Browsing by Author "Akar, G. B."

Now showing 1 - 9 of 9

Open Access
Bant genişliği kısıtı altında videonun en iyi iletimi
(IEEE, 2006-04) Gürses, E.; Akar, G. B.; Akar, Nail
In this paper, we propose an optimal video streaming framework using retransmissions based on the theory of Markov Decision Processes (MDP). Using MDPs, we calculate average reward optimal policies so as to maximize the on time delivery probability of video frames in the transmission window while conforming to network-imposed available bandwidth constraints. The effectiveness of the proposed approach is validated by comparing the results with theoretically obtained rate-distortion curves corresponding to the optimal policies by using the distortion model in [2] © 2006 IEEE.
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
E-museum: web-based tour and information system for museums
(IEEE, 2006) Baştanlar, Y.; Altıngövde, İsmail Şenol; Aksay, A.; Alav, O.; Çavuş, Özge; Yardımcı, Y.; Ulusoy, Ozgur; Güdükbay, Uğur; Çetin, A. Enis; Akar, G. B.; Aksoy, Selim
A web-based system - consisting of data entrance, access and retrieval modules - is constructed for museums. Internet users that visit the e-museum, are able to view the written and visual information belonging to the artworks in the museum, are able to follow the virtual tour prepared for the different sections of the museum, are able to browse the artworks according to certain properties, are able to search the artworks having the similar visual content with the viewed artwork. © 2006 IEEE.
Open Access
Impact of scalability in video transmission in promotion-capable differentiated services networks
(IEEE, 2002-09) Gürses, E.; Akar, G. B.; Akar, Nail
Transmission of high quality video over the Internet faces many challenges including unpredictable packet loss characteristics of the current Internet and the heterogeneity of receivers in terms of their bandwidth and processing capabilities. To address these challanges, we propose an architecture in this paper that is based on the temporally scalable and error resilient video coding mode of the H.263+ codec. In this architecture, the video frames will be transported over a new generation IP network that supports differentiated services (Diffserv). We also propose a novel Two Rate Three Color Promotion-Capable Marker (trTCPCM) to be used at the edge of the diffserv network. Our simulation study demonstrates that an average of 30 dB can be achieved in case of highly congested links.
Open Access
Rate-distortion optimization for stereoscopic video streaming with unequal error protection
(SpringerOpen, 2009) Tan, A. S.; Aksay, A.; Akar, G. B.; Arikan, E.
We consider an error-resilient stereoscopic streaming system that uses an H.264-based multiview video codec and a rateless Raptor code for recovery from packet losses. One aim of the present work is to suggest a heuristic methodology for modeling the end-toend rate-distortion (RD) characteristic of such a system. Another aim is to show how to make use of such a model to optimally select the parameters of the video codec and the Raptor code to minimize the overall distortion. Specifically, the proposed system models the RD curve of video encoder and performance of channel codec to jointly derive the optimal encoder bit rates and unequal error protection (UEP) rates specific to the layered stereoscopic video streaming. We define analytical RD curve modeling for each layer that includes the interdependency of these layers. A heuristic analytical model of the performance of Raptor codes is also defined. Furthermore, the distortion on the stereoscopic video quality caused by packet losses is estimated. Finally, analytical models and estimated single-packet loss distortions are used to minimize the end-to-end distortion and to obtain optimal encoder bit rates and UEP rates. The simulation results clearly demonstrate the significant quality gain against the nonoptimized schemes.
Open Access
A simple and effective mechanism for stored video streaming with TCP transport and server-side adaptive frame discard
(Elsevier, 2005) Gürses, E.; Akar, G. B.; Akar, N.
Transmission control protocol (TCP) with its well-established congestion control mechanism is the prevailing transport layer protocol for non-real time data in current Internet Protocol (IP) networks. It would be desirable to transmit any type of multimedia data using TCP in order to take advantage of the extensive operational experience behind TCP in the Internet. However, some features of TCP including retransmissions and variations in throughput and delay, although not catastrophic for non-real time data, may result in inefficiencies for video streaming applications. In this paper, we propose an architecture which consists of an input buffer at the server side, coupled with the congestion control mechanism of TCP at the transport layer, for efficiently streaming stored video in the best-effort Internet. The proposed buffer management scheme selectively discards low priority frames from its head-end, which otherwise would jeopardize the successful playout of high priority frames. Moreover, the proposed discarding policy is adaptive to changes in the bandwidth available to the video stream. © 2004 Elsevier B.V. All rights reserved.
Open Access
Super-resolution using multiple quantized images
(IEEE, 2010) Özçelikkale, Ayça; Akar, G. B.; Özaktas, Haldun M.
In this paper, we study the effect of limited amplitude resolution (pixel depth) in super-resolution problem. The problem we address differs from the standard super-resolution problem in that amplitude resolution is considered as important as spatial resolution. We study the trade-off between the pixel depth and spatial resolution of low resolution (LR) images in order to obtain the best visual quality in the reconstructed high resolution (HR) image. The proposed framework reveals great flexibility in terms of pixel depth and number of LR images in super-resolution problem, and demonstrates that it is possible to obtain target visual qualities with different measurement scenarios including images with different amplitude and spatial resolutions.
Open Access
Three-dimensional media for mobile devices
(Institute of Electrical and Electronics Engineers, 2011-04) Gotchev, A.; Akar, G. B.; Capin, T.; Strohmeier, D.; Boev, A.
This paper aims at providing an overview of the core technologies enabling the delivery of 3-D Media to next-generation mobile devices. To succeed in the design of the corresponding system, a profound knowledge about the human visual system and the visual cues that form the perception of depth, combined with understanding of the user requirements for designing user experience for mobile 3-D media, are required. These aspects are addressed first and related with the critical parts of the generic system within a novel user-centered research framework. Next-generation mobile devices are characterized through their portable 3-D displays, as those are considered critical for enabling a genuine 3-D experience on mobiles. Quality of 3-D content is emphasized as the most important factor for the adoption of the new technology. Quality is characterized through the most typical, 3-D-specific visual artifacts on portable 3-D displays and through subjective tests addressing the acceptance and satisfaction of different 3-D video representation, coding, and transmission methods. An emphasis is put on 3-D video broadcast over digital video broadcasting-handheld (DVB-H) in order to illustrate the importance of the joint source-channel optimization of 3-D video for its efficient compression and robust transmission over error-prone channels. The comparative results obtained identify the best coding and transmission approaches and enlighten the interaction between video quality and depth perception along with the influence of the context of media use. Finally, the paper speculates on the role and place of 3-D multimedia mobile devices in the future internet continuum involving the users in cocreation and refining of rich 3-D media content.
Open Access
Uçtan uca modelleme ile kesintisiz stereo video iletimi
(IEEE, 2008-04) Tan, A. Serdar; Aksay, A; Akar, G. B.; Arıkan, Erdal
Bu çalışmamızda, hata koruma yöntemi olarak oransız kodları (Raptor Kodları) kullanan kesintisiz bir stereo video iletim sistemi önermekteyiz. İlk olarak video kodlayıcının hızbozulum (HB) eğrisini ve kanal koruma kodunun performansını analitik olarak modelledik. Daha sonra, paket kayıplarından kaynaklanan stereo videodaki kalite bozulumunu kestirdik. Son olarak, analitik modelleri ve kestirilmiş paket kayıp bozulumlarını kullanarak uçtan uca bozulum enküçültmesi uyguladık ve en iyi video kodlayıcı bit hızlarını ve eşit olmayan hata koruması (EOHK) oranlarını elde ettik. Benzetim sonuçlarında, önerilen sistemin getirdiği önemli kalite kazanımları açıkça gözlenmektedir.