Browsing by Subject "Encoding"

Now showing 1 - 7 of 7

Open Access
Çok-akışlı eşler arası isteğe bağlı video sistemlerinin Markov zinciri tabanlı güvenilirlik modellemesi
(IEEE, 2008-04) Yazıcı, Mehmet Akif; Öztoprak, K.; Akar, Nail; Akar, G. B.
Çok-akışlı eşler-arası video, gelecek nesil isteğe bağlı video sistemleri için kullanılmaya aday teknolojilerdendir. Çok-akışlı video sistemlerinin sorunlarından birisi, eş dalgalanması adı verilen, eşlerin ağla olan bağlantılarının kopup düzelmesi durumudur. Eş dalgalanmasının bütün eşler-arası sistemlerde olumsuz etkileri olduğu bilinmektedir. Bu etkinin hafifletilmesi için çeşitli hata kontrollü alt-akış kodlama teknikleri önerilmiştir. Bu makalede, eş dalgalanması ve hata kontrolünün rolünü incelemek amacıyla sürekli zamanlı Markov zinciri tabanlı bir rassal model önerilmektedir. Bu model kullanılarak, hata kontrolünün rolü, gelecek nesil çok-akışlı eşler-arası isteğe bağlı video sistemlerinin tasarımında kullanılmak üzere nicel olarak ortaya konmaktadır.
Open Access
Hardware/software approaches for reducing the process variation impact on instruction fetches
(ACM New York, NY, 2013) Kadayif, I.; Turkcan, M.; Kiziltepe, S.; Ozturk, O.
As technology moves towards finer process geometries, it is becoming extremely difficult to control critical physical parameters such as channel length, gate oxide thickness, and dopant ion concentration. Variations in these parameters lead to dramatic variations in access latencies in Static Random Access Memory (SRAM) devices. This means that different lines of the same cache may have different access latencies. A simple solution to this problem is to adopt the worst-case latency paradigm. While this egalitarian cache management is simple, it may introduce significant performance overhead during instruction fetches when both address translation (instruction Translation Lookaside Buffer (TLB) access) and instruction cache access take place, making this solution infeasible for future high-performance processors. In this study, we first propose some hardware and software enhancements and then, based on those, investigate several techniques to mitigate the effect of process variation on the instruction fetch pipeline stage in modern processors. For address translation, we study an approach that performs the virtual-to-physical page translation once, then stores it in a special register, reusing it as long as the execution remains on the same instruction page. To handle varying access latencies across different instruction cache lines, we annotate the cache access latency of instructions within themselves to give the circuitry a hint about how long to wait for the next instruction to become available. © 2013 ACM.
Open Access
On the capacity of channels with Markov insertions, deletions and substitutions
(IEEE, 2024) Morozov, Ruslan; Duman, Tolga Mete
We consider channels with synchronization errors. A classical result for such channels is their information stability, when the synchronization errors are memoryless. In this paper, we extend this result to the case where the synchronization errors have memory. Specifically, we assume that the synchronization errors are governed by a stationary and ergodic finite state Markov chain, and prove that such channel is information-stable, which implies the existence and achievability of the limit of normalized mutual information. This result applies to a wide range of channels with synchronization errors, with different applications including DNA storage. The developed methodology may also be useful to prove other coding theorems for non-trivial channel sequences.
Open Access
Profile-encoding reconstruction for multiple-acquisition balanced steady-state free precession imaging
(John Wiley and Sons Inc., 2017) Ilicak, Efe; Senel, Lutfi Kerem; Biyik, Erdem; Çukur, Tolga
Purpose: The scan-efficiency in multiple-acquisition balanced steady-state free precession imaging can be maintained by accelerating and reconstructing each phase-cycled acquisition individually, but this strategy ignores correlated structural information among acquisitions. Here, an improved acceleration framework is proposed that jointly processes undersampled data across N phase cycles. Methods: Phase-cycled imaging is cast as a profile-encoding problem, modeling each image as an artifact-free image multiplied with a distinct balanced steady-state free precession profile. A profile-encoding reconstruction (PE-SSFP) is employed to recover missing data by enforcing joint sparsity and total-variation penalties across phase cycles. PE-SSFP is compared with individual compressed-sensing and parallel-imaging (ESPIRiT) reconstructions. Results: In the brain and the knee, PE-SSFP yields improved image quality compared to individual compressed-sensing and other tested methods particularly for higher N values. On average, PE-SSFP improves peak SNR by 3.8 ± 3.0 dB (mean ± s.e. across N = 2–8) and structural similarity by 1.4 ± 1.2% over individual compressed-sensing, and peak SNR by 5.6 ± 0.7 dB and structural similarity by 7.1 ± 0.5% over ESPIRiT. Conclusion: PE-SSFP attains improved image quality and preservation of high-spatial-frequency information at high acceleration factors, compared to conventional reconstructions. PE-SSFP is a promising technique for scan-efficient balanced steady-state free precession imaging with improved reliability against field inhomogeneity. Magn Reson Med 78:1316–1329, 2017.
Open Access
Quadratic signaling with prior mismatch at an encoder and decoder: equilibria, continuity, and robustness properties
(Institute of Electrical and Electronics Engineers, 2022-01-11) Kazikli, E.; Sartas, S.; Gezici, Sinan
We consider communications through a Gaussian noise channel between an encoder and a decoder which have subjective probabilistic models on the source distribution. Although they consider the same cost function, the induced expected costs are misaligned due to their prior mismatch, which requires a game theoretic approach. We consider two approaches: a Nash setup, with no prior commitment, and a Stackelberg solution concept, where the encoder is committed to a given announced policy apriori. We show that the Stackelberg equilibrium cost of the encoder is upper semi continuous, under the Wasserstein metric, as encoder's prior approaches the decoder's prior, and it is also lower semi continuous with Gaussian priors. For the Stackelberg setup, the optimality of affine policies for Gaussian signaling no longer holds under prior mismatch, and thus team-theoretic optimality of linear/affine policies are not robust to perturbations. We provide conditions under which there exist informative Nash and Stackelberg equilibria with affine policies. Finally, we show existence of fully informative Nash and Stackelberg equilibria for the cheap talk problem under an absolute continuity condition.
Open Access
Random access over wireless links: optimal rate and activity probability selection
(IEEE, 2017-12) Duman, Tolga M.; Karakoç, N.
In this paper, we consider a random access scheme over wireless fading channels based on slotted ALOHA where each user independently decides whether to send a packet or not to a common receiver at any given time slot. To characterize the system throughput, i.e., the expected sum- rate, an information theoretic formulation is developed. We consider two scenarios: classical slotted ALOHA where no multi-user detection (MUD) capability is available and slotted ALOHA with MUD. Our main contribution is that the optimal rates and channel activity probabilities can be characterized as a function of the user distances to the receiver to maximize the system throughput. In addition, we address the issue of fairness among the users and provide solutions, which guarantee a minimum amount of individual throughput.
Open Access
Reconstruction by calibration over tensors for multi-coil multi-acquisition balanced SSFP imaging
(John Wiley & Sons, 2018) Bıyık, Erdem; Ilıcak, Efe; Çukur, Tolga
Purpose: To develop a rapid imaging framework for balanced steady-state free precession (bSSFP) that jointly reconstructs undersampled data (by a factor of R) across multiple coils (D) and multiple acquisitions (N). To devise a multi-acquisition coil compression technique for improved computational efficiency. Methods: The bSSFP image for a given coil and acquisition is modeled to be modulated by a coil sensitivity and a bSSFP profile. The proposed reconstruction by calibration over tensors (ReCat) recovers missing data by tensor interpolation over the coil and acquisition dimensions. Coil compression is achieved using a new method based on multilinear singular value decomposition (MLCC). ReCat is compared with iterative self-consistent parallel imaging (SPIRiT) and profile encoding (PE-SSFP) reconstructions. Results: Compared to parallel imaging or profile-encoding methods, ReCat attains sensitive depiction of high-spatial-frequency information even at higher R. In the brain, ReCat improves peak SNR (PSNR) by 1.1 ± 1.0 dB over SPIRiT and by 0.9 ± 0.3 dB over PE-SSFP (mean ± SD across subjects; average for N = 2-8, R = 8-16). Furthermore, reconstructions based on MLCC achieve 0.8 ± 0.6 dB higher PSNR compared to those based on geometric coil compression (GCC) (average for N = 2-8, R = 4-16). Conclusion: ReCat is a promising acceleration framework for banding-artifact-free bSSFP imaging with high image quality; and MLCC offers improved computational efficiency for tensor-based reconstructions. Magn Reson Med 79:2542-2554, 2018.