630 research outputs found
Beampattern Design for Transmit Architectures Based on Reconfigurable Intelligent Surfaces
In this work, we consider a transmit architecture where few active antennas
(sources), each equipped with a dedicated radio frequency chain, illuminate a
reconfigurable intelligent surface (RIS) that control the beam-steering
capability of the whole system. In this framework, we tackle the beampattern
design problem, where the waveform emitted by the sources and the phase shifts
introduced by the RIS are designed so that the realized beampattern matches, in
a least-square sense, the desired one. The design of this architecture can be
useful in many areas, such as radar detection and tracking, millimeter wave,
sub-THz, and THz communications, and integrated sensing and communications. We
provide a sub-optimum solution to the beampattern design problem, and we report
an example to show that this RIS-based transmit architecture can be competitive
with respect to fully-digital MIMO systems, especially if constant-modulus
waveforms are required.Comment: Submitted for possible publication to IEEE Transactions on Signal
Processin
Hybrid Transceiver Optimization for Multi-Hop Communications
Multi-hop communication with the aid of large-scale antenna arrays will play
a vital role in future emergence communication systems. In this paper, we
investigate amplify-and-forward based and multiple-input multiple-output
assisted multi-hop communication, in which all nodes employ hybrid
transceivers. Moreover, channel errors are taken into account in our hybrid
transceiver design. Based on the matrix-monotonic optimization framework, the
optimal structures of the robust hybrid transceivers are derived. By utilizing
these optimal structures, the optimizations of analog transceivers and digital
transceivers can be separated without loss of optimality. This fact greatly
simplifies the joint optimization of analog and digital transceivers. Since the
optimization of analog transceivers under unit-modulus constraints is
non-convex, a projection type algorithm is proposed for analog transceiver
optimization to overcome this difficulty. Based on the derived analog
transceivers, the optimal digital transceivers can then be derived using
matrix-monotonic optimization. Numeral results obtained demonstrate the
performance advantages of the proposed hybrid transceiver designs over other
existing solutions.Comment: 32 pages, 6 figures. This manuscript has been submitted to IEEE
Journal on Selected Areas in Communications (special issue on Multiple
Antenna Technologies for Beyond 5G
Full-Duplex Wireless for 6G: Progress Brings New Opportunities and Challenges
The use of in-band full-duplex (FD) enables nodes to simultaneously transmit
and receive on the same frequency band, which challenges the traditional
assumption in wireless network design. The full-duplex capability enhances
spectral efficiency and decreases latency, which are two key drivers pushing
the performance expectations of next-generation mobile networks. In less than
ten years, in-band FD has advanced from being demonstrated in research labs to
being implemented in standards and products, presenting new opportunities to
utilize its foundational concepts. Some of the most significant opportunities
include using FD to enable wireless networks to sense the physical environment,
integrate sensing and communication applications, develop integrated access and
backhaul solutions, and work with smart signal propagation environments powered
by reconfigurable intelligent surfaces. However, these new opportunities also
come with new challenges for large-scale commercial deployment of FD
technology, such as managing self-interference, combating cross-link
interference in multi-cell networks, and coexistence of dynamic time division
duplex, subband FD and FD networks.Comment: 21 pages, 15 figures, accepted to an IEEE Journa
Antenna Array Enabled Space/Air/Ground Communications and Networking for 6G
Antenna arrays have a long history of more than 100 years and have evolved
closely with the development of electronic and information technologies,
playing an indispensable role in wireless communications and radar. With the
rapid development of electronic and information technologies, the demand for
all-time, all-domain, and full-space network services has exploded, and new
communication requirements have been put forward on various space/air/ground
platforms. To meet the ever increasing requirements of the future sixth
generation (6G) wireless communications, such as high capacity, wide coverage,
low latency, and strong robustness, it is promising to employ different types
of antenna arrays with various beamforming technologies in space/air/ground
communication networks, bringing in advantages such as considerable antenna
gains, multiplexing gains, and diversity gains. However, enabling antenna array
for space/air/ground communication networks poses specific, distinctive and
tricky challenges, which has aroused extensive research attention. This paper
aims to overview the field of antenna array enabled space/air/ground
communications and networking. The technical potentials and challenges of
antenna array enabled space/air/ground communications and networking are
presented first. Subsequently, the antenna array structures and designs are
discussed. We then discuss various emerging technologies facilitated by antenna
arrays to meet the new communication requirements of space/air/ground
communication systems. Enabled by these emerging technologies, the distinct
characteristics, challenges, and solutions for space communications, airborne
communications, and ground communications are reviewed. Finally, we present
promising directions for future research in antenna array enabled
space/air/ground communications and networking
Beam division multiple access for millimeter wave massive MIMO: Hybrid zero-forcing beamforming with user selection
Massive multiple-input multiple-output (MIMO) systems are considered a promising solution to minimize multiuser interference (MUI) based on simple precoding techniques with a massive antenna array at a base station (BS). This paper presents a novel approach of beam division multiple access (BDMA) which BS transmit signals to multiusers at the same time via different beams based on hybrid beamforming and user-beam schedule. With the selection of users whose steering vectors are orthogonal to each other, interference between users is significantly improved. While, the efficiency spectrum of proposed scheme reaches to the performance of fully digital solutions, the multiuser interference is considerably reduced
A Survey of Beam Management for mmWave and THz Communications Towards 6G
Communication in millimeter wave (mmWave) and even terahertz (THz) frequency
bands is ushering in a new era of wireless communications. Beam management,
namely initial access and beam tracking, has been recognized as an essential
technique to ensure robust mmWave/THz communications, especially for mobile
scenarios. However, narrow beams at higher carrier frequency lead to huge beam
measurement overhead, which has a negative impact on beam acquisition and
tracking. In addition, the beam management process is further complicated by
the fluctuation of mmWave/THz channels, the random movement patterns of users,
and the dynamic changes in the environment. For mmWave and THz communications
toward 6G, we have witnessed a substantial increase in research and industrial
attention on artificial intelligence (AI), reconfigurable intelligent surface
(RIS), and integrated sensing and communications (ISAC). The introduction of
these enabling technologies presents both open opportunities and unique
challenges for beam management. In this paper, we present a comprehensive
survey on mmWave and THz beam management. Further, we give some insights on
technical challenges and future research directions in this promising area.Comment: accepted by IEEE Communications Surveys & Tutorial
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