Research On Indoor Positioning Based On Visible Light Communications

LEDs are expected to become the dominant indoor lighting technology due to their numerous advantages.These lights can also be switched ON/OFF at high frequencies,enabling their additional use for wireless communication and indoor positioning.Compared with the radio frequency based indoor positioning,visible light positioning(VLP)has many advantages,such as rich bandwidth resource,high security,and most importantly,almost multipath-free propagation.An ideal indoor positioning system(IPS)which can reach real-world users should be accurate(sub-meter accuracy at least),be able to localize common handheld devices(such as smartphones and tablets),easily deployable on existing infrastructures,and robust to environment changes.However,there is no IPS,including VLP and other wireless positioning schemes,which can satisfy all the desired properties.Recently,light-to-camera communication(LCC)techniques have attracted particular interest in the area of indoor positioning.In most LCC-based positioning approaches,a beacon's identity or location is encoded in the modulation frequency,and optically broadcast by the LED luminaire.The smartphone decodes the message of the captured image of the LED(s),and then estimates its location via photogrammetry.However,the luminaire in the image needs to have enough resolution for decoding,which limits the light-to-camera distance.This paper studies the channel model of LCC,and first presents the none-line-of-sight(NLo S)LCC based indoor positioning solutions.This paper makes the following contributions:1)LCC is rapidly emerging as a compelling technology for short-range communication and indoor positioning.However,there is still a lack of theoretical basis for the LCC channel model.Based on the research of LED radiation model,optical channel model and image formation model,we propose the LCC channel model.Since an LCC link employs intensity modulation with direct detection(IM/DD),the single most important quantity characterizing a channel is the DC gain.Different from the photodetectors employed in visible light communication(VLC),which have high sampling rates,LCC utilizes rolling shutter cameras to sample optical signals.The sampling result is a convolution of the received optical power and the shutter function.2)The existing LCC systems either require cameras directly facing to the lights or can only communicate over a single link,resulting in low throughputs and being fragile to ambient illuminant interference.We present HYCACO,a novel LCC system,which enables spatial multiplexing for NLo S LCC.We propose a new modulation scheme,HPSK,to transmit messages from multiple LEDs and also propose the corresponding algorithm,SURD,to demodulate the signals.We first present the relationship between the exposure settings and the features of optical signals,and come up with the optimal optical frequency and camera exposure duration selection strategy.We propose a simple solution to recovery the original optical signals from the signal layer,which improves the robustness of the LCC systems.3)The existing LCC-based positioning systems require the presence of the luminaires in the image,which limits the light-to-camera distance and the range of orientation estimation.Based on the LCC channel model,we propose LIPO,the first camera-based VLP system that utilizes the received signal strength(RSS)for positioning.Compared with the photogrammetrybased approaches,LIPO can work in further light-to-camera distances and extend the range of orientation estimation to full 360?.We also design a modulation scheme to send the identities of LEDs without affecting the original lighting brightness.4)To further reduce the deployment cost and improve the user experience,based on the research results of LIPO,we propose STARLIT,a decimeter-level IPS that only needs one LED lamp.Based on the camera projection model and LCC channel model,we derive the channel model for each sensor pixel.STARLIT uses a smartphone camera to create a virtual sensor array to measure the RSS of the optical signal,and estimates the 3D location of the smartphone via an optimization algorithm.Beyond VLP,the LCC channel model and other techniques proposed in this paper however are more widely applicable for other problems such as device-free localization,intrusion detection,and virtual reality.