507 research outputs found
Holographic MIMO Communications exploiting the Orbital Angular Momentum
This study delves into the potential of harnessing the orbital angular
momentum (OAM) property of electromagnetic waves in near-field and
line-of-sight scenarios by utilizing large intelligent surfaces, in the context
of holographic multiple-input multiple-output (MIMO) communications. The paper
starts by characterizing OAM-based communications and investigating the
connection between OAM-carrying waves and optimum communication modes recently
analyzed for communicating with smart surfaces. Subsequently, it proposes
implementable strategies for generating and detecting OAM-based communication
signals using intelligent surfaces and optimization methods that leverage
focusing techniques. Then, the performance of these strategies is
quantitatively evaluated through simulations. The numerical results show that
OAM waves while constituting a viable and more practical alternative to optimum
communication modes are sub-optimal in terms of achievable capacity.Comment: 34 pages, 9 figures, 2 tables. Part of this article was presented at
IEEE GLOBECOM 202
Energy Efficiency Optimization for PSOAM Mode-Groups based MIMO-NOMA Systems
Plane spiral orbital angular momentum (PSOAM) mode-groups (MGs) and multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) serve as two emerging techniques for achieving high spectral efficiency (SE) in the next-generation networks. In this paper, a PSOAM MGs based multi-user MIMO-NOMA system is studied, where the base station transmits data to users by utilizing the generated PSOAM beams. For such scenario, the interference between users in different PSOAM mode groups can be avoided, which leads to a significant performance enhancement. We aim to maximize the energy efficiency (EE) of the system subject to the constraints of the total transmission power and the minimum data rate. This designed optimization problem is non-convex owing to the interference among users, and hence is quite difficult to tackle directly. To solve this issue, we develop a dual layer resource allocation algorithm where the bisection method is exploited in the outer layer to obtain the optimal EE and a resource distributed iterative algorithm is exploited in the inner layer to optimize the transmit power. Besides, an alternative resource allocation algorithm with Deep Belief Networks (DBN) is proposed to cope with the requirement for low computational complexity. Simulation results verify the theoretical findings and demonstrate the proposed algorithms on the PSOAM MGs based MIMO-NOMA system can obtain a better performance comparing to the conventional MIMO-NOMA system in terms of EE
How Can Optical Communications Shape the Future of Deep Space Communications? A Survey
With a large number of deep space (DS) missions anticipated by the end of
this decade, reliable and high capacity DS communications systems are needed
more than ever. Nevertheless, existing DS communications technologies are far
from meeting such a goal. Improving current DS communications systems does not
only require system engineering leadership but also, very crucially, an
investigation of potential emerging technologies that overcome the unique
challenges of ultra-long DS communications links. To the best of our knowledge,
there has not been any comprehensive surveys of DS communications technologies
over the last decade. Free space optical (FSO) technology is an emerging DS
technology, proven to acquire lower communications systems size, weight, and
power (SWaP) and achieve a very high capacity compared to its counterpart radio
frequency (RF) technology, the current used DS technology. In this survey, we
discuss the pros and cons of deep space optical communications (DSOC).
Furthermore, we review the modulation, coding, and detection, receiver, and
protocols schemes and technologies for DSOC. We provide, for the very first
time, thoughtful discussions about implementing orbital angular momentum (OAM)
and quantum communications (QC) for DS. We elaborate on how these technologies
among other field advances, including interplanetary network, and RF/FSO
systems improve reliability, capacity, and security and address related
implementation challenges and potential solutions. This paper provides a
holistic survey in DSOC technologies gathering 200+ fragmented literature and
including novel perspectives aiming to setting the stage for more developments
in the field.Comment: 17 pages, 8 Figure
Holographic MIMO Communications: Theoretical Foundations, Enabling Technologies, and Future Directions
Future wireless systems are envisioned to create an endogenously
holography-capable, intelligent, and programmable radio propagation
environment, that will offer unprecedented capabilities for high spectral and
energy efficiency, low latency, and massive connectivity. A potential and
promising technology for supporting the expected extreme requirements of the
sixth-generation (6G) communication systems is the concept of the holographic
multiple-input multiple-output (HMIMO), which will actualize holographic radios
with reasonable power consumption and fabrication cost. The HMIMO is
facilitated by ultra-thin, extremely large, and nearly continuous surfaces that
incorporate reconfigurable and sub-wavelength-spaced antennas and/or
metamaterials. Such surfaces comprising dense electromagnetic (EM) excited
elements are capable of recording and manipulating impinging fields with utmost
flexibility and precision, as well as with reduced cost and power consumption,
thereby shaping arbitrary-intended EM waves with high energy efficiency. The
powerful EM processing capability of HMIMO opens up the possibility of wireless
communications of holographic imaging level, paving the way for signal
processing techniques realized in the EM-domain, possibly in conjunction with
their digital-domain counterparts. However, in spite of the significant
potential, the studies on HMIMO communications are still at an initial stage,
its fundamental limits remain to be unveiled, and a certain number of critical
technical challenges need to be addressed. In this survey, we present a
comprehensive overview of the latest advances in the HMIMO communications
paradigm, with a special focus on their physical aspects, their theoretical
foundations, as well as the enabling technologies for HMIMO systems. We also
compare the HMIMO with existing multi-antenna technologies, especially the
massive MIMO, present various...Comment: double column, 58 page
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