Nam Ik Cho

Fast algorithm and implementation of 2-D discrete cosine transform

An algorithm for the fast computation of a 2-D discrete cosine transform (DCT) is presented. It is shown that the N*N DCT, where N=2/sup m/, can be computed using only N 1-D DCTs and additions, instead of using 2N 1-D DCTs as in the conventional row-column approach. Hence the total number of multiplications for the proposed algorithm is only half of that required for the row-column approach and is also less than that of most of other fast algorithms, whereas the number of additions is almost comparable to that of others. It is also shown that only N/2 1-D DCT module are required for hardware parallel implementation of the proposed algorithm. Thus the number of actual multipliers being used is only a quarter of that required for the conventional approach. >

On the adaptive lattice notch filter for the detection of sinusoids

A lattice notch filter for the detection and enchancement of sinusoids in noise is presented, and the convergence properties of the algorithm are investigated using ODE (ordinary differential equation) analysis. It is shown that the frequency estimate of the algorithm for a single sinusoid is unbiased, regardless of the pole-zero contraction factor and the noise variance. An expression for the MSE (mean square error) of the frequency estimate and the output SNR of the algorithm is derived. Simulation results are presented to verify the theoretical analysis. Based on cascading the proposed second-order adaptive notch filter, three different approaches for the detection of multiple sinusoids are presented. The first approach uses a linear cascade structure, and the second and third approaches use a triangular cascade structure. The performance of the algorithms for multiple sinusoids is investigated, and computer simulation results are presented and discussed. >

Improved linear soft-input soft-output detection via soft feedback successive interference cancellation

We propose an improved minimum mean square error (MMSE) vertical Bell Labs layered space-time (V-BLAST) detection technique, called a soft input, soft output, and soft feedback (SIOF) V-BLAST detector, for turbo multi-input multioutput (turbo-MIMO) systems. We derive a symbol estimator by minimizing the power of the interference plus noise, given a priori probabilities of undetected layer symbols and a posteriori probabilities for past detected layer symbols. For a low-complexity implementation, an approximate SIOF algorithm is presented, which allows for a time-invariant realization of the symbol ordering and an MMSE filtering process. Another implementation, referred to as the iterative SIOF algorithm is introduced, which decides on symbol detection order based on a posteriori symbol probabilities to improve the detection performance. Simulations performed on a space-time bit-interleaved coded modulation (STBICM) architecture over quasi-static MIMO fading channels demonstrate that the SIOF V-BLAST detector provides performance gains over previous turbo-BLAST detectors, most notably when more transmit antennas are used.

DCT algorithms for VLSI parallel implementations

Two algorithms are presented for computing the discrete cosine transform (DCT) on existing VLSI structures. First, it is shown that the N-point DCT can be implemented on the existing systolic architecture for the N-point discrete Fourier transform (DFT) by introducing some modifications. Second, a new prime factor DCT algorithm is presented for the class of DCTs of length N=N/sub 1/*N/sub 2/, where N/sub 1/ and N/sub 2/ are relatively prime and odd numbers. It is shown that the proposed algorithm can be implemented on the already existing VLSI structures for prime factor DFT. The number of multipliers required is comparable to that required for the other fast DCT algorithms. It is shown that the discrete sine transform (DST) can be computed by the same structure. >

Adaptive line enhancement by using an IIR lattice notch filter

Two simple methods for retrieving a single sinusoid corrupted with noise are proposed. They are based on the lattice form realization of an adaptive infinite-impulse-response (IIR) notch filter. The IIR filter is a cascade of second-order all-pole and all-zero filters, and the coefficients of the finite-impulse-response (FIR) section are adapted. The proposed algorithms keep the poles of the filter inside the unit circle. The computer simulation results show that the algorithms have considerable potential in adaptive notch filter applications, especially when the input signal-to-noise ratio is low. >

A fast 4*4 DCT algorithm for the recursive 2-D DCT

The authors present an efficient algorithm for the computation of the 4*4 discrete cosine transform (DCT). The algorithm is based on the decomposition of the 4*4 DCT into four 4-point 1-D DCTs. Thus, only 1-D transformations and some additions are required. It is shown that the proposed algorithm requires only 16 multiplications, which is half the number needed for the conventional row-column method. Since the 2/sup m/*2/sup m/ DCT can be computed using the 4*4 DCT recursively for any m, the proposed algorithm leads to a fast algorithm for the computation of the 2-D DCT. >

Panorama Mosaic Optimization for Mobile Camera Systems

In order to enable the real-time image mosaic in mobile devices that have very limited computing power and memory, we propose an efficient image mosaic algorithm with integer arithmetic. The proposed algorithm is focused not only on the computational efficiency, but also on the performance improvement of image mosaic. For the efficient projection without transform estimation, we obtain successive images through the semitransparent view finder which shows the fixed amount of right part of previously captured image. We project each images onto cylindrical surface by the proposed projection equation and integer arithmetic. We align the projected images by hierarchical hexagon search and a matching measure that is robust to illumination changes caused by different exposures and vignette distortion. Finally, the images are naturally blended using color compensation and dynamic programming based stitching. The proposed mosaic algorithm is embedded and tested in mobile phone systems. According to various tests and experiments, the proposed algorithm shows good panorama composition in real-time compared with the other PC-based methods.

Fixed-point error analysis of CORDIC processor based on the variance propagation formula

This paper presents a fixed-point mean-square error (MSE) analysis of coordinate rotation digital computer (CORDIC) processors based on the variance propagation method, whereas the conventional approaches provide only the error bound which results in large discrepancy between the analysis and actual implementation. The MSE analysis is aimed at obtaining a more accurate analysis of digital signal processing systems with CORDIC processor, especially when the design specification is given by the signal-to-noise ratio or MSE. For the MSE analysis, the error source and models are first defined and the output error is derived in terms of MSE in the rotation mode of the conventional CORDIC processor. It is shown that the proposed analysis can also be applied to the modified CORDIC algorithms. As an example of practical application, a fast Fourier transform processor using the CORDIC processor is presented in this paper, and its output error variance is analyzed with respect to the wordlength of CORDIC. The results show a close match between the analysis and simulation.

Intra prediction method based on the linear relationship between the channels for YUV 4∶2∶0 intra coding

In general, the transformation from RGB to YUV color space reduces the correlation between the channels. But some sources in the YUV space still have strong inter-channel correlation, which can be modeled as a linear function. Based on this linear model, we propose a new intra chrominance prediction method for color image compression in YUV 4∶2∶0 color space. A block of chrominance pixels to be encoded is predicted from the reconstructed luminance signal using the proposed prediction scheme and the residual is encoded based on the H.264/AVC. Also, an implicit prediction method that can obviate the transmission of side information is proposed. The experimental results show that there are about 0.35∼1.0dB gains for the luminance (Y) channel, and 0.5∼3.0dB gains for the chrominance (Cb or Cr) channels at the medium to high bit-rates. The proposed method also shows some gains at the low bit-rates.

Suppression of narrow-band interference in DS-Spread spectrum systems using adaptive IIR Notch filter

This paper proposes an algorithm for the suppression of narrow-band interference in direct sequence spread spectrum systems, based on the open-loop adaptive IIR notch filtering. In the open-loop notch filtering schemes, it is assumed that the frequency and power estimates are given or obtained by time-frequency analysis of input signal. In this paper, we estimate the frequency and power of the interference by using the adaptive lattice IIR notch filter. Another lattice IIR notch filter of the same structure is placed in front of the receiver, the notch of which is controlled by the frequency estimate in order to remove the interference. However, since the conventional IIR notch filters have zeros constrained on the unit circle, they also remove the information signal at the notch frequency while removing the interference at the same time. Hence, we adjust the depth of the notch with respect to the interference power, for the trade-off between data distortion and interference reduction. The objective function for adjusting the depth of the notch is defined as the overall signal to noise ratio (SNR). The SNR is expressed as a function of filter parameters, and the notch depth that maximizes the SNR is found. Simulation results show that the proposed algorithm yields comparable or better performance than the open-loop FIR notch filter, conventional FIR LMS, and nonlinear adaptive filters with long taps.