16 research outputs found
A survey on hybrid beamforming techniques in 5G : architecture and system model perspectives
The increasing wireless data traffic demands have driven the need to explore suitable spectrum regions for meeting the projected requirements. In the light of this, millimeter wave (mmWave) communication has received considerable attention from the research community. Typically, in fifth generation (5G) wireless networks, mmWave massive multiple-input multiple-output (MIMO) communications is realized by the hybrid transceivers which combine high dimensional analog phase shifters and power amplifiers with lower-dimensional digital signal processing units. This hybrid beamforming design reduces the cost and power consumption which is aligned with an energy-efficient design vision of 5G. In this paper, we track the progress in hybrid beamforming for massive MIMO communications in the context of system models of the hybrid transceivers' structures, the digital and analog beamforming matrices with the possible antenna configuration scenarios and the hybrid beamforming in heterogeneous wireless networks. We extend the scope of the discussion by including resource management issues in hybrid beamforming. We explore the suitability of hybrid beamforming methods, both, existing and proposed till first quarter of 2017, and identify the exciting future challenges in this domain
Beamforming Analysis and Design for Wideband THz Reconfigurable Intelligent Surface Communications
Reconfigurable intelligent surface (RIS)-aided terahertz (THz) communications
have been regarded as a promising candidate for future 6G networks because of
its ultra-wide bandwidth and ultra-low power consumption. However, there exists
the beam split problem, especially when the base station (BS) or RIS owns the
large-scale antennas, which may lead to serious array gain loss. Therefore, in
this paper, we investigate the beam split and beamforming design problems in
the THz RIS communications. Specifically, we first analyze the beam split
effect caused by different RIS sizes, shapes and deployments. On this basis, we
apply the fully connected time delayer phase shifter hybrid beamforming
architecture at the BS and deploy distributed RISs to cooperatively mitigate
the beam split effect. We aim to maximize the achievable sum rate by jointly
optimizing the hybrid analog/digital beamforming, time delays at the BS and
reflection coefficients at the RISs. To solve the formulated problem, we first
design the analog beamforming and time delays based on different RISs physical
directions, and then it is transformed into an optimization problem by jointly
optimizing the digital beamforming and reflection coefficients. Next, we
propose an alternatively iterative optimization algorithm to deal with it.
Specifically, for given the reflection coefficients, we propose an iterative
algorithm based on the minimum mean square error technique to obtain the
digital beamforming. After, we apply LDR and MCQT methods to transform the
original problem to a QCQP, which can be solved by ADMM technique to obtain the
reflection coefficients. Finally, the digital beamforming and reflection
coefficients are obtained via repeating the above processes until convergence.
Simulation results verify that the proposed scheme can effectively alleviate
the beam split effect and improve the system capacity
Switch-based Hybrid Beamforming Transceiver Design for Wideband Communications with Beam Squint
Hybrid beamforming (HBF) transceiver architectures based on
frequency-independent phase shifters (PS-HBF) are sensitive to the phases and
physical directions with limited capability to compensate for the detrimental
effects of the beam squint. Motivated by the fact that switches are
phase-independent and more power/cost efficient than PSs, we consider the
switch-based HBF (SW-HBF) for wideband large-scale multiple-input
multiple-output systems in this paper. We first derive a closed-form expression
of the beam squint ratio and compare the expected array gains of both SW-HBF
and PS-HBF architectures. The results show that SW-HBF is more robust to the
beam squint effect. We then focus on the SW-HBF designs to maximize the
spectral efficiency (SE) in both single-user and multiuser systems, which are
both non-convex mixed-integer problems. For the former, by combining the tabu
search (TS) method and projected gradient ascend (PGA), we propose an efficient
heuristic PGA-TS algorithm to design analog beamformers while the digital ones
admit closed-form solutions. For the latter, we develop a two-step algorithm
based on fractional programming and the PGA-TS method. Simulations show that
the proposed SW-HBF schemes are efficient and can outperform PS-based HBF
architectures in terms of both SE and energy efficiency in terahertz
communication systems.Comment: 15 pages, 15 figure
Energy and spectral-efficient lens antenna subarray design in MmWave MIMO Systems
Lens antenna subarray (LAS) is one of the recently introduced technologies for future wireless networks that significantly improves the energy efficiency of multiple-input multiple-output (MIMO) systems while achieving higher spectral efficiency compared to single-lens MIMO systems. However, a control mechanism for the LAS-MIMO design is considered a challenging task to efficiently manage the network resources and serve multiple users in the system. Therefore, in this paper, a sub-grouped LAS-MIMO architecture along with a hybrid precoding algorithm are proposed to reduce the cost and hardware overhead of traditional hybrid MIMO systems. Specifically, the LAS structure is divided into sub-groups to serve multiple users with different requirements, and an optimization problem based on the achievable sum-rate is formulated to maximize the spectral efficiency of the system. By splitting the sum-rate problem into sub-rate optimization problems, we develop a low-complexity hybrid precoding algorithm to effectively control the proposed architecture and maximize the achievable sum-rate of each subgroup. The proposed precoding algorithm selects the beam of each lens from a predefined set within a subgroup that maximizes the subgroup sum-rate, while the phase shifters and digital precoders in each subgroup are computed independently. The link between subgroups is updated based on successive interference cancelation to minimize interference between users of different subgroups. Our analysis and simulation results show that the proposed precoding algorithm of the sub-grouped LAS-MIMO architecture performs almost as well as traditional fully-connected hybrid MIMO systems in terms of spectral efficiency at low and high signal-to-noise ratio (SNR). It also outperforms traditional fully-connected and sub-connected hybrid MIMO systems in terms of energy efficiency, even when a large number of lenses are employed.National Science Foundation (NSF
Beamforming Design for the Distributed RISs-aided THz Communications with Double-Layer True Time Delays
In this paper, we investigate the reconfigurable intelligent surface
(RIS)-aided terahertz (THz) communication system with the sparse radio
frequency chains antenna structure at the base station (BS). To overcome the
beam split of the BS, different from the conventional single-layer
true-time-delay (TTD) scheme, we propose a double-layer TTD scheme that can
effectively reduce the number of large-range delay devices, which involve
additional insertion loss and amplification circuitry. Next, we analyze the
system performance under the proposed double-layer TTD scheme. To relieve the
beam split of the RIS, we consider multiple distributed RISs to replace an
ultra-large size RIS. Based on this, we formulate an achievable rate
maximization problem for the distributed RISs-aided THz communications via
jointly optimizing the hybrid analog/digital beamforming, time delays of the
double-layer TTD network and reflection coefficients of RISs. Considering the
practical hardware limitation, the finite-resolution phase shift, time delay
and reflection phase are constrained. To solve the formulated problem, we first
design an analog beamforming scheme including optimizing phase shift and time
delay based on the RISs' locations. Then, an alternatively optimization
algorithm is proposed to obtain the digital beamforming and reflection
coefficients based on the minimum mean square error and coordinate update
techniques. Finally, simulation results show the effectiveness of the proposed
scheme
Near-Field Communications: A Comprehensive Survey
Multiple-antenna technologies are evolving towards large-scale aperture
sizes, extremely high frequencies, and innovative antenna types. This evolution
is giving rise to the emergence of near-field communications (NFC) in future
wireless systems. Considerable attention has been directed towards this
cutting-edge technology due to its potential to enhance the capacity of
wireless networks by introducing increased spatial degrees of freedom (DoFs) in
the range domain. Within this context, a comprehensive review of the state of
the art on NFC is presented, with a specific focus on its 1) fundamental
operating principles, 2) channel modeling, 3) performance analysis, 4) signal
processing, and 5) integration with other emerging technologies. Specifically,
1) the basic principles of NFC are characterized from both physics and
communications perspectives, unveiling its unique properties in contrast to
far-field communications. 2) Based on these principles, deterministic and
stochastic near-field channel models are investigated for spatially-discrete
(SPD) and continuous-aperture (CAP) antenna arrays. 3) Rooted in these models,
existing contributions on near-field performance analysis are reviewed in terms
of DoFs/effective DoFs (EDoFs), power scaling law, and transmission rate. 4)
Existing signal processing techniques for NFC are systematically surveyed,
encompassing channel estimation, beamforming design, and low-complexity beam
training. 5) Major issues and research opportunities associated with the
integration of NFC and other emerging technologies are identified to facilitate
NFC applications in next-generation networks. Promising directions are
highlighted throughout the paper to inspire future research endeavors in the
realm of NFC.Comment: 56 pages, 23figures; submit for possible journa
A new technique for improving energy efficiency in 5g mm-wave hybrid precoding systems
In this article, we present a new approach to optimizing the energy efficiency of the cost-efficiency of quantized hybrid pre-encoding (HP) design. We present effective alternating minimization algorithms (AMA) based on the zero gradient method to produce completely connected structures (CCSs) and partially connected structures (PCSs). Alternative minimization algorithms offer lower complexity by introducing orthogonal constraints on digital pre-codes to concurrently maximize computing complexity and communication power. As a result, by improving CCS through advanced phase extraction, the alternating minimization technique enhances hybrid pre-encoding. For PCS, the energy-saving ratio grew by 45.3 %, while for CCS, it increased by 18.12 %
Two-step multiuser equalization for hybrid mmWave massive MIMO GFDM systems
Although millimeter-wave (mmWave) and massive multiple input multiple output
(mMIMO) can be considered as promising technologies for future mobile communications (beyond
5G or 6G), some hardware limitations limit their applicability. The hybrid analog-digital architecture
has been introduced as a possible solution to avoid such issues. In this paper, we propose a two-step
hybrid multi-user (MU) equalizer combined with low complexity hybrid precoder for wideband
mmWave mMIMO systems, as well as a semi-analytical approach to evaluate its performance.
The new digital non-orthogonal multi carrier modulation scheme generalized frequency division
multiplexing (GFDM) is considered owing to its efficient performance in terms of achieving higher
spectral efficiency, better control of out-of-band (OOB) emissions, and lower peak to average power
ratio (PAPR) when compared with the orthogonal frequency division multiplexing (OFDM) access
technique. First, a low complexity analog precoder is applied on the transmitter side. Then, at the
base station (BS), the analog coefficients of the hybrid equalizer are obtained by minimizing the
mean square error (MSE) between the hybrid approach and the full digital counterpart. For the
digital part, zero-forcing (ZF) is used to cancel the MU interference not mitigated by the analog
part. The performance results show that the performance gap of the proposed hybrid scheme to the
full digital counterpart reduces as the number of radio frequency (RF) chains increases. Moreover,
the theoretical curves almost overlap with the simulated ones, which show that the semi-analytical
approach is quite accurate.publishe