An enhanced version of the fast inter-prediction mode decision and
variable block size motion estimation scheme for the H.264 video encoder is proposed in this work. In particular, we focus on the rate estimation model and thresholds for early termination. They are adaptively updated to enhance the coding speed and the rate-distortion performance. More details about the threshold setting and the mode decision processes are also provided. The improved algorithm can achieve a speed-up factor ranging from 70 to 150 times as compared to the full-search algorithm.
The emerging H.264 video coding Standard can achieve a substantial
coding gain as compared with existing coding standards. One major contribution of its gain comes from a very rich syntax for motion compensated prediction at the expense of a higher computational complexity. To be more specific, seven modes of different block
sizes and shapes (i.e. 16x16, 16x8, 8x16, 8x8, 8x4, 4x8 and 4x4) are supported. To do full search over all modes requires an extremely large amount of computation. We propose a fast search algorithm for the variable block size motion estimation. The proposed algorithm includes three stages. First, an initial estimate of the motion vector is obtained by a multi-resolution motion search. Then, based on the estimated motion vector and its corresponding distortion measure, a rate-distortion model is used to select the initial mode for motion search. Finally, some early-termination rules are adopted to reject impossible block sizes and motion locatios sooner. By avoiding search through all block sizes, the amount of computation involved in the motion search can be substantially reduced. The proposed algorithm can achieve a speed-up factor up to 120 times when compared to the fastest full-search algorithm.
An embedded differential space-time coding method is proposed for wireless broadcast application in this work. Our previous work investigated embedded space-time codes for layered media broadcast. In such a system, a transmitter sends out multi-layer source signals by encoding different layers with different space-time codes. Then, the receiver can retrieve a different amount of information depending on the number of antennas it has as well as the level of receiving power. The receiving terminals with one antenna can decode only the base layer information with a low complexity while terminals with more antennas can retrieve more layers of information. In this research, we further consider the case when the channel state information (CSI) is unknwon. The differential coding technique is adopted here. Transmitted symbols are encoded as a certain combination of previous symbols so that the receiver can retrieve the information without CSI. We explore the embedded design with differential STC to enable layered media transmission. Differential detection with Kalman filtering is also investigated to help improve performance.
An embedded space-time coding method is proposed for wireless broadcast applications. In the proposed system, a transmitter sends out multi-layer source signals by encoding different layers with different space-time codes. Then, the receiver can retrieve different amount of information depending on the number of antennas. The receiver with only one antenna can decode only the base layer information with a low complexity, while the receiver with more antennas can retrieve more layers of information. We derive an analytic bound on the error probability, and show both analytic and experimental results in this work.
KEYWORDS: Receivers, Antennas, Video, Remote sensing, Transmitters, Signal detection, Signal to noise ratio, Data compression, Video coding, Error analysis
A layered space-time coding (STC) system is proposed to transmit video signal over wireless channels. An input video sequence is compressed and data-partitioned into layers with different priorities. Then, unequal error protection is incorporated with the space-time block coding to provide different levels of protection to the different layers. At the receiver, a minimum mean square error (MMSE) detector with interference cancellation (IC) is combined with the space-time decoder to reconstruct the signal effectively. We derive the analytic performance for error probability, and conduct the simulation for the transmission of the H.263 video bitstream. It is shown that the unequal error protection enhances the PSNR performance up to 10 dB in moderate signal to noise ratio environment.
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