| Summary: | 博士 === 國立交通大學 === 電子工程系所 === 96 === The design of power constrained video coding systems has drawn attentions in mobile devices or portable terminals due to the limited battery energy. Among the power constrained video coding applications, low power and power adaptive designs are two of the most attractive design topics. Inside the video coding system, motion estimation (ME) takes most of computation powers, and becomes the design bottleneck of the low power and power adaptive video coding systems. This thesis contains 2 major parts to address the design issues of low power and power adaptive motion estimation.
The first part is to propose a new Low Power-All Binary Motion Estimation (LP-AMBE) hardware design for motion estimation to achieve low power and bus bandwidth efficiency. Low power and high bus bandwidth efficiency are the two key issues for portable video applications. To address such issues, we first study an efficient algorithm called all binary motion estimation (ABME), and analyze its architecture issues in operational flow and bus access. Then, we propose an hardware architecture for ABME with four new features (1) macroblock level pre-processing (2) efficient binary pyramid search structure (3) parallel processing of 8x8 and 16x16 block searches (4) parallel processing of bi-directional search. Such architecture leads to a superior performance in bus access, speed and power. The experiments show that the power consumption is as low as 763uW for IPPPP CIF 30fps and 896uW for IPBPB CIF 30fps. The bus bandwidth savings are 54.3% for P-frame search and 67.1% for B-frame search.
The second part is to propose a new Power Adaptive Iterative Binary Search (PA-IBS) design for motion estimation to improve the power adaptation performance. In the prior power adaptive ME designs that use the hardware masking approach, there exist design overheads such as redundant bus access, unnecessary on-chip memory access, and poor hardware utilization that lead to poor power adaptation performance. Our proposed power adaptive solution addresses these issues with a new ME algorithm called Iterative Binary Search (IBS) and the associated hardware architecture called PA-IBS. The IBS uses eight binary searches where each search can be either an independent search or one of the eight joint searches. Hence, redundant bus and on-chip memory access are eliminated. A Content Adaptive Mechanism (CAM) is used to dynamically select the number of iterations on a macroblock basis. The PA-IBS uses the frequency scaling technique to provide a link between the number of iterations and the power consumption level. Therefore, it reduces hardware idling and enhances hardware utilization. Experiments show that the PA-IBS delivers lower peak power consumption, better power adaptation performance and lower bus bandwidth requirement as compared to the prior hardware masking based designs such as sub-sampling or least significant bits truncation methods. As compared to those approaches, the power adaptation performance is improved up to 19-125% and bus bandwidth is saved up to 87.5%.
In conclusion, we have presented two algorithm and architecture designs of motion estimation for different power constrained video coding applications, and showed the advantages in low power consumption and bus bandwidth requirements as compared to prior works. The proposed power adaptive design is also shown to have better power adaptation ability and better power-distortion performance. Moreover, the proposed low power and power adaptive ME designs can be applied to upcoming Scalable Video Coding (SVC) standard for further complexity and power reduction.
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