## 8 Conclusions  
In this paper, we have investigated the communications performance of a VLP system using a QADA receiver. We have shown that the FOV for communications (FOV-C) is different from the FOV for positioning (FOV-P), and that FOV-C is always larger than FOV-P. This is because, to be used in calculating the position of the receiver, the signals from a given luminaire must reach all four quadrants of the receiver quadrant PD, whereas for communications only one quadrant is required.  
In the SNR simulations of the VLP system, we assumed that the dominant source of noise is shot noise due ambient light. So that these simulations represent realistic situations, we calculated from first principles typical levels of shot noise when the ambient light is generated by LED lighting. These were shown to be much lower than the worst-case shot noise values often used in the literature. These new values were used in the simulations.  
SNR results were presented for the case where a single luminaire is transmitting. This transmitter is pointing directly downwards, and the receiver is placed on a plane 1.8 m below the transmitter and is pointing directly upwards. Results were presented as a function of receiver position for transmitters with two different Lambertian radiation patterns (\(m=1\) and \(m=4\)). In general, the SNRs of the signals received by different quadrants of the PD are different. It was shown that this diversity can be exploited to improve the overall SNR of the VLP system. Three different ways of exploiting this diversity were considered: selection combining, EGC and MRC. Expressions were derived for the SNR for EGC and MRC. The simulations showed that all combining methods increase the area in which the signals are received with high SNR and that MRC gives the best performance. For the more directional transmitter (\(m=4\)), the area with high received SNR is reduced.  
Simulation results of the VLP system were presented for receiver designs with two different FOV-Cs. These showed that reducing FOV-C reduces the area where signals are received with high SNR but increases the SNR for receiver positions directly below the transmitter. Finally, the effect of tilt was explored. The simulations showed that for all the cases considered, the SNR was always above 20 dB within the FOV-P. This demonstrates that the communication properties of the receiver will not be a limitation when a QADA is used in a VLP system.  
Most AOA positioning algorithms depend on receiving signals from at least three luminaires. To evaluate the communications performance in a complete positioning system, the BER as a function of position was calculated in a typical 3 m by 3 m room with four luminaires. The transmit power of the luminaires was chosen to meet typical standards for indoor illumination. ACO-OFDM with 4-QAM modulation was used. In all cases a BER less than \(10^{-4}\) was achieved within the FOV-P demonstrating again that communications performance is not going to limit the positioning performance of VLP systems that use QADA.  
Finally, experimental results were presented. These confirmed that reliable communications can be supported by the QADA and that using diversity combining significantly improves the performance.  
**Author Contributions:** conceptualization, M.M.A.M., S.C. and J.A.; methodology, M.M.A.M. and J.A.; software, M.M.A.M.; formal analysis, M.M.A.M. and C.H.; investigation, M.M.A.M.; writing-original draft preparation, M.M.A.M. and J.A.; writing-review and editing, M.M.A.M., C.H., S.C., A.N. and J.A.; visualization, M.M.A.M.; supervision, J.A.; project administration, J.A.; funding acquisition, A.N. and J.A. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Australian Research Council's (ARC) Discovery funding schemes (DP150100003 and DP180100872) and an Australian Government Research Training Program (RTP) Scholarship.  
**Conflicts of Interest:** The authors declare no conflict of interest.