13,681 research outputs found
Peak-Age Violation Guarantees for the Transmission of Short Packets over Fading Channels
We investigate the probability that the peak age of information in a
point-to-point communication system operating over a multiantenna wireless
fading channel exceeds a predetermined value. The packets are scheduled
according to a last-come first-serve policy with preemption in service, and are
transmitted over the channel using a simple automatic repetition request
protocol. We consider quadrature phase shift keying modulation, pilot-assisted
transmission, maximum-likelihood channel estimation, and mismatched scaled
nearest-neighbor decoding. Our analysis, which exploits nonasymptotic tools in
information theory, allows one to determine, for a given information packet
size, the physical layer parameters such as the SNR, the number of transmit and
receive antennas, the amount of frequency diversity to exploit, and the number
of pilot symbols, to ensure that the system operates below a target peak-age
violation probability.Comment: 6 pages, 6 figures. To be presented at Infocom 201
Entropy Bound for the Classical Capacity of a Quantum Channel Assisted by Classical Feedback
We prove that the classical capacity of an arbitrary quantum channel assisted
by a free classical feedback channel is bounded from above by the maximum
average output entropy of the quantum channel. As a consequence of this bound,
we conclude that a classical feedback channel does not improve the classical
capacity of a quantum erasure channel, and by taking into account energy
constraints, we conclude the same for a pure-loss bosonic channel. The method
for establishing the aforementioned entropy bound involves identifying an
information measure having two key properties: 1) it does not increase under a
one-way local operations and classical communication channel from the receiver
to the sender and 2) a quantum channel from sender to receiver cannot increase
the information measure by more than the maximum output entropy of the channel.
This information measure can be understood as the sum of two terms, with one
corresponding to classical correlation and the other to entanglement.Comment: v2: 6 pages, 1 figure, final version published in conference
proceeding
Entanglement-assisted communication of classical and quantum information
We consider the problem of transmitting classical and quantum information
reliably over an entanglement-assisted quantum channel. Our main result is a
capacity theorem that gives a three-dimensional achievable rate region. Points
in the region are rate triples, consisting of the classical communication rate,
the quantum communication rate, and the entanglement consumption rate of a
particular coding scheme. The crucial protocol in achieving the boundary points
of the capacity region is a protocol that we name the classically-enhanced
father protocol. The classically-enhanced father protocol is more general than
other protocols in the family tree of quantum Shannon theoretic protocols, in
the sense that several previously known quantum protocols are now child
protocols of it. The classically-enhanced father protocol also shows an
improvement over a time-sharing strategy for the case of a qubit dephasing
channel--this result justifies the need for simultaneous coding of classical
and quantum information over an entanglement-assisted quantum channel. Our
capacity theorem is of a multi-letter nature (requiring a limit over many uses
of the channel), but it reduces to a single-letter characterization for at
least three channels: the completely depolarizing channel, the quantum erasure
channel, and the qubit dephasing channel.Comment: 23 pages, 5 figures, 1 table, simplification of capacity region--it
now has the simple interpretation as the unit resource capacity region
translated along the classically-enhanced father trade-off curv
One-shot entanglement-assisted quantum and classical communication
We study entanglement-assisted quantum and classical communication over a
single use of a quantum channel, which itself can correspond to a finite number
of uses of a channel with arbitrarily correlated noise. We obtain
characterizations of the corresponding one-shot capacities by establishing
upper and lower bounds on them in terms of the difference of two smoothed
entropic quantities. In the case of a memoryless channel, the upper and lower
bounds converge to the known single-letter formulas for the corresponding
capacities, in the limit of asymptotically many uses of it. Our results imply
that the difference of two smoothed entropic quantities characterizing the
one-shot entanglement-assisted capacities serves as a one-shot analogue of the
mutual information, since it reduces to the mutual information, between the
output of the channel and a system purifying its input, in the asymptotic,
memoryless scenario.Comment: 10 pages, 2 figures. Title changed due to new results on the one-shot
entanglement-assisted quantum communication. In addition, an error in the
previous version regarding the converse proof of the one-shot EAC capacity
has been correcte
Applications of position-based coding to classical communication over quantum channels
Recently, a coding technique called position-based coding has been used to
establish achievability statements for various kinds of classical communication
protocols that use quantum channels. In the present paper, we apply this
technique in the entanglement-assisted setting in order to establish lower
bounds for error exponents, lower bounds on the second-order coding rate, and
one-shot lower bounds. We also demonstrate that position-based coding can be a
powerful tool for analyzing other communication settings. In particular, we
reduce the quantum simultaneous decoding conjecture for entanglement-assisted
or unassisted communication over a quantum multiple access channel to open
questions in multiple quantum hypothesis testing. We then determine achievable
rate regions for entanglement-assisted or unassisted classical communication
over a quantum multiple-access channel, when using a particular quantum
simultaneous decoder. The achievable rate regions given in this latter case are
generally suboptimal, involving differences of Renyi-2 entropies and
conditional quantum entropies.Comment: v4: 44 pages, v4 includes a simpler proof for an upper bound on
one-shot entanglement-assisted capacity, also found recently and
independently in arXiv:1804.0964
A hypothesis testing approach for communication over entanglement assisted compound quantum channel
We study the problem of communication over a compound quantum channel in the
presence of entanglement. Classically such channels are modeled as a collection
of conditional probability distributions wherein neither the sender nor the
receiver is aware of the channel being used for transmission, except for the
fact that it belongs to this collection. We provide near optimal achievability
and converse bounds for this problem in the one-shot quantum setting in terms
of quantum hypothesis testing divergence. We also consider the case of informed
sender, showing a one-shot achievability result that converges appropriately in
the asymptotic and i.i.d. setting. Our achievability proof is similar in spirit
to its classical counterpart. To arrive at our result, we use the technique of
position-based decoding along with a new approach for constructing a union of
two projectors, which can be of independent interest. We give another
application of the union of projectors to the problem of testing composite
quantum hypotheses.Comment: 21 pages, version 3. Added an application to the composite quantum
hypothesis testing. Expanded introductio
Entanglement generation with a quantum channel and a shared state
We introduce a new protocol, the channel-state coding protocol, to quantum
Shannon theory. This protocol generates entanglement between a sender and
receiver by coding for a noisy quantum channel with the aid of a noisy shared
state. The mother and father protocols arise as special cases of the
channel-state coding protocol, where the channel is noiseless or the state is a
noiseless maximally entangled state, respectively. The channel-state coding
protocol paves the way for formulating entanglement-assisted quantum
error-correcting codes that are robust to noise in shared entanglement.
Finally, the channel-state coding protocol leads to a Smith-Yard
superactivation, where we can generate entanglement using a zero-capacity
erasure channel and a non-distillable bound entangled state.Comment: 5 pages, 3 figure
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