153 research outputs found
Characterization of the Complexity of Computing the Capacity of Colored Noise Gaussian Channels
This paper explores the computational complexity involved in determining the
capacity of the band-limited additive colored Gaussian noise (ACGN) channel and
its capacity-achieving power spectral density (p.s.d.). The study reveals that
when the noise p.s.d. is a strictly positive computable continuous function,
computing the capacity of the band-limited ACGN channel becomes a
-complete problem within the set of polynomial time computable
noise p.s.d.s. Meaning that it is even more complex than problems that are
-complete. Additionally, it is shown that the capacity-achieving
distribution is also -complete. Furthermore, under the widely
accepted assumption that , it has two
significant implications for the ACGN channel. The first implication is the
existence of a polynomial time computable noise p.s.d. for which the
computation of its capacity cannot be performed in polynomial time, i.e., the
number of computational steps on a Turing Machine grows faster than all
polynomials. The second one is the existence of a polynomial time computable
noise p.s.d. for which determining its capacity-achieving p.s.d. cannot be done
within polynomial time
Transformer-aided Wireless Image Transmission with Channel Feedback
This paper presents a novel wireless image transmission paradigm that can
exploit feedback from the receiver, called DeepJSCC-ViT-f. We consider a block
feedback channel model, where the transmitter receives noiseless/noisy channel
output feedback after each block. The proposed scheme employs a single encoder
to facilitate transmission over multiple blocks, refining the receiver's
estimation at each block. Specifically, the unified encoder of DeepJSCC-ViT-f
can leverage the semantic information from the source image, and acquire
channel state information and the decoder's current belief about the source
image from the feedback signal to generate coded symbols at each block.
Numerical experiments show that our DeepJSCC-ViT-f scheme achieves
state-of-the-art transmission performance with robustness to noise in the
feedback link. Additionally, DeepJSCC-ViT-f can adapt to the channel condition
directly through feedback without the need for separate channel estimation. We
further extend the scope of the DeepJSCC-ViT-f approach to include the
broadcast channel, which enables the transmitter to generate broadcast codes in
accordance with signal semantics and channel feedback from individual
receivers
Beyond Transmitting Bits: Context, Semantics, and Task-Oriented Communications
Communication systems to date primarily aim at reliably communicating bit
sequences. Such an approach provides efficient engineering designs that are
agnostic to the meanings of the messages or to the goal that the message
exchange aims to achieve. Next generation systems, however, can be potentially
enriched by folding message semantics and goals of communication into their
design. Further, these systems can be made cognizant of the context in which
communication exchange takes place, providing avenues for novel design
insights. This tutorial summarizes the efforts to date, starting from its early
adaptations, semantic-aware and task-oriented communications, covering the
foundations, algorithms and potential implementations. The focus is on
approaches that utilize information theory to provide the foundations, as well
as the significant role of learning in semantics and task-aware communications.Comment: 28 pages, 14 figure
Secure, reliable, and efficient communication over the wiretap channel
Secure wireless communication between devices is essential for modern communication systems. Physical-layer security over the wiretap channel may provide an additional level of secrecy beyond the current cryptographic approaches. Given a sender Alice, a legitimate receiver Bob, and a malicious eavesdropper Eve, the wiretap channel occurs when Eve experiences a worse signal-to-noise ratio than Bob. Previous study of the wiretap channel has tended to make assumptions that ignore the reality of wireless communication. This thesis presents a study of short block length codes with the aim of both reliability for Bob and confusion for Eve. The standard approach to wiretap coding is shown to be very inefficient for reliability. Quantifying Eve's confusion in terms of entropy is not solved in many cases, though it is possible for codes with a moderate complexity trellis representation. Using error rate arguments, error correcting codes with steep performance curves turn out to be desirable both for reliability and confusion.Masteroppgave i informatikkINF399MAMN-INFMAMN-PRO
Information theoretic limits of MIMO wireless networks with bounded input and imperfect CSIT
In this thesis, we investigate some information theoretic limits of two specific types of MIMO wireless networks. In the first one, the effect of channel uncertainty at the transmitter (due to estimation error, feedback latency, and so on) in MIMO broadcast channels is investigated. In this setting, we capture this imperfectness in the bounds for the DoF region of the channel. The second one is the point to point deterministic MIMO channel with input amplitude constraint. For certain settings, the capacity of this channel is derived, while for the general problem, upper and lower bounds for the capacity are obtained.Open Acces
Deep Autoencoder-based Z-Interference Channels with Perfect and Imperfect CSI
A deep autoencoder (DAE)-based structure for endto-end communication over the
two-user Z-interference channel (ZIC) with finite-alphabet inputs is designed
in this paper. The proposed structure jointly optimizes the two encoder/decoder
pairs and generates interference-aware constellations that dynamically adapt
their shape based on interference intensity to minimize the bit error rate
(BER). An in-phase/quadrature-phase (I/Q) power allocation layer is introduced
in the DAE to guarantee an average power constraint and enable the architecture
to generate constellations with nonuniform shapes. This brings further gain
compared to standard uniform constellations such as quadrature amplitude
modulation. The proposed structure is then extended to work with imperfect
channel state information (CSI). The CSI imperfection due to both the
estimation and quantization errors are examined. The performance of the DAEZIC
is compared with two baseline methods, i.e., standard and rotated
constellations. The proposed structure significantly enhances the performance
of the ZIC both for the perfect and imperfect CSI. Simulation results show that
the improvement is achieved in all interference regimes (weak, moderate, and
strong) and consistently increases with the signal-to-noise ratio (SNR). For
example, more than an order of magnitude BER reduction is obtained with respect
to the most competitive conventional method at weak interference when SNR>15dB
and two bits per symbol are transmitted. The improvements reach about two
orders of magnitude when quantization error exists, indicating that the DAE-ZIC
is more robust to the interference compared to the conventional methods.Comment: 13 pages, 13 figures, 2 tables. Accepted for publication in the IEEE
Transactions on Communications. arXiv admin note: text overlap with
arXiv:2303.0831
Purposeful Co-Design of OFDM Signals for Ranging and Communications
This paper analyzes the fundamental trade-offs that occur in the co-design of
orthogonal frequency-division multiplexing signals for both ranging (via
time-of-arrival estimation) and communications. These trade-offs are quantified
through the Shannon capacity bound, probability of outage, and the Ziv-Zakai
bound on range estimation variance. Bounds are derived for signals experiencing
frequency-selective Rayleigh block fading, accounting for the impact of limited
channel knowledge and multi-antenna reception. Uncompensated carrier frequency
offset and phase errors are also factored into the capacity bounds. Analysis
based on the derived bounds demonstrates how Pareto-optimal design choices can
be made to optimize the communication throughput, probability of outage, and
ranging variance. Different signal design strategies are then analyzed, showing
how Pareto-optimal design choices change depending on the channel
On Cyclic Delay Diversity OFDM Based Channels
Orthogonal Frequency Division Multiplexing, so called OFDM, has found a prominent place
in various wireless systems and networks as a method of encoding data over multiple carrier
frequencies. OFDM-based communication systems, however, lacking inherent diversity, are capable of benefiting from different spatial diversity schemes. One such scheme, Cyclic Delay Diversity (CDD) is a method to provide spatial diversity which can be also interpreted as a Space-Time Block Coding (STBC) step. The main idea is to add more transmit antennas at the transmitter side sending the same streams of data, though with differing time delays.
In [1], the capacity of a point-to-point OFDM-based channel with CDD is derived for inputs with Gaussian and discrete constellations. In this dissertation, we use the same approach for an OFDM-based single-input single-output (SISO) two-user interference channel (IC). In our model, at the receiver side, the interference is treated as noise. Moreover, since the channel is time-varying (slow-fading), the Shannon capacity in the strict sense is not well-defined, so the expected value of the instantaneous capacity is calculated instead. Furthermore, the channel coefficients are unknown to the transmitters. Thus, in this setting, the probability of outage emerges as a reasonable performance measure. Adding an extra antenna in the transmitters, the SISO IC turns into an MISO IC, which results in increasing the diversity. Both the continuous and discrete inputs are studied and it turns out that decoding interference is helpful in some cases. The results of the simulations for discrete inputs indicate that there are improvements in terms of outage capacity compared to the ICs with single-antenna
transmitters
Analysis and Design of Line of Sight MIMO transmission systems
A cost-effective solution to the problem of guaranteeing backhaul connectivity in mobile cellular networks is the use of point-to-point microwave links in the Q-Band and E-Band. The always increasing rate in mobile data traffic makes these microwave radio links a potential bottleneck in the deployment of high-throughput cellular networks.
A fundamental way to characterize the impact of phase noise on the throughput of these systems is to study their Shannon capacity. Unfortunately, the capacity of the phase-noise channel is not known in closed-form, even for simple channel models.
The effect of phase noise in telecommunication systems is more evident in presence of multiple antennas at transmitter and receiver because of the overlapping of phase noise contribution in receivers.
We propose a simulated-based tool to compute a lower bound to channel capacity for SISO and MIMO systems in presence of phase noise with one oscillator shared among the antennas per side and we give a non asymptotic expression of an upper bound to capacity always for SISO and MIMO channels. Finally we present a low complex phase detector based on combination of Phase Locked Loop (PLL) exploiting the decisions made by a turbo decoder.
The aim of this work is showing a way to bound the channel capacity for single antenna and multiple antennas channels impaired by phase noise generated by instabilities in oscillators driving all the transceivers, and compare the performance of the proposed phase detector to those theoretical limits
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