501 research outputs found
Generalized Spatial Modulation in Large-Scale Multiuser MIMO Systems
Generalized spatial modulation (GSM) uses transmit antenna elements but
fewer transmit radio frequency (RF) chains, . Spatial modulation (SM)
and spatial multiplexing are special cases of GSM with and
, respectively. In GSM, in addition to conveying information bits
through conventional modulation symbols (for example, QAM), the
indices of the active transmit antennas also convey information bits.
In this paper, we investigate {\em GSM for large-scale multiuser MIMO
communications on the uplink}. Our contributions in this paper include: ()
an average bit error probability (ABEP) analysis for maximum-likelihood
detection in multiuser GSM-MIMO on the uplink, where we derive an upper bound
on the ABEP, and () low-complexity algorithms for GSM-MIMO signal detection
and channel estimation at the base station receiver based on message passing.
The analytical upper bounds on the ABEP are found to be tight at moderate to
high signal-to-noise ratios (SNR). The proposed receiver algorithms are found
to scale very well in complexity while achieving near-optimal performance in
large dimensions. Simulation results show that, for the same spectral
efficiency, multiuser GSM-MIMO can outperform multiuser SM-MIMO as well as
conventional multiuser MIMO, by about 2 to 9 dB at a bit error rate of
. Such SNR gains in GSM-MIMO compared to SM-MIMO and conventional MIMO
can be attributed to the fact that, because of a larger number of spatial index
bits, GSM-MIMO can use a lower-order QAM alphabet which is more power
efficient.Comment: IEEE Trans. on Wireless Communications, accepte
Coded Index Modulation for Non-DC-Biased OFDM in Multiple LED Visible Light Communication
Use of multiple light emitting diodes (LED) is an attractive way to increase
spectral efficiency in visible light communications (VLC). A non-DC-biased OFDM
(NDC OFDM) scheme that uses two LEDs has been proposed in the literature
recently. NDC OFDM has been shown to perform better than other OFDM schemes for
VLC like DC-biased OFDM (DCO OFDM) and asymmetrically clipped OFDM (ACO OFDM)
in multiple LEDs settings. In this paper, we propose an efficient multiple LED
OFDM scheme for VLC which uses {\em coded index modulation}. The proposed
scheme uses two transmitter blocks, each having a pair of LEDs. Within each
block, NDC OFDM signaling is done. The selection of which block is activated in
a signaling interval is decided by information bits (i.e., index bits). In
order to improve the reliability of the index bits at the receiver (which is
critical because of high channel correlation in multiple LEDs settings), we
propose to use coding on the index bits alone. We call the proposed scheme as
CI-NDC OFDM (coded index NDC OFDM) scheme. Simulation results show that, for
the same spectral efficiency, CI-NDC OFDM that uses LDPC coding on the index
bits performs better than NDC OFDM
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
Robust THP Transceiver Designs for Multiuser MIMO Downlink with Imperfect CSIT
In this paper, we present robust joint non-linear transceiver designs for
multiuser multiple-input multiple-output (MIMO) downlink in the presence of
imperfections in the channel state information at the transmitter (CSIT). The
base station (BS) is equipped with multiple transmit antennas, and each user
terminal is equipped with one or more receive antennas. The BS employs
Tomlinson-Harashima precoding (THP) for inter-user interference
pre-cancellation at the transmitter. We consider robust transceiver designs
that jointly optimize the transmit THP filters and receive filter for two
models of CSIT errors. The first model is a stochastic error (SE) model, where
the CSIT error is Gaussian-distributed. This model is applicable when the CSIT
error is dominated by channel estimation error. In this case, the proposed
robust transceiver design seeks to minimize a stochastic function of the sum
mean square error (SMSE) under a constraint on the total BS transmit power. We
propose an iterative algorithm to solve this problem. The other model we
consider is a norm-bounded error (NBE) model, where the CSIT error can be
specified by an uncertainty set. This model is applicable when the CSIT error
is dominated by quantization errors. In this case, we consider a worst-case
design. For this model, we consider robust i) minimum SMSE, ii)
MSE-constrained, and iii) MSE-balancing transceiver designs. We propose
iterative algorithms to solve these problems, wherein each iteration involves a
pair of semi-definite programs (SDP). Further, we consider an extension of the
proposed algorithm to the case with per-antenna power constraints.Comment: Accepted for publication in EURASIP Journal on Advances in Signal
Processing: Special Issue on Multiuser MIMO Transmission with Limited
Feedback, Cooperation, and Coordinatio
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