Yazar "İbrahim, Mostafa" seçeneğine göre listele

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    Air-ground channel modeling and waveform containment
    (İstanbul Medipol Üniversitesi Fen Bilimleri Enstitüsü, 2017) İbrahim, Mostafa; Arslan, Hüseyin
    The content of this work is divided into two main parts. Part I is dedicated for characterizing Air-Ground channels. Applications using Air-Ground communications are expected to grow in the future. Low altitude phases of these wireless links are considered severe channels, as they experience huge delay and Doppler spreads, however, they are not yet accurately characterized in the literature. Chapter 1 presents an analytic three-dimensional Air-Ground Doppler-delay spread spectrum model for dense scattering environments. In Chapter 2, a numerical terrain based Doppler-delay spread model simulator was proposed. It was demonstrated that the terrain topography affects the shape of the Doppler-delay spread spectrum. The scattering function becomes unique for each terrain and position of the ground station and air station. In Part II, waveform design and containment techniques are discussed. A scheme called Zero tail Filter Bank Spread Orthogonal Frequency Division Multiplexing (ZT FB-S-OFDM) is proposed in Chapter 3. In this scheme, Raised cosine (RC) pulses coexist in the same signal, with an abrupt transition of roll-off factors $\alpha$ at edges of the stream. The pulses near the edges are RC pulses with $\alpha=1$ and the ones in between have the value $\alpha=0$. In Chapter 4, the possibility of using the same scheme but with a smooth roll-off factors transition is introduced. This is proposed along with the time-frequency space warping principle to preserve the orthogonality between the pulses. Simulations show high containment gains for both of the proposed schemes.
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    Time-frequency warped waveforms
    (IEEE-Inst Electrical Electronics Engineers Inc, 2019) İbrahim, Mostafa; Demir, Ali Fatih; Arslan, Hüseyin
    The forthcoming communication systems are advancing toward improved flexibility in various aspects. Improved flexibility is crucial to cater diverse service requirements. This letter proposes a novel waveform design scheme that exploits axis warping to enable peaceful coexistence of different pulse shapes. A warping transform manipulates the lattice samples non-uniformly and provides flexibility to handle the time-frequency occupancy of a signal. The proposed approach enables the utilization of flexible pulse shapes in a quasi-orthogonal manner and increases the spectral efficiency. In addition, the rectangular resource block structure, which assists an efficient resource allocation, is preserved with the warped waveform design as well.
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    Time-frequency warped waveforms for well-contained massive machine type communications
    (IEEE-Institute of Electrical and Electronics Engineers Inc., 2023) İbrahim, Mostafa; Arslan, Hüseyin; Çırpan, Hakan Ali; Ekin, Sabit
    This paper proposes a novel time-frequency warped waveform for short symbols, massive machine-type communication (mMTC), and internet of things (IoT) applications. The waveform is composed of asymmetric raised cosine (RC) pulses to increase the signal containment in time and frequency domains. The waveform has low power tails in the time domain, hence better performance in the presence of delay spread and time offsets. The time-axis warping unitary transform is applied to control the waveform occupancy in time-frequency space and to compensate for the usage of high roll-off factor pulses at the symbol edges. The paper explains a step-by-step analysis for determining the roll-off factors profile and the warping functions. Gains are presented over the conventional Zero-tail Discrete Fourier Transform-spread-Orthogonal Frequency Division Multiplexing (ZT-DFT-s-OFDM), and Cyclic prefix (CP) DFT-s-OFDM schemes in the simulations section.
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    Zero tail filter bank spread OFDM
    (Institute of Electrical and Electronics Engineers Inc., 2016) İbrahim, Mostafa; Arslan, Hüseyin
    Waveforms proposed for future communication systems aim at fulfilling the demanding requirements of the next generation of 5G applications. In this paper, an enhancement over Zero Tail Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (ZT DFT-S-OFDM) is proposed. The presented Zero Tail Filter Bank Spread OFDM (ZT FB-S-OFDM) replaces the discrete Fourier transform (DFT) block with a filter bank (FB) block. The performance of the conventional system is degraded due to the non-perfect zero-tails. The proposed system suppresses the power over the zero-tails by using raised cosine (RC) shaped pulses near the zero-tails. An implementation scheme for the transmitter and the receiver is proposed. It is shown that suppressing the power over the zero-tail enhances the system bit error rate (BER) performance. Furthermore, results show extra improvements in the peak-to-average power ratio (PAPR) and out-of-band emission (OOBE) performances.