Continuous Decoding Research Articles

Fast decoding of LDPC codes using quantisation

A very fast quantised belief propagation algorithm is proposed for decoding low-density parity-check codes. This algorithm enables flexible quantisation schemes with low complexity and good performance near to or even better than that of continuous decoding. It can lower the error floor at high signal-to-noise ratios.

Scalable Internet video using MPEG-4

Real-time streaming of audio-visual content over Internet Protocol (IP) based networks has enabled a wide range of multimedia applications. An Internet streaming solution has to provide real-time delivery and presentation of a continuous media content while compensating for the lack of Quality-of-Service (QoS) guarantees over the Internet. Due to the variation and unpredictability of bandwidth and other performance parameters (e.g. packet loss rate) over IP networks, in general, most of the proposed streaming solutions are based on some type of a data loss handling method and a layered video coding scheme. In this paper, we describe a real-time streaming solution suitable for non-delay-sensitive video applications such as video-on-demand and live TV viewing. The main aspects of our proposed streaming solution are: 1. An MPEG-4 based scalable video coding method using both a prediction-based base layer and a fine-granular enhancement layer; 2. An integrated transport-decoder buffer model with priority re-transmission for the recovery of lost packets, and continuous decoding and presentation of video. In addition to describing the above two aspects of our system, we also give an overview of a recent activity within MPEG-4 video on the development of a fine-granular-scalability coding tool for streaming applications. Results for the performance of our scalable video coding scheme and the re-transmission mechanism are also presented. The latter results are based on actual testing conducted over Internet sessions used for streaming MPEG-4 video in real-time.

Novel algorithm for continuous decoding of turbo codes

A novel type of recursive algorithm for decoding turbo codes with a convolutional interleaver is proposed, based on a symbol-by-symbol maximum a posteriori probability algorithm. It requires only a forward recursion which can be performed in parallel, and the number of variables to be stored does not increase with decoding delay. This algorithm can be used in continuous decoding for both recursive and nonrecursive encoders. Simulation results of demonstrating its performance are presented.

Implementation and performance of a turbo/MAP decoder

The implementation and performance of a turbo/MAP decoder are described. A serial block MAP decoder operating in the logarithm domain is used to obtain a very-high-performance turbo decoder. Programmable gate arrays and EPROMs allow the decoder to be programmed for almost any code from four to 512 states, rate 1/3 to rate 1/7 (higher rates are achieved with puncturing) and interleaver block sizes to 65,536 bits. Seven decoding stages were implemented in parallel. For rate 1/3 and 1/7 16-state codes with an interleaver size of 65,536 bits and operating at up to 356 kbit/s the codec achieved an Eb/N0 of 0⋅32 and −0⋅30 dB respectively for a BER of 10−5. BERs down to 10−7 were also achieved for a small increase in Eb/N0. An efficient implementation of a continuous MAP decoder is also presented, along with a synchronization technique for turbo decoders. © 1998 John Wiley & Sons, Ltd.

Word hypothesizer for continuous speech decoding using stress-vowel centered bidirectional tree searches

A word hypothesis module for speech decoding consists of four submodules: vowel center detection, bidirectional tree searches around each vowel center, forward-backward pruning, and additional short words hypotheses. By detecting the strong energy vowel centers, a vowel-centered lexicon tree can be placed at each vowel center and searches can be performed in both the left and right directions, where only simple phone models are used for fast acoustic match. A stage-wise forward-backward technique computes the word-beginning and word-ending likelihood scores over the generated half-word lattice for further pruning of the lattice. To avoid potential miss of short words with weak energy vowel centers, a lexicon tree is compiled for these words and tree searches are performed between each pair of adjacent vowel centers. The integration of the word hypothesizer with a top-down Viterbi beam search in continuous speech decoding provides two-pass decoding which significantly reduces computation time.

Erasure-free sequential decoding of trellis codes

An erasure-free sequential decoding algorithm for trellis codes, called the buffer looking algorithm (BLA), is introduced. Several versions of the algorithm can be obtained by choosing certain parameters and selecting a resynchronization scheme. These can be categorized as block decoding or continuous decoding, depending on the resynchronization scheme. Block decoding is guaranteed to resynchronize at the beginning of each block, but suffers some rate loss when the block length is relatively short. The performance of a typical block decoding scheme is analyzed, and we show that significant coding gains over Viterbi decoding can be achieved with much less computational effort. A resynchronization scheme is proposed for continuous sequential decoding. It is shown by analysis and simulation that continuous sequential decoding using this scheme has a high probability of resynchronizing successfully. This new resynchronization scheme solves the rate loss problem resulting from block decoding. The channel cutoff rate, demodulator quantization, and the tail's influence on performance are also discussed. Although this paper considers only the decoding of trellis codes, the algorithm can also be applied to the decoding of convolutional codes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An efficient adaptive circular Viterbi algorithm for decoding generalized tailbiting convolutional codes

Viterbi decoding algorithms for convolutional codes are being considered for a number of applications in cellular mobile radio systems. There are three classes of Viterbi decoders depending on the nature of the formatting of the data: continuous decoding with a finite path memory, blockwise decoding with a terminating tail (known to the decoder), and blockwise decoding without a known tail. The latter class is also known as decoding of tailbiting convolutional codes. In this case, a coded message begins and ends in the same state which is unknown to the receiver. The authors present a class of Viterbi algorithms for tailbiting convolutional codes. These algorithms are used in blockwise transmission to save the overhead of a known tail. They call the new algorithm the circular Viterbi algorithm (CVA). The basic ideas are: (1) continue conventional seamless continuous Viterbi decoding beyond the block boundary by recording and repeating the received block of (soft) symbols; (2) start the decoding process in all states; and (3) end the decoding process either adaptively or with a fixed length. Three robust adaptive stopping rules are constructed and evaluated. Simulation results and comparison to previously known algorithms as well as the optimum algorithm are presented. The amount of computation required for previously reported iterative algorithms tends to increase dramatically as the channel bit error rate (BER) increases. In one reported instance, computation increased by over 900% while decoded BER increased from 8/spl times/10/sup /spl minus/6/ to 8/spl times/10/sup /spl minus/3/. For the same example, the CVA increase in computation was 11.4% and the worst case decoded BER was 4/spl times/10/sup /spl minus/3/. The authors conclude that for noisy channels the CVA decodes in a much shorter time with better performance than previously published iterative algorithms. >

Algorithms and architectures for continuous speech acoustic-phonetic decoding: Original French title: Algorithmes et architectures pour le décodage acoustico-phonétique de la parole continue

Algorithms and architectures for continuous speech acoustic-phonetic decoding: Original French title: Algorithmes et architectures pour le décodage acoustico-phonétique de la parole continue