Chromaticity-Adaptive Generalized Spatial Modulation for MIMO VLC With Multi-Color LEDs

Abstract

In this paper, we propose a chromaticity-adaptive generalized spatial modulation (CA-GSM) method for multiple-input multiple-output (MIMO) visible light communication (VLC) systems with quadrichromatic LEDs (QLEDs). After the MIMO-VLC system model is constructed, the CA-GSM method based on chromaticity-adaptive constellation optimization is brought forward accounting for the correlated MIMO channel with multi-color crosstalk and quadrangle chromaticity region. This work mainly investigates the optimal active QLED selection pattern in CA-GSM aiming at maximizing the minimum Euclidean distance of received multi-color constellation. Considering power, amplitude and chromaticity constraints, the optimization problem of chromaticity-adaptive constellation is transformed and solved by the linear approximation of Taylor series. Therefore, the design algorithm of CA-GSM is derived with the optimal QLED selection pattern. Simulation results verify that our proposed CA-GSM can achieve performance improvement compared to the multi-stream spatial modulation and the conventional design method without considering channel.

Effective Receiver Design for MIMO Visible Light Communication with Quadrichromatic LEDs

“…In this paper, each QLED is assumed to employ the general CSK constellation that satisfies the maximum total power [7]. The nonnegative signals also need to satisfy the maximum amplitude value constraint to avoid the clipping distortion and the chromaticity constraint [5]. Moreover, since the design of the transmit signal is not our focus, some issues such as the nonlinear, flickering, or synchronization effect are assumed to be perfect [5][6][7]10].…”

“…The nonnegative signals also need to satisfy the maximum amplitude value constraint to avoid the clipping distortion and the chromaticity constraint [5]. Moreover, since the design of the transmit signal is not our focus, some issues such as the nonlinear, flickering, or synchronization effect are assumed to be perfect [5][6][7]10]. Meanwhile, a data stream is mapped to a symbol vector chosen from the above constellation S. After transmitting through an optical channel, the received signal vector can be given by…”

“…H denotes the channel matrix between the transmitters and the receivers with optical filters. We consider herein the crosstalk between adjacent colors and the 4N t × 4N r mutli-color channel matrix H in [5] can be expressed by two matrices as…”

“…where h c ij represents the gain factor between the j-th QLED's chip of the c color and the i-th receiver's PD of c color. For simplicity, since both QLEDs and multi-color receivers are assumed to be assembled in a compact package, and the distances between the transmitters and the multi-color receivers are much larger than either the physical size of the QLED clusters or the receiver clusters; hence, both could be viewed as points [5] and [7], respectively. Consequently, we can consider the same channel matrices H c for c ∈ {R,A,G,B} and omit the color notation c for a simple representation.…”

“…Multi-color red/green/blue (RGB) LED with better color rendering index and multi-channel parallel transmission can provide a higher transmission rate with a lower error rate in comparison with ordinary LED [4]. Moreover, to improve the color qualities of white illumination light; quadrichromatic LED (QLED), usually with red/amber/green/blue (RAGB) colors, has been suggested as an alternative to RGB LED [5]. Color shift keying (CSK) is a modulation method that exploits the diversity of a multi color LED to modulate the data with the intensity signals of different colors [6].…”