QADA-PLUS: a novel two-stage receiver for visible light positioning

In this paper, we introduce a new two-stage receiver structure for visible light positioning (VLP) and a particular implementation of the new structure called the QADA-PLUS receiver. By using two sensors, one a photodiode (PD) based sensor and the other an image-based sensor, the new structure exploits the strengths of both technologies while avoiding their weaknesses. The QADA-PLUS uses a quadrant angular diversity aperture receiver (QADA) for the PD-based stage. The QADA has a very compact, planar structure suitable for incorporation in a smartphone or other small device and has been shown to provide good angular diversity in a proof-of-concept laboratory experiment. The QADA is also, unlike typical image sensors, able to reliably demodulate high frequency visible light signals. In this paper extensive simulation results for a range of typical indoor scenarios and realistic parameters show that the QADA has the potential to accurately estimate the polar and incident angle of light transmitted by LED luminaires. The average absolute error in estimation of incident angle was 0.0006° and for polar angle estimation was 0.005°. A limitation of these simulations is that it is assumed that the luminaires can be modelled as point sources and that the dimensions of the QADA are very precisely known. Incorporation of the QADA in the new two-stage QADA-PLUS receiver removes these limitations in two ways - the image-based receiver provides very accurate angle-of-arrival estimates and the use of visible reference points means that the QADA-PLUS is compatible with luminaires of any shape.