4,170 research outputs found
The capacity region of broadcast channels with intersymbol interference and colored Gaussian noise
We derive the capacity region for a broadcast channel with intersymbol interference (ISI) and colored Gaussian noise under an input power constraint. The region is obtained by first defining a similar channel model, the circular broadcast channel, which can be decomposed into a set of parallel degraded broadcast channels. The capacity region for parallel degraded broadcast channels is known. We then show that the capacity region of the original broadcast channel equals that of the circular broadcast channel in the limit of infinite block length, and we obtain an explicit formula for the resulting capacity region. The coding strategy used to achieve each point on the convex hull of the capacity region uses superposition coding on some or all of the parallel channels and dedicated transmission on the others. The optimal power allocation for any point in the capacity region is obtained via a multilevel water-filling. We derive this optimal power allocation and the resulting capacity region for several broadcast channel models
Models and information-theoretic bounds for nanopore sequencing
Nanopore sequencing is an emerging new technology for sequencing DNA, which
can read long fragments of DNA (~50,000 bases) in contrast to most current
short-read sequencing technologies which can only read hundreds of bases. While
nanopore sequencers can acquire long reads, the high error rates (20%-30%) pose
a technical challenge. In a nanopore sequencer, a DNA is migrated through a
nanopore and current variations are measured. The DNA sequence is inferred from
this observed current pattern using an algorithm called a base-caller. In this
paper, we propose a mathematical model for the "channel" from the input DNA
sequence to the observed current, and calculate bounds on the information
extraction capacity of the nanopore sequencer. This model incorporates
impairments like (non-linear) inter-symbol interference, deletions, as well as
random response. These information bounds have two-fold application: (1) The
decoding rate with a uniform input distribution can be used to calculate the
average size of the plausible list of DNA sequences given an observed current
trace. This bound can be used to benchmark existing base-calling algorithms, as
well as serving a performance objective to design better nanopores. (2) When
the nanopore sequencer is used as a reader in a DNA storage system, the storage
capacity is quantified by our bounds
Spectral Efficiency Optimization in Flexi-Grid Long-Haul Optical Systems
Flexible grid optical networks allow a better exploitation of fiber capacity,
by enabling a denser frequency allocation. A tighter channel spacing, however,
requires narrower filters, which increase linear intersymbol interference
(ISI), and may dramatically reduce system reach. Commercial coherent receivers
are based on symbol by symbol detectors, which are quite sensitive to ISI. In
this context, Nyquist spacing is considered as the ultimate limit to
wavelength-division multiplexing (WDM) packing.
In this paper, we show that by introducing a limited-complexity trellis
processing at the receiver, either the reach of Nyquist WDM flexi-grid networks
can be significantly extended, or a denser-than-Nyquist channel packing (i.e.,
a higher spectral efficiency (SE)) is possible at equal reach. By adopting
well-known information-theoretic techniques, we design a limited-complexity
trellis processing and quantify its SE gain in flexi-grid architectures where
wavelength selective switches over a frequency grid of 12.5GHz are employed.Comment: 7 pages, 9 figure
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