# Low-Complexity Channel Codes for Reliable Molecular Communication via Diffusion
## 3 Results and Discussion
### Simulation Results
The big difference between these figures relies on the \(\tau\) value, which in Figure 6 is 2, while in Figure 7 is increased to 10. Analyzing the results for the different \(\tau\) values, it is noticeable a BER improvement in Figure 7 which has a higher \(\tau\) value, and thus a higher \(T_{s}\). Increasing the \(T_{s}\) means that the molecules will have more time to diffuse and reach the receiver, reducing the ISI. Note, however, that a higher \(T_{s}\) also means a transmission rate decrease. We tested the system with the OOK modulation, see Figure 8. In Figure 7(a) are the results for NRZ pulses with \(\tau=10\), and in Figure 7(b) are the results for Manchester pulses at \(\tau=2\). Comparing as a first case Figure 6(a) with Figure 7(a), and as a second case Figure 7(a) with Figure 7(b), the results show that the tested channel codes methods had worse BER results in Figure 8, when OOK modulation was used. In the first case, considering a BER reference of \(10^{-2}\), it is observed an overall improvement of approximately 5 dB in terms of \(N_{meloc}/\sigma_{n}^{2}\) when the BCSK modulation is used. For the same reference BER of \(10^{-2}\) it can be observed in the second case (comparison between Figures 7(b) and 7(b)), an improvement of approximately 10 dB in terms of \(N_{meloc}/\sigma_{n}^{2}\) when BCSK modulation is used. Figure 6: BER comparison for all the considered channel codes, using BCSK modulation and with \(\tau=2\). Figure 7: BER comparison for all the considered channel codes, using BCSK modulation and with \(\tau=10\). In Figures 6-8 we can observe that TCH codes clearly had a lower BER than codes with similar rates:  
\(\bullet\) TCH(16,5) and TCH(32,10) codes performed better than HC(3,1) and ISI-mtg(16,5). For instance, in Figure 6b for a BER reference of \(10^{-2}\) it can be observed a gain between 4 dB to 5 dB in terms of \(N_{molce}/\sigma_{n}^{2}\),  
\(\bullet\) TCH(16,8) and TCH(16,10) codes performed better than HC(7,\(A\)) and ISI-mtg(16,8). This is illustrated, for example, in Figure 7a for a BER reference of \(10^{-2}\), they had a gain between 1 dB to 2 dB compared with the HC(7,\(A\)) and a gain between 3 dB to 4 dB compared with the ISI-mtg(16,8). Furthermore, TCH codes with higher codes rates had a better BER performance than other codes with lower rates:  
\(\bullet\) TCH(16,8) and TCH(16,10) were able to perform better than the HC(3,1) and the ISI-mtg(16,5). For example, in Figure 8a and considering a BER reference of \(10^{-2}\), it can be observed a gain between 2 dB to 3 dB in terms of \(N_{molce}/\sigma_{n}^{2}\). As expected, the TCH codes with the same code rate but longer codewords, namely the TCH(32,10) when compared against the TCH(16,5), achieve better BER performances. For instance in Figure 6b the TCH(32,10), considering a reference BER of \(10^{-2}\), had an improvement of approximately 1 dB in terms of \(N_{molce}/\sigma_{n}^{2}\) comparing to the TCH(16,5). Note that longer codewords incur in an additional delay. The results of our simulations proved that the TCH codes achieved a better BER performance against the other tested channel correcting codes, independently of the symbol duration, type of pulse, and modulation.