1,191 research outputs found
Efficient Detectors for MIMO-OFDM Systems under Spatial Correlation Antenna Arrays
This work analyzes the performance of the implementable detectors for
multiple-input-multiple-output (MIMO) orthogonal frequency division
multiplexing (OFDM) technique under specific and realistic operation system
condi- tions, including antenna correlation and array configuration.
Time-domain channel model has been used to evaluate the system performance
under realistic communication channel and system scenarios, including different
channel correlation, modulation order and antenna arrays configurations. A
bunch of MIMO-OFDM detectors were analyzed for the purpose of achieve high
performance combined with high capacity systems and manageable computational
complexity. Numerical Monte-Carlo simulations (MCS) demonstrate the channel
selectivity effect, while the impact of the number of antennas, adoption of
linear against heuristic-based detection schemes, and the spatial correlation
effect under linear and planar antenna arrays are analyzed in the MIMO-OFDM
context.Comment: 26 pgs, 16 figures and 5 table
Application of Expurgated PPM to Indoor Visible Light Communications - Part I: Single-User Systems
Visible light communications (VLC) in indoor environments suffer from the
limited bandwidth of LEDs as well as from the inter-symbol interference (ISI)
imposed by multipath. In this work, transmission schemes to improve the
performance of indoor optical wireless communication (OWC) systems are
introduced. Expurgated pulse-position modulation (EPPM) is proposed for this
application since it can provide a wide range of peak to average power ratios
(PAPR) needed for dimming of the indoor illumination. A correlation decoder
used at the receiver is shown to be optimal for indoor VLC systems, which are
shot noise and background-light limited. Interleaving applied on EPPM in order
to decrease the ISI effect in dispersive VLC channels can significantly
decrease the error probability. The proposed interleaving technique makes EPPM
a better modulation option compared to PPM for VLC systems or any other
dispersive OWC system. An overlapped EPPM pulse technique is proposed to
increase the transmission rate when bandwidth-limited white LEDs are used as
sources.Comment: Journal of Lightwave Technolog
Sub-Nyquist Field Trial Using Time Frequency Packed DP-QPSK Super-Channel Within Fixed ITU-T Grid
Sub-Nyquist time frequency packing technique was demonstrated for the first
time in a super channel field trial transmission over long-haul distances. The
technique allows a limited spectral occupancy even with low order modulation
formats. The transmission was successfully performed on a deployed Australian
link between Sydney and Melbourne which included 995 km of uncompensated SMF
with coexistent traffic. 40 and 100 Gb/s co-propagating channels were
transmitted together with the super-channel in a 50 GHz ITU-T grid without
additional penalty. The super-channel consisted of eight sub-channels with
low-level modulation format, i.e. DP-QPSK, guaranteeing better OSNR robustness
and reduced complexity with respect to higher order formats. At the receiver
side, coherent detection was used together with iterative maximum-a-posteriori
(MAP) detection and decoding. A 975 Gb/s DP-QPSK super-channel was successfully
transmitted between Sydney and Melbourne within four 50GHz WSS channels (200
GHz). A maximum potential SE of 5.58 bit/s/Hz was achieved with an OSNR=15.8
dB, comparable to the OSNR of the installed 100 Gb/s channels. The system
reliability was proven through long term measurements. In addition, by closing
the link in a loop back configuration, a potential SE*d product of 9254
bit/s/Hz*km was achieved
Performance analysis of modified asymmetrically-clipped optical orthogonal frequency-division multiplexing systems
A modification to the Asymmetrically-Clipped Optical Orthogonal Frequency-Division Multiplexing (ACO-OFDM) technique is proposed through unipolar encoding. A performance analysis of the Bit Error Rate (BER) is developed and Monte Carlo simulations are carried out to verify the analysis. Results are compared to that of the corresponding ACO-OFDM system under the same bit energy and transmission rate; an improvement of 1 dB is obtained at a BER of 10-4. In addition, the performance of the proposed system in the presence of atmospheric turbulence is investigated using single-input multiple-output (SIMO) configuration and its performance under that environment is compared to that of ACO-OFDM. Energy improvements of 4 dB and 2.2 dB are obtained at a BER of 10-4 for SIMO systems of 1 and 2 photodetectors at the receiver for the case of strong turbulence, respectively
Pulse Shaping, Localization and the Approximate Eigenstructure of LTV Channels
In this article we show the relation between the theory of pulse shaping for
WSSUS channels and the notion of approximate eigenstructure for time-varying
channels. We consider pulse shaping for a general signaling scheme, called
Weyl-Heisenberg signaling, which includes OFDM with cyclic prefix and
OFDM/OQAM. The pulse design problem in the view of optimal WSSUS--averaged SINR
is an interplay between localization and "orthogonality". The localization
problem itself can be expressed in terms of eigenvalues of localization
operators and is intimately connected to the concept of approximate
eigenstructure of LTV channel operators. In fact, on the L_2-level both are
equivalent as we will show. The concept of "orthogonality" in turn can be
related to notion of tight frames. The right balance between these two sides is
still an open problem. However, several statements on achievable values of
certain localization measures and fundamental limits on SINR can already be
made as will be shown in the paper.Comment: 6 pages, 2 figures, invited pape
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