Hindawi Publishing Corporation International Journal of Digital Multimedia Broadcasting Volume 2009, Article ID 319021, 11 pages doi:10.1155/2009/319021 Research Article New Adaptive Algorithms for GOP Size Control with Return Channel Suppression in Wyner-Ziv Video Coding Charles Yaacoub, 1, 2 Joumana Farah, 1 and B´ eatrice Pesquet-Popescu 2 1 Engineering Department, Faculty of Sciences and Computer Engineering, Holy-Spirit University of Kaslik, P.O. Box 446, Jounieh, Keserwan, Mount Lebanon, Lebanon 2 Signal and Image Processing Department, TELECOM ParisTech, 46 Rue Barrault, 75634 Paris Cedex 13, France Correspondence should be addressed to Charles Yaacoub, charlesyaacoub@usek.edu.lb Received 28 June 2008; Revised 8 September 2008; Accepted 22 October 2008 Recommended by Jorge Sastre Mart´ ınez We present novel algorithms for adaptive GOP size control in distributed Wyner-Ziv video coding, where an H.264 video codec is used for intracoding of key frames. The proposed algorithms rely on theoretical calculations to estimate the bit rate necessary for the successful decoding of Wyner-Ziv frames without the need for a feedback channel, which makes the system suitable for broadcasting applications. Additionally, in regions where H.264 intracoding outperforms Wyner-Ziv coding, the system automatically switches to intracoding mode in order to improve the overall performance. Simulations results show a significant gain in the average PSNR that can reach 3 dB compared to pure H.264 intracoding, and 0.8 dB compared to fixed-GOP Wyner-Ziv coding. Copyright © 2009 Charles Yaacoub et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. Introduction Distributed source coding [1–20] has recently become a topic of great interest for the research community, especially in the world of video communications. In traditional video coding techniques, such as MPEG or H.26x, motion estimation is performed at the encoder side, which yields very complex encoders, but simple decoders. This is suitable for applications where a video sequence is encoded once and decoded several times, such as video broadcasting or video streaming on demand. A simple decoder is desired in this case to allow low-cost receivers for the end users. On the other hand, some applications require simple encoders. Distributed Video Coding (DVC) was introduced [7, 8] to permit low-complexity encoding for small power- limited and memory-limited devices, such as camera- equipped mobile phones or wireless video sensors, by moving the computation burden from the encoder side to the decoder. Increased decoding complexity can be tolerated in this case since, in such applications, the decoder is usually located in a base station with sufficient resources. It is known from information theory that, given two statistically dependent sources X and Y , each source can be independently compressed to its entropy limit, H (X ) and H (Y ), respectively. However, by exploiting the correlation statistics between these sources, X and Y can be jointly compressed to the joint entropy H (X , Y ). This results in a more efficient compression since H (X , Y ) ≤ H (X )+ H (Y ). The idea behind DVC goes back to the 1970s when Slepian and Wolf [21] proved that, if the source Y is compressed to its entropy limit H (Y ), X can be transmitted at a rate very close to the conditional entropy H (X |Y ), provided that Y is available at the receiver as side information for decoding X . Since H (X , Y ) = H (Y )+ H (X |Y ), X and Y can be independently encoded and jointly decoded without any loss in the compression efficiency, compared to the case where both sources are jointly encoded and decoded. The application of this concept to lossy source coding is known as the Wyner-Ziv coding [22]. In practical DVC systems, a subset of frames, known as key frames, is usually compressed using traditional intracoding techniques. One or more frames following each key frame, known as Wyner-Ziv (WZ) frames, are then