S.C. Kwatra

An efficient decoding algorithm for block turbo codes

An efficient soft-input soft-output iterative decoding algorithm for block turbo codes (BTCs) is proposed. The proposed algorithm utilizes Kanekos (1994) decoding algorithm for soft-input hard-output decoding. These hard outputs are converted to soft-decisions using reliability calculations. Three different schemes for reliability calculations incorporating different levels of approximation are suggested. The algorithm proposed here presents a major advantage over existing decoding algorithms for BTCs by providing ample flexibility in terms of performance-complexity tradeoff. This makes the algorithm well suited for wireless multimedia applications. The algorithm can be used for optimal as well as suboptimal decoding. The suboptimal versions of the algorithm can be developed by changing a single parameter (the number of error patterns to be generated). For any performance, the computational complexity of the proposed algorithm is less than the computational complexity of similar existing algorithms. Simulation results for the decoding algorithm for different two-dimensional BTCs over an additive white Gaussian noise channel are shown. A performance comparison of the proposed algorithm with similar existing algorithms is also presented.

An Adaptive Algorithm for Motion Compensated Color Image Coding

This paper presents an adaptive algorithm for motion compensated color image coding. The algorithm can be used for video teleconferencing or broadcast signals. Activity segmentation is used to reduce the bit rate and a variable stage search is conducted to save computations. The adaptive algorithm is compared with the nonadaptive algorithm and it is shown that with approximately 60 percent savings in computing the motion vector and 33 percent additional compression, the performance of the adaptive algorithm is similar to the nonadaptive algorithm. The adaptive algorithm results also show improvement of up to 1 bit/pel over interframe DPCM coding with nonuniform quantization. The test pictures used for this study were recorded directly from broadcast video in color.

Analysis of puncturing pattern for high rate turbo codes

Turbo codes have performance superior than all other coding techniques. The main factors that make turbo codes so efficient include, parallel concatenation structure of the encoding system, recursive convolutional encoder, interleaver, puncturing pattern and iterative decoding. In this research, we have investigated the effect of the puncturing pattern on the performance of high rate turbo codes. Based on simulation results, we claim that for most of the code rates, when a pseudo random interleaver is applied, the selection of puncturing pattern does not have significant effect on the code performance. However, for some rates, a commonly used puncturing patterns does cause much poorer performance. For these rates, a modified puncturing pattern is proposed which restores the performance back to the Shannon limit.

A VLSI architecture for real-time image coding using a vector quantization based algorithm

Digital image coding using vector quantization (VQ) based techniques provides low-bit rates and high quality coded images, at the expense of intensive computational demands. The computational requirement due to the encoding search process, had hindered application of VQ to real-time high-quality coding of color TV images. Reduction of the encoding search complexity through partitioning of a large codebook into the on-chip memories of a concurrent VLSI chip set is proposed. A real-time vector quantizer architecture for encoding color images is developed. The architecture maps the mean/quantized residual vector quantizer (MQRVQ) (an extension of mean/residual VQ) onto a VLSI/LSI chip set. The MQRVQ contributes to the feasibility of the VLSI architecture through the use of a simple multiplication free distortion measure and reduction of the required memory per code vector. Running at a clock rate of 25 MHz the proposed hardware implementation of this architecture is capable of real-time processing of 480*768 pixels per frame with a refreshing rate of 30 frames/s. The result is a real-time high-quality composite color image coder operating at a fixed rate of 1.12 b per pixel. >

A New Technique for Monitoring Heart Signals-Part I: Instrumentation Design

A new noninvasive method for obtaining the human electrocardiogram is investigated in this paper. The proposed technique uses a composite conductive medium formed by the patients body and the external liquid medium such as tap water in a bathtub. In this Part I of a two part paper, the emphasis is on the instrumentation design. An in-depth study of the frequency characteristics of the liquid medium interface with the sensing electrodes and the electronic instrumentation system is also presented. Filtering and amplifying circuitry is designed to obtain ECG signals from the noisy bathtub signals. This improves the signal-to-noise ratio from approximately -20 to about 40 dB while amplifying the signal level from 0.1 mV to 1 V. In Part II, signal processing techniques are developed to extract the standard orthogonal leads from the bathtub signals.

An analysis of the MPSK scheme with differential recursive detection (DRD)

A differential recursive detection (DRD) technique for multiple phase shift keying (MPSK) is proposed, and its performance is analyzed and computer simulated. By combining the multiple-symbol differential detection algorithm with conventional (one-symbol) differential detection, based on maximum-likelihood estimation for a multisymbol observation interval, it is possible to construct a recursive algorithm with a much simpler structure and comparable performance in error rate. Results from computer simulation show 1.25 dB, 2 dB, and 2.55 dB gain over conventional differential detection for the input symbol sequence length of N=3, 5, and 10, respectively, at a bit error rate of 10/sup -5/ in additive white Gaussian noise. For N of more than 10, the performance of DRD is close to that of ideal coherent detection for the differentially encoded signal.<<ETX>>

A New Technique for Monitoring Heart Signals-Part II: Orthogonal Lead Extraction

In Part I, instrumentation design is given for recording ECG signals from a home bathtub setup. In Part II, it is asserted that these bathtub signals are the projections of the heart dipole vector. This assertion is tested and the corresponding coefficients of the projection matrix are computed by monitoring the bathtub ECG signals for a subject as well as his orthogonal X, Y, Z leads on a PDP-9 computer. The least-squares estimation technique is used to determine the projection matrix. To compensate for the magnitude and phase distortion of the bathtub ECG signals, suitable digital as well as analog compensators are designed. A comparison of orthogonal leads extracted from bathtub leads and similar leads obtained from the HP1520A vectorcardiograph is given for five different subjects. It is shown that the average standard deviation obtained for these five subjects is 12.6 percent.

Low-complexity subband encoding for HDTV images

The transmission of high-definition television (HDTV) signals on available digital networks and satellites requires the adoption of sophisticated compression techniques to limit the bit rate requirements and to provide high-quality and reliable service to customers. For processing and transmission of image signals, a low-complexity codec without visible degradation is desired. A low-complexity intraframe subband image coding algorithm is developed. The low band is DPCM encoded and the high bands are PCM encoded. An efficient entropy coder is designed which reduces the overall bit rate significantly. It is shown that high-quality HDTV images can be obtained at as low a bit rate as 45 Mb/s or less with a very low-complexity encoder. For dividing the image into subbands, a new class of quadrature mirror filters (QMFs) called generalized quadrature mirror filters (GQMFs) is used for filtering. Performance is also evaluated by using short kernel filters (SKFs), which are easy to implement and require very few computations. >

LSB coded 8PSK signals

An 8PSK scheme with the least significant bit (LSB) Golay coded is proposed and its performance is analyzed. With hard decision decoding, the proposed scheme can achieve 1 dB asymptotic coding gain and also save 26% bandwidth, as compared with uncoded QPSK scheme. >

Low complexity video compression algorithm using AMBTC

A computationally simple algorithm for video compression is presented in this paper. The algorithm gives excellent quality image sequence reconstruction at a peak-signal-to-noise-ratio (PSNR) of approximately 37 decibels (dB) and a very low bit rate of 0.2 bits-per-pixel (bpp). The scheme utilizes absolute moment block truncation coding (AMBTC) for intraframe coding, in conjunction with a three step algorithm for block based motion compensation, and a simple quantization scheme for interframe error coding. The procedural steps in the algorithm are very similar to the MPEG standard, which can facilitate the implementation of the proposed algorithm in the existing infrastructure. The results of the simulations performed on three different image sequences depicting different amounts of motion and background activity are presented. The qualitative and quantitative comparisons of the proposed algorithm, with an existing video compression standard and with other similar research are presented. The significant advantage gained in terms of computational complexity and the probable use of the algorithm for progressive transmission of video is illustrated. The modifications of the basic algorithm are also presented in this paper.