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Öğe A novel transceiver design in wideband massive mimo for beam squint minimization(2024) Afeef, Liza; Kihero, Abuu Bakari; Arslan, HüseyinWhen using ultra-wideband signaling on massive multiple-input multiple-output (mMIMO) systems, the electromagnetic wave incurs an extra delay (across the array elements) comparable to or larger than the symbol duration, which translates into a shift in beam direction known as the beam squint effect. The beam squinting problem degrades the array gain and reduces the system capacity. This paper proposes a novel transceiver design based on lens antenna subarray and analog subband filters to compensate for the beam squinting effect. Specifically, the proposed design chunks the wideband signal from the phase shifters into groups of narrowband signals and controls their squints through an exhaustive search-based switching/precoding mechanism under the lenses. Furthermore, a simplified, thresholded search-based precoding algorithm is proposed, which demonstrates good performance while significantly minimizing complexity. The proposed system is analyzed in terms of beam gain, complexity, power consumption, and capacity. The numerical results demonstrate significant performance enhancement for the proposed system design as compared to the conventional mMIMO system with an uncompensated beam squinting problem.Öğe Beam squint effect in multi-beam mmWave massive MIMO systems(Institute of Electrical and Electronics Engineers Inc., 2022) Afeef, Liza; Arslan, HüseyinIn multicarrier wideband millimeter-wave (mmWave) communications, as the size of antenna array increases, as in massive multiple-input multiple-output (MIMO), an additional propagation delay of the electromagnetic wave at each antenna element is introduced comparable to (or greater than) the symbol duration, resulting in producing a displacement in beam direction at each subcarrier frequency or as it calls beam squinting. With multi-beam transmission in massive MIMO systems, due to beam squinting effect, an additional inter-beam interference (IBI) can be introduced to the system which significantly decreases the overall system capacity. Therefore, in this paper, IBI under beam squint effect is modeled for different subcarrier frequencies and beam angles in a multi-beam mmWave massive MIMO system. In addition, the impact of this IBI model on the system capacity is evaluated. The analysis results show that beam squinting causes a significant increase in IBI level, even when transmitting with orthogonal beams. Moreover, the results provide the optimal number of beams for a given antenna array size to maximize the system's capacity considering beam squinting phenomena.Öğe Beam squint inspired multiple access technique in massive MIMO systems(Institute of Electrical and Electronics Engineers Inc., 2022) Kihero, Abuu B.; Afeef, Liza; Arslan, HüseyinMassive multiple-input multiple-output (mMIMO) systems implementing wideband signaling have been found to suffer from beam squinting problem. In multicarrier systems, beam squint causes spreading of the beam to multiple undesired directions, thereby degrading system capacity. This paper proposes user scheduling and precoding techniques that controls and exploit the beam squinting phenomenon to serve multiple users and improve the overall system capacity. The proposed techniques are based on the lens antenna subarray (LAS) mMIMO system. The proposed system design is explained and numerically evaluated in terms of beam gain and capacity with different number of users and RF chains. The simulation results exhibit significant performance enhancement in terms of beam gain and capacity, corroborating the idea of exploiting the beam squinting phenomenon to serve multiple spatially separated groups of users.Öğe Dynamic sidelobe multiplexing in beamspace MIMO systems(IEEE-Institute of Electrical and Electronics Engineers Inc, 2020) Karabacak, Murat; Afeef, Liza; Arslan, HüseyinRecent studies on multiplexing concept over beamspace multiple-input-multiple-output (MIMO) can reduce the need for using phase shifters while keeping the directivity performance at similar levels. Thus, beamspace MIMO provides cost-effective and simple hardware designs for millimeter-wave (mmWave) systems. However, the number of users/streams that can be supported at the same time-frequency resource is limited to the number of radio-frequency (RF) chains. In this letter, to overcome this restriction, dynamic sidelobe multiplexing (DSM) algorithm is proposed. The proposed multiplexing technique precodes the transmitted data over transmitter beams in order to open up a new path to the receiver. Therefore, the proposed method provides an opportunity to exceed the limits of conventional hardware usage in beamspace MIMO. The numerical results show that the proposed approach enhance the system performance for more than 50% compared to conventional beamspace MIMO techniques.Öğe Energy and spectral-efficient lens antenna subarray design in MmWave MIMO Systems(IEEE-Institute Electrical Electronics Engineers Inc, 2022) Afeef, Liza; Mumcu, Gökhan; Arslan, HüseyinLens antenna subarray (LAS) is one of the recently introduced technologies for future wireless networks that significantly improves the energy efficiency of multiple-input multiple-output (MIMO) systems while achieving higher spectral efficiency compared to single-lens MIMO systems. However, a control mechanism for the LAS-MIMO design is considered a challenging task to efficiently manage the network resources and serve multiple users in the system. Therefore, in this paper, a sub-grouped LAS-MIMO architecture along with a hybrid precoding algorithm are proposed to reduce the cost and hardware overhead of traditional hybrid MIMO systems. Specifically, the LAS structure is divided into sub-groups to serve multiple users with different requirements, and an optimization problem based on the achievable sum-rate is formulated to maximize the spectral efficiency of the system. By splitting the sum-rate problem into sub-rate optimization problems, we develop a low-complexity hybrid precoding algorithm to effectively control the proposed architecture and maximize the achievable sum-rate of each subgroup. The proposed precoding algorithm selects the beam of each lens from a predefined set within a subgroup that maximizes the subgroup sum-rate, while the phase shifters and digital precoders in each subgroup are computed independently. The link between subgroups is updated based on successive interference cancelation to minimize interference between users of different subgroups. Our analysis and simulation results show that the proposed precoding algorithm of the sub-grouped LAS-MIMO architecture performs almost as well as traditional fully-connected hybrid MIMO systems in terms of spectral efficiency at low and high signal-to-noise ratio (SNR). It also outperforms traditional fully-connected and sub-connected hybrid MIMO systems in terms of energy efficiency, even when a large number of lenses are employed.Öğe Heuristic inspired precoding for millimeter-wave MIMO systems with lens antenna subarrays(Institute of Electrical and Electronics Engineers Inc., 2022) Çetinkaya, Şinasi; Afeef, Liza; Mumcu, Gökhan; Arslan, HüseyinA traditional array (TA) multiple-input multiple-output (MIMO) architecture in mmWave with hybrid beamforming suffers from high power consumption and hardware overhead. Therefore, a lens antenna subarray (LAS)-MIMO architecture has been recently proposed as a promising technology for a power-efficient system and reducing hardware cost and complexity. Additionally, the LAS-MIMO can offer spectral efficiency (SE) performance close to TA-MIMO and higher than single-lens antenna array (SLA)-MIMO. In this paper, we propose a hybrid precoding algorithm for the LAS-MIMO in mmWave to efficiently control the LAS design. The precoding problem is formulated as a sparse reconstruction problem due to the sparse behavior of mmWave channel. The proposed algorithm is an iterative process developed jointly using artificial bee colony (ABC) optimization with orthogonal matching pursuit (OMP) algorithms. In each iteration, the algorithm first selects the switches for each lens randomly using ABC and then uses OMP to approximate optimal unconstrained precoders. This process continues until achieving maximum SE. The simulation results show that LAS has around a 30% increase in SE compared to SLA while providing a significant gain in energy efficiency (EE) for single radio-frequency (RF) chain and multi RF chain scenarios.Öğe Physical layer authentication in wireless communication systems(Institution of Engineering and Technology, 2023) Afeef, Liza; Arslan, Hüseyin[Abstract Not Available]Öğe Physical layer authentication scheme in beamspace MIMO systems(Institute of Electrical and Electronics Engineers Inc., 2022) Afeef, Liza; Furqan, Haji M.; Arslan, HüseyinThe broadcast nature of wireless communication makes it vulnerable to various security threats such as spoofing attacks. Physical layer (PL) authentication has emerged as a promising and powerful approach to secure future wireless technologies for next-generation communication networks. In this work, we propose a PL authentication scheme against spoofing attacks based on a novel distance signature that exploits the properties of beamspace multiple-input multiple-output (MIMO) channels in millimeter-wave (mmWave) networks. The proposed signature is derived from the positions of the principal components in beamspace channel domain by measuring their displacement from the original point and sorting the distance values in descending order based on the phases of the principal components. In addition, a mutual coupling effect is introduced into the system, which is a hardware property of multiple antenna design. This is then combined with the proposed distance signature to form a hybrid signature that further improves the authentication performance. Simulation results have confirmed the validity and effectiveness of our proposed system in terms of detection rate and false alarm.Öğe Quantum laboratory setup for future wireless communication systems(American Institute of Physics Inc., 2019) Solaija, Muhammad Sohaib J.; Janjua, Muhammad Bilal; Afeef, Liza; Tusha, Armed; Duranay, Ahmet Enes; Arslan, Hüseyin; Hasekio?lu, OrkunFifth generation of wireless communication envisages a diverse network that imposes stringent requirements regarding capacity, reliability, security, latency and seamless connectivity. These lofty goals have driven researchers to look for technologies capable of supporting conventional methods. Application of quantum mechanics to the domain of communications has been considered for a while now but the reliance of any quantum phenomena on experimental verification remains an obstacle in its widespread use. To serve this purpose, we propose establishing a quantum optics laboratory in Turkey which will allow implementation, analysis and investigation of the various promising quantum communication tools. This work is directed towards description and experimental verification of some well-known quantum experiments, from relatively simpler ones such as single or entangled photon generation to the more evolved experiments like quantum random number generation and quantum key distribution.Öğe Reconfigurable intelligent surface (RIS): Eigenvalue decomposition-based separate channel estimation(Institute of Electrical and Electronics Engineers Inc., 2021) Zegrar, Salah Eddine; Afeef, Liza; Arslan, HüseyinReconfigurable intelligent surface (RIS) has recently drawn significant attention in wireless communication technologies. However, identifying, modeling, and estimating the RIS channel in multiple-input multiple-output (MIMO) systems are considered challenging in recent studies. In this paper, a disassembled channel estimation framework for the RIS-MIMO system is proposed based on the eigenvalue decomposition (EVD) concept to separate the cascaded channel links and estimate each link separately. This estimation is based on modeling the RIS-MIMO channel as a keyhole MIMO system model. Numerical results show that the proposed estimation method has a low estimation time overhead while providing less estimation error.Öğe Robust tracking-based phy-authentication in mmwave mimo systems(2024) Afeef, Liza; Furqan, Haji Muhammad; Arslan, HüseyinPhysical Layer Authentication (PLA) is a topic of considerable interest in ensuring strong security for upcoming wireless networks. However, existing PLA methods face challenges in maintaining performance in dynamic environments. To overcome this, we propose a novel tracking-based PLA approach, utilizing properties of the beamspace multiple-input multiple-output (MIMO) channel in narrowband millimeter-wave (mmWave) networks. Specifically, In particular, the proposed technique involves extracting a distance signature vector from the positions of the principal components within the beamspace MIMO channel representation. These components are then sorted in descending order based on their indices. To address mobility concerns in dynamic settings, a tracking filter is introduced. This filter allows the authentication system to continuously track and update the stored signature, enhancing overall authentication performance. Additionally, the proposed technique is extended to ultra-wideband signaling. In this extension, the richness of the derived signature is further improved by exploiting the beam squint effect, contributing to a more robust authentication process. Simulation results demonstrate that our approach overcomes the limitations of previous methods, resulting in improved authentication performance measured by detection and false alarm rates.Öğe Visibility region exploitation for phy authentication in xl-mimo systems(2025) Demirci, Senanur; Afeef, Liza; Arslan, HüseyinWireless networks are open to identity spoofing attacks because of their broadcast nature, emphasizing the need for strong security. Physical layer authentication (PLA) is a crucial strategy for securing wireless networks against such threats. Extra-large multiple-input multiple-output (XL-MIMO) technology, with its unique visibility region (VR) concept due to the near-field effect, offers a promising way to enhance network performance. This letter proposes a PLA approach using VR to create unique and robust signatures from the power and beamspace domain of XL-MIMO. Simulation results confirm the effectiveness of the proposed method in detecting attacks with high accuracy and low false alarm rates.
