Showing papers on "Bandwidth expansion published in 2000"

Improved frame erasure concealment for CELP-based coders

Abstract: This paper describes new techniques for concealing frame erasures for CELP-based speech coders Two main approaches were followed: interpolative, where both past and future information are used to reconstruct the missing data, and repetition-based, where no future information is required Key features of the repetition-based approach include improved muting, pitch delay jittering, and LPC bandwidth expansion The interpolative approach can be employed in voice over IP scenarios at no extra cost in terms of delay Applied to the ITU-T G729 ACELP 8 kb/s speech coding standard, both interpolation- and repetition-based techniques outperform standard concealment in informal listening tests

Robust image communication using bandwidth reducing and expanding mappings

Abstract: Combined source-channel coding can be an efficient way to exploit a noisy channel for transmitting signals representing natural sources. In this paper, we propose a coding system for transmission of still images on a time discrete, amplitude continuous, additive white Gaussian noise channel. The coder is an extension of earlier work by Lervik and Ramstad (1996). We introduce a method for bandwidth expansion which gives extra protection to the most important symbols. An improvement of the PSNR up to 5 dB is demonstrated for the proposed coder compared to the reference coder.

Channel Coding Aspects in an OFDM-CDMA System

Abstract: | This paper investigates coding aspects in an OFDM-CDMA environment. The inherent bandwidth expansion in CDMA systems offers many possibilities for the application of powerful codes with low code rates. Three different coding strategies are under consideration: the combination of convolutional and repetition codes (conventional DS-CDMA system), a code-spread system consisting of one very low rate convolutional code, and a serial concatenation of convolutional, Walsh and repetition code. Analytical and simulation results turn out that the Walsh coded system is the best choice among the considered scenarios.

Coding of PPM based modulation techniques to improve the performance of infrared WLANs

Abstract: In this communication we consider the use of PPM based modulation methods, such as the hybrid modulation method called amplitude and pulse-position modulation (APPM) and overlapping pulse-position modulation (OPPM), to improve the performance of infrared WLANs. The bandwidth efficiency expressions of these modulation schemes are presented and compared against the one of pulse-position modulation (PPM), which allows to conclude that both APPM and OPPM can be used to improve the performance of PPM without significant bandwidth expansion, using trellis-coded modulation (TCM) codes. We also derive the best codes for some APPM and OPPM schemes, and the results show that non-negligible coding gains without bandwidth expansion can be obtained with trellis codes of moderate complexity.

Audio information processing system

Abstract: A tone-quality improving portion applies a bit expansion process, an oversampling process, and a bandwidth expansion process to audio information that is decoded by a decoder, and then supplies resultant information to a D/A converter. Accordingly, the audio information can be played back in high tone quality without complicating a configuration of the D/A converter.

Speech bandwidth expansion

Abstract: The present invention relates to a method for the band expansion of speech for telephones, in particular for mobile telephones, by increasing the effective sampling rate of the speech signal by the insertion of additional samples and subsequent filtering of the expanded bandwidth speech signal.

Delay estimation of code-spread CDMA systems

Abstract: Delay estimation of a code-spread code division multiple access (CS-CDMA) system using low-rate maximum free distance (MFD) convolutional codes for bandwidth expansion is studied. Using the repetitive structure of the low-rate MFD codes, the codewords are first permuted using a criterion based on the Cramer-Rao bound that results in good delay estimation properties. Thereafter, an approximate maximum-likelihood estimator that jointly estimate the channel gain, the codewords and the delay is used. Using the derived algorithm we show that it is in fact possible to estimate the delay in a code-spread system.

A novel approach to channel coding without bandwidth expansion

Abstract: This paper introduces a new block coding technique without bandwidth expansion. The proposed technique derives from the multiple access concept recently introduced to increase the number of users on a multiple access channel. The basic principle consists of time spreading the parity-check symbols to the block length using Walsh-Hadamard (WH) sequences and superimposing the resulting signals to the block of information symbols. The interference between the two groups of symbols is handled using an iterative detection/decoding technique whose operation resembles that of turbo decoders. Several code constructions are presented using very simple block codes. Performance of the proposed coding technique is evaluated by means of computer simulations. After observing that correlation of the intermediate decision errors in this iterative detection/decoding process limits the achievable performance, a block interleaver is introduced and is shown to substantially reduce the performance degradation due to interference between the serially transmitted symbols and the WH-spread symbols.