| Summary: | Currently, visible light positioning (VLP) enabling an illumination infrastructure requires a costly retrofit. Intensity modulation systems not only necessitate changes to the internal LED driving module, but decrease the LEDs’ radiant flux as well. This hinders the infrastructure’s ability to meet the maintained illuminance standards. Ideally, the LEDs could be left unmodulated, i.e., unmodulated VLP (uVLP). uVLP systems, inherently low-cost, exploit the characteristics of the light signals of opportunity (LSOOP) to infer a position. In this paper, it is shown that proper signal processing allows using the LED’s characteristic frequency (CF) as a discriminative feature in photodiode (PD)-based received signal strength (RSS) uVLP. This manuscript investigates and compares the aptitude of (future) RSS-based uVLP and VLP systems in terms of their feasibility, cost and accuracy. It demonstrates that CF-based uVLP exhibits an acceptable loss of accuracy compared to (regular) VLP. For point source-like LEDs, uVLP only worsens the trilateration-based median <inline-formula><math display="inline"><semantics><msub><mi>p</mi><mn>50</mn></msub></semantics></math></inline-formula> and 90th percentile root-mean-square error <inline-formula><math display="inline"><semantics><msub><mi>p</mi><mn>90</mn></msub></semantics></math></inline-formula> from <inline-formula><math display="inline"><semantics><mrow><mn>5.3</mn><mspace width="0.277778em"></mspace><mi mathvariant="normal">c</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula> to <inline-formula><math display="inline"><semantics><mrow><mn>7.9</mn><mspace width="0.277778em"></mspace><mi mathvariant="normal">c</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula> (+50%) and from <inline-formula><math display="inline"><semantics><mrow><mn>9.6</mn><mspace width="0.277778em"></mspace><mi mathvariant="normal">c</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula> to <inline-formula><math display="inline"><semantics><mrow><mn>15.6</mn><mspace width="0.277778em"></mspace><mi mathvariant="normal">c</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula> (+62%), in the <inline-formula><math display="inline"><semantics><mrow><mn>4</mn><mspace width="0.277778em"></mspace><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula> × <inline-formula><math display="inline"><semantics><mrow><mn>4</mn><mspace width="0.277778em"></mspace><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula> room under consideration. A large experimental validation shows that employing a robust model-based fingerprinting localisation procedure, instead of trilateration, further boosts uVLP’s <inline-formula><math display="inline"><semantics><msub><mi>p</mi><mn>50</mn></msub></semantics></math></inline-formula> and <inline-formula><math display="inline"><semantics><msub><mi>p</mi><mn>90</mn></msub></semantics></math></inline-formula> accuracy to <inline-formula><math display="inline"><semantics><mrow><mn>5.0</mn><mspace width="0.277778em"></mspace><mi mathvariant="normal">c</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula> and <inline-formula><math display="inline"><semantics><mrow><mn>10.6</mn><mspace width="0.277778em"></mspace><mi mathvariant="normal">c</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula>. When collating with VLP’s <inline-formula><math display="inline"><semantics><mrow><msub><mi>p</mi><mn>50</mn></msub><mo>=</mo><mn>3.5</mn><mspace width="0.277778em"></mspace><mi mathvariant="normal">c</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula> and <inline-formula><math display="inline"><semantics><mrow><msub><mi>p</mi><mn>90</mn></msub><mo>=</mo><mn>6.8</mn><mspace width="0.277778em"></mspace><mi mathvariant="normal">c</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula>, uVLP exhibits a comparable positioning performance at a significantly lower cost and at a higher maintained illuminance, all of which underline uVLP’s high adoption potential. With this work, a significant step is taken towards the development of an accurate and low-cost tracking system.
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