Browsing by Author "Saberali, S. M."

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    DMT analysis and optimal scheduling for two-hop parallel relay networks
    (Elsevier, 2021-06) Khayatian, H.; Parvaresh, F.; Abouei, J.; Saberali, S. M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
    Two-hop parallel networks with half-duplex relays over quasi-static Rayleigh fading channels are considered. Assuming relays have only local channel state information, optimal communication schemes for these networks in terms of the diversity multiplexing trade-off (DMT) are obtained. It is shown that the dynamic quantize-map-and-forward (DQMF) and the static quantize-map-and-forward (SQMF) communication strategies achieve the optimal DMT at different ranges of the multiplexing gain. In the DQMF scheme, a relay sets its transmitting/listening times according to the instantaneous source-relay channel condition. However, in the SQMF scheme, a relay sets its transmitting/listening times to be a constant independent of the instantaneous source-relay channel gain. Essentially, we calculate the DMT of the network under the general setting for arbitrary average signal-to-noise ratios over links and it is shown that the DMT of the proposed schemes matches the upper bounds. Moreover, the optimal transmitting/listening times of the half-duplex relays as functions of the instantaneous channel realizations are derived for different communication strategies in the general setting. Finally, various simulation scenarios are considered and the DMT of the proposed schemes and the dynamic decode and forward communication strategy are compared.
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    Performance investigation of the modified costas carrier recovery loop for a QPSK modulated signal in the presence of co-channel interference
    (IEEE, 2016) Heidarpour, Ali Reza; Montazerolghaem, M. A.; Saberali, S. M.; Heidarpour, Ali Reza
    One of the important challenges in communication systems is drift in the carrier frequency of received signal due to the clock skew and Doppler effect. Every communication receiver requires an automatic frequency control (AFC) loop to estimate the carrier drift in the received signal. One of the well-known AFC loops in communication systems is the Costas loop. In this paper a modified version of Costas loop for binary phase-shift keying (BPSK) modulation is presented which is capable to estimate the carrier frequency of the quadrature phase-shift keying (QPSK) modulation, and therefore significantly simplifies practical implementation. The performance of the modified Costas loop is investigated for the carrier recovery of a QPSK signal in the presence of a co-channel interference. Both simulations and analytical results illustrate that the modified Costas loop may estimate the carrier frequency drift of received signal when the desired signal is stronger than interference.