757 research outputs found
Outage Capacity for the Optical MIMO Channel
MIMO processing techniques in fiber optical communications have been proposed
as a promising approach to meet increasing demand for information throughput.
In this context, the multiple channels correspond to the multiple modes and/or
multiple cores in the fiber. In this paper we characterize the distribution of
the mutual information with Gaussian input in a simple channel model for this
system. Assuming significant cross talk between cores, negligible
backscattering and near-lossless propagation in the fiber, we model the
transmission channel as a random complex unitary matrix. The loss in the
transmission may be parameterized by a number of unutilized channels in the
fiber. We analyze the system in a dual fashion. First, we evaluate a
closed-form expression for the outage probability, which is handy for small
matrices. We also apply the asymptotic approach, in particular the Coulomb gas
method from statistical mechanics, to obtain closed-form results for the
ergodic mutual information, its variance as well as the outage probability for
Gaussian input in the limit of large number of cores/modes. By comparing our
analytic results to simulations, we see that, despite the fact that this method
is nominally valid for large number of modes, our method is quite accurate even
for small to modest number of channels.Comment: Revised version includes more details, proofs and a closed-form
expression for the outage probabilit
Mode-Dependent Loss and Gain: Statistics and Effect on Mode-Division Multiplexing
In multimode fiber transmission systems, mode-dependent loss and gain
(collectively referred to as MDL) pose fundamental performance limitations. In
the regime of strong mode coupling, the statistics of MDL (expressed in
decibels or log power gain units) can be described by the eigenvalue
distribution of zero-trace Gaussian unitary ensemble in the small-MDL region
that is expected to be of interest for practical long-haul transmission.
Information-theoretic channel capacities of mode-division-multiplexed systems
in the presence of MDL are studied, including average and outage capacities,
with and without channel state information.Comment: 22 pages, 8 figure
On the Performance of Millimeter Wave-based RF-FSO Links with HARQ Feedback
This paper studies the performance of hybrid radio-frequency (RF) and
free-space optical (FSO) links in the cases with and without hybrid automatic
repeat request (HARQ). Considering millimeter wave (mmwave) characteristics in
the RF link and pointing errors in the FSO link, we derive closed-form
expressions for the message decoding probabilities as well as the throughput
and the outage probability of the RF-FSO setups. We also evaluate the effect of
various parameters such as power amplifiers efficiency, different transmission
techniques in the FSO link, pointing errors in the FSO link as well as
different coherence times/symbol rates of the RF and the FSO links on the
throughput and outage probability. The results show the efficiency of the
RF-FSO links in different conditions. Moreover, the HARQ can effectively
improve the outage probability/energy efficiency, and compensate the effect of
hardware impairments in RF-FSO links.Comment: Under review in PIMRC'201
Frequency Diversity in Mode-Division Multiplexing Systems
In the regime of strong mode coupling, the modal gains and losses and the
modal group delays of a multimode fiber are known to have well-defined
statistical properties. In mode-division multiplexing, mode-dependent gains and
losses are known to cause fluctuations in the channel capacity, so that the
capacity at finite outage probability can be substantially lower than the
average capacity. Mode-dependent gains and losses, when frequency-dependent,
have a coherence bandwidth that is inversely proportional to the modal group
delay spread. When mode-division-multiplexed signals occupy a bandwidth far
larger than the coherence bandwidth, the mode-dependent gains and losses are
averaged over frequency, causing the outage capacity to approach the average
capacity. The difference between the average and outage capacities is found to
be inversely proportional to the square-root of a diversity order that is given
approximately by the ratio of the signal bandwidth to the coherence bandwidth.Comment: 8 pages, 6 figure
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