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    A unified framework for multi-hop wireless relaying with hardware impairments
    (IEEE-Inst Electrical Electronics Engineers Inc, 2024) Soleimani-Nasab, Ehsan; Department of Electrical and Electronics Engineering; Ergen, Sinem Çöleri; Department of Electrical and Electronics Engineering;  ; College of Engineering;  
    Relaying increases the coverage area and reliability of wireless communications systems by mitigating the fading effect on the received signal. Most technical contributions in the context of these systems assume ideal hardware (ID) by neglecting the non-idealities of the transceivers, which include phase noise, in-phase/quadrature mismatch and high power amplifier nonlinearities. These non-idealities create distortion on the received signal by causing variations in the phase and attenuating the amplitude. The resulting deterioration of the performance of wireless communication systems is further magnified as the frequency of transmission increases. In this paper, we investigate the aggregate impact of hardware impairments (HI) on the general multi-hop relay system using amplify-and-forward (AF) and decode-and-forward (DF) relaying techniques over a general bf H-fading model. bf H-fading model includes free space optics, radio frequency, millimeter wave, Terahertz, and underwater fading models. Closed-form expressions of outage probability, bit error probability and ergodic capacity are derived in terms of bf H-functions. Following an asymptotic analysis at high signal-to-noise ratio (SNR), practical optimization problems have been formulated with the objective of finding the optimal level of HI subject to the limitation on the total HI level. The analytical solution has been derived for the Nakagami-m fading channel which is a special case of bf H-fading for AF and DF relaying techniques. The overall instantaneous signal-to-noise-plus-distortion ratio has been demonstrated to reach a ceiling at high SNRs which has a reciprocal proportion to the HI level of all hops' transceivers on the contrary to the ID.
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    Antenna array structures for enhanced cluster index modulation
    (IEEE, 2023) Koc, Asil; Le-Ngoc, Tho; Department of Electrical and Electronics Engineering; Raeisi, Mahmoud; Yıldırım, İbrahim; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; Communications Research and Innovation Laboratory (CoreLab)
    This paper investigates the effect of various antenna array structures, i.e., uniform linear array (ULA), uniform rectangular array (URA), uniform circular array (UCA), and concentric circular array (CCA), on cluster index modulation (CIM) enabled massive multiple-input multiple-output (mMIMO) millimeter-wave (mmWave) communications systems. As the CIM technique indexes spatial clusters to convey additional information bits, the different radiation characteristics caused by different array structures can significantly affect system performance. By analyzing the effects of array characteristics such as radiation pattern, array directivity, half-power beam width (HPBW), and radiation side lobes on bit error rate (BER) performance, we reveal that URA achieves better error performance than its counterparts in a CIM-enabled mmWave system. We demonstrate that narrower beams alone cannot guarantee better BER performance in a CIM-based system. Instead, other radiation characteristics, especially radiation side lobes, can significantly influence system performance by entailing extra interference in the non-intended directions. Illustrative results show that URA owes its superiority to its lower side lobes. We also propose an algorithm to implement fixed phase shifters (FPS) as a hardware-efficient (HE) analog network structure (beamformer/combiner) to reduce cost and energy consumption in mmWave systems and investigate the effect of a non-ideal analog network on the BER performance for different array structures. It is demonstrated that HE systems with a few FPSs can achieve similar BER performance compared to the optimum (OP) analog network structure.
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    Cluster index modulation for reconfigurable intelligent surface-assisted mmwave massive MIMO
    (IEEE-Inst Electrical Electronics Engineers Inc, 2024) Koç, Asil; Le-Ngoc, Tho; Department of Electrical and Electronics Engineering; Raeisi, Mahmoud; Yıldırım, İbrahim; Başar, Ertuğrul; Department of Electrical and Electronics Engineering;  ; Graduate School of Sciences and Engineering; College of Engineering; Communications Research and Innovation Laboratory (CoreLab)
    In this paper, we propose a transmission mechanism for a reconfigurable intelligent surface (RIS)-assisted millimeter wave (mmWave) system based on cluster index modulation (CIM), named best-gain optimized cluster selection CIM (BGCS-CIM). The proposed BGCS-CIM scheme considers effective cluster power gain and spatial diversity gain obtained by the additional paths within the indexed cluster to construct an efficient codebook. We also integrate the proposed scheme into a practical system model to create a virtual path between transmitter and receiver where the direct link has been blocked. Thanks to the designed whitening filter, a closed-form expression for the upper bound on the average bit error rate (ABER) is derived and used to validate the simulation results. It has been shown that the proposed BGCS-CIM scheme outperforms the existing benchmarks thanks to its higher effective cluster gain, spatial diversity of indexed clusters, and lower inter-cluster interference.
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    Compact femtosecond lasers based of novel multipass cavities
    (Institute of Electrical and Electronics Engineers (IEEE), 2004) Kowalevicz Jr., Andrew M.; Ippen, Erich P.; Fujimoto, James G.; Department of Electrical and Electronics Engineering; Sennaroğlu, Alphan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 23851
    This paper provides a comprehensive description of the design of compact femtosecond solid-state lasers that are based on novel multipass cavity (MPC) configurations to extend the resonator length. of special importance are the q-preserving MPCs, which leave invariant the original spotsize distribution and Kerr lens mode-locking point of the short cavity. The general design guidelines of q-preserving MPCs are first reviewed and a novel configuration is proposed for the case where the MPC consists of notch mirrors. A class of non-q-preserving compact cavities is also analyzed and conditions needed to minimize the deviation from the q-preserving configuration are discussed. The design and performance of a q-preserving and a non-q-preserving mode-locked Ti: Al2 O3 laser are then described as examples. These compact oscillators measuring only 30 cm × 45 cm could produce pulses as short as 19 fs at a repetition rate of around 31 MHz. Up to ∼ 3.6 nJ of pulse energy could be obtained with only ∼ 1.5 W of pump power. Finally, two-mirror MPC geometries are examined to investigate the limits of compactness and energy scaling.
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    Coordinate interleaved OFDM with repeated in-phase/quadrature index modulation
    (IEEE-Inst Electrical Electronics Engineers Inc, 2024)  ; Department of Electrical and Electronics Engineering; Tuğtekin, Ömer Furkan; Doğukan, Ali Tuğberk; Arslan, Emre; Başar, Ertuğrul; Department of Electrical and Electronics Engineering;  ; Graduate School of Sciences and Engineering; College of Engineering; Communications Research and Innovation Laboratory (CoreLab)
    Orthogonal frequency division multiplexing with index modulation (OFDM-IM), which transmits information bits through ordinary constellation symbols and indices of active subcarriers, is a promising multicarrier transmission scheme and has attracted the attention of researchers due to numerous benefits such as flexibility and simplicity. Nonetheless, OFDM-IM cannot satisfy the needs of future wireless communication services such as superior reliability, high data rates, and low complexity. In this article, we propose a novel OFDM-IM scheme named coordinate interleaved OFDM with repeated in-phase/quadrature IM (CI-OFDM-RIQIM), which provides superior error performance and enhanced spectral efficiency due to its diversity order of two and clever subcarrier activation pattern (SAP) detection mechanism, respectively. In addition, CI-OFDM-RIQIM is further extended to coordinate interleaved OFDM with in-phase/quadrature IM (CI-OFDM-IQIM) by doubling information bits transmitted by IM. Furthermore, log-likelihood ratio (LLR) based low-complexity detectors are designed for both proposed schemes. Theoretical analyses are performed and an upper bound on the bit error probability is derived. Comprehensive computer simulations under perfect and imperfect channel state information (CSI), are conducted to compare the proposed and reference schemes. It is shown that CI-OFDM-RIQIM and CI-OFDM-IQIM show superior results and can be considered promising candidates for next-generation wireless communication systems.
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    Frequency-domain detection for molecular communication with cross-reactive receptors
    (IEEE-Inst Electrical Electronics Engineers Inc, 2024)  ; Department of Electrical and Electronics Engineering; Civaş, Meltem; Akan, Özgür Barış; Department of Electrical and Electronics Engineering;  ; Graduate School of Sciences and Engineering; College of Engineering;  
    Molecular Communications (MC) is a bio-inspired communication paradigm using molecules as information carriers, necessitating novel transceivers and modulation/detection techniques. In realizing practical MC receivers (MC-Rxs), biosensor field-effect transistor (bioFET)-based architectures are promising, having surface receptors that undergo reversible reactions with ligands. These interactions are converted into electrical signals via field effect, enabling the decoding of transmitted information. A significant challenge in these receivers is the limited specificity of receptors to target ligands, which leads to molecular cross-talk from similar interfering ligands co-existing in the MC channel. Decoding transmitted symbols under such interference is challenging in the time domain, especially when MC-Rx lacks prior knowledge of interferer statistics or operates near saturation. To address this, we introduce a frequency-domain detection (FDD) technique for bioFET-based MC-Rxs, which exploits the distinct binding reaction rates of different ligand types, reflected in the power spectrum of binding noise. Compared to conventional time-domain detection (TDD) technique, this method offers improved detection performance under stochastic molecular interference. We analyze the bit error probability (BEP) of FDD, confirming its superior performance in various interference scenarios. Moreover, the theoretical performance limits of FDD are validated through a particle-based spatial stochastic simulator, simulating binding reactions on MC-Rx within microfluidic channels. © 1972-2012 IEEE.
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    Guest editorial special feature on bio-chem-ICTs: synergies between bio/nanotechnologies and molecular communications
    (IEEE-Inst Electrical Electronics Engineers Inc, 2023) Stano, Pasquale; Egan, Malcolm; Barros, Michael T.; Ünlütürk, Bige Deniz; Payne, Gregory F.; Department of Electrical and Electronics Engineering; Kuşcu, Murat; Department of Electrical and Electronics Engineering;  ; College of Engineering;  
    The Transfer of 'information' via molecules is a theme that resonates across the realm of nature, underlying collective behavior, homeostasis, and many disorders and diseases, and potentially holding the answers to some of the life's most profound questions. The prospects of understanding and manipulating this natural modality of communication have attracted a significant research interest from information and communication theorists (ICT) over the past two decades. The aim is to provide novel means of understanding and engineering biological systems. These efforts have produced substantial body of literature that sets the groundwork for bio-inspired, artificial Molecular Communication (MC) systems. This ICT-based perspective has also contributed to the understanding of natural MC, with many of the results from these endeavors being published in this journal.
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    Index modulation-based information harvesting for far-field RF power transfer
    (IEEE-Inst Electrical Electronics Engineers Inc, 2024) İlter, Mehmet C.; Wichman, Risto; Hamalainen, Jyri; Department of Electrical and Electronics Engineering; Pıhtılı, Mehmet Ertuğ; Başar, Ertuğrul; Department of Electrical and Electronics Engineering;  ; Graduate School of Sciences and Engineering; College of Engineering; Communications Research and Innovation Laboratory (CoreLab)
    As wireless information transmission (WIT) progresses into its sixth generation (6G), a challenge arises in sustaining terminal operations with limited batteries for Internet-of-Things (IoT) platforms. To address this, wireless power transfer (WPT) emerges as a solution, empowering battery-less infrastructures and enabling nodes to harvest energy for sustainable operations. Thus, the eclectic integration of WPT with WIT mechanisms becomes crucial to mitigate the need for battery replacements while providing secure and reliable communication. A novel protocol that amalgamates WIT and WPT called Information Harvesting (IH) has recently been proposed to effectively handle challenges in wireless information and power transfer (WIPT) by employing index modulation (IM) techniques for data communication atop the existing far-field WPT mechanism. This paper presents a unified framework for IM-based IH mechanisms and evaluates their energy harvesting capability, bit error rate (BER), and ergodic secrecy rate (ESR) performance for diverse IM schemes. The findings indicate the significant potential of the IM-based IH mechanism in facilitating reliable data communication within existing far-field WPT systems while underscoring promising refinements in green and secure communication paradigms for next-generation IoT wireless networks. Authors
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    Indoor measurements for RIS-aided communication: practical phase shift optimization, coverage enhancement, and physical layer security
    (IEEE-Inst Electrical Electronics Engineers Inc, 2024) Hökelek, İbrahim; Görçin, Ali; Department of Electrical and Electronics Engineering; Kayraklık, Sefa; Yıldırım, İbrahim; Gevez, Yarkın; Başar, Ertuğrul; Department of Electrical and Electronics Engineering;  ; Graduate School of Sciences and Engineering; College of Engineering; Communications Research and Innovation Laboratory (CoreLab)
    Practical experiments are a crucial step to demonstrate the viability of reconfigurable intelligent surface (RIS)-empowered communication, which is one of the emerging technologies for next-generation networks. In this paper, we present practical measurements to demonstrate the RIS capabilities for enhancing signal coverage and providing physical layer security (PLS) in an indoor environment. First, extensive measurements are performed in a single-user deployment using iterative, grouping, and codebook-based phase shift optimization methods. The iterative method achieves approximately 10 dB performance improvement in the received signal power through careful adjustments of RIS phase configurations when the receiver is placed at different locations. The grouping method reduces the training time to find a suitable RIS configuration by sacrificing only a few dBs in the received signal power. Another set of experiments is conducted for a multi-user deployment to exhibit PLS, where the RIS is partitioned into two regions serving the intended and unintended users. The results demonstrate that the codebook method can effectively boost the secrecy capacity on the move without utilizing feedback other than the users' positions during the phase shift optimization process, while the iterative method requires a continuous feedback channel for the received signal powers.
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    Intelligent surfaces empowered wireless network: recent advances and the road to 6G
    (Institute of Electrical and Electronics Engineers Inc, 2024) Wu, Qingqing; Zheng, Beixiong; You, Changsheng; Zhu, Lipeng; Shen, Kaiming; Shao, Xiaodan; Mei, Weidong; Di, Boya; Zhang, Hongliang; Song, Lingyang; Di Renzo, Marco; Luo, Zhi-Quan; Zhang, Rui; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; College of Engineering
    Intelligent surfaces (ISs) have emerged as a key technology to empower a wide range of appealing applications for wireless networks, due to their low cost, high energy efficiency, flexibility of deployment, and capability of constructing favorable wireless channels/radio environments. Moreover, the recent advent of several new IS architectures further expanded their electromagnetic functionalities from passive reflection to active amplification, simultaneous reflection, and refraction, as well as holographic beamforming. However, the research on ISs is still in rapid progress and there have been recent technological advances in ISs and their emerging applications that are worthy of a timely review. Thus, in this article, we provide a comprehensive survey on the recent development and advances of ISs-aided wireless networks. Specifically, we start with an overview on the anticipated use cases of ISs in future wireless networks such as 6G, followed by a summary of the recent standardization activities related to ISs. Then, the main design issues of the commonly adopted reflection-based IS and their state-of-the-art solutions are presented in detail, including reflection optimization, deployment, signal modulation, wireless sensing, and integrated sensing and communications. Finally, recent progress and new challenges in advanced IS architectures are discussed to inspire future research.