# An Optical Interference Suppression Scheme for TCSPC Flash LiDAR Imagers
## 7 Conclusions and Future Work  
This work presents the successful implementation of an optical interference suppression scheme for TCSPC flash LiDAR imagers. By applying the method described in this paper, a TCSPC flash LiDAR can effectively operate in environments shared with devices emitting modulated optical signals of arbitrary shape. This is a critical requirement for LiDAR imagers intended to operate in uncontrolled environments where other LiDAR cameras with various architectures and characteristics are expected to be present and active. The robustness of this method against intentional attacks \begin{table}
\begin{tabular}{c c} \hline \hline \(L\)**[bits]** & **PRF\({}_{\text{eff}}\)** \\ \hline
3 & 963.9 KHz \\
4 & 919.5 KHz \\
5 & 842.1 KHz \\
6 & 720.7 KHz \\
8 & 386.5 KHz \\
16 & 2.4 KHz \\
32 & 0.04 Hz \\ \hline \hline \end{tabular}
\end{table} 
Table 2: This table provides a correspondence between the length of the LFSR and the effective PRF of the system running at 80 MHz and using complete m-sequences. Figure 12: This plot illustrates the interference suppression ratio as a function of the width of the bit-mask used to define the modulo operator. The experiment was run at \(T_{\text{int}}=100\) ms integration time. By applying a modulo operator to the state of a 32-bit LFSR, we can guarantee a long, non-repeating sequence (property of long registers) and a minimal impact on PRF\({}_{\text{eff}}\) (property of short registers). The increased randomness of the sequence translates directly into a better and more uniform dispersion of the aggressor. The result is a net improvement of the suppression ratio that reaches 50 dB for \(W_{m}=6\). depends on the ability of the aggressor to predict the emission time of each laser pulse of the victim. The method presented in this paper is independent of the specific RNG used. In this paper, we chose to implement a fixed m-sequence generated by a LFSR as an example of an RNG. Hardening the method against intentional interference implies choosing a high-entropy RNG producing long sequences of non-repeating values. Typical applications in which this work will prove to be useful are automotive sensing for ADAS and autonomous driving, automated guided vehicle (AGV) navigation, and simultaneous localization and mapping (SLAM). This work is especially significant for flash LiDAR imagers as they are more susceptible to optical interference than scanning LiDARs. Several directions could be taken to improve and further develop the technique presented in this paper. One interesting possibility to be examined is the extension of this work to include the rejection of MPI self-interference. The authors intend to investigate the properties of alternative pseudorandom number generators (PRNGs) with different statistical distributions and the possibility of using quasi-continuous delay steps, as a necessary measure to enhance the victim's resilience against intentional attacks. [PERSON] conceived the method and performed the theoretical analysis. [PERSON] contributed to the refinement of the concept and the implementation of the necessary firmware. [PERSON] and [PERSON] designed the experiments. [PERSON] executed the experiments, collected raw data, and validated it. [PERSON] performed the final data treatment and extracted the figures of merit. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 783119 (project SECREDAS, covering security for automated systems). The authors gratefully acknowledge the contribution of the following individuals and institutions: [PERSON] and his team at HuCE microLab for designing and building the FPGA-based development kit used in this work; [PERSON] for executing preliminary simulations and contributing to technical documentation; and the R&D team at Fastree3D for the useful exchanges during the execution of the experiments and the redaction of the paper. The authors declare no conflict of interest.