Browsing by Author "Schober, R."

Now showing 1 - 6 of 6

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Enhanced MRC for decode-and-forward cooperative diversity systems
(IEEE, 2012-10) Nasri, A.; Schober, R.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this letter, we propose a novel enhanced maximal-ratio combining (E-MRC) scheme for multi-branch decode-and-forward (DF) cooperative diversity systems consisting of a source, a destination, and multiple relays. This scheme employs adjustable parameters at the relays and the destination which enable this scheme to appropriately adapt to variations in the source-relay and relay-destination channel gains. For the proposed E-MRC scheme, we analyze the asymptotic error rate performance for high signal-to-noise ratios and Rayleigh fading. Based on the obtained analytical expressions, we find the optimal parameters that lead to minimization of the asymptotic error rate. Furthermore, we compare the error rate performance as well as the feedback overhead of E-MRC with those of important DF schemes, namely, cooperative MRC (C-MRC) and two DF schemes based on the link adaptive regeneration (LAR) concept, namely, LAR-αinst and LAR-α. We show that although the feedback requirements of E-MRC are similar to those of LAR-α, E-MRC achieves a performance similar to that of LAR-αinst, which has a substantially higher feedback overhead.
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Introduction
(Cambridge University Press, 2012) Arnon, S.; Barry, J.; Aragiannidis, G.; Schober, R.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
Optical wireless communications is a dynamic area of research and development. Combining fundamental theory with a broad overview, this book is an ideal reference for anyone working in the field, as well as a valuable guide for self-study. It begins by describing important issues in optical wireless theory, including coding and modulation techniques for optical wireless, wireless optical CDMA communication systems, equalization and Markov chains in cloud channels and optical MIMO systems, as well as explaining key issues in information theory for optical wireless channels. The next section describes unique channels that could be found in optical wireless applications, such as NLOS UV atmospheric scattering channels, underwater communication links and a combination of hybrid RF/optical wireless systems. The final section describes applications of optical wireless technology, such as quantum encryption, visible light communication, IR links and sensor networks, with step-by-step guidelines to help reduce design time and cost.
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Link allocation for multiuser systems with hybrid RF/FSO backhaul: Delay-limited and delay-tolerant designs
(IEEE, 2016-05) Jamali, V.; Michalopoulos, D. S.; Uysal, Murat; Schober, R.; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we consider a cascaded radio frequency (RF) and hybrid RF/free space optical (FSO) system where several mobile users transmit their data over an RF link to a decode-and-forward relay node (e.g., a small cell base station) and the relay forwards the information to a destination (e.g., a macro-cell base station) over a hybrid RF/FSO backhaul link. The relay and the destination employ multiple antennas for transmission and reception over the RF links while each mobile user has a single antenna. The RF links are orthogonal to the FSO link but half-duplex with respect to each other, i.e., either the user-relay RF link or the relay-destination RF link is active. For this communication setup, we derive the optimal fixed and adaptive link allocation policies for sharing the transmission time between the RF links based on the statistical and instantaneous channel state information (CSI) of the RF and FSO links, respectively. Thereby, we consider the following two scenarios depending on the delay requirements: 1) delay-limited transmission where the relay has to immediately forward the packets received from the users to the destination, and 2) delay-tolerant transmission where the relay is allowed to store the packets received from the users in its buffer and forward them to the destination when the quality of the relay-destination RF link is favorable. Our numerical results illustrate the effectiveness of the proposed communication architecture and link allocation policies, and their superiority compared to existing schemes, which employ only one type of backhaul link.
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Mixed RF and hybrid RF/FSO relaying
(IEEE, 2015) Jamali, V.; Michalopoulos, D. S.; Uysal, Murat; Schober, R.; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we consider a mixed RF and hybrid RF/FSO system where several mobile users transmit their data over an RF link to a relay node (e.g. a small cell base station) and the relay forwards the information to a destination (e.g. a macro cell base station) over a hybrid RF/FSO backhaul link. The relay and the destination employ multiple antennas for transmission and reception over the RF links while each mobile user has a single antenna. The RF links are orthogonal with respect to the FSO link and half-duplex with respect to each other, i.e., either the user-relay RF link or the relay-destination RF link is active. For this communication setup, we derive the optimal policy for sharing the RF transmission time between the RF links. Our numerical results show the effectiveness of the proposed communication architecture and link allocation policy, and their superiority compared to existing schemes which employ only one type of backhaul link.
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Outage analysis of q-duplex RF/FSO relaying
(IEEE, 2015) Jamali, V.; Michalopoulos, D. S.; Uysal, Murat; Schober, R.; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we propose and analyze a novel q-duplex radio frequency/free space optical (RF/FSO) relaying protocol for a mixed RF and hybrid RF/FSO communication system. In our scheme, several mobile users transmit their data over an RF link to a relay node (e.g. a small cell base station) and the relay forwards the information to a destination (e.g. a macro cell base station) over a hybrid RF/FSO backhaul link. The RF links are full-duplex with respect to the FSO link and half-duplex with respect to each other, i.e., either the user-relay RF link or the relay-destination RF link is active. Depending on the channel statistics, the q-duplex relaying protocol may reduce to full-duplex relaying, when the quality of the FSO link is sufficiently high, or to half-duplex relaying, when the FSO link becomes unavailable due to severe atmospheric conditions. We derive an analytical expression for the end-to-end outage probability of the proposed protocol when the fading for the user-relay RF link, the relay-destination RF link, and the relay-destination FSO link are modelled as Rayleigh, Ricean, and Gamma-Gamma distributed, respectively. Our simulation results confirm the analytical derivations and reveal the effectiveness of the proposed q-duplex protocol and its superiority compared to existing schemes.
Open Access
Performance and optimization of network-coded cooperative diversity systems
(IEEE, 2013-03) Nasri, A.; Schober, R.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we study network–coded cooperative diversity (NCCD) systems comprising multiple sources, one relay, and one destination, where the relay detects the packets received from all sources and performs Galois ﬁeld (GF) network coding over GF(2m) before forwarding a single packet to the destination. Assuming independent Rayleigh fading for all links of the network, we derive simple and accurate closed–formapproximations for the asymptotic symbol and bit error rates of NCCD systems. The derived error rate expressions are valid for arbitrary numbers of sources, arbitrary modulation schemes, and arbitrary constellation mappings and provide signiﬁcantinsight into the impact of various system and channel parameters on performance. Moreover, these expressions can be exploited for optimization of the constellation mapping as well as for formulation of various NCCD system optimization problemsincluding optimal power allocation, relay selection, and relay placement.