# A Novel Ranging Technique Based on Optical Camera Communications and Time Difference of Arrival
## 7 Discussion
The angular accuracy (vertical resolution over FOV) has the same impact as the object's physical size since it affects the projected image in the same manner. Finally, the smaller \(T_{guard}\) is, the more possible acquiring complete pulses within the ROI is (Equation (6)). Furthermore, significant values of \(T_{guard}\) may lead to a situation in which some frames could present energy-less ROI. This means that no pulse would be allocated inside and, hence, more frames must be acquired with the subsequent increment of the overall measurement time. Table 3 compares the system's error performance and complexity with the current state-of-the-art image-based location systems. It can be observed that the use of the proposed TDoA-assisted OCC-based ranging enhances the performance compared to traditional image-based systems. This table shows the performance using the baseline parameters of Table 2, but they could be pushed further by properly selecting them. In this work, blooming has been neglected assuming that the irradiance is small enough, but it would affect the error introducing a distance-independent bias and lower bound on \(T_{guard}\). Therefore, the potential effect of blooming could be easily calibrated and compensated. A possible limitation of the proposed strategy is the possibility of synchronism between emitter and receiver. This occurs when the emitter's blinking rate is an integer (or close) multiple of the receiver's capture rate. Then, the acquired frames would not comply with the assumed statistical uncorrelation. To mitigate this harmful effect, a random back-off (e.g., exponential back-off) could be used instead of a fixed \(T_{guard}\). Finally, the effect of background illumination (sunlight or other light sources) has not been analyzed in this work. Nevertheless, its effects on the measurement performance would be presumably negligible. On the one side, the use of imaging optics maps solid angles to camera pixels, separating the measurement lamp and other illumination sources in the captured frames. This reduces to zero the interference unless the other background sources were overlapped with the ROI. On the other hand, reflections of these background sources (including the sunlight) on the measurement lamp could introduce bias to the perceived signal (the lamp's projection would present some energy even when is OFF). This effect could reduce the peak-to-peak value of the received signal. Nonetheless, these contributions are first- or second-order reflections, which imply very low energy, and hence very small impact on the system's performance. Conceptualization, J.R. ([PERSON]) and V.G. ; Data curation, V.G. and J.R. ([PERSON]); Formal analysis, J.R. ([PERSON]), V.G., C.G., J.R. ([PERSON]) and R.P.-J. ; Funding acquisition, J.R. ([PERSON])and R.P.-J. ; Investigation, J.R. ([PERSON])and V.G. ; Methodology, J.R. ([PERSON]); Project administration, J.R. ([PERSON]); Resources, R.P.-J. ; Software, V.G. and C.G. ; Supervision, [PERSON] ([PERSON]); Visualization, [PERSON], C.G. and [PERSON]. ([PERSON]); Writing--original draft, [PERSON] ([PERSON]), V.G. and C.G. ; and Writing--review and editing, [PERSON] ([PERSON]), V.G., C.G., [PERSON] ([PERSON]) and R.P.-J. This research was funded in part by the Spanish Research Administration (MUCIU, Project OSCAR, Ref. TEC2017-84065-C3-1-R) and the Canary Islands Regional Government (Project ATICCuA ProLID2017010053)  
The authors declare that they do not have any conflict of interest regarding the contents of this paper.