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Numrering	Referens	Omslagsbild	Hitta
1.	Abbas, Q., et al. (författare) A Markovian Model for the Analysis of Age of Information in IoT Networks 2021 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers Inc.. - 2162-2337 .- 2162-2345. ; 10:7, s. 1596-1600 Tidskriftsartikel (refereegranskat)abstract Age of Information (AoI) is a critical metric in status update systems as these systems require the fresh updates. This letter investigates the uplink of an Internet-of-Thing (IoT) network where L nodes transmit their information packets to a base station. The effects of the arrival rate of packets at the nodes, the number of nodes in the system, and queue length of each node have been studied by devising a discrete time Markov chain (MC) model. This model helps in predicting the values of AoI and probability of packet drops in such systems. The notion of first-in first-out is used for queuing, which transmits the oldest packet first, resulting in decreasing the overall AoI of the system. The results show that AoI increases with the increase in queue length, number of nodes and arrival rate and we quantify the aforementioned metrics using the MC model. The results found using the MC model are also validated using extensive simulations. © 2012 IEEE.
2.	Abdullah, Zaid, et al. (författare) Impact of Phase-Noise and Spatial Correlation on Double-RIS-Assisted Multiuser MISO Networks 2022 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; , s. 1-1 Tidskriftsartikel (refereegranskat)
3.	Alexandropoulos, G. C., et al. (författare) Localization via Multiple Reconfigurable Intelligent Surfaces Equipped with Single Receive RF Chains 2022 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 11:5, s. 1072-1076 Tidskriftsartikel (refereegranskat)abstract The extra degrees of freedom resulting from the consideration of Reconfigurable Intelligent Surfaces (RISs) for smart signal propagation can be exploited for high accuracy localization and tracking. In this paper, capitalizing on a recent RIS hardware architecture incorporating a single receive Radio Frequency (RF) chain for measurement collection, we present a user localization method with multiple RISs. The proposed method includes an initial step for direction estimation at each RIS, followed by maximum likelihood position estimation, which is initialized with a least squares line intersection technique. Our numerical results showcase the accuracy of the proposed localization, verifying our theoretical estimation analysis.
4.	Bacci, Giacomo, et al. (författare) Spherical Wavefronts Improve MU-MIMO Spectral Efficiency When Using Electrically Large Arrays 2023 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 12:7, s. 1219-1223 Tidskriftsartikel (refereegranskat)abstract Modern multiple-input multiple-output (MIMO) communication systems are almost exclusively designed assuming locally plane wavefronts over antenna arrays. This is known as the far-field approximation and is soundly justified at sub-6-GHz frequencies at most relevant transmission ranges. However, when higher frequencies and shorter transmission ranges are used, the wave curvature over the array is no longer negligible, and arrays operate in the so-called radiative near-field region. This letter aims to show that the classical far-field approximation may significantly underestimate the achievable spectral efficiency of multi-user MIMO communications operating in the 30-GHz bands and above, even at ranges beyond the Fraunhofer distance. For planar arrays with typical sizes, we show that computing combining schemes based on the far-field model significantly reduces channel gain and spatial multiplexing capability. When the radiative near-field model is used, interference rejection schemes, such as the optimal minimum mean-square-error combiner, appear to be very promising, when combined with electrically large arrays, to meet the requirements of next-generation networks.
5.	Bai, Jianan, et al. (författare) Activity Detection in Distributed MIMO: Distributed AMP via Likelihood Ratio Fusion 2022 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 11:10, s. 2200-2204 Tidskriftsartikel (refereegranskat)abstract We develop a new algorithm for activity detection for grant-free multiple access in distributed multiple-input multiple-output (MIMO). The algorithm is a distributed version of the approximate message passing (AMP) based on a soft combination of likelihood ratios computed independently at multiple access points. The underpinning theoretical basis of our algorithm is a new observation that we made about the state evolution in the AMP. Specifically, with a minimum mean-square error denoiser, the state maintains a block-diagonal structure whenever the covariance matrices of the signals have such a structure. We show by numerical examples that the algorithm outperforms competing schemes from the literature.
6.	Bashar, Manijeh, et al. (författare) Limited-Fronthaul Cell-Free Massive MIMO With Local MMSE Receiver Under Rician Fading and Phase Shifts 2021 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 10:9, s. 1934-1938 Tidskriftsartikel (refereegranskat)abstract A cell-free Massive multiple-input multiple-output (MIMO) system is considered, where the access points (APs) are linked to a central processing unit (CPU) via the limited-capacity fronthaul links. It is assumed that only the quantized version of the weighted signals are available at the CPU. The achievable rate of a limited fronthaul cell-free massive MIMO with local minimum mean square error (MMSE) detection is studied. We study the assumption of uncorrelated quantization distortion, which is commonly used in literature. We show that this assumption will not affect the validity of the insights obtained in our work. To investigate this, we compare the uplink per-user rate with different system parameters for two different scenarios; 1) the exact uplink per-user rate and 2) the uplink per-user rate while ignoring the correlation between the inputs of the quantizers. Finally, we present the conditions which imply that the quantization distortions across APs can be assumed to be uncorrelated.
7.	Becirovic, Ema, et al. (författare) Activity Detection in Distributed Massive MIMO With Pilot-Hopping and Activity Correlation 2023 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 12:2, s. 272-276 Tidskriftsartikel (refereegranskat)abstract Many real-world scenarios for massive machine-type communication involve sensors monitoring a physical phenomenon. As a consequence, the activity pattern of these sensors will be correlated. In this letter, we study how the correlation of user activities can be exploited to improve detection performance in grant-free random access systems where the users transmit pilot-hopping sequences and the detection is performed based on the received energy. We show that we can expect considerable performance gains by adding regularizers, which take the activity correlation into account, to the non-negative least squares, which has been shown to work well for independent user activity.
8.	Björnson, Emil, Professor, 1983-, et al. (författare) Intelligent Reflecting Surface Versus Decode-and-Forward : How Large Surfaces are Needed to Beat Relaying? 2020 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 9:2, s. 244-248 Tidskriftsartikel (refereegranskat)abstract The rate and energy efficiency of wireless channels can be improved by deploying software-controlled metasurfaces to reflect signals from the source to the destination, especially when the direct path is weak. While previous works mainly optimized the reflections, this letter compares the new technology with classic decode-and-forward (DF) relaying. The main observation is that very high rates and/or large metasurfaces are needed to outperform DF relaying, both in terms of minimizing the total transmit power and maximizing the energy efficiency, which also includes the dissipation in the transceiver hardware.
9.	Björnson, Emil, et al. (författare) Rayleigh Fading Modeling and Channel Hardening for Reconfigurable Intelligent Surfaces 2021 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 10:4, s. 830-834 Tidskriftsartikel (refereegranskat)abstract A realistic performance assessment of any wireless technology requires the use of a channel model that reflects its main characteristics. The independent and identically distributed Rayleigh fading channel model has been (and still is) the basis of most theoretical research on multiple antenna technologies in scattering environments. This letter shows that such a model is not physically appearing when using a reconfigurable intelligent surface (RIS) with rectangular geometry and provides an alternative physically feasible Rayleigh fading model that can be used as a baseline when evaluating RIS-aided communications. The model is used to revisit the basic RIS properties, e.g., the rank of spatial correlation matrices and channel hardening.
10.	Chen, Zheng, et al. (författare) Over-the-Air Computation With Multiple Receivers: A Space-Time Approach 2023 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 12:8, s. 1399-1403 Tidskriftsartikel (refereegranskat)abstract The emerging concept of Over-the-Air (OtA) computation has shown great potential for achieving resource-efficient data aggregation across large wireless networks. However, current research in this area has been limited to the standard many-to-one topology, where multiple nodes transmit data to a single receiver. In this letter, we address the problem of applying OtA computation to scenarios with multiple receivers, and propose a novel communication design that exploits joint precoding and decoding over multiple time slots. To determine the optimal precoding and decoding vectors, we formulate an optimization problem that aims to minimize the mean squared error of the desired computations while satisfying the unbiasedness condition and power constraints. Our proposed multi-slot design is shown to be effective in saving communication resources (e.g., time slots) and achieving smaller estimation errors compared to the baseline approach of separating different receivers over time.
11.	de Araujo, Gilderlan T., et al. (författare) Semi-Blind Joint Channel and Symbol Estimation in IRS-Assisted Multiuser MIMO Networks 2022 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 11:7, s. 1553-1557 Tidskriftsartikel (refereegranskat)abstract Intelligent reflecting surface (IRS) is a promising technology for beyond of the wireless communications. In fully passive IRS-assisted systems, channel estimation is challenging and should be carried out only at the base station or at the terminals since the elements of the IRS are incapable of processing signals. In this letter, we formulate a tensor-based semi-blind receiver that solves the joint channel and symbol estimation problem in an IRS-assisted multi-user multiple-input multiple-output system. The proposed approach relies on a generalized PARATUCK tensor model of the signals reflected by the IRS, based on a two-stage closed-form semi-blind receiver using Khatri-Rao and Kronecker factorizations. Simulation results demonstrate the superior performance of the proposed semi-blind receiver, in terms of the normalized mean squared error and symbol error rate, as well as a lower computational complexity, compared to recently proposed parallel factor analysis-based receivers.
12.	Demir, Ozlem Tugfe, et al. (författare) Channel Modeling and Channel Estimation for Holographic Massive MIMO With Planar Arrays 2022 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 11:5, s. 997-1001 Tidskriftsartikel (refereegranskat)abstract In a realistic wireless environment, the multi-antenna channel usually exhibits spatially correlated fading. This is more emphasized when a large number of antennas is densely deployed, known as holographic massive MIMO (multiple-input multiple-output). In the first part of this letter, we develop a channel model for holographic massive MIMO by considering both non-isotropic scattering and directive antennas. With a large number of antennas, it is difficult to obtain full knowledge of the spatial correlation matrix. In this case, channel estimation is conventionally done using the least-squares (LS) estimator that requires no prior information of the channel statistics or array geometry. In the second part of this letter, we propose a novel channel estimation scheme that exploits the array geometry to identify a subspace of reduced rank that covers the eigenspace of any spatial correlation matrix. The proposed estimator outperforms the LS estimator, without using any user-specific channel statistics.
13.	Fascista, Alessio, et al. (författare) Low-Complexity Downlink Channel Estimation in mmWave Multiple-Input Single-Output Systems 2022 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 11:3, s. 518-522 Tidskriftsartikel (refereegranskat)abstract This paper tackles the problem of channel estimation in mmWave multiple-input single-output systems, where users are equipped with single-antenna receivers. By leveraging broadcast transmissions in the downlink channel, two novel low-complexity estimation approaches are devised, able to operate even in presence of a reduced number of transmit antennas or limited bandwidth. Numerical results show that the proposed algorithms provide accurate estimates of the channel parameters, achieving at the same time about 50% complexity reduction compared to existing approaches.
14.	Guo, Hao, 1992, et al. (författare) On Delay-limited Average Rate of HARQ-based Predictor Antenna Systems 2021 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 10:8, s. 1628-1632 Tidskriftsartikel (refereegranskat)abstract Predictor antenna (PA) system is referred to as a system with two sets of antennas on the roof of a vehicle, where the PAs positioned in the front of the vehicle are used to predict the channel state observed by the receive antennas (RAs) that are aligned behind the PAs. In this work, we study the effect of spatial mismatch on the accuracy of channel state information estimation, and analyze the delay-constrained average rate of hybrid automatic repeat request (HARQ)-based PA systems. We consider variable-length incremental redundancy (INR) HARQ protocol, and derive a closed-form expression for the maximum average rate subject to a maximum delay constraint. Moreover, we study the effect of different parameters such as the vehicle speed, the antenna distance and the rate allocation on the system performance. The results indicate that, compared to the open-loop case, the delay-limited average rate is considerably improved with our proposed PA-HARQ scheme.
15.	Guo, Hao, 1992, et al. (författare) Power Allocation in HARQ-based Predictor Antenna Systems 2020 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 9:12, s. 2025-2029 Tidskriftsartikel (refereegranskat)abstract In this work, we study the performance of predictor antenna (PA) systems using hybrid automatic repeat request (HARQ). Here, the PA system is referred to as a system with two sets of antennas on the roof of a vehicle. In this setup, the PA positioned in the front of the vehicle can be used to predict the channel state information at the transmitter (CSIT) for the receive antenna (RA) that is aligned behind the PA. Considering spatial mismatch due to mobility, we derive closed-form expressions for the optimal power allocation and the minimum average power of PA systems under different outage probability constraints. The results are presented for different types of HARQ protocols and we study the effect of different parameters on the performance of PA systems. As we show, our proposed approximation scheme enables us to analyze PA systems with high accuracy. Moreover, for different vehicle speeds, we show that HARQ-based feedback can reduce the outage-limited power consumption of PA systems by orders of magnitude.
16.	Guo, Hao, 1992, et al. (författare) Rate Adaptation in Predictor Antenna Systems 2020 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 9:4, s. 448-451 Tidskriftsartikel (refereegranskat)abstract Predictor antenna (PA) system is referred to as a system with two sets of antennas on the roof of a vehicle, where the PAs positioned in the front of the vehicle are used to predict the channel state observed by the receive antennas (RAs) that are aligned behind the PAs. This letter studies the performance of PA systems in the presence of the mismatching problem, i.e., when the channel observed by the PA is not exactly the same as the channel experienced by the RA. Particularly, we study the effect of spatial mismatching on the accuracy of channel state information estimation and rate adaption. We derive closed-form expressions for instantaneous throughput, outage probability, and the throughput-optimized rate adaptation. Also, we take the temporal evolution of the channel into account and evaluate the system performance in temporally-correlated conditions. The simulation and analytical results show that, while PA-assisted adaptive rate adaptation leads to considerable performance improvement, the throughput and the outage probability are remarkably affected by the spatial mismatch and temporal correlations.
17.	He, Jiguang, et al. (författare) Learning to Estimate RIS-Aided mmWave Channels 2022 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 11:4, s. 841-845 Tidskriftsartikel (refereegranskat)abstract Inspired by the remarkable learning and prediction performance of deep neural networks (DNNs), we apply one special type of DNN framework, known as model-driven deep unfolding neural network, to reconfigurable intelligent surface (RIS)-aided millimeter wave (mmWave) single-input multiple-output (SIMO) systems. We focus on uplink cascaded channel estimation, where known and fixed base station combining and RIS phase control matrices are considered for collecting observations. To boost the estimation performance and reduce the training overhead, the inherent channel sparsity of mmWave channels is leveraged in the deep unfolding method. It is verified that the proposed deep unfolding network architecture can outperform the least squares (LS) method with a relatively smaller training overhead and online computational complexity.
18.	He, Jiguang, et al. (författare) Leveraging Location Information for RIS-aided mmWave MIMO Communications 2021 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 10:7, s. 1380-1384 Tidskriftsartikel (refereegranskat)abstract Location information offered by external positioning systems, e.g., satellite navigation, can be used as prior information in the process of beam alignment and channel parameter estimation for reconfigurable intelligent surface (RIS)-aided millimeter wave (mmWave) multiple-input multiple-output networks. Benefiting from the availability of such prior information, albeit imperfect, the beam alignment and channel parameter estimation processes can be significantly accelerated with less candidate beams explored at all the terminals. We propose a practical channel parameter estimation method via atomic norm minimization, which outperforms the standard beam alignment in terms of both the mean square error and the effective spectrum efficiency for the same training overhead.
19.	Huang, Shaocheng, et al. (författare) Decentralized Beamforming Design for Intelligent Reflecting Surface-Enhanced Cell-Free Networks 2021 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 10:3, s. 673-677 Tidskriftsartikel (refereegranskat)abstract Cell-free networks are considered to be a promising distributed network architecture to satisfy the increasing number of users and high rate expectations in beyond-5G systems. However, to further enhance network capacity, an increasing number of high-cost base stations (BSs) is required. To address this problem and inspired by the cost-effective intelligent reflecting surface (IRS) technique, we propose a fully decentralized design framework for cooperative beamforming in IRS-aided cell-free networks. We first transform the centralized weighted sum-rate maximization problem into a tractable consensus optimization problem, and then an incremental alternating direction method of multipliers (ADMM) algorithm is proposed to locally update the beamformer. The complexity and convergence of the proposed method are analyzed, and these results show that the performance of the new scheme can asymptotically approach that of the centralized one as the number of iterations increases. Results also show that IRSs can significantly increase the system sum-rate of cell-free networks and the proposed method outperforms existing decentralized methods.
20.	Huang, Shaocheng, et al. (författare) Hybrid Beamforming for Millimeter Wave Multi-User MIMO Systems using Learning Machine 2020 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 9:11, s. 1914-1918 Tidskriftsartikel (refereegranskat)abstract Hybrid beamforming (HBF) design is a crucial stage in millimeter wave (mmWave) multi-user multi-input multi-output (MU-MIMO) systems. However, conventional HBF methods are still with high complexity and strongly rely on the quality of channel state information. We propose an extreme learning machine (ELM) framework to jointly optimize transmitting and receiving beamformers. Specifically, to provide accurate labels for training, we first propose a factional-programming and majorization-minimization based HBF method (FP-MM-HBF). Then, an ELM based HBF (ELM-HBF) framework is proposed to increase the robustness of beamformers. Both FP-MM-HBF and ELM-HBF can provide higher system sum-rate compared with conventional methods. Moreover, ELM-HBF cannot only provide robust HBF performance but also consume very short computation time.
21.	Huang, Yiqian, et al. (författare) A Novel Maximum Distance Separable Coded OFDM-RIS for 6G Wireless Communications 2023 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 12:5, s. 927-931 Tidskriftsartikel (refereegranskat)abstract The vision of the sixth generation mobile communication (6G) calls for extremely reliable data transmission over complex and diverse wireless channels. By combining the maximum distance separable (MDS) codes with the classic orthogonal frequency division multiplexing (OFDM), we present a new paradigm with the assistance of the reconfigurable intelligent surfaces (RIS). In our design, the RIS with limited phase shifts are adopted and the pairwise error probability (PEP) of the proposed system is first derived. Then, in order to further minimize the bit error rate (BER), we provide a novel method based on phase alignment to obtain the optimal solution for the discrete phase shifts. Our simulation results show that the proposed scheme provides considerable BER performance improvements compared to conventional OFDM systems. Moreover, the proposed discrete phase optimization algorithm is capable of achieving performance similar to that of the system with continuous phase shifts.
22.	Ibrahim, Emad Farouk, et al. (författare) Binary Polarization Shift Keying with Reconfigurable Intelligent Surfaces 2022 Ingår i: IEEE Wireless Communications Letters. - : IEEE. - 2162-2337 .- 2162-2345. ; 11:5, s. 908-912 Tidskriftsartikel (refereegranskat)abstract We propose a novel binary polarization shift keying modulation scheme for a line-of-sight environment by exploiting the polarization control ability of the reconfigurable intelligent surface (RIS). The RIS encodes the information data in terms of the polarization states of either the reflected wave from the RIS or the composite wireless channel between an RF source and receiver. In the first case, polarization mismatch correction becomes essential at the receiver. In the second case, the RIS pre-codes the reflected wave to compensate for the polarization mismatch which allows non-coherent demodulation at the receiver.
23.	Jirhandeh, Milad Javadzadeh, et al. (författare) Super-resolution DOA estimation for wideband signals using non-uniform linear arrays with no focusing matrix 2022 Ingår i: IEEE Wireless Communications Letters. - : IEEE. - 2162-2337 .- 2162-2345. ; 11:3, s. 641-644 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract We focus on developing an effective Direction Of Arrival (DOA) estimation method for wideband sources based on the super-resolution concept. In this letter, we represent the data model of a wideband DOA estimation problem in a new form. Then, using this model, we propose an atomic norm minimization problem that leads to an accurate wideband DOA estimation method with no need for any focusing matrices. Moreover, this method requires no initial estimate and can be implemented by non-uniform linear arrays. Numerical simulations show that in comparison to some well-known techniques, the proposed method generates outstanding accuracy and higher robustness to noise. The effectiveness of the method is also verified in presence of close adjacent sources.
24.	Kakkavas, Anastasios, et al. (författare) Position Information from Reflecting Surfaces 2021 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 10:6, s. 1300-1304 Tidskriftsartikel (refereegranskat)abstract In the context of positioning an agent with a single-anchor, this contribution focuses on the Fisher information about the position, orientation and clock offset of the agent provided by single-bounce reflections. The availability of prior knowledge of the agent’s environment is taken into account via a prior distribution of the position of virtual anchors, and the rank, intensity and direction of provided information is studied. We show that when no prior knowledge is available, single-bounce reflections offer position information in the direction parallel to the reflecting surface, irrespective of the agent’s and anchor’s locations. We provide a geometrically intuitive explanation of the results and present numerical examples demonstrating their potential implications.
25.	Kallehauge, Tobias, et al. (författare) A Primer on the Statistical Relation between Wireless Ultra-Reliability and Location Estimation 2022 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 11:8, s. 1600-1604 Tidskriftsartikel (refereegranskat)abstract Location information is often used as a proxy to infer the performance of a wireless communication link. Using a very simple model, this letter unveils a basic statistical relation between the location estimation uncertainty and wireless link reliability. First, a Cramér-Rao bound for the localization error is derived. Then, wireless link reliability is characterized by how likely the outage probability is to be above a target threshold. We show that the reliability is sensitive to location errors, especially when the channel statistics are also sensitive to the location. Finally, we highlight the difficulty of choosing a rate that meets target reliability while accounting for the location uncertainty.
26.	Khorsandmanesh, Yasaman, et al. (författare) Beam Coherence Time Analysis for Mobile Wideband mmWave Point-to-Point MIMO Channels 2024 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 13:6, s. 1546-1550 Tidskriftsartikel (refereegranskat)abstract Multi-Gbps data rates are achievable in millimeter-wave (mmWave) bands, but a prominent issue is the tiny wavelength that results in rapid fading variations and significant pilot signaling for channel estimation. In this letter, we recognize that the angles of scattering clusters seen from the UE vary slowly compared to the small-scale fading. We characterize the beam coherence time, which quantifies how frequently the UE must update its downlink receive combining matrix. The exact beam coherence time is derived in the single-cluster case, and an achievable lower bound is proposed for the multi-cluster case. These values are determined so that at least half of the received signal gain is maintained in between the combining updates. We demonstrate how the beam coherence time can be hundreds of times larger than the channel coherence time of the small-scale fading.
27.	Kong, L., et al. (författare) Unified framework for secrecy characteristics with mixture of gaussian (MoG) distribution 2020 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 9:10, s. 1625-1628 Tidskriftsartikel (refereegranskat)
28.	Lee, Woong-Hee, et al. (författare) Sparse Channel Estimation in Wideband Systems With Geometric Sequence Decomposition 2022 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 11:1, s. 169-172 Tidskriftsartikel (refereegranskat)abstract The sparsity of multipaths in the wideband channel has motivated the use of compressed sensing for channel estimation. In this letter, we propose a different approach to sparse channel estimation. We exploit the fact that L taps of channel impulse response in time domain constitute a non-orthogonal superposition of L geometric sequences in frequency domain. This converts the channel estimation problem into the extraction of the parameters of geometric sequences. Numerical results show that the proposed scheme is superior to existing algorithms in high signal-to-noise ratio (SNR) and large bandwidth conditions.
29.	Lei, Wanlu, et al. (författare) Adaptive Beam Sweeping With Supervised Learning 2022 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 11:12, s. 2650-2654 Tidskriftsartikel (refereegranskat)abstract Utilizing millimeter-wave (mmWave) frequencies for wireless communication in mobile systems is challenging since continuous tracking of the beam direction is needed. For the purpose, beam sweeping is performed periodically. Such approach can be sufficient in the initial deployment of the network when the number of users is small. However, a more efficient solution is needed when lots of users are connected to the network due to higher overhead consumption. We explore a supervised learning approach to adaptively perform beam sweeping, which has low implementation complexity and can improve cell capacity by reducing beam sweeping overhead. By formulating the beam tracking problem as a binary classification problem, we applied supervised learning methods to solve the formulated problem. The methods were tested on two scenarios: ray-tracing outdoor scenario and over-the-air (OTA) testing dataset from Ericsson. Both experimental results show that the proposed methods significantly increase cell throughput comparing with existing exhaustive sweeping and periodical sweeping strategies.
30.	Li, Zhixing, et al. (författare) An Iterative 5G Positioning and Synchronization Algorithm in NLOS Environments with Multi-Bounce Paths 2023 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 12:5, s. 804-808 Tidskriftsartikel (refereegranskat)abstract 5G positioning is a very promising area that presents many opportunities and challenges. Many existing techniques rely on multiple anchor nodes and line-of-sight (LOS) paths, or single reference node and single-bounce non-LOS (NLOS) paths. However, in dense multipath environments, identifying the LOS or single-bounce assumptions is challenging. The multi-bounce paths will make the positioning accuracy deteriorate significantly. We propose a robust 5G positioning algorithm in NLOS multipath environments to mitigate the effects of multi-bounce paths.
31.	Li, Zhixing, et al. (författare) An Iterative 5G Positioning and Synchronization Algorithm in NLOS Environments with Multi-Bounce Paths 2023 Ingår i: IEEE Wireless Communications Letters. - Piscataway : IEEE. - 2162-2337 .- 2162-2345. ; 12:5, s. 804-808 Tidskriftsartikel (refereegranskat)abstract 5G positioning is a very promising area that presents many opportunities and challenges. Many existing techniques rely on multiple anchor nodes and line-of-sight (LOS) paths, or single reference node and single-bounce non-LOS (NLOS) paths. However, in dense multipath environments, identifying the LOS or single-bounce assumptions is challenging. The multi-bounce paths will make the positioning accuracy deteriorate significantly. We propose a robust 5G positioning algorithm in NLOS multipath environments to mitigate the effects of multi-bounce paths. © 2023 IEEE.
32.	Liu, Yanping, et al. (författare) Coordinated Multi-Beam Transmissions for Reliable Millimeter-Wave Communications with Independent and Correlated Blockages 2023 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 12:9, s. 1523-1527 Tidskriftsartikel (refereegranskat)abstract Millimeter-Wave (mmWave) communication has been considered as one of enabling technologies for the sixth generation (6G) network and beyond to boost the system throughput, which however is hard to provide robust and reliable transmissions since it is easy to be blocked. Coordinated multi-beam transmission has emerged as an effective way to overcome this challenge. In this letter, we first define an incomplete blockage probability and a correlated blockage probability for each user equipment (UE) to measure the robustness and reliability in coordinated multi-beam transmissions, and then formulate the coordinated multi-beam selection and transmission power allocation problem to maximize the sum rate of all UEs in consideration of the independent blockage probability and dependent blockage probability constraints of each UE in mmWave networks. To solve the considered problem efficiently, we reformulate it as a hierarchical game model and design a decentralized algorithm to search the Nash Equalibriums (NEs) of the games. Finally, we present extensive simulation results to demonstrate the effectiveness of the proposed scheme.
33.	Manoj, Banugondi Rajashekara, et al. (författare) Sensing and Classification Using Massive MIMO : A Tensor Decomposition-Based Approach 2021 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 10:12, s. 2649-2653 Tidskriftsartikel (refereegranskat)abstract Wireless-based activity sensing has gained significant attention due to its wide range of applications. We investigate radio-based multi-class classification of human activities using massive multiple-input multiple-output (MIMO) channel measurements in line-of-sight and non line-of-sight scenarios. We propose a tensor decomposition-based algorithm to extract features by exploiting the complex correlation characteristics across time, frequency, and space from channel tensors formed from the measurements, followed by a neural network that learns the relationship between the input features and output target labels. Through evaluations of real measurement data, it is demonstrated that the classification accuracy using a massive MIMO array achieves significantly better results compared to the state-of-the-art even for a smaller experimental data set.
34.	Masoudi, Meysam, 1991-, et al. (författare) Low Power Wide Area IoT Networks : Reliability Analysis in Coexisting Scenarios 2021 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 10:7, s. 1405-1409 Tidskriftsartikel (refereegranskat)abstract Low-power wide-area networks (LPWANs) are emerging technologies aiming at serving sporadic IoT traffic. While reliability of LPWANs in single-technology deployment has been well investigated, there is lack of research on performance evaluation in coexisting scenarios. To tackle this problem, we start by modeling statistics of aggregated interference from asynchronous sources over shared radio resources. Then, using stochastic geometry, we derive the closed-form statistics of reliability, mean success probability, and the mean local delay, defined as the mean time (in numbers of attempts) until a packet is successfully received by the nearest access point. We further investigate the interplay between traffic-load, access points density, and quality of communications in coexistence scenarios. Then, we derive the communications parameters regions, in terms of transmission power, access point density, and time activity factor, for which, the mean local delay is finite. The numerical and simulation results also corroborate the analysis.
35.	Matthiesen, Bho, et al. (författare) Intelligent Reflecting Surface Operation Under Predictable Receiver Mobility : A Continuous Time Propagation Model 2021 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 10:2, s. 216-220 Tidskriftsartikel (refereegranskat)abstract The operation of an intelligent reflecting surface (IRS) under predictable receiver mobility is investigated. We develop a continuous time system model for multipath channels and discuss the optimal IRS configuration with respect to received power, Doppler spread, and delay spread. It is shown that the received power can be maximized without adding Doppler spread to the system. In a numerical case study, we show that an IRS having the size of just two large billboards can improve the link budget of ground to Low Earth Orbit (LEO) satellite links by up to 6dB. It also adds a second, almost equivalently strong, communication path that improves the link reliability.
36.	Moltafet, Mohammad, et al. (författare) Moment Generating Function of the AoI in a Two-Source System With Packet Management 2021 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 10:4, s. 882-886 Tidskriftsartikel (refereegranskat)abstract We consider a status update system consisting of two independent sources and one server in which packets of each source are generated according to the Poisson process and packets are served according to an exponentially distributed service time. We derive the moment generating function (MGF) of the age of information (AoI) for each source in the system by using the stochastic hybrid systems (SHS) under two existing source-aware packet management policies which we term self-preemptive and non-preemptive policies. In the both policies, the system (i.e., the waiting queue and the server) can contain at most two packets, one packet of each source; when the server is busy and a new packet arrives, the possible packet of the same source in the waiting queue is replaced by the fresh packet. The main difference between the policies is that in the self-preemptive policy, the packet under service is replaced upon the arrival of a new packet from the same source, whereas in the non-preemptive policy, this new arriving packet is blocked and cleared. We use the derived MGF to find the first and second moments of the AoI and show the importance of higher moments.
37.	Moltafet, Mohammad, et al. (författare) Worst Case Age of Information in Wireless Sensor Networks: A Multi-Access Channel 2020 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 9:3, s. 321-325 Tidskriftsartikel (refereegranskat)abstract Freshness of status update packets is essential for enabling a wide range of applications in wireless sensor networks (WSNs). Accordingly, we consider a WSN where sensors communicate status updates to a destination by contending for the channel access based on a carrier sense multiple access (CSMA) method. We analyze the worst case average age of information (AoI) and average peak AoI from the view of one sensor in a system where all the other sensors have a saturated queue. Numerical results illustrate the importance of optimizing the contention window size and the packet arrival rate to maximize the information freshness.
38.	Mukherjee, Anshu, et al. (författare) On the Optimality of the Stationary Solution of Secrecy Rate Maximization for MIMO Wiretap Channel 2022 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 11:2, s. 357-361 Tidskriftsartikel (refereegranskat)abstract To achieve perfect secrecy in a multiple-input multiple-output (MIMO) Gaussian wiretap channel (WTC), we need to find its secrecy capacity and optimal signaling, which involves solving a difference of convex functions program known to be non-convex for the non-degraded case. To deal with this, a class of existing solutions have been developed but only local optimality is guaranteed by standard convergence analysis. Interestingly, our extensive numerical experiments have shown that these local optimization methods indeed achieve global optimality. In this letter, we provide an analytical proof for this observation. To achieve this, we show that the Karush-Kuhn-Tucker (KKT) conditions of the secrecy rate maximization problem admit a unique solution for both degraded and non-degraded cases. Motivated by this, we also propose a low-complexity algorithm to find a stationary point. Numerical results are presented to verify the theoretical analysis.
39.	Niu, Hong, et al. (författare) On the Efficient Design of RIS-Assisted Secure MISO Transmission 2022 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 11:8, s. 1664-1668 Tidskriftsartikel (refereegranskat)abstract For the sake of improving the physical-layer security, reconfigurable intelligent surface (RIS) has been suggested to assist artificial noise (AN) to bridge both their advantages in multiple-input single-output (MISO) systems. Specifically, for achieving the trade-off between the reliability and security of transmission, the phase shifts (PSs) and beamforming are jointly designed based on the oblique manifold (OM) algorithm (Wang et al., 2020) without eavesdropper's channel state information (CSI). In order to alleviate the computational complexity, a novel alternating direction (AD) algorithm is proposed in this contribution. Specifically, the initial problem is transformed into several subproblems, each of which determines a specific RIS unit via a closed-form solution when the other configurations are fixed. Furthermore, the AD algorithm is investigated to exhibit the low-complexity advantage in contrast to OM. Simulation results illustrate that AD can converge faster and more stably compared to OM with the same performance.
40.	Ramachandran, Viswanathan (författare) Joint Communication and State Estimation Over a State-Dependent Fading Gaussian Channel 2022 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 11:2, s. 367-370 Tidskriftsartikel (refereegranskat)
41.	Ribeiro, Yuri S., et al. (författare) Low-Complexity Joint Active and Passive Beamforming Design for IRS-Assisted MIMO 2024 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 13:3, s. 607-611 Tidskriftsartikel (refereegranskat)abstract In this letter, we consider an intelligent reflecting surface (IRS)-assisted multiple input multiple output (MIMO) communication and we optimize the joint active and passive beamforming by exploiting the geometrical structure of the propagation channels. Due to the inherent Kronecker product structure of the channel matrix, the global beamforming optimization problem is split into lower dimensional horizontal and vertical sub-problems. Based on this factorization property, we propose two closed-form methods for passive and active beamforming designs, at the IRS, the base station, and user equipment, respectively. The first solution is a singular value decomposition (SVD)-based algorithm independently applied on the factorized channels, while the second method resorts to a third-order rank-one tensor approximation along each domain. Simulation results show that exploiting the channel Kronecker structures yields a significant improvement in terms of computational complexity at the expense of negligible spectral efficiency (SE) loss. We also show that under imperfect channel estimation, the tensor-based solution shows better SE than the benchmark and proposed SVD-based solutions.
42.	Rivetti, Steven, et al. (författare) Malicious Reconfigurable Intelligent Surfaces : How Impactful Can Destructive Beamforming be? 2024 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 13:7, s. 1918-1922 Tidskriftsartikel (refereegranskat)abstract Reconfigurable intelligent surfaces (RISs) have demonstrated significant potential for enhancing communication system performance if properly configured. However, a RIS might also pose a risk to the network security. In this letter, we explore the impact of a malicious RIS on a multi-user multiple-input single-output (MISO) system when the system is unaware of the RIS's malicious intentions. The objective of the malicious RIS is to degrade the signal-to-noise ratio (SNR) of a specific user equipment (UE), with the option of preserving the SNR of the other UEs, making the attack harder to detect. To achieve this goal, we derive the optimal RIS phase-shift pattern, assuming perfect channel state information (CSI) at the hacker. We then relax this assumption by introducing CSI uncertainties and subsequently determine the RIS's phase-shift pattern using a robust optimization approach. Our simulations reveal a direct proportionality between the performance degradation caused by the malicious RIS and the number of reflective elements, along with resilience toward CSI uncertainties.
43.	Rivetti, Steven, 1998, et al. (författare) Spatial Signal Design for Positioning via End-to-End Learning 2023 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 12:3, s. 525-529 Tidskriftsartikel (refereegranskat)abstract This letter considers the problem of end-to-end (E2E) learning for joint optimization of transmitter precoding and receiver processing for mmWave downlink positioning. Considering a multiple-input single-output (MISO) scenario, we propose a novel autoencoder (AE) architecture to estimate user equipment (UE) position with multiple base stations (BSs) and demonstrate that E2E learning can match model-based design, both for angle-of-departure (AoD) and position estimation, under ideal conditions without model deficits and outperform it in the presence of hardware impairments.
44.	Santos, Pablo Millán, et al. (författare) Universal Adversarial Attacks on Neural Networks for Power Allocation in a Massive MIMO System 2022 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 11:1, s. 67-71 Tidskriftsartikel (refereegranskat)abstract Deep learning (DL) architectures have been successfully used in many applications including wireless systems. However, they have been shown to be susceptible to adversarial attacks. We analyze DL-based models for a regression problem in the context of downlink power allocation in massive multiple-input-multiple-output systems and propose universal adversarial perturbation (UAP)-crafting methods as white-box and black-box attacks. We benchmark the UAP performance of white-box and black-box attacks for the considered application and show that the adversarial success rate can achieve up to 60% and 40%, respectively. The proposed UAP-based attacks make a more practical and realistic approach as compared to classical white-box attacks.
45.	Sun, Hongguang, et al. (författare) Average AoI-Minimal Trajectory Design for UAV-Assisted IoT Data Collection System: A Safe-TD3 Approach 2024 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 13:2, s. 530-534 Tidskriftsartikel (refereegranskat)abstract This letter investigates an unmanned aerial vehicle (UAV)-assisted data collection strategy where the UAV trajectory is optimally designed to collect status update from several Internet of Things (IoT) nodes, so as to minimize the average Age of Information (AoI). We consider a practical three-dimensional (3D) urban environment, and design the UAV's trajectory by considering the data collection, flight, and energy constraints. Motivated by the critical safety requirements for the UAV, i.e., the energy constraint during the data collection, we exploit the twin delayed deep deterministic policy gradient (TD3) approach by enforcing the safety constraint throughout the training, and propose a Safe-TD3 based trajectory design for average AoI minimization. By evaluating the long-term safety constraint via the integrated cost network, we illustrate the superiority of the proposed Safe-TD3 based trajectory design algorithm over the benchmarks in reducing the safety constraint violations during the training process while achieving a lower average AoI.
46.	Torres, Andrea de Jesus, et al. (författare) Electromagnetic Interference in RIS-Aided Communications 2022 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 11:4, s. 668-672 Tidskriftsartikel (refereegranskat)abstract The prospects of using a reconfigurable intelligent surface (RIS) to aid wireless communication systems have recently received much attention. Among the different use cases, the most popular one is where each element of the RIS scatters the incoming signal with a controllable phase-shift, without increasing its power. In prior literature, this setup has been analyzed by neglecting the electromagnetic interference, consisting of the inevitable incoming waves from external sources. In this letter, we provide a physically meaningful model for the electromagnetic interference that can be used as a baseline when evaluating RIS-aided communications. The model is used to show that electromagnetic interference has a non-negligible impact on communication performance, especially when the size of the RIS grows large. When the direct link is present (though with a relatively weak gain), the RIS can even reduce the communication performance. Importantly, it turns out that the SNR grows quadratically with the number of RIS elements only when the spatial correlation matrix of the electromagnetic interference is asymptotically orthogonal to that of the effective channel (including RIS phase-shifts) towards the intended receiver. Otherwise, the SNR only increases linearly.
47.	Ullah, Syed Asad, et al. (författare) Opportunistic CR-NOMA Transmissions for Zero-Energy Devices : A DRL-driven Optimization Strategy 2023 Ingår i: IEEE Wireless Communications Letters. - 2162-2337 .- 2162-2345. ; 12:5, s. 893-897 Tidskriftsartikel (refereegranskat)abstract To efficiently accommodate RF energy-harvesting (EH) capable device in a wireless network with prescheduled devices, this letter designs the deep reinforcement learning (DRL)-driven energy-efficient transmission strategy. The transmission strategy handles the EH-device uplink transmissions opportunistically using cognitive radio-inspired non-orthogonal multiple access (CR-NOMA) scheme while maximizing energy efficiency (EE). In this respect, firstly, we formulate the EE optimization problem of the EH-device while considering its RF circuit power consumption. Secondly, we divide the original, non-convex problem into a two-layer optimization problem, and solve it sequentially as i) we theoretically derive the optimal transmit power and time-sharing coefficient parameters from the first layer, and ii) using the derived parameters in the second layer, we solve the one-dimensional continuous space optimization problem through a DRL technique, recognized as a combined experience replay deep deterministic policy gradient (CER-DDPG). Finally, the numerical results show that, under different operational scenarios, the proposed approach outperforms benchmark DDPG and Stochastic algorithms in terms of EE.
48.	Van Chien, Trinh, et al. (författare) Outage Probability Analysis of IRS-Assisted Systems Under Spatially Correlated Channels 2021 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 10:8, s. 1815-1819 Tidskriftsartikel (refereegranskat)abstract This letter investigates the impact of spatial channel correlation on the outage probability of intelligent reflecting surface (IRS)-assisted single-input single-output (SISO) communication systems. In particular, we derive a novel closed-form expression of the outage probability for arbitrary phase shifts and correlation matrices of the indirect channels. To shed light on the impact of the spatial correlation, we further attain the closed-form expressions for two common scenarios met in the literature when the large-scale fading coefficients are expressed by the loss over a propagation distance. Numerical results validate the tightness and effectiveness of the closed-form expressions. Furthermore, the spatial correlation offers significant decreases in the outage probability as the direct channel is blocked.
49.	Vega-Sanchez, Jose David, et al. (författare) A Simple Method for the Performance Analysis of Fluid Antenna Systems Under Correlated Nakagami-m Fading 2024 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 13:2, s. 377-381 Tidskriftsartikel (refereegranskat)abstract By recognizing the tremendous flexibility of the emerging fluid antenna system (FAS), which allows dynamic reconfigurability of the location of the antenna within a given space, this letter investigates the performance of a single-antenna FAS over spatially correlated Nakagami- ${m}$ fading channels. Specifically, simple and highly accurate closed-form approximations for the cumulative density function of the FAS channel and the outage probability of the proposed system are obtained by employing a novel asymptotic matching method, which is an improved version of the well-known moment matching. With this method, the outage probability can be computed simply without incurring complex multi-fold integrals, thus requiring negligible computational effort. Finally, the accuracy of the proposed approximations is validated, and it is shown that the FAS can meet or even exceed the performance attained by the conventional maximal ratio combining (MRC) technique.
50.	Vega-Sanchez, Jose David, et al. (författare) Novel Expressions for the Outage Probability and Diversity Gains in Fluid Antenna System 2024 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 13:2, s. 372-376 Tidskriftsartikel (refereegranskat)abstract The flexibility and reconfigurability at the radio frequency (RF) front-end offered by the fluid antenna system (FAS) make this technology promising for providing remarkable diversity gains in networks with small and constrained devices. Toward this direction, this letter compares the outage probability (OP) performance of non-diversity and diversity FAS receivers undergoing spatially correlated Nakagami- ${m}$ fading channels. Although the system properties of FAS incur in complex analysis, we derive a simple yet accurate closed-form approximation by relying on a novel asymptotic matching method for the OP of a maximum-gain combining-FAS (MGC-FAS). The approximation is performed in two stages, the approximation of the cumulative density function (CDF) of each MGC-FAS branch, and then the approximation of the end-to-end CDF of the MGC-FAS scheme. With these results, closed-form expressions for the OP and the asymptotic OP are derived. Finally, numerical results validate our approximation of the MGC-FAS scheme and demonstrate its accuracy under different diversity FAS scenarios.

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