Optimal Power Efficiency of Spatial Multiplexing in
Optical Wireless MIMO Channels
Xiangchuan Gao,Yuanyuan Zhang, Zhongyong Wang, Xingye Wang, Linlin Duan
School of Information and Engineering
Zheng Zhou University, Zheng Zhou, China
Email: iexcgao@zzu.edu.cn
Abstract—This paper investigates the problem of power effi-
ciency for spatially multiplexed multiple-input multiple-output
(MIMO) visible light communication (VLC) system. In this
system, it combines the optical communication with illumination,
but the offset power, which is used to satisfy the nonnegative
constraint of the transmitter-side signal after precoding, leads
to the reduction of power efficiency. In this paper, a negative
inverse diagonal(NID) matrix based on optimal maximum like-
lihood (ML) criterion and suboptimal criterion is designed to
minimise the offset power consumption, which has no effect in
the conventional power allocation. We theoretically derive the
detection signal at receiver with multiplying by the same NID
matrix. The focus of this paper is the capacity and average power
efficiency performance of the system. Simulation results show
that our proposed method improves power efficiency significantly.
Furthermore, we show that our scheme provides higher capacity
of the system than the method without designing the NID matrix.
Index Terms—Visible light communicationVLC, Optical wire-
less MIMO, SVD, Negative inverse diagonal(NID) matrix
I. INTRODUCTION
Light emitting diodes (LED) and laser diodes (LD) are
expected to be the substitute of conventional lighting sources
due to its lower power consumption, high efficiency and longer
lifetime. Since it is possible to modulate electric signals to
visible lightwave, LED can be used as transmitters of signals
containing information bits [1], [2]. The indoor visible light
communication (VLC) using optical sources (white LED)
which can be simultaneously utilized for illumination and
data transmission has attracted many researchers interests.
Owing to the demand for higher date rate in communication,
it is essential for VLC system to support high date rate. In
practice, the modulation bandwidth of white LED, which is
typically several MHz, limits the available data rate. Filters
at transceiver such as blue filters, pre-equalizers, and post-
equalizers are used to improve this disadvantage in [3]-[6].
In addition, The authors of [7] proposes wavelength division
multiplexing (WDM) using red, green, and blue (RGB) LED
as one of the possible solutions .
Furthermore, multiple input and multiple output (MIMO)
technique appears attractive to provide high data rate without
wasting additional resources such as power and frequency
[8]. Recognizing that MIMO technique can be beneficial to
improve the performance of the VLC system, researchers
have given various reports. The authors of [9],[10] show
that a very high signal to noise ratio (SNR) is available
in VLC systems. Non-imaging and imaging optical MIMO
approaches are introduced and simulation results verify the
improvement in [9]. In addition, a efficient power and offset
allocation method with SVD-precoder for an arbitrary number
of transmit and receive antennas for optical wireless MIMO
systems is derived in [11], which based on three constraints,
namely, the nonnegativity, the aggregate optical power, and
the bit error rate requirement, simulation results show that the
proposed allocation method gives a better spectral efficiency .
However, with the SVD-precoder, there are negative element
of the precoding matrix to achieve orthogonality. In order to
guarantee the nonnegative constraint of the transmitter-side,
it requires adding a DC gain to the signal after precoding.
It means the offset power is essential, and that will waste
additional power result in reducing power efficiency.
In this paper, we consider a negative inverse diagonal(NID)
matrix to minimise the offset power, without effecting in the
power allocation in [11]. The NID matrix is designed based on
optimal maximum likelihood (ML) criterion and suboptimal
criterion. With multiplying the NID matrix by the transmit
precoding matrix, the negative value number of the transmitted
signal will be reduced, and the sum-value of the offset vector
will be less, too. That means the offset power will be drop to
improve the power efficiency. With multiplying by the same
NID matrix at receive, we can recover the detection signal. We
verify from our some selective simulations that the proposed
method improves the power efficiency significantly, and the
proposed scheme provides higher capacity of the system than
the method without the NID matrix.
The rest of this paper is organized as follows. The system
model including channel model, transmitter and receiver is
described in Section II. Section III presents the problem to de-
sign NID matrix respectively based on optimal and suboptimal
criterion. Simulation results for the performance comparison
will be shown and interpreted in Section IV. Finally, Section
V gives the conclusion of the paper.
Throughout this paper, we use the following notations.
Upper case and lower case boldface are used to employ
matrices and vectors, respectively. For arbitrary matrix A, A
|
and A
−1
denotes the transpose and the inverse of matrix A,
respectively. ⊗ denotes the convolution operator, and E[•]
denotes the expectation operator.
2014 9th International Conference on Communications and Networking in China (CHINACOM)
978-1-4799-5970-9 © 2014 IEEE422