11 sonuçlar
Arama Sonuçları
Listeleniyor 1 - 10 / 11
Yayın Optimum power control for transmitter cooperation in OFDMA based wireless networks(IEEE, 2011) Bakım, İsmail Sezi; Kaya, OnurFor a cooperative orthogonal frequency division multiple access (OFDMA) system with two transmitters (TXs), and full channel state information (CSI), we obtain the optimal power allocation (PA) policies which maximize the rate region achievable by a recently introduced version of block Markov superposition encoding (BMSE): inter-subchannel cooperative encoding (ISCE) [1]. We provide the optimality conditions that need to be satisfied by the powers associated with the transmitted codewords. We propose two algorithms that yield the optimal power distribution: a subgradient algorithm which achieves an arbitrary rate point on the achievable rate region boundary, and an iterative waterfilling-like algorithm which maximizes the sum rate, and converges much faster. We observe that, utilization of power control to take advantage of the diversity offered by the cooperative OFDMA system, not only leads to a remarkable improvement in achievable rates, but also may help determine how the subchannels have to be instantaneously allocated to various tasks in cooperation.Yayın Cooperative strategies and achievable rates for two user OFDMA channels(IEEE-INST Electrical Electronics Engineers Inc, 2011-12) Bakım, İsmail Sezi; Kaya, OnurWe propose three encoding strategies for a two user cooperative Orthogonal Frequency Division Multiple Access (OFDMA) system, based on block Markov superposition encoding (BMSE). We obtain the expressions for the resulting achievable rate regions for all three encoding strategies. We show that, by allowing for re-partitioning and re-encoding of the cooperative messages across subchannels, it is possible to better exploit the diversity created by OFDMA, and higher rates can be achieved. We demonstrate potential rate gains attained by cooperative OFDMA, through simulations.Yayın Birleşik çöz/sıkıştır ve ilet tabanlı işbirlikçi çoklu erişim(IEEE, 2012-04-18) Güneş, Mehmet; Kaya, OnurBu bildiride, iki kullanıcılı bir işbirlikçi çoklu erişim kanalı için çöz-ilet ve sıkıştır-ilet tekniklerinin eş zamanlı kullanılmasına dayalı kodlama ve kodçözme teknikleri geliştiriyor, ve karşılık gelen erişilebilir veri hızı ifadelelerini türetiyoruz. Sonuçlarımızı bilinen bazı çift yönlü işbirliği stratejilerinin veri hızları ile kıyaslayarak, iki tekniğin bir arada kullanılmasının erişilebilir veri hızı bölgesini genişletebildiğini benzetimler yolu ile gösteriyoruz.Yayın Achievable rates for two user cooperative OFDMA(IEEE, 2010) Bakım, İsmail Sezi; Kaya, OnurWe propose two encoding strategies for a two user cooperative Orthogonal Frequency Division Multiple Access (OFDMA) system, based on block Markov superposition encoding. We obtain the expressions for the resulting achievable rate regions for both encoding strategies, and evaluate them through simulations. We show that, by allowing for re-partitioning and re-encoding of the cooperative messages across subchannels, it is possible to better exploit the diversity created by OFDMA, and higher rates can be achieved.Yayın Power control in the cognitive cooperative multiple access channel(IEEE, 2012) Kaya, Onur; İşleyen, MuratWe extend several encoding and decoding techniques from cooperative communications framework, to a cognitive radio system consisting of a primary user (PU) and a secondary user (SU), sending their messages to a common receiver. Assuming that the transmitters and the receiver have full channel state information (CSI) collected and distributed by the common receiver, and that the SU knows the PU's codebook, the cooperation is obtained by block Markov superposition coding, and backwards decoding, which yield a causal overlay scenario. We formulate two rate optimization problems with the aim of, (i) maximizing the sum rate of the system, and (ii) maximizing the rate of the secondary user. We obtain the optimal power allocations for both cases, and the resulting rate regions. The power controlled cooperation turns out to be especially useful when maximizing the sum rate of the system, as it gives the PU significant rate rewards for allowing the cognitive transmitter to access its resources.Yayın Energy harvesting cooperative multiple access channel with decoding costs(IEEE, 2016) Arafa, Ahmed M.; Kaya, Onur; Ulukuş, ŞennurWe consider an energy harvesting cooperative multiple access channel (AC) with decoding costs. In this setting, users cooperate at the physical layer (data cooperation) in order to increase the achievable rates. Data cooperation comes at the expense of decoding costs: each user spends some amount of its harvested energy to decode the message of the other user, before forwarding both messages to the receiver. The decoding power spent is an increasing convex function of the incoming message rate. We characterize the optimal power scheduling policies that achieve the boundary of the maximum departure region subject to energy causality constraints and decoding costs by using a generalized water-filling algorithm.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 Window and backwards decoding achieve the same sum rate for the fading cooperative Gaussian multiple access channel(IEEE, 2006) Kaya, OnurFor a two user fading Gaussian multiple access channel with user cooperation, we show that window decoding achieves the same sum rate as backwards decoding, when the encoding is done using block Markov superposition coding. We prove this result by showing that when optimum power control is employed, the additional constraints on the sum rate imposed by the use of window decoding instead of backwards decoding are never active. While doing so, we also provide some properties of power allocation that is jointly optimal with block Markov coding and window decoding.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.
