25,167 research outputs found
Power Control in Parallel Symmetric α-Stable Noise Channels
International audienceParallel channels form a basic building block for communication systems, including those based on OFDM and CDMA. While parallel Gaussian noise channels have been widely studied, parallel impulsive noise channels have received significantly less attention despite their importance in a range of modern communication systems. In this paper, this problem is addressed and a power allocation strategy is developed for parallel symmetric α-stable noise channels-a key class of impulsive noise channels. We show that our strategy can improve achievable rates by up to a factor of 1.5 over the standard waterfilling algorithm that assumes the noise is Gaussian
Stabilization of Linear Systems Over Gaussian Networks
The problem of remotely stabilizing a noisy linear time invariant plant over
a Gaussian relay network is addressed. The network is comprised of a sensor
node, a group of relay nodes and a remote controller. The sensor and the relay
nodes operate subject to an average transmit power constraint and they can
cooperate to communicate the observations of the plant's state to the remote
controller. The communication links between all nodes are modeled as Gaussian
channels. Necessary as well as sufficient conditions for mean-square
stabilization over various network topologies are derived. The sufficient
conditions are in general obtained using delay-free linear policies and the
necessary conditions are obtained using information theoretic tools. Different
settings where linear policies are optimal, asymptotically optimal (in certain
parameters of the system) and suboptimal have been identified. For the case
with noisy multi-dimensional sources controlled over scalar channels, it is
shown that linear time varying policies lead to minimum capacity requirements,
meeting the fundamental lower bound. For the case with noiseless sources and
parallel channels, non-linear policies which meet the lower bound have been
identified
Communicating over Filter-and-Forward Relay Networks with Channel Output Feedback
Relay networks aid in increasing the rate of communication from source to
destination. However, the capacity of even a three-terminal relay channel is an
open problem. In this work, we propose a new lower bound for the capacity of
the three-terminal relay channel with destination-to-source feedback in the
presence of correlated noise. Our lower bound improves on the existing bounds
in the literature. We then extend our lower bound to general relay network
configurations using an arbitrary number of filter-and-forward relay nodes.
Such network configurations are common in many multi-hop communication systems
where the intermediate nodes can only perform minimal processing due to limited
computational power. Simulation results show that significant improvements in
the achievable rate can be obtained through our approach. We next derive a
coding strategy (optimized using post processed signal-to-noise ratio as a
criterion) for the three-terminal relay channel with noisy channel output
feedback for two transmissions. This coding scheme can be used in conjunction
with open-loop codes for applications like automatic repeat request (ARQ) or
hybrid-ARQ.Comment: 15 pages, 8 figures, to appear in IEEE Transactions on Signal
Processin
Distributed Decision Through Self-Synchronizing Sensor Networks in the Presence of Propagation Delays and Asymmetric Channels
In this paper we propose and analyze a distributed algorithm for achieving
globally optimal decisions, either estimation or detection, through a
self-synchronization mechanism among linearly coupled integrators initialized
with local measurements. We model the interaction among the nodes as a directed
graph with weights (possibly) dependent on the radio channels and we pose
special attention to the effect of the propagation delay occurring in the
exchange of data among sensors, as a function of the network geometry. We
derive necessary and sufficient conditions for the proposed system to reach a
consensus on globally optimal decision statistics. One of the major results
proved in this work is that a consensus is reached with exponential convergence
speed for any bounded delay condition if and only if the directed graph is
quasi-strongly connected. We provide a closed form expression for the global
consensus, showing that the effect of delays is, in general, the introduction
of a bias in the final decision. Finally, we exploit our closed form expression
to devise a double-step consensus mechanism able to provide an unbiased
estimate with minimum extra complexity, without the need to know or estimate
the channel parameters.Comment: To be published on IEEE Transactions on Signal Processin
Parity solitons in nonresonantly driven-dissipative condensate channels
We study analytically and numerically the condensation of a
driven-dissipative exciton-polariton system using symmetric nonresonant pumping
geometries. We show that the lowest condensation threshold solution carries a
definite parity as a consequence of the symmetric excitation profile. At higher
pump intensities competition between the two parities can result in critical
quenching of one and saturation of the other. Using long pump channels, we show
that the competition of the condensate parities gives rise to a different type
of topologically stable defect propagating indefinitely along the condensate.
The defects display repulsive interactions and are characterized by a sustained
wavepacket carrying a pair of opposite parity domain walls in the condensate
channel
A Multi-cell MMSE Precoder for Massive MIMO Systems and New Large System Analysis
In this paper, a new multi-cell MMSE precoder is proposed for massive MIMO
systems. We consider a multi-cell network where each cell has users and
orthogonal pilot sequences are available, with and
being the pilot reuse factor over the network. In comparison with conventional
single-cell precoding which only uses the intra-cell channel estimates, the
proposed multi-cell MMSE precoder utilizes all channel directions that can
be estimated locally at a base station, so that the transmission is designed
spatially to suppress both parts of the inter-cell and intra-cell interference.
To evaluate the performance, a large-scale approximation of the downlink SINR
for the proposed multi-cell MMSE precoder is derived and the approximation is
tight in the large-system limit. Power control for the pilot and payload,
imperfect channel estimation and arbitrary pilot allocation are accounted for
in our precoder. Numerical results show that the proposed multi-cell MMSE
precoder achieves a significant sum spectral efficiency gain over the classical
single-cell MMSE precoder and the gain increases as or grows.
Compared with the recent M-ZF precoder, whose performance degrades drastically
for a large , our M-MMSE can always guarantee a high and stable performance.
Moreover, the large-scale approximation is easy to compute and shown to be
accurate even for small system dimensions.Comment: 6 pages, 4 figures, accepted by Globecom 2015. arXiv admin note: text
overlap with arXiv:1509.0175
- …