Browsing by Author "Odabasioglu, N."

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    An adaptive modulation scheme for coded free-space optical systems
    (IEEE, 2014) Hariq, S. H.; Odabasioglu, N.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
    For very slowly-varying fading channels as in the case of atmospheric turbulence-induced fading, it is possible to reliably estimate the channel state information and send it back to the transmitter. The transmitter can use this information to vary the transmission parameters such as power, modulation size, code rate etc according to the channel conditions. This is known as link adaptation. In this paper, we consider a turbo-coded free-space optical (FSO) system with M-ary pulse position modulation over log-normal turbulence channels and propose an adaptive modulation scheme under peak power constraints. Our simulation results demonstrate significant performance improvements of the proposed adaptive scheme over non-adaptive counterparts.
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    Adaptive relay selection method for asynchronous amplify and forward cooperative communications
    (IEEE, 2016) Celik, Y.; Odabasioglu, N.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
    In this paper, we propose a new adaptive relay selection method named as Adaptive Best Relay Assessment (ABRA) for cooperative communication with amplify and forward (AF) relaying. ABRA is based on two relay selection criteria which are cascaded channel gain coefficient and cascaded time offset in source-relay-destination (S-R-D) channel. Our simulation results demonstrate that the channel gain coefficient is the best criteria at low signal-to-noise ratio (SNR) regimes and time offset at high SNR regimes. Therefore, we combine these two criteria to select best relay for all SNR values. Finally, ABRA achieves the best bit error rate (BER) performance in asynchronous AF cooperative communications for three different path gain ratios 30 dB, 0 dB, and -30 dB.