2 research outputs found
Quantum-noise limited communication with low probability of detection
We demonstrate the achievability of a square root limit on the amount of
information transmitted reliably and with low probability of detection (LPD)
over the single-mode lossy bosonic channel if either the eavesdropper's
measurements or the channel itself is subject to the slightest amount of excess
noise. Specifically, Alice can transmit bits to Bob
over channel uses such that Bob's average codeword error probability is
upper-bounded by an arbitrarily small while a passive eavesdropper,
Warden Willie, who is assumed to be able to collect all the transmitted photons
that do not reach Bob, has an average probability of detection error that is
lower-bounded by for an arbitrarily small . We
analyze the thermal noise and pure loss channels. The square root law holds for
the thermal noise channel even if Willie employs a quantum-optimal measurement,
while Bob is equipped with a standard coherent detection receiver. We also show
that LPD communication is not possible on the pure loss channel. However, this
result assumes Willie to possess an ideal receiver that is not subject to
excess noise. If Willie is restricted to a practical receiver with a non-zero
dark current, the square root law is achievable on the pure loss channel
Covert Communication Gains from Adversary's Ignorance of Transmission Time
The recent square root law (SRL) for covert communication demonstrates that
Alice can reliably transmit bits to Bob in uses of
an additive white Gaussian noise (AWGN) channel while keeping ineffective any
detector employed by the adversary; conversely, exceeding this limit either
results in detection by the adversary with high probability or non-zero
decoding error probability at Bob. This SRL is under the assumption that the
adversary knows when Alice transmits (if she transmits); however, in many
operational scenarios he does not know this. Hence, here we study the impact of
the adversary's ignorance of the time of the communication attempt. We employ a
slotted AWGN channel model with slots each containing symbol
periods, where Alice may use a single slot out of . Provided that Alice's
slot selection is secret, the adversary needs to monitor all slots for
possible transmission. We show that this allows Alice to reliably transmit
bits to Bob (but no more) while
keeping the adversary's detector ineffective. To achieve this gain over SRL,
Bob does not have to know the time of transmission provided , .Comment: v2: updated references/discussion of steganography, no change in
results; v3: significant update, includes new theorem 1.2; v4 and v5: fixed
minor technical issue