Special Issue "Massive MIMO Systems"

A special issue of Electronics (ISSN 2079-9292). This special issue belongs to the section "Microwave and Wireless Communications".

Deadline for manuscript submissions: closed (31 July 2019).

Special Issue Editors

Dr. Kazuki Maruta
Website
Guest Editor
Graduate School of Engineering, Chiba University, Chiba 263-8522, Japan
Interests: adaptive array, massive MIMO, cooperative base station, multihop relay

Special Issue Information

Dear Colleagues,

We are going to see the first decade since the fundamental concept of Massive MIMO (or called large-scale MIMO) has emerged. Massive MIMO technologies are now in implementation and trial stages towards 5G and beyond. Thanks to its excessive degree of freedom (DoF), massive MIMO has unlimited potentiality to further enhance system capabilities and still expands various research topics with depth. It can be further discussed and believed to break limitations in wireless communications such as spectral and energy efficiencies for better support of continuously increasing mobile data traffic, as well as terminals.

This Special Issue accordingly calls recent advances related to massive MIMO technologies that cover all signal processing, system level analysis, and implementation aspects. Topics of interest in this Special Issue include, but are not limited to, the following:

  • Hybrid beamforming
  • Beam tracking for moving target
  • Millimeter wave
  • Full digital-signal processing
  • Energy efficiency and wireless power transfer
  • Localization and direction-of-arrival (DoA) estimation
  • Compressed sensing
  • Pilot decontamination and channel estimation
  • Antenna array configuration
  • Machine learning approach for pre/post coding
  • Implementation and caribration
  • Proof-of-concept (PoC) and trials

Dr. Kazuki Maruta
Prof. Francisco Falcone
Guest Editors

Manuscript Submission Information

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Published Papers (20 papers)

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Editorial

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Open AccessFeature PaperEditorial
Massive MIMO Systems: Present and Future
Electronics 2020, 9(3), 385; https://doi.org/10.3390/electronics9030385 - 26 Feb 2020
(This article belongs to the Special Issue Massive MIMO Systems)

Research

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Open AccessArticle
Spatio-Radio Resource Management and Hybrid Beamforming for Limited Feedback Massive MIMO Systems
Electronics 2019, 8(10), 1061; https://doi.org/10.3390/electronics8101061 - 20 Sep 2019
Cited by 2
Abstract
In this paper, a joint spatio–radio frequency resource allocation and hybrid beamforming scheme for the massive multiple-input multiple-output (MIMO) systems is proposed. We consider limited feedback two-stage hybrid beamformimg for decomposing the precoding matrix at the base-station. To reduce the channel state information [...] Read more.
In this paper, a joint spatio–radio frequency resource allocation and hybrid beamforming scheme for the massive multiple-input multiple-output (MIMO) systems is proposed. We consider limited feedback two-stage hybrid beamformimg for decomposing the precoding matrix at the base-station. To reduce the channel state information (CSI) feedback of massive MIMO, we utilize the channel covariance-based RF precoding and beam selection. This beam selection process minimizes the inter-group interference. The regularized block diagonalization can mitigate the inter-group interference, but requires substantial overhead feedback. We use channel covariance-based eigenmodes and discrete Fourier transforms (DFT) to reduce the feedback overhead and design a simplified analog precoder. The columns of the analog beamforming matrix are selected based on the users’ grouping performed by the K-mean unsupervised machine learning algorithm. The digital precoder is designed with joint optimization of intra-group user utility function. It has been shown that more than 50 % feedback overhead is reduced by the eigenmodes-based analog precoder design. The joint beams, users scheduling and limited feedbacK-based hybrid precoding increases the sum-rate by 27.6 % compared to the sum-rate of one-group case, and reduce the feedback overhead by 62.5 % compared to the full CSI feedback. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
A Novel Iterative Discrete Estimation Algorithm for Low-Complexity Signal Detection in Uplink Massive MIMO Systems
Electronics 2019, 8(9), 980; https://doi.org/10.3390/electronics8090980 - 02 Sep 2019
Cited by 1
Abstract
In this paper, a novel iterative discrete estimation (IDE) algorithm, which is called the modified IDE (MIDE), is proposed to reduce the computational complexity in MIMO detection in uplink massive MIMO systems. MIDE is a revision of the alternating direction method of multipliers [...] Read more.
In this paper, a novel iterative discrete estimation (IDE) algorithm, which is called the modified IDE (MIDE), is proposed to reduce the computational complexity in MIMO detection in uplink massive MIMO systems. MIDE is a revision of the alternating direction method of multipliers (ADMM)-based algorithm, in which a self-updating method is designed with the damping factor estimated and updated at each iteration based on the Euclidean distance between the iterative solutions of the IDE-based algorithm in order to accelerate the algorithm’s convergence. Compared to the existing ADMM-based detection algorithm, the overall computational complexity of the proposed MIDE algorithm is reduced from O N t 3 + O N r N t 2 to O N t 2 + O N r N t in terms of the number of complex-valued multiplications, where Ntand Nr are the number of users and the number of receiving antennas at the base station (BS), respectively. Simulation results show that the proposed MIDE algorithm performs better in terms of the bit error rate (BER) than some recently-proposed approximation algorithms in MIMO detection of uplink massive MIMO systems. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Energy Efficiency Optimization for Massive MIMO Non-Orthogonal Unicast and Multicast Transmission with Statistical CSI
Electronics 2019, 8(8), 857; https://doi.org/10.3390/electronics8080857 - 01 Aug 2019
Cited by 2
Abstract
We study the energy efficiency (EE) optimization problem in non-orthogonal unicast and multicast transmission for massive multiple-input multiple-output (MIMO) systems with statistical channel state information of all receivers available at the transmitter. Firstly, we formulate the EE maximization problem. We reduce the number [...] Read more.
We study the energy efficiency (EE) optimization problem in non-orthogonal unicast and multicast transmission for massive multiple-input multiple-output (MIMO) systems with statistical channel state information of all receivers available at the transmitter. Firstly, we formulate the EE maximization problem. We reduce the number of variables to be solved and simplify this large-dimensional-matrix-valued problem into a real-vector-valued problem. Next, we lower the computational complexity significantly by replacing the objective with its deterministic equivalent to avoid the high-complex expectation operation. With guaranteed convergence, we propose an iterative algorithm on beam domain power allocation using the minorize maximize algorithm and Dinkelbach’s transform and derive the locally optimal power allocation strategy to achieve the optimal EE. Finally, we illustrate the significant EE performance gain of our EE maximization algorithm compared with the conventional approach through conducting numerical simulations. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Artificial Intelligence-Based Discontinuous Reception for Energy Saving in 5G Networks
Electronics 2019, 8(7), 778; https://doi.org/10.3390/electronics8070778 - 11 Jul 2019
Cited by 3
Abstract
5G is expected to deal with high data rates for different types of wireless traffic. To enable high data rates, 5G employs beam searching operation to align the best beam pairs. Beam searching operation along with high order modulation techniques in 5G, exhausts [...] Read more.
5G is expected to deal with high data rates for different types of wireless traffic. To enable high data rates, 5G employs beam searching operation to align the best beam pairs. Beam searching operation along with high order modulation techniques in 5G, exhausts the battery power of user equipment (UE). LTE network uses discontinuous reception (DRX) with fixed sleep cycles to save UE energy. LTE-DRX in current form cannot work in 5G network, as it does not consider multiple beam communication and the length of sleep cycle is fixed. On the other hand, artificial intelligence (AI) has a tendency to learn and predict the packet arrival-time values from real wireless traffic traces. In this paper, we present AI based DRX (AI-DRX) mechanism for energy efficiency in 5G enabled devices. We propose AI-DRX algorithm for multiple beam communications, to enable dynamic short and long sleep cycles in DRX. AI-DRX saves the energy of UE while considering delay requirements of different services. We train a recurrent neural network (RNN) on two real wireless traces with minimum root mean square error (RMSE) of 5 ms for trace 1 and 6 ms for trace 2. Then, we utilize the trained RNN model in AI-DRX algorithm to make dynamic short or long sleep cycles. As compared to LTE-DRX, AI-DRX achieves 69 % higher energy efficiency on trace 1 and 55 % more energy efficiency on trace 2, respectively. The AI-DRX attains 70 % improvement in energy efficiency for trace 2 compared with Poisson packet arrival model for λ = 1 / 20 . Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Throughput Enhancement in Downlink MU-MIMO Using Multiple Dimensions
Electronics 2019, 8(7), 758; https://doi.org/10.3390/electronics8070758 - 05 Jul 2019
Cited by 1
Abstract
This paper focuses on the throughput performance enhancement in the single cell multi-user MIMO (MU-MIMO) downlink system model. For better quality of service, this paper proposes the scheme that increases system throughput and improves the spectral efficiency. Specifically, the signal transmission and detection [...] Read more.
This paper focuses on the throughput performance enhancement in the single cell multi-user MIMO (MU-MIMO) downlink system model. For better quality of service, this paper proposes the scheme that increases system throughput and improves the spectral efficiency. Specifically, the signal transmission and detection schemes are proposed by using multiple dimensions. At the transmitter side, two dimensions (power and space) are adopted at the same time. To achieve multiple access (MA), the space domain is exploited by using a block diagonalization (BD) precoding technique, and the power domain is exploited to transmit more data symbols. At the receiver, the signal detection structure corresponding to a transmitter is also proposed. In the simulation results, comparisons of throughput performance are presented in various aspects. As a result, the proposed scheme outperforms the conventional schemes using only one dimension in terms of throughput. This paper shows strong performance in MU-MIMO senarios by adopting multiple dimensions. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Multiple-Symbol Non-Coherent Detection for Differential QAM Modulation in Uplink Massive MIMO Systems
Electronics 2019, 8(6), 693; https://doi.org/10.3390/electronics8060693 - 20 Jun 2019
Cited by 1
Abstract
In this paper, we propose a novel multiple-symbol detector based on maximum likelihood metric for differential quadrature amplitude modulation in massive multiple-input multiple-output (MIMO) systems. While current research on differential modulation in massive MIMO has focused on two consecutive symbols, our proposed detector [...] Read more.
In this paper, we propose a novel multiple-symbol detector based on maximum likelihood metric for differential quadrature amplitude modulation in massive multiple-input multiple-output (MIMO) systems. While current research on differential modulation in massive MIMO has focused on two consecutive symbols, our proposed detector is based on multiple-symbol, which is larger than or equal to two. Moreover, we derive new distance based on the proposed detector. To encode and decode data, we apply existing look-up table algorithm using the proposed distance, which is known as optimum encoding algorithm for differential modulation. Simulation results show the improvement based on the bit-error-rate performance since the proposed detector and distance vary according to the channel statistic information. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessFeature PaperArticle
High-Isolation Leaky-Wave Array Antenna Based on CRLH-Metamaterial Implemented on SIW with ±30o Frequency Beam-Scanning Capability at Millimetre-Waves
Electronics 2019, 8(6), 642; https://doi.org/10.3390/electronics8060642 - 06 Jun 2019
Cited by 8
Abstract
The paper presents a feasibility study on the design of a new metamaterial leaky-wave antenna (MTM-LWA) used in the construction of a 1 × 2 array which is implemented using substrate-integrated waveguide (SIW) technology for millimetre-wave beamforming applications. The proposed 1 × 2 [...] Read more.
The paper presents a feasibility study on the design of a new metamaterial leaky-wave antenna (MTM-LWA) used in the construction of a 1 × 2 array which is implemented using substrate-integrated waveguide (SIW) technology for millimetre-wave beamforming applications. The proposed 1 × 2 array antenna consists of two LWAs with metamaterial unit-cells etched on the top surface of the SIW. The metamaterial unit-cell, which is an E-shaped transverse slot, causes leakage loss and interrupts current flow over SIW to enhance the array’s performance. The dimensions of the LWA are 40 × 10 × 0.75 mm3. Mutual-coupling between the array elements is suppressed by incorporating a metamaterial shield (MTM-shield) between the two antennas in the array. The LWA operates over a frequency range of 55–65 GHz, which is corresponding to 16.66% fractional bandwidth. The array is shown to exhibit beam-scanning of ±30° over its operating frequency range. Radiation gain in the backward (−30°), broadside (0°), and forward (+30°) directions are 8.5 dBi, 10.1 dBi, and 9.5 dBi, respectively. The decoupling slab is shown to have minimal effect on the array’s performance in terms of impedance bandwidth and radiation specifications. The MTM-shield is shown to suppress the mutual coupling by ~25 dB and to improve the radiation gain and efficiency by ~1 dBi and ~13% on average, respectively. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessFeature PaperArticle
Mobile-Phone Antenna Array with Diamond-Ring Slot Elements for 5G Massive MIMO Systems
Electronics 2019, 8(5), 521; https://doi.org/10.3390/electronics8050521 - 10 May 2019
Cited by 5
Abstract
A design of mobile-phone antenna array with diamond-ring slot elements is proposed for fifth generation (5G) massive multiple-input/multiple-output (MIMO) systems. The configuration of the design consists of four double-fed diamond-ring slot antenna elements placed at different corners of the mobile-phone printed circuit board [...] Read more.
A design of mobile-phone antenna array with diamond-ring slot elements is proposed for fifth generation (5G) massive multiple-input/multiple-output (MIMO) systems. The configuration of the design consists of four double-fed diamond-ring slot antenna elements placed at different corners of the mobile-phone printed circuit board (PCB). A low-cost FR-4 dielectric with an overall dimension of 75 × 150 mm2 is used as the design substrate. The antenna elements are fed by 50-Ohm L-shaped microstrip-lines. Due to the orthogonal placement of microstrip feed lines, the diamond-ring slot elements can exhibit the polarization and radiation pattern diversity characteristic. A good impedance bandwidth (S11 ≤ −10 dB) of 3.2–4 GHz has been achieved for each antenna radiator. However, for S11 ≤ −6 dB, this value is 3–4.2 GHz. The proposed design provides the required radiation coverage of 5G smartphones. The performance of the proposed MIMO antenna design is examined using both simulation and experiment. High isolation, high efficiency and sufficient gain-level characteristics have been obtained for the proposed MIMO smartphone antenna. In addition, the calculated total active reflection coefficient (TARC) and envelope correlation coefficient (ECC) of the antenna elements are very low over the whole band of interest which verify the capability of the proposed multi-antenna systems for massive MIMO and diversity applications. Furthermore, the properties of the design in Data-mode/Talk-mode are investigated and presented. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Downlink Channel Estimation in Massive Multiple-Input Multiple-Output with Correlated Sparsity by Overcomplete Dictionary and Bayesian Inference
Electronics 2019, 8(5), 473; https://doi.org/10.3390/electronics8050473 - 28 Apr 2019
Cited by 2
Abstract
We exploited the temporal correlation of channels in the angular domain for the downlink channel estimation in a massive multiple-input multiple-output (MIMO) system. Based on the slow time-varying channel supports in the angular domain, we combined the channel support information of the downlink [...] Read more.
We exploited the temporal correlation of channels in the angular domain for the downlink channel estimation in a massive multiple-input multiple-output (MIMO) system. Based on the slow time-varying channel supports in the angular domain, we combined the channel support information of the downlink angular channel in the previous timeslot into the channel estimation in the current timeslot. A downlink channel estimation method based on variational Bayesian inference (VBI) and overcomplete dictionary was proposed, in which the support prior information of the previous timeslot was merged into the VBI for the channel estimation in the current timeslot. Meanwhile the VBI was discussed for a complex value in our system model, and the structural sparsity was utilized in the Bayesian inference. The Bayesian Cramér–Rao bound for the channel estimation mean square error (MSE) was also given out. Compared with other algorithms, the proposed algorithm with overcomplete dictionary achieved a better performance in terms of channel estimation MSE in simulations. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
An Efficient Pilot Assignment Scheme for Addressing Pilot Contamination in Multicell Massive MIMO Systems
Electronics 2019, 8(4), 372; https://doi.org/10.3390/electronics8040372 - 27 Mar 2019
Cited by 2
Abstract
The reuse of the same pilot group across cells to address bandwidth limitations in a network has resulted in pilot contamination. This causes severe inter-cell interference at the targeted cell. Pilot contamination is associated with multicell massive multiple-input multiple-output (MIMO) systems which degrades [...] Read more.
The reuse of the same pilot group across cells to address bandwidth limitations in a network has resulted in pilot contamination. This causes severe inter-cell interference at the targeted cell. Pilot contamination is associated with multicell massive multiple-input multiple-output (MIMO) systems which degrades the system performance even when extra arrays of antennas are added to the network. In this paper, we propose an efficient pilot assignment (EPA) scheme to address this issue by maximizing the minimum uplink rate of the target cell’s users. To achieve this, we exploit the large-scale characteristics of the fading channel to minimize the amount of outgoing inter-cell interference at the target cell. Results from the simulation show that the EPA scheme outperforms both the conventional and the smart pilot assignment (SPA) schemes by reducing the effect of inter-cell interference. These results, show that the EPA scheme has significantly improved the system performance in terms of achievable uplink rate and cumulative distribution function (CDF) for both signal-to-interference-plus-noise ratio (SINR), and uplink rate. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Evaluation of Multi-Beam Massive MIMO Considering MAC Layer Using IEEE802.11ac and FDD-LTE
Electronics 2019, 8(2), 225; https://doi.org/10.3390/electronics8020225 - 18 Feb 2019
Cited by 1
Abstract
Massive multiple-input multiple-output (MIMO) transmission has attracted attention as a key technology for use in fifth-generation mobile communication systems. Multi-beam massive MIMO systems that apply beam selection in analog components and blind algorithms in digital components to eliminate the requirement for channel state [...] Read more.
Massive multiple-input multiple-output (MIMO) transmission has attracted attention as a key technology for use in fifth-generation mobile communication systems. Multi-beam massive MIMO systems that apply beam selection in analog components and blind algorithms in digital components to eliminate the requirement for channel state information have been proposed as a method for reducing overhead. In this study, we developed an adaptive modulation scheme for implementing multi-beam massive MIMO and used computer simulation to compare it with digital and analog–digital hybrid beam-forming methods. The effectiveness of the proposed system was verified in a medium access control layer based on the IEEE802.11ac and frequency division duplex-LTE representative wireless communication standards. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessFeature PaperArticle
Hybrid Beamforming for Millimeter-Wave Heterogeneous Networks
Electronics 2019, 8(2), 133; https://doi.org/10.3390/electronics8020133 - 28 Jan 2019
Cited by 6
Abstract
Heterogeneous networks (HetNets) employing massive multiple-input multiple-output (MIMO) and millimeter-wave (mmWave) technologies have emerged as a promising solution to enhance the network capacity and coverage of next-generation 5G cellular networks. However, the use of traditional fully-digital MIMO beamforming methods, which require one radio [...] Read more.
Heterogeneous networks (HetNets) employing massive multiple-input multiple-output (MIMO) and millimeter-wave (mmWave) technologies have emerged as a promising solution to enhance the network capacity and coverage of next-generation 5G cellular networks. However, the use of traditional fully-digital MIMO beamforming methods, which require one radio frequency (RF) chain per antenna element, is not practical for large-scale antenna arrays, due to the high cost and high power consumption. To reduce the number of RF chains, hybrid analog and digital beamforming has been proposed as an alternative structure. In this paper, therefore, we consider a HetNet formed with one macro-cell base station (MBS) and multiple small-cell base stations (SBSs) equipped with large-scale antenna arrays that employ hybrid analog and digital beamforming. The analog beamforming weight vectors of the MBS and the SBSs correspond to the the best-fixed multi-beams obtained by eigendecomposition schemes. On the other hand, digital beamforming weights are optimized to maximize the receive signal-to-interference-plus-noise ratio (SINR) of the effective channels consisting of the cascade of the analog beamforming weights and the actual channel. The performance is evaluated in terms of the beampatterns and the ergodic channel capacity and shows that the proposed hybrid beamforming scheme achieves near-optimal performance with only four RF chains while requiring considerably less computational complexity. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
LOS-Based Equal Gain Transmission and Combining in General Frequency-Selective Ricean Massive MIMO Channels
Electronics 2019, 8(1), 79; https://doi.org/10.3390/electronics8010079 - 10 Jan 2019
Cited by 1
Abstract
In general frequency-selective Ricean fading environments with doubly-ended spatial correlation, this paper investigates the spectral efficiency of a broadband massive multiple-input multiple-output (MIMO) system. In particular, in order to reduce overhead of channel estimation effectively, it proposes a scheme of equal gain transmission [...] Read more.
In general frequency-selective Ricean fading environments with doubly-ended spatial correlation, this paper investigates the spectral efficiency of a broadband massive multiple-input multiple-output (MIMO) system. In particular, in order to reduce overhead of channel estimation effectively, it proposes a scheme of equal gain transmission and combining, which is only based on line- of-sight (LOS) component and has low hardware complexity. With the scheme, several interesting transmit power scaling properties without and with spatial correlation are derived when the number of antennas at the transmitter or the number of antennas at the receiver grows in an unlimited way. Furthermore, the asymptotical rate analysis is extended to the cooperative relaying scenarios with decode-and-forward and amplify-and-forward protocols, respectively, and then two novel power scaling laws are given. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Efficient Pilot Decontamination Schemes in 5G Massive MIMO Systems
Electronics 2019, 8(1), 55; https://doi.org/10.3390/electronics8010055 - 03 Jan 2019
Cited by 2
Abstract
Massive Multiple-input Multiple-output (MIMO) is an emerging technology for the 5G wireless communication systems which has the potential to provide high spectral efficient and improved link reliability and accommodate large number of users. Aiming at the problem of pilot contamination in massive MIMO [...] Read more.
Massive Multiple-input Multiple-output (MIMO) is an emerging technology for the 5G wireless communication systems which has the potential to provide high spectral efficient and improved link reliability and accommodate large number of users. Aiming at the problem of pilot contamination in massive MIMO systems, this paper proposes two algorithms to mitigate it. The first algorithm is depending on the idea of Path Loss to perform User Grouping (PLUG) which divide the users into the center and edge user groups depending on different levels of pilot contamination. It assigns the same pilot sequences to the center users which slightly suffer from pilot contamination and assign orthogonal pilot sequences to the edge users which severely suffer from pilot contamination. It is assumed that the number of users at the edge of each cell is the same. Therefore, to overcome such limitations of PLUG algorithm, we propose an improved PLUG (IPLUG) algorithm which provides the decision parameters for user grouping and selects the number of central and edge users in each cell in a dynamic manner. Thus, the algorithm prevents the wrong division of users in good channel conditions being considered as an edge user which causes large pilot overhead, and also identifies the users with worst channel conditions and prevents the wrong division of such users from the center user group. The second algorithm for pilot decontamination utilizes the idea of pseudo-random codes in which orthogonal pilot are assigned to different cells. Such codes are deployed to get a transmission pilot by scrambling the user pilot in the cell. Since the pilot contamination is generated because different cells multiplex the same set of orthogonal pilots and the pseudo-random sequences have good cross-correlation characteristics, this paper uses this feature to improve the orthogonality of pilots between different cells. Simulation results show that the proposed algorithms can effectively improve channel estimation performance and achievable rate as compared with other schemes. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Channel Sounding for Multi-User Massive MIMO in Distributed Antenna System Environment
Electronics 2019, 8(1), 36; https://doi.org/10.3390/electronics8010036 - 01 Jan 2019
Cited by 2
Abstract
We propose a generation scheme for a sounding reference signal (SRS) suitable for supporting a large number of users in massive multi-input multi-output (MIMO) system with a distributed antenna system (DAS) environment. The proposed SRS can alleviate the pilot contamination problem which occurs [...] Read more.
We propose a generation scheme for a sounding reference signal (SRS) suitable for supporting a large number of users in massive multi-input multi-output (MIMO) system with a distributed antenna system (DAS) environment. The proposed SRS can alleviate the pilot contamination problem which occurs inherently in the multi-user system due to the limited number of orthogonal sequences. The proposed SRS sequence is generated by applying a well-chosen phase rotation to the conventional LTE/LTE-A SRS sequences without requiring an increased amount of resource usage. We also propose using the correlation-aided channel estimation algorithm as a supplemental scheme to obtain more reliable and refined channel estimation. It is shown that the proposed SRS sequence and the supplemental channel estimation scheme improve significantly the channel estimation performance in multi-user massive MIMO systems. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Spectral and Energy Efficiency of Distributed Massive MIMO with Low-Resolution ADC
Electronics 2018, 7(12), 391; https://doi.org/10.3390/electronics7120391 - 04 Dec 2018
Cited by 1
Abstract
In this paper, considering a more realistic case where the low-resolution analog-to-digital convertors (ADCs) are employed at receiver antennas, we investigate the spectral and energy efficiency in multi-cell multi-user distributed massive multi-input multi-output (MIMO) systems with two linear receivers. An additive quantization noise [...] Read more.
In this paper, considering a more realistic case where the low-resolution analog-to-digital convertors (ADCs) are employed at receiver antennas, we investigate the spectral and energy efficiency in multi-cell multi-user distributed massive multi-input multi-output (MIMO) systems with two linear receivers. An additive quantization noise model is provided first to study the effects of quantization noise. Using the model provided, the closed-form expressions for the uplink achievable rates with a zero-forcing (ZF) receiver and a maximum ratio combination (MRC) receiver under quantization noise and pilot contamination are derived. Furthermore, the asymptotic achievable rates are also given when the number of quantization bits, the per user transmit power, and the number of antennas per remote antenna unit (RAU) go to infinity, respectively. Numerical results prove that the theoretical analysis is accurate and show that quantization noise degrades the performance in spectral efficiency, but the growth in the number of antennas can compensate for the degradation. Furthermore, low-resolution ADCs with 3 or 4 bits outperform perfect ADCs in energy efficiency. Numerical results imply that it is preferable to use low-resolution ADCs in distributed massive MIMO systems. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Planar Array Diagnostic Tool for Millimeter-Wave Wireless Communication Systems
Electronics 2018, 7(12), 383; https://doi.org/10.3390/electronics7120383 - 03 Dec 2018
Cited by 1
Abstract
In this paper, a diagnostic tool or procedure based on Bayesian compressive sensing (BCS) is proposed for identification of failed element(s) which manifest in millimeter-wave planar antenna arrays. With adequate a priori knowledge of the reference antenna array radiation pattern, a diagnostic problem [...] Read more.
In this paper, a diagnostic tool or procedure based on Bayesian compressive sensing (BCS) is proposed for identification of failed element(s) which manifest in millimeter-wave planar antenna arrays. With adequate a priori knowledge of the reference antenna array radiation pattern, a diagnostic problem of faulty elements was formulated. Sparse recovery algorithms, including total variation (TV), mixed 1 / 2 norm, and minimization of the 1 , are readily available in the literature, and were used to diagnose the array under test (AUT) from measurement points, consequently providing faster and better diagnostic schemes than the traditional mechanisms, such as the back propagation algorithm, matrix method algorithm, etc. However, these approaches exhibit some drawbacks in terms of effectiveness and reliability in noisy data, and a large number of measurement data points. To overcome these problems, a methodology based on BCS was adapted in this paper. From far-field radiation pattern samples, planar array diagnosis was formulated as a sparse signal recovery problem where BCS was applied to recover the locations of the faults using relevance vector machine (RVM). The resulted BCS approach was validated through simulations and experiments to provide suitable guidelines for users, as well as insight into the features and potential of the proposed procedure. A Ka-band ( 28.9   GHz ) 10 × 10 rectangular microstrip patch antenna array that emulates failure with zero excitation was designed for far-field measurements in an anechoic chamber. Both simulated and measured far-field samples were used to test the proposed approach. The proposed technique is demonstrated to detect diagnostic problems with fewer measurements provided the prior knowledge of the array radiation pattern is known, and the number of faults is relatively smaller than the array size. The effectiveness and reliability of the technique is verified experimentally and via simulation. In addition to a faster diagnosis and better reconstruction accuracy, the BCS-based technique shows more robustness to additive noisy data compared to other compressive sensing methods. The proposed procedure can be applied to next-generation transceivers, aerospace systems, radar systems, and other communication systems. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Computationally Efficient Channel Estimation in 5G Massive Multiple-Input Multiple-output Systems
Electronics 2018, 7(12), 382; https://doi.org/10.3390/electronics7120382 - 03 Dec 2018
Cited by 8
Abstract
Traditional channel estimation algorithms such as minimum mean square error (MMSE) are widely used in massive multiple-input multiple-output (MIMO) systems, but require a matrix inversion operation and an enormous amount of computations, which result in high computational complexity and make them impractical to [...] Read more.
Traditional channel estimation algorithms such as minimum mean square error (MMSE) are widely used in massive multiple-input multiple-output (MIMO) systems, but require a matrix inversion operation and an enormous amount of computations, which result in high computational complexity and make them impractical to implement. To overcome the matrix inversion problem, we propose a computationally efficient hybrid steepest descent Gauss–Seidel (SDGS) joint detection, which directly estimates the user’s transmitted symbol vector, and can quickly converge to obtain an ideal estimation value with a few simple iterations. Moreover, signal detection performance was further improved by utilizing the bit log-likelihood ratio (LLR) for soft channel decoding. Simulation results showed that the proposed algorithm had better channel estimation performance, which improved the signal detection by 31.68% while the complexity was reduced by 45.72%, compared with the existing algorithms. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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Open AccessArticle
Downlink Spectral Efficiency Analysis in Distributed Massive MIMO with Phase Noise
Electronics 2018, 7(11), 317; https://doi.org/10.3390/electronics7110317 - 12 Nov 2018
Cited by 1
Abstract
To achieve the advantages provided by massive multiple-input multiple-output (MIMO), a large number of antennas need to be deployed at the base station. However, for the reason of cost, inexpensive hardwares are employed in the realistic scenario, which makes the system distorted by [...] Read more.
To achieve the advantages provided by massive multiple-input multiple-output (MIMO), a large number of antennas need to be deployed at the base station. However, for the reason of cost, inexpensive hardwares are employed in the realistic scenario, which makes the system distorted by hardware impairments. Hence, in this paper, we analyze the downlink spectral efficiency in distributed massive MIMO with phase noise and amplified thermal noise. We provide an effective channel model considering large-scale fading, small-scale fast fading and phase noise. Based on the model, the estimated channel state information (CSI) is obtained during the pilot phase. Under the imperfect CSI, the closed-form expressions of downlink achievable rates with maximum ratio transmission (MRT) and zero-forcing (ZF) precoders in distributed massive MIMO are derived. Furthermore, we also give the user ultimate achievable rates when the number of antennas tends to infinity with both precoders. Based on these expressions, we analyze the impacts of phase noise on the spectral efficiency. It can be concluded that the same limit rate is achieved with both precoders when phase noise is present, and phase noise limits the spectral efficiency. Numerical results show that ZF outdoes MRT precoder in spectral efficiency and ZF precoder is more affected by phase noise. Full article
(This article belongs to the Special Issue Massive MIMO Systems)
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