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Yayın Cognitive cooperative MAC with one primary and two secondary users: achievable rates and optimal power control(IEEE-INST Electrical Electronics Engineers Inc, 2014-11) Edemen, Çağatay; Kaya, OnurWe consider a three-user fading cognitive cooperative multiple access channel (MAC) with one primary and two secondary transmitters. We propose two encoding/decoding strategies with varying levels of cooperation, based on block Markov superposition encoding and backward decoding. The first is an overlay model, where the secondary users (SUs) aid the transmission of the primary user (PU) by causally decoding the PU message and forwarding it while also cooperating among each other. The second is an underlay model, where the SUs cooperate by decoding and forwarding each other's messages while treating the signal received from the PU as noise. In either case, the PU is guaranteed to operate at its maximum achievable single user rate. We characterize the achievable SU rate region for both models and maximize this region as a function of the transmit powers. The simulation results show that the SU rate region can be significantly enlarged, particularly using the overlay model.Yayın Radio resource management for OFDMA-based mobile relay enhanced heterogenous cellular networks(IEEE, 2013) Baştürk, İlhan; Özbek, Berna; Edemen, Çağatay; Tan, Ahmet Serdar; Zeydan, Engin; Ergüt, SalihIn this paper, we focus on the radio resource management problem for the Orthogonal Frequency Division Multiple Access (OFDMA)-based mobile relay-enhanced het erogenous cellular networks. We combine mobile relaying and data offloading scenarios to increase the capacity of the system and cope with the mobile data traffic volume that is increased by the number of wireless subscribers accessing mobile data services. We propose network interface selection, relay selection and resource allocation solutions for this scenario and show effect of relaying and data offloading on the system capacity and on the ratio of satisfied users.Yayın Design and optimization of multiuser cooperative protocols for wireless networks(Işık Üniversitesi, 2014-09-12) Edemen, Çağatay; Kaya, Onur; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Elektronik Mühendisliği Doktora ProgramıRecently, the main trend in wireless communications has shifted from voice transmission to data communication. Naturally, this shift caused an increase in the data rate and bandwidth requirements. Being a limited and thus expensive resource, wireless spectrum needs to be used efficiently. For higher spectral and data rate efficiency, new spectrum allocation policies as well as new transmission techniques are needed. Cooperative and cognitive radios are promising emerging technologies, which can enable efficient spectrum resource utilization as well as high data rate transmission in the next generation wireless networks. This thesis addresses wireless relay networks consisting of multiple cooperative and/or cognitive nodes. The main contribution of this thesis is the extension of cooperative strategies from two users to three user settings, focusing on mutual cooperation. In the first part of this dissertation, we concentrate on a superposition block Markov encoding based three user cooperative communication scheme for a fading Gaussian multiple access channel. We consider all possible channel conditions between users and propose a channel adaptive block Markov encoding strategy. In the second part of this thesis, for the same three user MAC model we discuss a new channel non-adaptive superposition block Markov encoding structure which enables all three users to cooperate collectively as well as in pairs. The proposed cooperation models not only provide increased diversity to all participating users, but also contain as special cases the multiple relay channel and the multiple access relay channel. In the third part, we focus on the joint use of cognition and cooperation. In particular, we consider overlay and underlay cooperative-cognitive radio models with one primary and two secondary users. We extend the cooperative encoding models developed for the three user MAC to the cognitive set-up. In all three problems studied in this thesis, we obtain new and improved achievable rate regions, by cognition and/or cooperation.Yayın Channel adaptive encoding and decoding strategies and rate regions for the three user cooperative multiple access channel(IEEE, 2008) Edemen, Çağatay; Kaya, OnurFor a cooperative Gaussian multiple access channel (MAC), we propose a new channel adaptive three user cooperation strategy, based on a non-trivial extension of block Markov super-position encoding. We obtain the expressions for the resulting achievable rate region. We demonstrate through simulations that the participation of an extra user in cooperation provides significant rate improvements. The proposed strategy also improves upon our earlier results on the three user cooperative MAC [1], under certain channel conditions.Yayın Achievable rates for the three user cooperative multiple access channel(IEEE, 2008) Edemen, Çağatay; Kaya, OnurFor a three user Gaussian multiple access channel (MAC), we propose a new superposition block Markov encoding based cooperation scheme. Our scheme allows the three users to simultaneously cooperate both in pairs, and collectively, by dividing the transmitted messages into sub messages intended for each cooperating partner. The proposed encoding and decoding at the transmitters take into account the relative qualities of the cooperation links between the transmitters. We obtain and evaluate the achievable rate region based on our encoding strategy, and compare it with the achievable rates for the two user cooperative MAC. We demonstrate that the added diversity by the presence of the third user improves the region of achievable rates, and this improvement is especially significant as far as the sum rate of the system is concerned.Yayın A new block Markov coding strategy for pairwise and collective cooperation in the three user MAC(IEEE, 2013) Edemen, Çağatay; Kaya, OnurFor a three user cooperative multiple access channel (MAC), we propose a new block Markov superposition encoding strategy, which enables all three users to cooperate collectively as well as in pairs. We obtain the resulting achievable rate expressions and compare them with existing two and three user cooperative strategies. We demonstrate that significant rate gains may be possible, without resorting to adaptive encoding/decoding techniques. We investigate the contributions from pairwise and collective cooperation signals while achieving tuples on the rate region boundary, and compare by simulations the sum rates achievable by two user versus three user grouping in cooperative MACs with fixed total resources.Yayın Channel adaptive user cooperation strategies for fading wireless channels(Işık Üniversitesi, 2006) Edemen, Çağatay; Kaya, Onur; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Elektronik Mühendisliği Yüksek Lisans ProgramıIn this dissertation, a channel adaptive method is proposed for a two user halfduplex cooperative communication system under the assumption of perfect channel state information at the transmitters and the receiver. An achievable rate region for the proposed method is characterized, and evaluated by computer simulation.Yayın Visible light communication with solar cell receiver for indoor IoT applications(Institute of Electrical and Electronics Engineers Inc., 2024) Bonakdar, Roozbeh; Edemen, Çağatay; Akbulut, Muhammed Emin; Keskin, Onur; Kaya, Onur; Uysal, MuratThe rapid increase of Internet of Things (IoT) devices has ushered in a new era of connectivity, with an increasing reliance on efficient communication models. In this context, Optical Wireless Communications (OWC) presents a promising avenue for transmitting data at the speed of light, utilizing the optical spectrum to alleviate congestion in urban environments. Leveraging Light Emitting Diodes (LEDs) as transmitters and solar cells as receivers, this paper explores the feasibility of indoor OWC systems. Moreover, we present an experimental setup focusing on bandwidth measurement, data transmission, and energy harvesting. Our results indicate a maximum data rate of 19.2 Kbps using On-Off Keying (OOK) modulation at a 15 cm link distance. Notably, by avoiding the utilization of external circuitry for performance enhancement of the solar cell, we tried to maintain the system's suitability for IoT applications. Our findings contribute to understanding solar cell-based data reception from LEDs, offering simulation results for practical implementation and performance considerations for indoor IoT communication systems.
