Hardware optimizations of variable block size hadamard transform for H.264/AVC FREXT

Variable block size (VBS) transform technique is adopted in Fidelity Range Extensions (FRExt) of H.264/AVC, in which 8 x 8/4 x 4 Hadamard transforms are adaptively employed during the fractional motion estimation. The hardwired VBS Hadamard transform unit is developed by authors and the following contributions are described in this literature: (1) Hardware reusing scheme is adopted in the architecture design; (2) In the light of the noise analysis, the intermediate data bit-truncation scheme is developed to reduce the hardware cost while maintaining its computational precision well; (3) With mathematical analysis, the bit-width of SATD value is reduced as compared to the intuitive implementation, therefore, the power and hardware cost are both optimized for the SATD generator implementation; (4) Hybrid 4:2/3:2 compressor based CSA tree is analyzed in the circuits design of SATD generator; and (5) Clock-gating technique is employed to reduce the power dissipation of 4x4 transform operation. With TSMC 0.18μm CMOS technology, experimental results reveal that 12.2-30.4% saving in hardware cost and 12.4-32.4% saving in power consumption are achieved by using our algorithms.