941 research outputs found
EVM and Achievable Data Rate Analysis of Clipped OFDM Signals in Visible Light Communication
Orthogonal frequency division multiplexing (OFDM) has been considered for
visible light communication (VLC) thanks to its ability to boost data rates as
well as its robustness against frequency-selective fading channels. A major
disadvantage of OFDM is the large dynamic range of its time-domain waveforms,
making OFDM vulnerable to nonlinearity of light emitting diodes (LEDs). DC
biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM
(ACO-OFDM) are two popular OFDM techniques developed for the VLC. In this
paper, we will analyze the performance of the DCO-OFDM and ACO-OFDM signals in
terms of error vector magnitude (EVM), signal-to-distortion ratio (SDR), and
achievable data rates under both average optical power and dynamic optical
power constraints. EVM is a commonly used metric to characterize distortions.
We will describe an approach to numerically calculate the EVM for DCO-OFDM and
ACO-OFDM. We will derive the optimum biasing ratio in the sense of minimizing
EVM for DCO-OFDM. Additionally, we will formulate the EVM minimization problem
as a convex linear optimization problem and obtain an EVM lower bound against
which to compare the DCO-OFDM and ACO-OFDM techniques. We will prove that the
ACO-OFDM can achieve the lower bound. Average optical power and dynamic optical
power are two main constraints in VLC. We will derive the achievable data rates
under these two constraints for both additive white Gaussian noise (AWGN)
channel and frequency-selective channel. We will compare the performance of
DCO-OFDM and ACO-OFDM under different power constraint scenarios
Optical Non-Orthogonal Multiple Access for Visible Light Communication
The proliferation of mobile Internet and connected devices, offering a
variety of services at different levels of performance, represents a major
challenge for the fifth generation wireless networks and beyond. This requires
a paradigm shift towards the development of key enabling techniques for the
next generation wireless networks. In this respect, visible light communication
(VLC) has recently emerged as a new communication paradigm that is capable of
providing ubiquitous connectivity by complementing radio frequency
communications. One of the main challenges of VLC systems, however, is the low
modulation bandwidth of the light-emitting-diodes, which is in the megahertz
range. This article presents a promising technology, referred to as "optical-
non-orthogonal multiple access (O-NOMA)", which is envisioned to address the
key challenges in the next generation of wireless networks. We provide a
detailed overview and analysis of the state-of-the-art integration of O-NOMA in
VLC networks. Furthermore, we provide insights on the potential opportunities
and challenges as well as some open research problems that are envisioned to
pave the way for the future design and implementation of O-NOMA in VLC systems
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
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