Yu-Hao Chen

Dual-Mode Low-Complexity Codebook Searching Algorithm and VLSI Architecture for LTE/LTE-Advanced Systems

Codebook is a useful precoding technique for bandwidth limited systems because only few bits are required to feedback channel information. Many researchers propose several codebook selection criteria for linear receivers. However, these selection criteria are very computationally intensive, and most of them are not feasible for aperiodic feedback reporting in both LTE and LTE-Advanced (LTE-A) systems. Under the limited processing hardware and feedback delay constraints, low-complexity receivers with efficient codebook selection scheme are desirable. In this work, a low-complexity codebook searching engine is proposed to support both LTE and LTE-A operations. Also, it can be operated for both aperiodic and periodic feedback reporting. The properties and mutual correlations of the LTE and LTE-A codebooks are firstly analyzed. Then, a low-complexity grouping FFT-based codebook searching algorithm is proposed, which can be shared by LTE and LTE-A systems. Since the proposed algorithm is an algorithmic transformation, there is no performance loss. The proposed schemes have significant effect of reducing the number of multiplications by 56% compared with referenced works. Finally, a dual-mode low-complexity codebook searching engine with TSMC 90 nm is implemented. The IP size is 2.2 mm2 and the equivalent gate count is 547.6 K. The operating frequency is 125 MHz.

VLSI implementation of real-time motion compensated beamforming in synthetic transmit aperture imaging

Synthetic transmit aperture (STA) has been widely investigated in ultrasound system recently due to its high frame rate and low cost characteristics. Since the high-resolution image (HRI) of STA is formed by summation of low-resolution images (LRIs), it is susceptible to motion between firings. In this work, we propose a low-complexity two-dimensional motion compensation algorithm. The velocity and direction of motion can be evaluated by cross-correlation between specific beams according to geometry characteristics of STA. Compared to the uncompensated image, simulation results which used Field II program show that proposed method can improve the contrast ratio (CR) and contrast noise ratio (CNR) about 8.6 dB and 1.3 dB. The whole imaging system was implemented in TSMC 90nm technology. Operating at 125 MHz, the circuit with 11% hardware overhead for motion compensation can beamform 64 image lines consisting of 1024 complex samples at the rate of 45 frames per second.

Coherent Image Herding of Inhomogeneous Motion Compensation for Synthetic Transmit Aperture in Ultrasound Image

Synthetic transmit aperture (STA) has been extensively used in ultrasound system recently because of its high frame rate and high image quality. However, STA is susceptible to motion artifacts. Some studies have proposed strategies to overcome this problem, but the image quality still degrades in inhomogeneous motion environment, which means that tissue moves in different directions and speed. In this work, we propose the coherent image herding (CIH) method to form high resolution image (HRI) with better image quality by determining whether the compensated low resolution image (LRI) needs to be chosen to form better HRI and subsequently performing a cross-correlation analysis on the raw channel data between the selected LRIs. In simulation results, the proposed method can obtain better HRI in the inhomogeneous motion environment, and it improves the contrast ratio (CR) and contrast noise ratio (CNR) about 9.5 dB and 1.5 dB respectively with only 0.71% computational complexity larger than the referenced work in the cyst phantom simulation using Field II program.

Estimating two-dimensional angles of arrival in coherent source environment

Estimating the two-dimensional (2-D) angle of arrival for radiating sources in a coherent environment is studied. The concept of spatial smoothing is first extended to a rectangular planar array, and a 2-D search function is formed to estimate the source directions. To avoid performing a 2-D search, an approach based on two one-dimensional (1-D) searches is also discussed. This approach uses rows and columns of the rectangular array to perform 1-D searches. To match the data obtained, a 2-D verification is then performed. Computer simulation results for both approaches based on the MUSIC method are presented.<<ETX>>

Low-Complexity Motion-Compensated Beamforming Algorithm and Architecture for Synthetic Transmit Aperture in Ultrasound Imaging

Synthetic transmit aperture (STA) has been widely investigated in ultrasound system recently with characteristics of high frame rate and low hardware cost. Since the high-resolution image (HRI) of STA is formed by summation of low-resolution images (LRIs), it is susceptible to inter-firing motions. In this paper, we propose a low-complexity global motion compensation algorithm. We use the common region of interest (ROIcom) between different transmissions of STA imaging to beamform backward and forward beam vectors. Then, the magnitude and direction of motion can be evaluated by cross-correlations between specific beam vectors in STA imaging. Compared with the uncompensated image in two-dimentional (2D) motion environment, the proposed motion compensation algorithm can improve the contrast ratio (CR) and contrast-to-noise ratio (CNR) by 13.73 and 2.04 dB, respectively. Also, the proposed algorithm improves the CR and CNR about 7.84 and 1.36 dB comparing with the reference work, respectively. In the Field II breath model, the proposed method also improves the CR and CNR about 6.65 and 1.04 dB than the reference method, respectively. Moreover, we propose a low-complexity delay generator in the architecture design to further reduce the computational complexity of the whole beamforming system. Finally, we verify the proposed low-complexity motion compensation beamforming engine by using the VLSI implementation with CMOS 90 nm technology. In the post-layout result, the core size is 2.39 mm2 at 125 MHz operating frequency and the frame rate of the beamforming system is 42.23 frames per second.

Accelerating motion-compensated adaptive color Doppler engine on CUDA-based GPU platform

Color Doppler imaging is used to observe the blood flow distribution during doctors diagnosis. However, the desired blood signal is greatly affected by clutter noise and probe motions. In previous works, a color Doppler engine was proposed consisting algorithms which can effectively eliminate clutter noises and motion artifacts. Since a large number of data and computations are involved, the color Doppler engine cannot achieve real-time imaging on CPU-based PCs. Therefore, we accelerate the color Doppler engine by parallelizing the executions on many-core GPU. In this work, we explore the parallelism and data locality of the motion-compensated color Doppler algorithms, and implement it on CUDA-based GPU platform. The speedup can be up to 55.5 by using the proposed design methodology.

Motion artifact elimination algorithm with eigen-based clutter filter for color Doppler processing

Color Doppler imaging is used to visualize the distribution of blood flow in the region of interest. Slight relative motion may cause severe image corruption and incorrect blood velocity estimation. In this work, we propose a velocity bias cancellation algorithm based on the autocorrelation technique widely used in color Doppler and eigen-based clutter filter to eliminate the motion artifact. The proposed algorithm assists clutter filter to suppress tissue noises effectively and compensates the biased blood velocity. It has more than 3-9 dB better performance and the error of blood velocity estimation can be reduced by more than 69%.

High-throughput QC-LDPC decoder with cost-effective early termination scheme for non-volatile memory systems

This paper presents a high-throughput layered min-sum quasi-cyclic LDPC (QC-LDPC) decoder for non-volatile memory systems (NVMs). A cost-effective column-based early termination (CB-ET) scheme is proposed to early terminate decoding process within iteration. The throughput improvement is 37.7% compared to the state-of-the-art early termination scheme when raw bit error rate of flash memory is 3×10-3. The QC-LDPC decoder with proposed early termination scheme is synthesized by TSMC 90nm CMOS technology, and the area overhead is only 2.20%.

Motion-tracking adaptive persistence and adaptive-size median filter for color Doppler processing in ultrasound systems on multicore platform

Color Doppler processing in the ultrasound imaging systems is mainly used to observe the blood flow in the region of interest. The desired blood signal will be greatly affected by the speckle noises, and the major design issues are to eliminate these kinds of noises effectively. In this work, we propose the time-domain (1) motion-tracking adaptive persistence and spatial-domain (2) adaptive-size median filter for effectively eliminating the speckle noises, respectively. The proposed two filters have individually 2~3 dB better performance than the referenced algorithms, and the proposed adaptive de-speckle filters can also work together in the same system to obtain even better performances. At last, the proposed signal-processing algorithms are implemented on the multi-core platform, and the property of parallel processing significantly accelerates the computation.