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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 Emulation techniques for small scale fading aspects by using reverberation chamber(Ieee-Inst Electrical Electronics Engineers Inc, 2019) Kihero, Abuu Bakari; Karabacak, Murat; Arslan, HüseyinReverberation chambers (RVCs) are used to provide an efficient and reliable testbed for emulating the wireless channel effects in the laboratory environment. In the literature, various techniques have been studied to enrich the channel emulation capabilities of RVCs. However, insufficient control of some of the emulated channel characteristics (such as time and frequency dispersions) still leaves an open problem for RVC-based channel emulators. In this paper, novel channel emulation techniques by using RVC are introduced to enhance the flexibility in controlling the emulated time and frequency dispersions of the channels. Surface acoustic wave delay lines and power controllers (i.e., amplifiers and attenuators) are used to add degrees of freedom for manipulating the power delay profile during delay spread emulation. This technique also overcomes the challenge of achieving higher delay spread values with benchtop-sized RVC. The second technique is aimed to control the Doppler spectrum shape emulated in the chamber by judiciously placing radio frequency absorbers around the mechanical stirrer. Experimental and mathematical analyses are conducted to evaluate the proposed techniques, and the results show that the proposed methods can improve the channel emulation in the RVCs.Öğe Emulation techniques for small scale fading aspects of wireless channels by using reverberation chamber(İstanbul Medipol Üniversitesi Fen Bilimleri Enstitüsü, 2018) Kihero, Abuu Bakari; Arslan, HüseyinReverberation chambers (RVCs) are used to provide an effective and reliable testbed for emulating wireless channel effects in the laboratory environment. Various techniques that enrich the capabilities of the RVC in channel emulation have been studied in the literature, however, insufficient control of some of the emulated channel characteristics (like time and frequency dispersions) still leave an open problem for RVC based channel emulators. In this thesis, novel channel emulation techniques by using RVC are introduced to enhance the flexibility in controlling the emulated time and frequency dispersions of the channels. Surface Acoustic Wave (SAW) delay lines and power controllers (i.e amplifiers and attenuators) are used to add degrees of freedom for manipulating the Power Delay Profile (PDP) during delay spread emulation. This technique also overcomes the challenge of achieving higher delay spread values with bench-top sized RVC. The second technique is aimed at enhancing the control of the shape of the Doppler spectrum emulated in the chamber. The proposed techniques are evaluated through mathematical analyses and comparison with the on-site measurement results available in the literature.Öğe Flexible guard structure for timing synchronization in coordinated networks(Institute of Electrical and Electronics Engineers Inc., 2022) Kihero, Abuu Bakari; Furqan, Haji Muhammad; Arslan, HüseyinIn this letter, a novel and flexible hybrid guard duration (HGD) based on zero tail (ZT) and cyclic prefix (CP) concepts is proposed for facilitating timing synchronization (TS) in coordinated multi-point (COMP) networks. The proposed HGD harmoniously provides enough guard duration for mitigating the channel's delay spread and facilitating TS without extending the total symbol duration while supporting both COMP and non-COMP users. That is, unlike the traditional extended CP (E-CP) approach that degrades the system's spectral efficiency (SE) and elevates the transmission latency due to the extended symbol duration, HGD maintains the usage of the normal CP size and the total symbol duration, thereby ensuring better SE performance and relatively low latency. The proposed HGD is evaluated and compared with the traditional E-CP in terms of bit error rate, SE, and latency.Öğe Guard band reduction for 5G and beyond multiple numerologies(IEEE, 2020) Memişoğlu, Ebubekir; Kihero, Abuu Bakari; Başar, Ertuğrul; Arslan, HüseyinThe existence of inter-numerology interference (INI) is a major drawback for the flexible multi-numerology frame structure proposed for the upcoming fifth generation New Radio (5G-NR). Insertion of a guard band (GB) between adjacent numerologies has been widely used in the literature as one of the effective ways to reduce the INI. However, the conventional way of implementing GBs is inefficient in terms of spectrum usage. In this letter, we exploit the inherent INI characteristics of the scalable multi-numerology structure to propose a more spectrally efficient way of implementing GBs. It is shown through simulations that the proposed GB insertion technique enhances the GB utilization up to 50% while achieving the same bit error rate performance as the conventionally implemented GB.Öğe Inter numerology interference analysis for 5G and beyond(Institute of Electrical and Electronics Engineers Inc., 2018) Kihero, Abuu Bakari; Solaija, Muhammad Sohaib J.; Yazar, Ahmet; Arslan, HüseyinOne of the defining characteristics of 5G is the flexibility it offers for supporting different services and communication scenarios. For this purpose, usage of multiple numerologies has been proposed by the 3rd Generation Partnership Project (3GPP). The flexibility provided by multi-numerology system comes at the cost of additional interference, known as inter-numerology interference (INI). This paper comprehensively explains the primary cause of INI, and then identifies and describes the factors affecting the amount of INI experienced by each numerology in the system. These factors include subcarrier spacing, number of used subcarriers, power offset, windowing operations and guard bands.Öğe Inter-numerology interference for beyond 5G(Institute of Electrical and Electronics Engineers Inc., 2019) Kihero, Abuu Bakari; Solaija, Muhammad Sohaib J.; Arslan, HüseyinFifth generation (5G) radio access technology (RAT) is designed to flexibly serve multiple services with extremely diverse requirements. One of the steps taken toward fulfilling this vision of 5G-RAT is the introduction of multi-numerology concept, where multiple frame structures with different subcarrier spacings coexist in one frequency band. Though efficient in providing the required flexibility, this approach introduces a new kind of interference into the system known as inter-numerology interference (INI). In this study, a novel cyclic prefix (CP) insertion technique (referred to as common CP) for multi-numerology system is mathematically analyzed in terms of the INI problem and its extensive comparison with the conventional CP configuration (referred to as individual CP) standardized for the 5G multi-numerology systems is presented. An in-depth discussion of various critical issues concerning multi-numerology system such as frequency domain multiplexing, time domain symbol alignment, and orthogonality between subcarriers of different numerologies is presented in the light of both, individual and common CP configurations. The analyses reveal that common CP has an advantage of restructuring the INI pattern in the system in a manner that paves the way for developing better techniques of avoiding or minimizing INI in the future generations.Öğe Wireless channel and interference(Wiley, 2021) Kihero, Abuu Bakari; Tusha, Armed; Arslan, HüseyinThis chapter focuses on various critical aspects of wireless channel starting with explanation of the dominant propagation phenomena and their resultant effects on the system. It then touches upon mechanisms employed for empirical measurement of these channel effects, as well as techniques commonly used to represent them in a way that is useful for system design (i.e. channel modeling). The features of interference caused by wireless channel are grouped considering the fading characteristics of the medium, such as large-scale and small-scale fading. In order to enable the control of wireless environment, several approaches have been proposed and discussed in the literature. The chapter also focuses on two promising techniques: reconfigurable antenna and reconfigurable intelligent surface. Finally, it explains basic channel emulation techniques which are used to reproduce various propagation effects in the laboratory environment for system testing.Öğe Wireless channel from physical layer security perspective(Institution of Engineering and Technology, 2023) Kihero, Abuu Bakari; Furqan, Haji Muhammad; Arslan, Hüseyin[Abstract Not Available]
