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Yayın Optimal primary-secondary user pairing and power allocation in cognitive cooperative multiple access channels(IEEE, 2014) Bakşi, Saygın; Kaya, OnurWe develop jointly optimal power control and primary-secondary user partnering strategies for a cognitive cooperative multiple access channel with K primary and K secondary users. For each primary user, a cooperating secondary user is assigned. We consider both underlay and overlay modes for cognition/cooperation. In overlay mode, each secondary user decodes and relays part of its assigned primary user's message, and simultaneously transmits its own independent message, while ensuring the primary user achieves at least its single user capacity with power control. The encoding is based on channel adaptive block Markov superposition coding, where the powers assigned to primary and secondary user codewords are optimized so as to maximize either the system's sum rate, or the sum of secondary users' rates. In underlay mode, each secondary user employs independent signalling and allocates its power to maximize its own rate, without decreasing its assigned primary user's rate. The partnering problem for either mode is reduced to a maximum weighted matching (MWM) problem on a bipartite graph, and solved jointly optimally with the power allocation problem.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 Decoder-side super-resolution and frame interpolation for improved H.264 video coding(IEEE, 2013) Ateş, Hasan FehmiIn literature decoder-side motion estimation is shown to improve video coding efficiency of both H.264 and HEVC standards. In this paper we introduce enhanced skip and direct modes for H.264 coding using decoder-side super-resolution (SR) and frame interpolation. P-and B-frames are downsampled and H.264 encoded at lower resolution (LR). Then reconstructed LR frames are super-resolved using decoder-side motion estimation. Alternatively for B-frames, bidirectional true motion estimation is performed to synthesize a B-frame from its reference frames. For P-frames, bicubic interpolation of the LR frame is used as an alternative to SR reconstruction. A rate-distortion optimal mode selection algorithm determines for each MB which of the two reconstructions to use as skip/direct mode prediction. Simulations indicate an average of 1.04 dB PSNR improvement or 23.0% bitrate reduction at low bitrates when compared to H.264 standard. Average PSNR gains reach as high as 3.95 dB depending on the video content and frame rate.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 Low complexity inter-mode selection for H.264(IEEE, 2006) Ba, Seydou Nourou; Altunbaşak, Yücel; Ateş, Hasan FehmiThe coding efficiency of the H.264/AVC standard enables the transmission of high quality video over bandwidth limited networks. Due to the use of multiple Macroblock (MB) partitions, the Motion estimation module has extremely high complexity that makes it unpractical for most real-time applications on resource-limited platforms such as hand held devices. In this paper we propose a novel algorithm that significantly reduces the encoding complexity while maintaining high rate distortion performance. The proposed method reduces the Motion estimation (ME) computational complexity by accurately predicting the optimal MB partitions and restricting the number of candidate modes based on a-priori probabilities computed from spatio-temporal information. The experimental results show that the speed up of UmHexagonS [1] (one of the most efficient ME algorithms) can be doubled while maintaining the coding efficiency of Full Search.Yayın Decoder side true motion estimation for very low bitrate b-frame coding(IEEE, 2011) Ateş, Hasan Fehmi; Çizmeci, BurakIn H.264 standard, coding of motion vectors constitutes a significant portion of total bitrate especially at low bitrate regimes. This is because differential coding of motion vectors is inefficient when the bit budget is very low. In this paper, we propose a novel estimation and coding algorithm for motion vectors of B-frames at very low bitrates. In this method, the encoder selects the optimal motion vector from a limited set of candidate vectors that are determined at the decoder side using true motion estimation. Since these candidate vector sets are fixed by the decoder for each macroblock, there is no need for explicit coding of motion information, which reduces the bitrate required for coding. Also, true motion vector estimates are used for improved direct mode coding in B-frames. The algorithm provides an average of 0.68 dB PSNR gain for B-frames when compared to the reference H.264 results at the same bitrates. Simulation results also indicate significant improvement in visual quality of the compressed B-frames.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 Blind channel estimation for space-time coding systems with Baum-Welch algorithm(IEEE, 2002) Çırpan, Hakan Ali; Panayırcı, ErdalIn recent years, space-time coding is proposed to provide significant capacity gains over the traditional communication systems in fading wireless channels. In this paper, we consider the problem of blind estimation of the channel parameters along with space-time coded signals. Our proposed approach exploits the finite alphabet property of the space-time coded signals and is based on the unconditional signal model by treating the information sequence as stochastic I.I.D. sequences. The iterative Baum-Welch algorithm is then adapted to solve resulting unconditional ML optimization cost function. Finally, some simulation results are presented.Yayın A novel noise robust and low bit rate speech coding algorithm(IEEE, 2009) Güz, Ümit; Gürkan, Hakan; Yarman, Bekir Sıddık BinboğaIn this work, a new noise robust and variable length frame based speech modeling method is introduced. This method consists of three major steps which includes noise removal algorithm, coding and encoding algorithms, respectively. Coding and encoding parts are developed based on SYMPES (SYsteMatic Procedure for Predefined Envelope and Signature sequence sets). These sets have been developed in two types which represent voiced and unvoiced parts of the speech signals separately in order to obtain more efficient coding strategy and higher compression ratio while preserving the perceptual quality of the speech signals. As an extension of our previous works our new framework is not only consider the coding of the clean speech signals but also noisy speech signals. The new noise robust module suppresses the noise and delivers the clean speech signal to the newly designed modeling part. The modeling part promises higher compression ratios by switching to the more appropriate type of predefined sets take into account the voiced and unvoiced frames.
