Secure voice for mobile satellite applications

The initial system studies are described which were performed at JPL on secure voice for mobile satellite applications. Some options are examined for adapting existing Secure Telephone Unit III (STU-III) secure telephone equipment for use over a digital mobile satellite link, as well as for the evolution of a dedicated secure voice mobile earth terminal (MET). The work has included some lab and field testing of prototype equipment. The work is part of an ongoing study at JPL for the National Communications System (NCS) on the use of mobile satellites for emergency communications. The purpose of the overall task is to identify and enable the technologies which will allow the NCS to use mobile satellite services for its National Security Emergency Preparedness (NSEP) communications needs. Various other government agencies will also contribute to a mobile satellite user base, and for some of these, secure communications will be an essential feature

Comparison of CELP speech coder with a wavelet method

This thesis compares the speech quality of Code Excited Linear Predictor (CELP, Federal Standard 1016) speech coder with a new wavelet method to compress speech. The performances of both are compared by performing subjective listening tests. The test signals used are clean signals (i.e. with no background noise), speech signals with room noise and speech signals with artificial noise added. Results indicate that for clean signals and signals with predominantly voiced components the CELP standard performs better than the wavelet method but for signals with room noise the wavelet method performs much better than the CELP. For signals with artificial noise added, the results are mixed depending on the level of artificial noise added with CELP performing better for low level noise added signals and the wavelet method performing better for higher noise levels

Joint Source-Channel CELP Coding

The method of speech coding CELP is extensively used in much voice communication-, multimedia-, video conference and other systems. There are a lot of papers related to CELP coding characteristics improvement for a better speech quality after decoding. Most of the papers are dedicated to lower the rate of CELP coded speech transmission. One problem related to low rate CELP speech transmission with a good speech decoding quality is noising in the channel for transmission. The goal of this paper is to combine the advantages and the possibilities of CELP speech coding to reduce the rate of transmission and the methods of channel coding to protect the most important CELP coding parameters in each speech frame such as line prediction coefficients, excitation indexes etc

Low bit rate speech coding methods and a new interframe differential coding scheme for line spectrum pairs

Ankara : Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 1992.Thesis (Master's) -- Bilkent University, 1992.Includes bibliographical references leaves 30-32.Low bit rate speech coding techniques and a new coding scheme for vocal tract parameters are presented. Linear prediction based voice coding techniques (linear predictive coding and code excited linear predictive coding) are examined and implemented. A new interframe differential coding scheme for line spectrum pairs is developed. The new scheme reduces the spectral distortion of the linear predictive filter while maintaining a high compression ratio.Erzin, EnginM.S

Quantisation mechanisms in multi-protoype waveform coding

Prototype Waveform Coding is one of the most promising methods for speech coding at low bit rates over telecommunications networks. This thesis investigates quantisation mechanisms in Multi-Prototype Waveform (MPW) coding, and two prototype waveform quantisation algorithms for speech coding at bit rates of 2.4kb/s are proposed. Speech coders based on these algorithms have been found to be capable of producing coded speech with equivalent perceptual quality to that generated by the US 1016 Federal Standard CELP-4.8kb/s algorithm. The two proposed prototype waveform quantisation algorithms are based on Prototype Waveform Interpolation (PWI). The first algorithm is in an open loop architecture (Open Loop Quantisation). In this algorithm, the speech residual is represented as a series of prototype waveforms (PWs). The PWs are extracted in both voiced and unvoiced speech, time aligned and quantised and, at the receiver, the excitation is reconstructed by smooth interpolation between them. For low bit rate coding, the PW is decomposed into a slowly evolving waveform (SEW) and a rapidly evolving waveform (REW). The SEW is coded using vector quantisation on both magnitude and phase spectra. The SEW codebook search is based on the best matching of the SEW and the SEW codebook vector. The REW phase spectra is not quantised, but it is recovered using Gaussian noise. The REW magnitude spectra, on the other hand, can be either quantised with a certain update rate or only derived according to SEW behaviours

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression

in a low bit-rate CELP speech coder *

The pitch filter in a low bit-rate CELP speech coder has a strong impact on the quality of the reconstructed speech. In this paper we propose a pseudo-multi-tap pitch filter with fewer degrees of freedom than the number of prediction coefficients, but which gives a higher pitch prediction gain and a more appropriate frequency response than a conventional one-tap pitch filter. First, we present an analysis model for the pseudo-multi-tap pitch prediction filter. Then, we introduce a pseudo-multi-tap pitch prediction filter with a fractional pitch lag. The prediction gain of the pseudo-multi-tap pitch filter is compared to that of conventional one-tap and three-tap pitch filters with integer and non-integer pitch lags. A switching configuration is also studied. This filter switches modes depending on the prediction gain. The stability of a pseudo-multi-tap pitch synthesis filter in a CELP coder is considered. We propose a stabilization method with a relaxed stability test. This relaxed test gives better results than a strict stability test. Finally, we have incorporated the pseudo-multi-tap pitch filter into a 4.8 kbit/s CELP speech coder. Both the objective SNR and subjective quality are better than for a conventional one-tap pitch filter. Zusammenfassung Das Sprachgrundfrequenzfilter in einem CELP-Sprachcoder mit geringer Bitrate iibt einen starken Einflul3 auf die rekonstruierte Sprache aus. In diesem Artikel schlagen wir ein pseudo-multi-tap (pseudo Polykoeffizienten