10,416 research outputs found
Reconfigurable Intelligent Surfaces for Wireless Communications: Principles, Challenges, and Opportunities
Recently there has been a flurry of research on the use of reconfigurable
intelligent surfaces (RIS) in wireless networks to create smart radio
environments. In a smart radio environment, surfaces are capable of
manipulating the propagation of incident electromagnetic waves in a
programmable manner to actively alter the channel realization, which turns the
wireless channel into a controllable system block that can be optimized to
improve overall system performance. In this article, we provide a tutorial
overview of reconfigurable intelligent surfaces (RIS) for wireless
communications. We describe the working principles of reconfigurable
intelligent surfaces (RIS) and elaborate on different candidate implementations
using metasurfaces and reflectarrays. We discuss the channel models suitable
for both implementations and examine the feasibility of obtaining accurate
channel estimates. Furthermore, we discuss the aspects that differentiate RIS
optimization from precoding for traditional MIMO arrays highlighting both the
arising challenges and the potential opportunities associated with this
emerging technology. Finally, we present numerical results to illustrate the
power of an RIS in shaping the key properties of a MIMO channel.Comment: to appear in the IEEE Transactions on Cognitive Communications and
Networking (TCCN
Raking the Cocktail Party
We present the concept of an acoustic rake receiver---a microphone beamformer
that uses echoes to improve the noise and interference suppression. The rake
idea is well-known in wireless communications; it involves constructively
combining different multipath components that arrive at the receiver antennas.
Unlike spread-spectrum signals used in wireless communications, speech signals
are not orthogonal to their shifts. Therefore, we focus on the spatial
structure, rather than temporal. Instead of explicitly estimating the channel,
we create correspondences between early echoes in time and image sources in
space. These multiple sources of the desired and the interfering signal offer
additional spatial diversity that we can exploit in the beamformer design.
We present several "intuitive" and optimal formulations of acoustic rake
receivers, and show theoretically and numerically that the rake formulation of
the maximum signal-to-interference-and-noise beamformer offers significant
performance boosts in terms of noise and interference suppression. Beyond
signal-to-noise ratio, we observe gains in terms of the \emph{perceptual
evaluation of speech quality} (PESQ) metric for the speech quality. We
accompany the paper by the complete simulation and processing chain written in
Python. The code and the sound samples are available online at
\url{http://lcav.github.io/AcousticRakeReceiver/}.Comment: 12 pages, 11 figures, Accepted for publication in IEEE Journal on
Selected Topics in Signal Processing (Special Issue on Spatial Audio
Performance analysis of joint precoding and MUD techniques in multibeam satellite systems
This paper considers interference mitigation techniques in the forward link of multibeam satellite systems. In contrast to previous works, either devoted to receiver interference mitigation (e.g. multiuser detection) or transmitter interference mitigation (precoding), this work evaluates the achievable rates of the joint combination of both techniques. On the one hand, precoding cannot properly mitigate all the inter- beam interference while maintaining a sufficiently high signal-to-noise ratio. On the other hand, the receiver cost and complexity exponentially increases with the number of signals to be simultaneously detected. This highlights that the receiver cannot deal with all the interferences so that in general only 2 signals are jointly detected. As a result, the use of precoding within a coverage area jointly with multiuser detection can both benefit from each other and extremely increase the achievable rates of the system. This is numerically evaluated in a close-to-real coverage area considering simultaneous non-unique decoding strategies. The results show the benefits of this joint scheme that eventually can increase the current precoding performance a 23%.Peer ReviewedPostprint (author's final draft
Approaching the ultimate capacity limit in deep-space optical communication
The information capacity of an optical channel under power constraints is
ultimately limited by the quantum nature of transmitted signals. We discuss
currently available and emerging photonic technologies whose combination can be
shown theoretically to enable nearly quantum-limited operation of a noisy
optical communication link in the photon-starved regime, with the information
rate scaling linearly in the detected signal power. The key ingredients are
quantum pulse gating to facilitate mode selectivity, photon-number-resolved
direct detection, and a photon-efficient high-order modulation format such as
pulse position modulation, frequency shift keying, or binary phase shift keyed
Hadamard words decoded optically using structured receivers.Comment: 9 pages, 4 figures. Presented at Free-Space Laser Communications
XXXI, 4-6 February 2019, San Francisco, C
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