plays an important role for efficient and reliable data transfer. In wireless DigiAID the topology is dynamically changing due to body movements and postures. In order to cope with dynamically changing topology we have used Collection Tree Protocol (CTP) [51], a default routing protocol in TinyOS [52]. CTP has a capability to efficiently switch to second route in case the first fails, with almost 90% reliability of packet transmission. Therefore, to examine topological effects for wireless DigiAID, all motes are programmed with CTP using TinyOS. Each node is labeled with unique Identification (ID) from 1 to 8 respectively and the BS is assigned with ID = 0. All the readings are taken for an estimated time of 10 to 15 min. The transmission power is managed by the IRIS mote radio. It provides 16 transmission levels ranging from +3 dBm to \(-\)17.2 dBm. The radio power is tuned accordingly to check the reliability of packets and to monitor the change in topology for each body movement (sitting, walking and sleeping). In order to estimate the packet reception, data is transmitted and allowed to form different topology for each power level. The data rate of each sensor node is one packet per second. For HR and RR, the frequency of data is low from the sensor. Thus, the loss of data is minimal and fulfil the requirement for proof of concept. However, for more sophisticated health parameters such as ECG or EEG, where the frequency of data from sensors is high the data can be aggregated [53; 54] and/or the data rate can be increased [55; 56]. For retrieving data from multiple sensors we adapted random timers to transmit the data. For higher data rates various MAC protocols for WBAN can be considered to avoid collisions [57; 58]. The readings are taken at four different transmission (TX) power levels, that is, \(TX_{1}\) = 3.0 dBm (maximum power of IRIS mote), \(TX_{2}\) = \(-\)2.2 dBm, \(TX_{3}\) = \(-\)17.2 dBm (minimum power of IRIS mote) and \(TX_{4}\) = \(-\)17.2 dBm (the antenna is covered with aluminum foil). The aluminum foil is used to further degrade the channel beyond the minimum power of IRIS mote to observe its impact on the communication. For each  
Figure 3: Wireless DigiAID system. body movement four experiments have been performed to observe the effect of the power on the topology formed. According to Reference [59], the total radio energy consumed during data transmission is given as follows  
\[E_{TX}(k,d,n)=E_{TX_{el}}*k+E_{a}(n)*k*d^{n}\]  
where, \(k\) is the number of bits transmitted over distance \(d\), with the path loss coefficient \(n\). \(E_{TX_{el}}\) and \(E_{a}\) are the transmitter energy dissipated by its circuitry and amplifier respectively. By keeping all parameters of above equation constant, except \(d\) and \(n\), the equation becomes,  
\[E_{TX}\propto d^{n}\]  
This elucidation says greater node separation and greater path loss exponent results in a greater expenditure of energy during transmission. This energy wastage is due to the increase of path loss with the increasing distance. To estimate the path loss with the increasing distance for a wireless BSN, from Reference [60] it is given as,  
\[PL_{dB}=PL_{0,dB}+10*n*log(d/d_{o})\]  
The \(PL_{dB}\) gives us path loss at distance \(d\) while considering the reference path loss \(PL_{0,dB}\) at a reference distance of \(d_{o}\). For WBSN environment, from Reference [61]\(n=5.9\) and \(PL_{0,dB}=48.8\) dB at \(d_{o}=10\) cm. The relation of path loss corresponding to increasing distance would be given as in Figure 4. Here, the Non-Line-Of-Sight (NLOS) communication is considered due to the obstructed irregular surface of the human body. Considering the movement of walking as shown in Figure 5, if we consider the node of ankle, it can be shown that with every step a person is taking, distance between sending node and BS node is continuously changing. Sometimes minimum power is enough to send our data reliably or sometimes it may result in loss of data.