Total Number Of Antennas Research Articles

Energy‐efficient hybrid beamforming for millimeter‐wave‐based massive multiple‐input multiple‐output system

SummaryThe advanced wireless communication system requires abridged energy consumption, enhanced data rate, and good signal coverage. The massive MIMO technology for 5G systems has been developed to accommodate several users simultaneously with superior throughput. The claim for high data rate wireless communication services is expanding quickly as time goes. Thus, the key difficulty is that as the number of users grows, the number of phase shifters grows as well, causing the system to consume more power; as a result, the system's energy efficiency decreases. Hybrid beamforming has recently emerged as an attractive technique for millimeter‐wave (mmWave) communication systems. The analog beamformer in the RF domain and digital beamformer in the baseband are coupled through a minimal number of RF chains in hybrid beamforming architecture. Hybrid beamforming utilizes fewer RF (radio frequency) chains than the total number of antennas to have a lower energy consumption design. The hybrid beamforming for a mmWave‐based massive MIMO system through different phase shifter selection mechanisms is proposed to achieve the highest energy efficiency for mmWave communications systems. The fully connected with phase shifter selection, sub‐connected with phase shifter selection (SPSS), and fully connected and sub‐connected with phase shifter selection with halved and doubled switches are considered for this research. The simulation results show the SPSS with halved switch outperforms on energy efficiency.

Cell-Free Massive MIMO for URLLC: A Finite-Blocklength Analysis

We present a general framework for the characterization of the packet error probability achievable in cell-free Massive multiple-input multiple output (MIMO) architectures deployed to support ultra-reliable low-latency (URLLC) traffic. The framework is general and encompasses both centralized and distributed cell-free architectures, arbitrary fading channels and channel estimation algorithms at both network and user-equipment (UE) sides, as well as arbitrary combing and precoding schemes. The framework is used to perform numerical experiments on specific scenarios, which illustrate the superiority of cell-free architectures compared to cellular architectures in supporting URLLC traffic in uplink and downlink. Also, these numerical experiments provide the following insights into the design of cell-free architectures for URLLC: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> ) minimum mean square error (MMSE) spatial processing must be used to achieve the URLLC targets; <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ii</i> ) for a given total number of antennas per coverage area, centralized cell-free solutions involving single-antenna access points (APs) offer the best performance in the uplink, thereby highlighting the importance of reducing the average distance between APs and UEs in the URLLC regime; <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">iii</i> ) this observation applies also to the downlink, provided that the APs transmit precoded pilots to allow the UEs to estimate accurately the precoded channel.

Joint design of antenna selection and transmit linear array beamformer for integrated radar and communications

The design of integrated radar-communication (IRC) systems is seen as a promising solution to alleviate the congestion of spectrum resource in recent years. Additionally, with the deployment of large-scaled arrays in base stations, sparse array design via antenna selection has become prominent to reduce system overheads and alleviate mutual coupling effect. In this paper, we propose a joint design of antenna selection and transmit beamformer for IRC systems to realize the dual operations of radar and communications. Specifically, we propose a joint model that achieves a trade-off between minimizing the total number of antennas for IRC and suppressing the peak sidelobe level (PSL) of overall transmit beampattern with well-controlled mainlobe ripples. Unlike the existing schemes that focus on individual beamformer design with varying sparse array configurations, we impose a group sparsity on the beamforming matrix and jointly optimize multiple beamformers to obtain a common sparse array for the constellation of all communication symbols. To solve the resulting non-convex problem, we employ the alternating direction method of multipliers to split the original problem into parallel subproblems which are then solved iteratively. Simulation results illustrate the superiority of the proposed method over the conventional approaches in obtaining a lower PSL using fewer antennas with dual functions.

Performance of Multi-Antenna Proactive Eavesdropping in 5G Uplink Systems

This paper studies the performance of multi-antenna proactive eavesdropping in 5G uplink systems with spatially correlated Rayleigh fadings, where the base station (BS) serves an illegal user and a multi-antenna legitimate monitor eavesdrops the suspicious link with the help of jamming attack. Based on a practical assumption of channel state information (CSI) in 5G uplink, i.e., imperfect instantaneous CSI of the suspicious link at the BS and that of eavesdropping link at the monitor, and only jamming channel statistics at the monitor, we first give a statistical jamming beamforming design. Then, semi-closed form expressions of eavesdropping non-outage probability and relative average eavesdropping rate are, respectively, derived for delay-sensitive and delay-tolerant scenarios. Via reasonable approximations and asymptotic analysis, we gain many insights on the effect of key system parameters, e.g., location-dependent channel path loss and angular spread, jamming energy and the number of antennas. Further, we provide the optimal energy allocation between pilot and data jamming and the optimal antenna allocation between jamming and eavesdropping under total energy constraint and total antenna number, respectively, which are both explicit functions of system parameters. Finally, simulation results validate our analytical results.

Transmit Antenna Selection for Sum-Rate Maximization with Multiclass Scalable Gaussian Process Classification

Antenna selection techniques are extensively applied to reduce hardware cost and power consumption in multiple-input multiple-output (MIMO) systems. This paper proposed a low-cost antenna selection method for system sum-rate maximization based on multiclass scalable Gaussian process classification (SGPC) which is capable to perform analytical inference and is scalable for massive data. Simulation results show that the average sum-rate obtained by SGPC is 1. 9 bps/Hz more than that obtained by conventional optimization driven user-centric antenna selection (UCAS) algorithm and 1 bps/Hz more than that obtained by the up-to-date learning scheme based on a deep neural network (DNN) when signal-to-noise ratio (SNR) is 10 dB, the number of total antennas at BS is 6, the number of selected antennas is 4, and the number of single-antenna users is 4. The superiority of SGPC over UCAS and DNN is more obvious as SNR, the number of selected antennas, or the number of users increases.

Covert Communication in Downlink NOMA Systems With Channel Uncertainty

With the gradual promotion of the fifth generation (5G) mobile communication and Internet of Things (IoT) applications, wireless communication transmission will be more vulnerable to illegal interceptions and/or attacks. To ensure communication security, we study covert communication of downlink nonorthogonal multiple access (NOMA) systems, where the channel knowledge of users is uncertain. A multiantenna transmitter tries to covertly transmit information to a covert user (strong user) through the shield of a public communication link (weak user), while the warden tries to detect the communication behavior between the transmitter and the covert user. To improve security and energy efficiency, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> th best antenna of the transmitter is selected, since the optimal antenna may be not available due to some schedule and/or other reasons. Aiming to evaluate the proposed framework performance, we start by deriving exact expressions for the minimum detection error probability and the optimal detection threshold of the warden, followed by a calculation analysis of the expected minimum detection error probability (EMDEP) and the outage probability of NOMA users. The asymptotic behavior for the outage probability is investigated at high signal-to-noise ratio (SNR) to acquire greater useful insights. With the goal of improving the system covertness performance, we propose that a scheme is optimized to enhance the covert throughput of the system to the maximum. Simulation results show that the following hold: 1) channel estimation errors have a significant effect on system performance; 2) reliability performance tends to build up, as the total number of antennas grows large; and 3) as the transmitting power and number of antennas increases, there is an upper bound for maximizing the covert throughput.

Alternate Distributed Beamforming with Power Allocation for Decode-and-Forward Multirelay Systems Using Buffers

In this paper, a novel transmission policy referred as alternate distributed beamforming (ADB) for buffer-aided half-duplex (HD) multirelay systems is proposed, in which the relays are divided into two groups and activated alternately in their transmitter and receiver modes, with one group receiving the same information broadcast from the source while the other group simultaneously transmitting the common messages to the destination via distributed beamforming in each time slot. It is worth noting that the relays used for reception and transmission are determined without the instantaneous channel state information (CSI). Theoretical analysis of the achievable throughput of the proposed scheme in Rayleigh fading channels is provided, and the approximate closed-form expressions are derived for multiantenna relay scenario, with single-antenna relay scenario as a special case. Moreover, the asymptotic expressions for the maximum achievable throughput of the proposed scheme and corresponding optimal power allocation in the high- and low-SNR regimes are derived as well. Numerical results in accordance with theoretical analysis demonstrate that the proposed policy achieves a significant improvement in the maximum achievable throughput compared with benchmark schemes. It is shown that for the ADB scheme, the almost or exact symmetric relay grouping may achieve the best performance in the high-SNR regime. It is also shown that increasing the number of antennas equipped at each relay is better than increasing the number of relays equipped with a single antenna when the total number of antennas at the relays is fixed.

Real-time detection of small anomaly from limited-aperture measurements in real-world microwave imaging

This study concerns a subspace migration technique used to identify the shape and location of an unknown anomaly from scattered parameter data collected within the scattering matrix for a limited-aperture inverse scattering problem. The mathematical theories of subspace migration are partially understood in terms of limited-aperture inverse scattering problems, but little investigation of real-world applications, such as microwave imaging, has taken place. Hence, we perform further research to analyze the subspace migration and explain the reasons for a number of unexplained phenomena. For theoretical corroboration, we prove that the imaging function of subspace migration is composed of an infinite series of integer-order Bessel functions of the first kind, and we outline the arrangement and the total number of antennas for transmitting and receiving signals. This is based on the application of the Born approximation to the identification of an anomaly and the uniform convergence of the Jacobi–Anger expansion formula. Various results of numerical simulations with synthetic and real data are exhibited to support the theoretical results of the imaging function and explain the reasons for a number of phenomena as well as the fundamental limitations. Further, we suggest a method of antenna arrangement to obtain better results and confirm the improvements through simulations.

Proximity co-located massive MIMO systems over correlated Rician fading channels

This paper considers the downlink transmission in a single-cell proximity co-located massive MIMO (PC-MIMO) system, in which antennas of the base station (BS) are divided into multiple antenna units (AUs) and these AUs are connected to a backhaul processor unit (BPU). The AUs are geographically deployed very close to the BPU which controls them to serve all users in the cell. Considering correlated Rician fading channels, we derive a closed-form expression of the sum spectral efficiency under the maximum-ratio transmission and statistical channel state information at each user. Based on the obtained expression, it is shown that as the number of AUs approaches infinity, the sum spectral efficiency approaches a constant value. Furthermore, we also give a closed-form expression of the average sum spectral efficiency when the arrival angles to the users seen from the AUs are varying. For the cases of correlated Rayleigh fading and uncorrelated Rician fading, we show how to find the number of antennas at each AU to maximize the average sum spectral efficiency when the total number of antennas at the BS is fixed.

Effective Minimization of Side Lobe Level of Sparse Thinned Planar Array Antenna in Multiple Planes with Constraints

ABSTRACT In this paper, the authors propose to design thinned sparse planar array antenna in multiple planes using meta-heuristic optimization algorithm such as Teaching Learning-Based Optimization (TLBO) algorithm. The objective is to achieve the minimum value of side lobe level (SLL) in the radiation pattern in two vertical planes as well as in all vertical planes. The optimal positions of the isotropic antennas in the array are obtained having multiple optimization constraints such as total number of antennas in the array, aperture area and minimum inter-element spacing. The simulation results demonstrate that the proposed method is found to be relatively simpler but promising compared to the results reported using other competitive methods.

Evaluation of an Antenna Selection Strategy for Reduced Massive MIMO Complexity

AbstractMassive Multiple‐Input Multiple‐Output (MIMO) is emerging as one promising technology for the fifth generation (5G), but the hardware and software complexity arising from the sheer number of transmitting elements is a bottleneck. Antenna selection strategies have been reported as an appealing solution for hybrid beamforming architectures to select a number of radio‐frequency (RF) chains less than the total number of antennas but are yet to be fully defined and evaluated. In this work, a generic strategy relying on the receiver (Rx) spatial correlation is investigated to select the best antenna subset from a full array. It is evaluated from ray‐traced massive MIMO radio channels using propagation metrics, and also sum‐rate capacity computation. The results demonstrate that (1) for a fixed number of users, a subset with wisely selected distributed elements outperforms a collocated one for all studied metrics with performance close to the full array and (2) using a proposed optimization algorithm for a dynamic number of users, the number of active Tx antennas can be further optimized for the different studied subsets. Moreover, for a fixed number of users, the best antenna subset presenting the lowest Rx correlation values is found to reach the optimal sum‐rate capacity using simple linear precoders compared with dirty paper coding. This is achieved with only a third of the initial RF chain hardware complexity, thus validating the proposed approach. Also, experimental measurements, presented for an industrial scenario, validate the proposed approach.

Worst-Case Detection Performance for Distributed SIMO Physical Layer Authentication

Feature-based physical layer authentication (PLA) schemes, using position-specific channel characteristics as identifying features, can provide lightweight protection against impersonation attacks in overhead-limited applications like e.g., mission-critical and low-latency scenarios. However, with PLA-aware attack strategies, an attacker can maximize the probability of successfully impersonating the legitimate devices. In this paper, we provide worst-case detection performance bounds under such strategies for a distributed PLA scheme that is based on the channel-state information (CSI) observed at multiple distributed remote radio-heads. This distributed setup exploits the multiple-channel diversity for enhanced detection performance and mimics distributed antenna architectures considered for 4G and 5G radio access networks. We consider (i) a power manipulation attack, in which a single-antenna attacker adopts optimal transmit power and phase; and (ii) an optimal spatial position attack. Interestingly, our results show that the attacker can achieve close-to-optimal success probability with only statistical CSI, which significantly strengthens the relevance of our results for practical scenarios. Furthermore, our results show that, by distributing antennas to multiple radio-heads, the worst-case missed detection probability can be reduced by 4 orders of magnitude without increasing the total number of antennas, illustrating the superiority of distributed PLA over a co-located antenna setup.

Cell-Free Massive MIMO Systems With Low-Resolution ADCs: The Rician Fading Case

This article studies the uplink and downlink achievable rates of cell-free massive multi-input multi-output (MIMO) systems over Rician fading channels, assuming that each access point possesses multiple antennas that are connected with low-resolution analog-to-digital converters (ADCs). Achievable closed-form rate expressions for both uplink and downlink are derived, which enable us to explore the design issues surrounded by the key parameters, such as the number of total antennas, the transmit power, the ADC resolution, and the Rician <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {{\it K}}$</tex-math></inline-formula> -factor. Moreover, the weighted max–min fairness power optimization algorithms are proposed. Specifically, the proposed algorithms for uplink and downlink can be formulated as geometric programming and second-order-cone programming, respectively. All the theoretical analyses and the effectiveness of the proposed algorithms are verified by simulation experiments.

Half-duplex multiple-relay multiple-antenna diamond networks with perfect full-duplex performance

Diversity-multiplexing tradeoff (DMT) of a full-duplex diamond network where the inter-relay interference (IRI) is suppressed, global channel state information (CSI) is available in all nodes, and perfect self-interference cancellation (SIC) technique is used, which we call it the perfect full-duplex diamond network, is an upper bound for the DMT of the equivalent half-duplex diamond network, i.e., the perfect full-duplex diamond network outperforms the half-duplex case. Nevertheless, the implementation of the perfect full-duplex diamond network is a high-cost operation and requires significant hardware changes in current systems. The main question addressed in this paper is: under which condition (or perhaps conditions) does a prevalent half-duplex diamond network provide the same performance as the perfect full-duplex one? In this regard, first, we calculate the DMT of a perfect full-duplex multiple-relay and multiple-antenna (MRMA) symmetric diamond network. Then, we demonstrate that for the same network but with half-duplex relays, when the number of antennas in relays satisfies a specific condition, there exists a fixed listen-transmit schedule combined with quantize-map-and-forward (QMF) relaying to achieve the optimal DMT. Also, we attain a lower bound for the total number of antennas of the MRMA symmetric diamond network to achieve the optimal DMT.

Securing Untrusted Full-Duplex Relay Channels in the Presence of Multiple External Cluster-Based Eavesdroppers

We investigate the physical layer security of a wireless cooperative network where communication between Alice and Bob is assisted by a full-duplex (FD) untrusted relay, Ray, in the presence of multiple external eavesdroppers, Eves. A cluster-based colluding eavesdropping setting is considered, where illegitimate nodes with common interests are grouped in a cluster. To confuse the different eavesdropping clusters, we employ artificial-noise (AN) aided beamforming at the source node. Moreover, FD relay jamming is used to improve the system's security. To maintain secure communications against the untrusted relay node, an FD destination jamming scheme is adopted. Our proposed scheme is designed based on the channel state information of the legitimate nodes only. We optimize the transmit power allocation factors between data and AN signals, the data and AN precoders at Alice, the AN precoder at Bob, and the data and AN precoders at Ray. Numerical results show that the optimal power allocation factor between data and AN depends on the total number of antennas of the different colluding eavesdropping clusters.

Distributed Signal Compressive Quantization and Parallel Interference Cancellation for Cloud Radio Access Network

The explosive growth of wireless traffic requires revolutionary wireless communication techniques. The cloud radio access network (C-RAN) is a solution to leverage the spatial multiplexing gain by utilizing a number of antennas distributed in a certain area. However, in most of the current literature, due to the limited front-haul capacity, each remote radio head (RRH) can use only a single antenna, and thus the total number of antennas can be utilized are limited. In this work, we propose a distributed baseband signal compressive quantization scheme for the uplink of a multi-antenna C-RAN where each RRH uses multiple antennas. At each RRH, the baseband signals of multiple time instants are embedded into a vector with low dimension using delay-and-add so that more bits can be allocated to each value, and the quantization noise power caused by the front-haul link capacity deficit is reduced. The delay-and-add operation is low complexity that can be realized using basic buffering and adding, and it does not require channel information in the RRHs. Therefore, the low deployment cost feature of C-RAN is preserved. As a result, a large number of antennas can be utilized by deploying a lot of multi-antenna RRHs, which provide rich spatial diversity that assists the detection which happens in the baseband units. In the symbol detection phase, the corresponding weight vectors are designed to detect the symbols from the compressive quantized baseband signal. A parallel interference cancellation algorithm is proposed to further improve the accuracy of the symbol detection. Numerical results show that the proposed scheme is efficient in tackling the front-haul capacity challenge. We also apply the proposed scheme to orthogonal frequency-division multiplexing-based multi-antenna C-RAN, where we find that the system can utilize larger bandwidth with limited front-haul capacity. It facilitates the deployment of C-RAN based on both 4G and 5G wireless communications.

Asynchronous Two-Way MIMO Relaying: A Multi-Relay Scenario

We consider a single-carrier asynchronous relay network where two transceivers exchange information with the help of multiple multi-antenna relays. The network is assumed to be asynchronous , meaning that the signal transmitted by any of the two transceivers arrives at different relays with different delays and also signals transmitted by different relays arrive at any of the two transceivers with different delays. We further assume that each relay obtains the vector of the relay transmit signals via multiplying the vector of the relay received signals by a beamforming matrix. For such an asynchronous two-way network with multi-antenna relays, our goal is to obtain symmetric relay beamforming matrices and the transceivers’ transmit powers such that the total power consumed in the entire network is minimized while guaranteeing given data rates at the two transceivers. To this end, we develop a model for the end-to-end channel and use this model to solve the total power minimization problem. Assuming symmetric relay beamforming matrices, we present a computationally efficient solution to this problem. Our simulation results suggest that for a given total number of antennas, there appears to be an optimal number of antennas per relays which results in the lowest power consumption in the network.

Performance of Transceiver Antenna Selection in Two Way Full-Duplex Relay Networks Over Rayleigh Fading Channels

A novel transceiver antenna selection (TRAS) strategy selecting a pair of antennas for transmission and reception at terminal sources for full-duplex amplify-forward multi-input multi-output two way relay networks is proposed. Antenna pair is selected in accordance with maximum and second maximum signal to self-interference-plus-noise ratio between the sources and relay, where the terminal sources and relay are full-duplex. Unlike reciprocal channel gains, forward and backward paths between the sources and relay are taken to be different. With four different antenna selection (AS) scenarios, the exact sum outage probability (SOP) for fading self-interference (SI) and the exact, approximated, and asymptotic SOP expressions for nonfading SI over Rayleigh fading channels are derived and validated via Monte Carlo simulation technique. The proposed AS strategy uses all antenna space for either transmission or reception which results in a reduction in total number of antennas at each terminal node. It is shown that performance can be significantly improved by usage of offered TRAS strategy at terminal sources. For example, up to 25 dB gain is obtained for five antennas at the sources with respect to no selection case of two antennas. In addition, it outperforms the selection strategy using maximum paths from two divided antenna sets at each source, where one set is only used for transmission and the other one for reception. The diversity order of the system is proven to be dependent on SI and varies between zero and minimum of the total number of antennas of two sources minus 1. For different SI values, optimum power allocations are demonstrated and factors affecting optimum relay location are also elaborated. Each AS scenario produces the lowest SOP for different combinations of SI occurrences, power allocations, and relay locations.

New upper degree of freedom in transmission system based on wireless G-MIMO communication channel

We study a general type of multiple-input multiple-output (G-MIMO) relay channels, which consist of two groups (A and B) of source nodes and one relay node. Both groups have arbitrarily many source nodes each of which is in turn equipped with an arbitrary number of antennas. A G-MIMO relay channel engages in two-way transmission of independent information via the relay node. We obtain a tight upper bound on the total degrees of freedom (DoF) for such G-MIMO relay channels. Under the reasonable assumption that the number of antennas at the relay node is no more than the total number of antennas of either Group A or B, we design an efficient transmission scheme to achieve the upper bound by using techniques of signal alignment and joint transceiver design for interference cancellation. At the end of the paper, we propose a future research topic to quantify the relationship between graded levels of network security and the corresponding DoF of the G-MIMO relay channels.

Degrees of Freedom of the Full-Duplex Asymmetric MIMO 3-Way Channel with Unicast and Broadcast Messages

In this paper, we characterize the total degrees of freedom (DoFs) of the full-duplex asymmetric multiple-input multiple- output (MIMO) three-way channel. Each node has a separate-antenna full-duplex MIMO transceiver with a different number of antennas, where each antenna can be configured for either signal transmission or reception. We study this system under two message configurations; the first configuration is when each node has two unicast messages to be delivered to the two other nodes, while the second configuration is when each node has two unicast messages as well as one broadcast message to be delivered to the two other nodes. For each configuration, we first derive upper bounds on the total DoF of the system. Cut-set bounds in conjunction with genie-aided bounds are derived to characterize the achievable total DoF. Afterward, we analytically derive the optimal number of transmit and receive antennas at each node to maximize the total DoF of the system, subject to the total number of antennas at each node. Finally, the achievable schemes for each configuration are constructed. The proposed schemes are mainly based on zero-forcing and null-space transmit beamforming. We show that the derived outer and inner bounds on the total DoF are tight for each message configuration.