680 research outputs found
Optical Asymmetric Modulation for VLC Systems
The explosive growth of connected devices and the increasing number of broadband users have led to an unprecedented growth in traffic demand. To this effect, the next generation wireless systems are envisioned to meet this growth and offer a potential data rate of 10 Gbps or more. In this context, an attractive solution to the current spectrum crunch issue is to exploit the visible light spectrum for the realization of high-speed commutation systems. However, this requires solutions to certain challenges relating to visible light communications (VLC), such as the stringent requirements of VLC-based intensity modulation and direct detection (IM/DD), which require signals to be real and unipolar. The present work proposes a novel power-domain multiplexing based optical asymmetric modulation (OAM) scheme for indoor VLC systems, which is particularly adapted to transmit high-order modulation signals using linear real and unipolar constellations that fit into the restrictions of IM/DD systems. It is shown that the proposed scheme provides improved system performance that outperforms alternative modulation schemes, at no extra complexity
Design guidelines for spatial modulation
A new class of low-complexity, yet energyefficient Multiple-Input Multiple-Output (MIMO) transmission techniques, namely the family of Spatial Modulation (SM) aided MIMOs (SM-MIMO) has emerged. These systems are capable of exploiting the spatial dimensions (i.e. the antenna indices) as an additional dimension invoked for transmitting information, apart from the traditional Amplitude and Phase Modulation (APM). SM is capable of efficiently operating in diverse MIMO configurations in the context of future communication systems. It constitutes a promising transmission candidate for large-scale MIMO design and for the indoor optical wireless communication whilst relying on a single-Radio Frequency (RF) chain. Moreover, SM may also be viewed as an entirely new hybrid modulation scheme, which is still in its infancy. This paper aims for providing a general survey of the SM design framework as well as of its intrinsic limits. In particular, we focus our attention on the associated transceiver design, on spatial constellation optimization, on link adaptation techniques, on distributed/ cooperative protocol design issues, and on their meritorious variants
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
DC-Informative Joint Color-Frequency Modulation for Visible Light Communications
In this paper, we consider the problem of constellation design for a visible
light communication (VLC) system using red/green/blue light-emitting diodes
(RGB LED), and propose a method termed DC-informative joint color-frequency
modulation (DCI-JCFM). This method jointly utilizes available diversity
resources including different optical wavelengths, multiple baseband
subcarriers, and adaptive DC-bias. Constellation is designed in a high
dimensional space, where the compact sphere packing advantage over lower
dimensional counterparts is utilized. Taking into account multiple practical
illumination constraints, a non-convex optimization problem is formulated,
seeking the least error rate with a fixed spectral efficiency. The proposed
scheme is compared with a decoupled scheme, where constellation is designed
separately for each LED. Notable gains for DCI-JCFM are observed through
simulations where balanced, unbalanced and very unbalanced color illuminations
are considered.Comment: submitted to Journal of Lightwave Technology, Aug. 5th 201
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
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