# Ambient Environmental Parameter Estimation for Reliable Diffusive Molecular Communications
## 4 Performance Evaluation and Discussion  
### Computer Simulation Configuration  
The results obtained by the simulation based on the CIR were compared with those obtained by the finite element method (FEM) in the system model of diffusive molecular communication. This confirmed that the system model proposed in the study can be used to simulate molecular communication based on the finite element method. As for the heterogeneous temperature distribution shown in Figure 4, the boundary between the regions is set at 0.25 \(\upmu\)m from the transmitting molecule. The number of simulation trials was set to \(10^{6}\) for the BER performance evaluation. Table 1 summarizes the simulation parameters.  
To validate the simulation method based on the FEM in this study, Figure 6 demonstrates calculation examples obtained by simulation and theoretical results. It indicates that the simulation based on the finite element method is effective in diffusive molecule communication because theoretical values and simulation results are in good agreement. A simulation based on the finite element method was applied to a model in which the CIR cannot be easily derived.  
\begin{table}
\begin{tabular}{l l l} \hline \(N_{A}\) & Number of \(A\) molecules & 5000 \\ \(D_{A}\) & Diffusion coefficient of \(A\) molecule & \(5\times 10^{-9}\) m\({}^{2}\) s\({}^{-1}\) \\ \(r_{0}\) & Transmitter and receiver distance & 1.0 \(\upmu\)m \\ \(a\) & Radius of receiver distance & 0.5 \(\upmu\)m \\ \(k_{f}\) & Forward reaction constant & \(2.5\times 10^{-14}\) m\({}^{3}\) s\({}^{-1}\) \\ \(k_{b}\) & Backward reaction constant & \(2\times 10^{4}\) s\({}^{-1}\) \\ \(k_{d}\) & Degradation reaction constant & \(1\times 10^{4}\) s\({}^{-1}\) \\ \(M\) & Number of receptors & 3000 \\ \(r_{s}\) & Radius of receptor & 13.95 nm \\ \(T\) & Temperature & 15, 25, 35 \({}^{\circ}\)C \\ \(a_{TX}\) & Radius of Transmitter & 0, 0.10, 0.20, 0.30 \(\upmu\)m \\ \hline \end{tabular}
\end{table}
Table 1: Channel parameters of diffusive molecular communication.  
As for the evaluation of the communication performance, we used a simulation to transmit transmission signals as sequence length \(L\) and symbol period \(T_{p}\). The communication characteristics of this setup were evaluated via the BER. Figure 7 shows the configuration of the BER performance evaluation with the parameters in Table 2. It is noted that the threshold-based method has a simple detection structure, whereas the MLSE method is based on the optimal detection based on the maximum likelihood estimation.  
The signaling molecules released from the transmitting molecule reaches the surface of the receiving molecule by spreading the molecular communication channel. Therefore, inter-symbol interference is considered [23]. Additionally, additive white gaussian noise (AWGN) was added as an observation error when observing the number of received molecules. This is based on thermal noise in the amplifier, which is used for amplifying the acquired signal intensity when measuring light intensity with a photodetector using GFP as a receiver nanomachine [24].