727 research outputs found
Optical MIMO-OFDM with Generalized LED Index Modulation
Due to copyright restrictions, the access to the full text of this article is only available via subscription.Visible light communications (VLC) is a promising and uncharted new technology for the next generation of wireless communication systems. This paper proposes a novel generalized light emitting diode (LED) index modulation method for multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM)-based VLC systems. The proposed scheme avoids the typical spectrum efficiency losses incurred by time- and frequency-domain shaping in OFDM signals. This is achieved by exploiting spatial multiplexing along with LED index modulation. Accordingly, real and imaginary components of the complex time-domain OFDM signals are separated first, then resulting bipolar signals are transmitted over a VLC channel by encoding sign information in LED indexes. As a benchmark, we demonstrate the performance analysis of our proposed system for both analytical and physical channel models. Furthermore, two novel receiver designs are proposed. Each one is suitable for frequency-flat or selective channel scenarios. It has been shown via extensive computer simulations that the proposed scheme achieves considerably better bit error ratio versus signal-to-noise-ratio performance than the existing VLC-MIMO-OFDM systems that use the same number of transmit and receive units [LEDs and photo diodes (PDs)]. Compared with the single-input single-output (SISO) DC biased optical (DCO)-OFDM system, both spectral efficiency and DC bias can be doubled and removed respectively simply by exploiting a MIMO configuration.European Cooperation in Science and Technology (COST); The Scientific and Technological Research Council of Turkey (TUBITAK) Research; EPSRC under Established Career Fellowshi
Index Modulation-Aided OFDM for Visible Light Communications
Index modulation-aided orthogonal frequency-division multiplexing(IM-OFDM) is a promising modulation technique to achieve high spectral and energy efficiency. In this chapter, the conventional optical OFDM schemes are firstly reviewed, followed by the principles of IM-OFDM. The application of IM-OFDM in visible light communication (VLC) systems is introduced, and its performance is compared with conventional optical OFDM, which verifies its superiority. Finally, the challenges and opportunities of IM-OFDM are discussed for the VLC applications
Precoded Chebyshev-NLMS based pre-distorter for nonlinear LED compensation in NOMA-VLC
Visible light communication (VLC) is one of the main technologies driving the
future 5G communication systems due to its ability to support high data rates
with low power consumption, thereby facilitating high speed green
communications. To further increase the capacity of VLC systems, a technique
called non-orthogonal multiple access (NOMA) has been suggested to cater to
increasing demand for bandwidth, whereby users' signals are superimposed prior
to transmission and detected at each user equipment using successive
interference cancellation (SIC). Some recent results on NOMA exist which
greatly enhance the achievable capacity as compared to orthogonal multiple
access techniques. However, one of the performance-limiting factors affecting
VLC systems is the nonlinear characteristics of a light emitting diode (LED).
This paper considers the nonlinear LED characteristics in the design of
pre-distorter for cognitive radio inspired NOMA in VLC, and proposes singular
value decomposition based Chebyshev precoding to improve performance of
nonlinear multiple-input multiple output NOMA-VLC. A novel and generalized
power allocation strategy is also derived in this work, which is valid even in
scenarios when users experience similar channels. Additionally, in this work,
analytical upper bounds for the bit error rate of the proposed detector are
derived for square -quadrature amplitude modulation.Comment: R. Mitra and V. Bhatia are with Indian Institute of Technology
Indore, Indore-453552, India, Email:[email protected],
[email protected]. This work was submitted to IEEE Transactions on
Communications on October 26, 2016, decisioned on March 3, 2017, and revised
on April 25, 2017, and is currently under review in IEEE Transactions on
Communication
Generalized Spatial Modulation in Indoor Wireless Visible Light Communication
In this paper, we investigate the performance of generalized spatial
modulation (GSM) in indoor wireless visible light communication (VLC) systems.
GSM uses light emitting diodes (LED), but activates only of them at
a given time. Spatial modulation and spatial multiplexing are special cases of
GSM with and , respectively. We first derive an analytical
upper bound on the bit error rate (BER) for maximum likelihood (ML) detection
of GSM in VLC systems. Analysis and simulation results show that the derived
upper bound is very tight at medium to high signal-to-noise ratios (SNR). The
channel gains and channel correlations influence the GSM performance such that
the best BER is achieved at an optimum LED spacing. Also, for a fixed
transmission efficiency, the performance of GSM in VLC improves as the
half-power semi-angle of the LEDs is decreased. We then compare the performance
of GSM in VLC systems with those of other MIMO schemes such as spatial
multiplexing (SMP), space shift keying (SSK), generalized space shift keying
(GSSK), and spatial modulation (SM). Analysis and simulation results show that
GSM in VLC outperforms the other considered MIMO schemes at moderate to high
SNRs; for example, for 8 bits per channel use, GSM outperforms SMP and GSSK by
about 21 dB, and SM by about 10 dB at BER
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