Showing papers by "M. Omair Ahmad published in 2003"

A low-power systolic array-based adaptive Viterbi decoder and its FPGA implementation

Abstract: In this paper, the design and FPGA implementation of a low-power adaptive Viterbi decoder with a constraint length of 9 and code rate of 1/2 is presented. In this design, a novel systolic array-based architecture with time multiplexing and arithmetic pipelining for implementing the adaptive Viterbi algorithm is used. A scheme for providing a tolerance to clock-to-data skew to avoid timing violation is proposed. A process of eliminating spurious toggles, for reducing power consumption, is also developed. It is shown that the total power consumption in the implementation of the adaptive algorithm can be reduced by up to 43% compared to that in the implementation of a corresponding non-adaptive Viterbi algorithm, with a negligible increase in the hardware.

A continuous tracking algorithm for long-term memory motion estimation.

Abstract: It is known that long-term memory motion estimation can bring a significant coding gain to a video coding system. In this paper, a fast algorithm for long-term memory motion estimation is presented. The proposed algorithm attempts to track the direction of the best long-term motion vector in a frame-by-frame manner from the most recent reference frame to the oldest reference frame. Nine direction patterns for the direction tracking are used and the search locations of the long-term memory motion estimation are adaptively selected according to the chosen direction pattern. Simulation results demonstrate that the proposed algorithms can speed up long-term motion estimation by more than 40 times.

Region-wise motion compensation technique using enhanced motion vectors

Abstract: Despite the fact that the existing region-wise motion compensation techniques (RWMC) are more efficient than the conventional variable size block motion compensation technique, they still do not use the visual characteristic of a frame in terms of brightness, contrast and sharpness in order to determine the motion information of the partitioned regions in a most efficient manner. The objective of this paper is to present a quad-tree structured region-wise motion compensation technique using enhanced motion vectors. The scheme described in this paper uses the brightness information of a frame in order to reach the objective of having motion vectors with a higher accuracy. Even though using enhanced motion vectors reduces the distortion, it causes the bit rate to increase. This poses the challenge of optimizing the bit rate-distortion performance. The proposed method partitions a frame based on a fine to coarse resolution strategy through the merging and combining processes. The merging process permits 4-to-1, 3-to-1 and 2-to-1 merges. For such merges, the main idea is to minimize the distortion subject to the constraint that the bit rate should not exceed a pre-defined value. The combining process further reduces the total number of partitioned regions by combining some of the regions that have the same enhanced motion vectors. The proposed technique uses a 2-bit code for coding the quad-tree structure while two different code lengths encode the enhanced motion vectors of the partitioned regions depending on the differential brightness threshold value. The proposed method is applied to a number of video sequences and compared with the other existing methods. The test results show that the new method can significantly improve the rate-distortion performance.