Spatial Multiplexing for Non-Line-of-Sight Light-to-Camera Communications

Abstract

Light-to-Camera Communications (LCC) have emerged as a new wireless communication technology with great potential to benefit a broad range of applications. However, 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 multiple light emitting diodes (LEDs) with an unaltered camera to communicate via the non-line-of-sight (NLoS) links. Different from other NLoS LCC systems, the proposed scheme is resilient to the complex indoor luminous environment. HYCACO can decode the messages by exploring the mixed reflected optical signals transmitted from multiple LEDs. By further exploiting the rolling shutter mechanism, we present the optimal optical frequencies and camera exposure duration selection strategy to achieve the best performance. We built a hardware prototype to demonstrate the efficiency of the proposed scheme under different application scenarios. The experimental results show that the system throughput reaches 4.5 kbps on iPhone 6s with three transmitters. With the robustness, improved system throughput and ease of use, HYCACO has great potentials to be used in a wide range of applications such as advertising, tagging objects, and device certifications.

Push the Limit of Light-to-Camera Communication

“…Although the transmitters are distributed spatially, it is still another form of ASK. HYCACO [3] presents hybrid phase-shift keying which enables spatial multiplexing for NLOS LCC. RoCLight [20] provides roaming support to LCC systems, which can relay a communication session between neighboring LED luminaries.…”

“…Light-to-camera communication (LCC) has emerged as an up-and-coming area of research [1], which benefits a wide range of applications, e.g., short-range wireless communication [2], [3], indoor localization [4], [5], and vehicle-to-vehicle communication [6], [7]. Widespread use of light-emitting diodes (LEDs) and ubiquitous smartphones offer the opportunity to establish LCC.…”

“…Nevertheless, the reflection light blends multiple transmissions and other light emissions together, which causes severe interference. This challenge can be addressed by exploiting high-order modulation schemes for single transmitter systems [11], or enabling multiplexing for multiple transmitter systems [3]. Although higher symbol rate is desirable for higher throughput, there are two limiting factors, the signal frequency and the camera features.…”

Optical camera communications: Survey, use cases, challenges, and future trends

“…The achievable data rate of DisCo was up to 1 kbps. Recently the authors in [94] developed an OCC system called HYCACO which is based on spatial multiplexing and exploits the non-line of sight optical signals to improve the data rate up to 4.5 kbps. A LEDA2C communication system was proposed in [95] where near-infrared LEDs were used for transmission.…”

Modelization and Characterization of a CMOS Camera as an Optical Real-Time Oscilloscope

“…In various OCC studies, many different challenges were investigated. As an example, blooming and source size-related issues in Directed Line-of-Sight (DLOS) configuration [10]- [13] or signal weakness and background impact in Non Line-of-Sight (NLOS) [14]- [17]. Single-color and RGB LEDs sources were used to implement Multiple Input Multiple Output (MIMO) architectures [18], [19] or Wavelength Division Multiplexing (WDM) systems [20]- [23]; similar systems were also demonstrated using screen-to-camera communication systems [24]- [26], which takes advantage of the detectors array of CMOS cameras and their ability to spatially divide multiple sources and detect separately RGB colors; RGB LEDs were also used to realize Color Shift Keying (CSK) systems using the camera as a single RX for this modulation format [27]- [29]; the spatial separation of the different sources was exploited to calculate the device relative position, thus providing accurate localization and navigation indoor [30]- [32].…”