# Polarization Differential Visible Light Communication: Theory and Experimental Evaluation +
## 5 Conclusions  
In this work, a differential polarization modulation scheme using orthogonal polarizers at both the transmitter and receiver end of the VLC link is demonstrated. A general method to evaluate the \(SNR\) as a function of the receiver rotation with regard to the transmitters is determined and experimentally confirmed by measurements. It is shown that differential polarization VLC provides a reliable link for indoor communication due to the high SNR. The \(SNR\) is however highly dependent on the receiver orientation. As the relative rotation angle nears 45\({}^{\circ}\), the performance of the communication decreases rapidly. It is demonstrated theoretically and proven experimentally that an additional differential receiver pair rotated over 45\({}^{\circ}\) can mitigate this effect drastically by selecting the receiver pair with the highest \(SNR\) for demodulation. The maximum attenuation due to unfavorable receiver rotation is in this case lowered by 3 dB. This demonstrates that the proposed modulation scheme certainly has potential to provide an additional means of transmitting information. In cases where the bounds of the receiver orientation are close to 0\({}^{\circ}\) such as in e.g., Vehicle-to-Vehicle (V2V) communication, a single differential receiver pair can suffice. If this is not the case and any receiver rotation is bound to occur, a second receiver pair can resolve this issue. While the received intensity without receiver polarizers is constant over time, this polarization-based modulation scheme allows for parallel operation alongside conventional intensity-based VLC with no interference. Similarly, the differential operation assures intensity-based VLC does not impede on the polarization-based modulation. As part of future work, there are some interesting points that can be improved upon or further researched. This includes increasing the data rate by modifying the hardware, further automating the data acquisition for different angles using stepper motors, and comparing the proposed modulation technique in terms of performance and robustness to intensity-based modulation in different scenarios. Furthermore, the impact of transmitter induced noise  
Figure 13: Measured \(SNR\) as a function of receiver rotation \(\theta\) at \(h=1.35\,\mathrm{m}\) for setup B.  
components can be further studied to be included in the model. Additionally, the signal processing in this work was executed in post-processing. The performance can be evaluated in real time using dedicated hardware to execute the signal processing, including some important receiver design improvements such as an AC-filter stage and a differential amplifier stage. Finally, complementary polarization-based variants of other conventional modulation schemes such as Phase Shift Keying and Pulse Position Modulation can be evaluated. Conceptualization, J.D.B. and N.S. ; methodology, J.D.B. and N.S. ; software, J.D.B. and W.R.; validation, J.D.B. and W.R.; formal analysis, J.D.B. ; investigation, J.D.B. ; resources, N.S. ; data curation, J.D.B., writing-original draft preparation, J.D.B. ; writing-review and editing, S.Z. and N.S. ; visualization, J.D.B. ; supervision, N.S. ; project administration, S.Z. and N.S. ; funding acquisition, S.Z. and N.S. All authors have read and agreed to the published version of the manuscript. This work was funded by the Central Europe Leuven Strategic Alliance under the Polarization In wireless CommuNICations project (PICNIC - CELSA-19-172). The authors of this work want to thank the involved universities (KU Leuven and CTU Prague) for supporting this research by means of the Central Europe Leuven Strategic Alliance (CELSA) project \"Polarization In wireless CommuNICations (PICNIC)\". The authors declare no conflict of interest. The following abbreviations are used in this manuscript: