3 sonuçlar
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Yayın Power control for fading cooperative multiple access channels(IEEE, 2007-08) Kaya, Onur; Ulukuş, ŞennurFor a fading Gaussian multiple access channel with user cooperation, we obtain the power allocation policies that maximize the average rates achievable by block Markov superposition coding, subject to average power constraints. The optimal policies result in a coding scheme that is simpler than the one for a general multiple access channel with generalized feedback. This simpler coding scheme also leads to the possibility of formulating an otherwise non-concave optimization problem as a concave one. Using the perfect channel state information available at the transmitters to adapt the powers, we demonstrate gains over the achievable rates for existing cooperative systems.Yayın Energy and data cooperative multiple access channel with intermittent data arrivals(IEEE, 2018-03) Gürakan, Berk; Kaya, Onur; Ulukuş, ŞennurWe consider an energy harvesting two user cooperative Gaussian multiple access channel, where both of the users harvest energy from nature. The users cooperate at the physical layer (data cooperation) by establishing common messages through overheard signals and then cooperatively sending them. We study two scenarios within this model. In the first scenario, the data packets arrive intermittently over time. We find the optimal offline transmit power and rate allocation policy that maximize the departure region. We first show that there exists an optimal policy, in which the single user rate constraints in each time slot are tight, yielding a one-to-one relation between the powers and rates. Then, we formulate the departure region maximization problem as a weighted sum departure maximization in terms of rates only. Next, we propose a sequential convex approximation method to approximate the problem at each step and show that it converges to the optimal solution. We solve the approximate problems using an inner-outer decomposition method. In the second scenario, the data packets are available at the beginning of the transmission, but the users now have the ability to cooperate at the battery level (energy cooperation), in addition to data cooperation. The energy cooperation is facilitated by wireless energy transfer and is bidirectional. For this scenario, we find the jointly optimal offline transmit power and rate allocation policy together with the energy transfer policy that maximize the departure region. We provide necessary conditions for energy transfer and prove some properties of the optimal transmit policy, thereby shedding some light on the interplay between energy and data cooperation.Yayın Delay tolerant cooperation in the energy harvesting multiple access channel(IEEE, 2016) Kaya, Onur; Su, Nuğman; Ulukuş, Şennur; Koca, MutluWe consider the optimum transmit scheduling problem for a two user energy harvesting cooperative multiple access channel. We assume a slotted model where energy harvests in each slot are known a priori. We propose a delay tolerant cooperation model: the transmitters create common information in a given slot, but need not cooperatively send the created common information immediately; they may relegate all or part of the cooperative message transmission to upcoming slots. We propose a modified block Markov superposition coding scheme based on message re-partitioning, that spans multiple slots. We characterize the corresponding achievable departure region by a deadline, and maximize it subject to energy harvesting constraints. We show that, delay tolerant cooperation need not necessarily improve the departure region over delay constrained cooperation, and derive a sufficient condition for the equivalence of the two policies. We compare optimal delay constrained and delay tolerant cooperation policies, and their achievable departure regions via simulations.
