# Optical Boundaries for LED-Based Indoor Positioning System
## 6 Conclusions  
The boundary of LED footprints plays a vital role in position estimation of proximity LED-based IPS. In this work, the boundary of an LED footprint is defined based on the properties of a mobile receiver. This technique can be used in RSS, AoA, and fingerprinting positioning systems that involve overlap of LED beams and use the PDM multiplexing technique. This work shows that by properly defining the optical boundary, unnecessary delays in positioning time can be prevented. It first establishes and validates a relationship between the BER and PDR of packets received at the receiver and then shows the effect of encoding protocol design on the BER. These relationships are used to show how signal quality deterioration due to undefined optical boundary affects the positioning time of the IPS. For a single LED transmitter, the defined optical boundary reduced the positioning delay by a factor of 13 for a 4-bit packet and by 230 for 12-bit packets. When overlap, which is used to improve positioning accuracy, is considered, the defined optical boundary reduces the positioning delay by a factor of 12 and 287 for 4-bit and 12-bit packets, respectively. The effect of a tilted receiver is also studied, and this work shows that for a 4\({}^{\circ}\) tilt, the positioning time is improved by a factor of 22 and 1464 for 4-bit and 12-bit packets, respectively. In conclusion, full angle boundaries waste positioning time, and hence are not usable for LED based positioning. In terms of positioning accuracy, the use of a threshold angle maintains a systems positioning accuracy by changing the number of LEDs required. With 32 LEDs, a positioning error of 230.99 mm is achieved, and the error reduces as the number of LEDs increases. This work has shown that a desired positioning accuracy can be achieved while using a receiver based threshold angle in the positioning system design to reduce positioning delay significantly. This facilitates the design of a simple lightweight wearable receiver for indoor positioning.  
For future work, the effect of using other encoding schemes to design the positioning protocol will be determined.  
Conceptualization, O.R.P. and S.S.; Formal analysis, O.R.P., S.S., W.O.P. and R.R.-I.; Funding acquisition, S.S.; Investigation, O.R.P., S.S., W.O.P. and R.R.-I.; Methodology, O.R.P., S.S., W.O.P. and R.R.-I.; Project administration, S.S., W.O.P. and R.R.-I.; Resources, O.R.P.; Software, O.R.P.; Supervision, S.S., W.O.P. and R.R.-I; Validation, O.R.P.; Visualization, O.R.P.; Writing original draft, O.R.P.; Writing review and editing, S.S., W.O.P. and R.R.-I.  
This research received no external funding.  
The authors would like to appreciate the support for this research work from the School of Engineering and Built Environment of Glasgow Caledonian University through the University sponsored research studentship.  
The authors declare no conflict of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} LED & Light emitting diode \\ IPS & Indoor positioning system \\ RF & Radio frequency \\ RSS & Received signal strength \\ \end{tabular}