59,047 research outputs found
Constellation Design for Channels Affected by Phase Noise
In this paper we optimize constellation sets to be used for channels affected
by phase noise. The main objective is to maximize the achievable mutual
information of the constellation under a given power constraint. The mutual
information and pragmatic mutual information of a given constellation is
calculated approximately assuming that both the channel and phase noise are
white. Then a simulated annealing algorithm is used to jointly optimize the
constellation and the binary labeling. The performance of optimized
constellations is compared with conventional constellations showing
considerable gains in all system scenarios.Comment: 5 pages, 6 figures, submitted to IEEE Int. Conf. on Communications
(ICC) 201
Linear Precoding for MIMO Channels with QAM Constellations and Reduced Complexity
In this paper, the problem of designing a linear precoder for Multiple-Input
Multiple-Output (MIMO) systems in conjunction with Quadrature Amplitude
Modulation (QAM) is addressed. First, a novel and efficient methodology to
evaluate the input-output mutual information for a general Multiple-Input
Multiple-Output (MIMO) system as well as its corresponding gradients is
presented, based on the Gauss-Hermite quadrature rule. Then, the method is
exploited in a block coordinate gradient ascent optimization process to
determine the globally optimal linear precoder with respect to the MIMO
input-output mutual information for QAM systems with relatively moderate MIMO
channel sizes. The proposed methodology is next applied in conjunction with the
complexity-reducing per-group processing (PGP) technique, which is
semi-optimal, to both perfect channel state information at the transmitter
(CSIT) as well as statistical channel state information (SCSI) scenarios, with
high transmitting and receiving antenna size, and for constellation size up to
. We show by numerical results that the precoders developed offer
significantly better performance than the configuration with no precoder, and
the maximum diversity precoder for QAM with constellation sizes , and
and for MIMO channel size
Impact of 4D channel distribution on the achievable rates in coherent optical communication experiments
We experimentally investigate mutual information and generalized mutual
information for coherent optical transmission systems. The impact of the
assumed channel distribution on the achievable rate is investigated for
distributions in up to four dimensions. Single channel and wavelength division
multiplexing (WDM) transmission over transmission links with and without inline
dispersion compensation are studied. We show that for conventional WDM systems
without inline dispersion compensation, a circularly symmetric complex Gaussian
distribution is a good approximation of the channel. For other channels, such
as with inline dispersion compensation, this is no longer true and gains in the
achievable information rate are obtained by considering more sophisticated
four-dimensional (4D) distributions. We also show that for nonlinear channels,
gains in the achievable information rate can also be achieved by estimating the
mean values of the received constellation in four dimensions. The highest gain
for such channels is seen for a 4D correlated Gaussian distribution
A Simple Approximation for the Bit-Interleaved Coded Modulation Capacity
The generalized mutual information (GMI) is an achievable rate for bit-interleaved coded modulation (BICM) and is highly dependent on the binary labeling of the constellation. The BICM-GMI, sometimes called the BICM capacity, can be evaluated numerically. This approach, however, becomes impractical when the number of constellation points and/or the constellation dimensionality grows, or when many different labelings are considered. A simple approximation for the BICM-GMI based on the area theorem of the demapper's extrinsic information transfer (EXIT) function is proposed. Numerical results show the proposed approximation gives good estimates of the BICM-GMI for labelings with close to linear EXIT functions, which includes labelings of common interest, such as the natural binary code, binary reflected Gray code, etc. This approximation is used to optimize the binary labeling of the 32-APSK constellation defined in the DVB-S2 standard. Gains of approximately 0.15 dB are obtained
On the Information Loss of the Max-Log Approximation in BICM Systems
We present a comprehensive study of the information rate loss of the max-log
approximation for -ary pulse-amplitude modulation (PAM) in a bit-interleaved
coded modulation (BICM) system. It is widely assumed that the calculation of
L-values using the max-log approximation leads to an information loss. We prove
that this assumption is correct for all -PAM constellations and labelings
with the exception of a symmetric 4-PAM constellation labeled with a Gray code.
We also show that for max-log L-values, the BICM generalized mutual information
(GMI), which is an achievable rate for a standard BICM decoder, is too
pessimistic. In particular, it is proved that the so-called "harmonized" GMI,
which can be seen as the sum of bit-level GMIs, is achievable without any
modifications to the decoder. We then study how bit-level channel
symmetrization and mixing affect the mutual information (MI) and the GMI for
max-log L-values. Our results show that these operations, which are often used
when analyzing BICM systems, preserve the GMI. However, this is not necessarily
the case when the MI is considered. Necessary and sufficient conditions under
which these operations preserve the MI are provided
Performance Prediction of Nonbinary Forward Error Correction in Optical Transmission Experiments
In this paper, we compare different metrics to predict the error rate of
optical systems based on nonbinary forward error correction (FEC). It is shown
that the correct metric to predict the performance of coded modulation based on
nonbinary FEC is the mutual information. The accuracy of the prediction is
verified in a detailed example with multiple constellation formats, FEC
overheads in both simulations and optical transmission experiments over a
recirculating loop. It is shown that the employed FEC codes must be universal
if performance prediction based on thresholds is used. A tutorial introduction
into the computation of the threshold from optical transmission measurements is
also given.Comment: submitted to IEEE/OSA Journal of Lightwave Technolog
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