## 3 Analysis of I2O WBAN Systems
### Link Budget Analysis  
The I2O human body environment is lossy producing and high attenuation, so it is important to analyze the link budget when designing wireless communication systems for several scenarios. Two significant elements are: (i) an energy consumption calculation for a required communication link quality; (ii) the effective communication distance estimation when employing a certain transmitting power.  
Based on the European Research Council (ERC) regulations, the maximum input power is 25 \(\mu\)W [19]. In this paper, typical transmitting power values of 1, 10 and 25 \(\mu\)W are selected for further research and discussions. Given the high QoS requirements of healthcare communication systems, similar to other I2O body communication systems, a predetermined BER threshold of \(10^{-3}\) was selected to ensure the communication performance is acceptable [5; 28; 29; 30; 31]. According to Figure 5, the threshold \(SNR_{thr}\) values for BPSK, QPSK, 16 QAM and 16 PSK are approximately 11 dB, 13 dB and 15.5 dB and 18 dB, respectively. The parameters used in the link budget simulations are summarized in Table 4.  
One valuable system parameter that can effectively evaluate the reliability of the communication system using the threshold BER performance is the system margin, \(M_{s}\). A communication channel  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Simulation Parameter** & **Value** \\ \hline Frequency band (GHz) & 2.45 \\ \hline Tx output power (\(\mu\)W) & 1, 10, 25 \\ \hline Antenna gain (dBi) & 0 \\ \hline Coding gain (dB) & 0 \\ \hline Ambient temperature (K) & 310 \\ \hline Liver tissue temperature (K) & 306 \\ \hline Boltzmann constant (JK\({}^{-1}\)) & \(1.38\times 10^{-23}\) \\ \hline BER (predetermined) & \(10^{-3}\) \\ \hline SNR (threshold) (dB) & 11 (BPSK), 13 (QPSK) \\ - & 15.5 (16 QAM), 18 (16 PSK) \\ Selected data rate (Mbps) & 0.25, 5, 30 \\ \hline Selected distance (m) & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Parameters for the Link Budget Simulations.  
Figure 5: BER performance comparison between BPSK, QPSK, 16 QAM and 16 PSK.  
with a negative link margin has insufficient power to transmit data and thus, is essential to offer adequate link to ensure that the communication system is reliable [33]. \(M_{s}\) is given by determining the SNR above the threshold level (\(SNR_{thr}\)) as:  
\[M_{s}=SNR_{dB}-SNR_{thr}>0 \tag{13}\]  
Figures 6-9 show the dependence of system margin versus communication link distance, with several levels of data rates and multiple modulation techniques utilizing transmitter powers of 1 \(\upmu\)W, 10 \(\upmu\)W and 25 \(\upmu\)W. For health IoT applications, such as hospital real-time healthcare monitoring services, where the receiving sensor or device is normally placed 1 meter away from patients, all the above-mentioned methods could support satisfactory wireless data transmission [1; 2; 23]. Due to the constraints on the battery energy supply of the implantable device or sensor, trade-offs between transmitting power and communication channel quality should be taken into account [11; 12]. Results show that, as one might expect, higher transmitting power can achieve longer communication distances for a certain data rate. The communication system can also cover longer distances by using lower transmission data rates when compared with higher data rates. For conditions when under the same data rates and transmitting powers, the BPSK modulation scheme can achieve more reliable transmission than the other investigated modulation schemes. Furthermore, we suggest a fade system margin of a few dBs that accounts for energy losses caused by the antenna orientations and body movements to ensure the reliability of the data transmission, when designing real-time healthcare wireless monitoring systems.  
Figure 6: Link margin versus distance using BPSK at multiple levels of data rates and powers.  
Figure 7: Link margin versus distance employing QPSK at multiple levels of data rates and powers.