Visible light communications (VLC) based on intensity-modulation with direct-detection (IM/DD) is a promising technology to offer broadband wireless Internet access. A VLC system based on the well-known multi-carrier orthogonal frequency-division multiplexing (OFDM) modulation has the potential to coexist with radio frequency (RF) technologies such as WiFi. Recently, the VLC technology is considered to enable wireless connectivity of resource limited devices, thus enabling the Internet-of-Things (IoT) vision. This paper presents a novel concept for modulating multiple light sources to realize a lightweight version of OFDM communication chain suitable for resource limited IoT devices. In such proposed system, different sinusoidal streams from an array of light sources are carrying the encoded OFDM time-domain samples, thus enabling the realization of the Fourier transformation in the optical domain. Accordingly, the fast Fourier transform (FFT) operation required for the demodulation at the receiver side is eliminated, which is crucial for resource limited IoT devices. In addition, the proposed concept, (1) offers the same spectral efficiency as the well-known asymmetrically clipped optical OFDM (ACO-OFDM), (2) reduces the bandwidth requirement from individual light sources, (3) reduces the peak-to-average power ratio (PAPR) of the signal formed and transmitted over the optical channel, and (4) supports simultaneous sensing applications using the different sinusoidal streams that are acting as unique beaconing signals. The proposed concept is numerically evaluated and compared with ACO-OFDM. The obtained results reveal a clear reduction in the PAPR with ∼ 5dB at a complementary cumulative distribution function (CCDF) of 10<sup>−2</sup> and remarkable enhancement in bit-error performance.
In this paper, we consider the problem of designing energy efficient light emitting diodes (LEDs) layout
while satisfying the illumination constraints. Towards this objective, we present a simple approach to the
illumination design problem based on the concept of the virtual LED. We formulate a constrained optimization
problem for minimizing the power consumption while maintaining a near-uniform illumination throughout
the room. By solving the resulting constrained linear program, we obtain the number of required LEDs and
the optimal output luminous intensities that achieve the desired illumination constraints.