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Time evolution in LPC spectrum coding

IEEE TRANSACTIONS ON SPEECH AND AUDIO PROCESSING 2004年第3期12卷 290-301页

作者： Nordén, F Eriksson, T Aalborg Univ Dept Commun Technol DK-9220 Aalborg Denmark Chalmers Univ Technol Dept Signals & Syst S-41296 Gothenburg Sweden

Many current speech coders use a source-filter model in which the signal is decomposed on a frame-wise basis into an excitation component and a filter component. The filter component is then parameterized and coded by a separate spectrum encoder. The performance of such spectrum encoders is often evaluated in terms of a spectral distortion measure that treats each frame independently. Doing this therefore neglects the time evolution of quantization errors. In this paper, we focus on the time evolution of spectrum vectors in speech spectrum coding. We show that the human auditory system prefers a slowly evolving spectrum quantization noise, resulting in smooth spectrum trajectories. This result is the basis for a new distortion criterion for spectrum coding which introduces interframe memory into the standard spectral distortion measure, thereby having the ability to penalize a poor spectrum evolution. Further, a number of coding schemes for explicit spectrum evolution control are evaluated, and we show gains in the order of 2-4 bits, compared to schemes with no evolution control.

关键词： perception spectral distortion spectrum coding speech coding time evolution

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Memory-based vector quantization of LSF parameters by a power series approximation

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IEEE TRANSACTIONS ON AUDIO SPEECH AND LANGUAGE PROCESSING 2007年第4期15卷 1146-1155页

作者： Eriksson, Thomas Norden, Fredrik Chalmers Dept Signals & Syst S-41296 Gothenburg Sweden Imego AB S-41133 Gothenburg Sweden

In this paper, memory-based quantization is studied in detail. We propose a new framework, power series quantization (PSQ), for memory-based quantization. With linear spectral frequency (LSF) quantization as the application, several common memory-based quantization methods (FSVQ, predictive VQ, VPQ, safety-net, etc.) are analyzed and compared with the proposed method, and it is shown that the proposed method performs better than all other tested methods. The proposed PSQ method is fully general, in that it can simulate all other memory-based quantizers if it is allowed unlimited complexity.

关键词： memory-based quantization spectrum coding speech coding vector quantization (VQ)

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Channel optimized predictive vector quantization

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IEEE TRANSACTIONS ON SPEECH AND AUDIO PROCESSING 2000年第4期8卷 370-384页

作者： Lindén, J Chalmers Univ Technol Dept Signals & Syst SE-41296 Gothenburg Sweden

The objective of this work is to investigate how channel optimization techniques ran be applied to predictive vector quantizers. In particular, an efficient encoder search procedure and two design methods are derived. The design methods proposed here, one sample iterative and one block iterative, simultaneously optimize the predictor and the codebook, Extensive simulations show the advantage of this quantization method compared to other memory based quantization schemes as well as memoryless VQ, We also demonstrate that the design methods can be used to obtain index assignments that are advantageous to what is obtained by post process index assignment algorithms.

关键词： channel optimized vector quantization index assignment noisy channels predictive vector quantization spectrum coding vector quantization

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A hybrid spreading/despreading function with good SNR performance for band-limited DS-CDMA

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 1996年第8期14卷 1576-1582页

作者： Yu, L Salt, JE TELECOMMUN RES LABS SASKATOONSK S7N 0W0CANADA

The efficiency of a direct-sequence spread-spectrum code-division multiple-access (DS-CDMA) system depends heavily on the shape of the spectrum of the spread signal. Maximum efficiency is obtained with an ideal brick-wall bandpass spectrum. There are two approaches toward achieving such a spectrum. One is to use a simple spreader that produces a broad spectrum and then follow it with a precise, high order filter to band limit the spectrum. A second approach, which is the approach taken in this paper, is to use a spreader that produces a spectrum close to the ideal spectrum and then employ a simple fitter to control the out-of-band power. The proposed spreader/despreader is based on a simple hybrid function and can be easily implemented. An analysis provides a compact expression for the signal-to-noise ratio (SNR) of a RAKE receiver. The expression includes the effects of baseband, intermediate frequency (IF) and RF filtering as well as the effects of the spectral densities of the spreading/despreading functions. The analysis shows that the proposed spreader/despreader yields superior performance over a conventional pseudo noise (PN) spreading/despreading mechanism.

关键词： Spectra Direct-sequence code-division multiple access direct sequence spread spectrum spectrum coding Intermediate frequencies telecommunication services Spreaders RAKE receivers Code division multiple access Spectral density

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Bounded support Gaussian mixture modeling of speech spectra

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IEEE TRANSACTIONS ON SPEECH AND AUDIO PROCESSING 2003年第1期11卷 88-99页

作者： Lindblom, J Samuelsson, J Chalmers Univ Technol Informat Theory Grp Gothenburg Sweden

Lately, Gaussian mixture (GM) models have found new applications in speech processing, and particularly in speech coding. This paper provides a review of GM based quantization and prediction. The main contribution is a discussion on GM model optimization. Two previously presented algorithms of EM-type are analyzed in some detail, and models are estimated and evaluated experimentally using theoretical measures as well as GM based speech spectrum coding and prediction. It has been argued that since many sources have a bounded support, this should be utilized in both the choice of model, and the optimization algorithm. By low-dimensional modeling examples, illustrating the behavior of the two algorithms graphically, and by full-scale evaluation of GM based systems, the advantages of a bounded support approach are quantified. For all evaluation techniques in the study, model accuracy is improved when the bounded support approach is adopted. The gains are typically largest for models with diagonal covariance matrices.

关键词： bounded support cepstrum EM expectation maximization Gaussian mixture modeling (GMM) spectrum coding spectrum prediction speech coding speech spectrum vector quantization

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LIMITS TO THE ENcoding AND BOUNDS ON THE PERFORMANCE OF COHERENT ULTRASHORT LIGHT-PULSE CODE-DIVISION MULTIPLE-ACCESS SYSTEMS

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IEEE TRANSACTIONS ON COMMUNICATIONS 1992年第2期40卷 325-336页

作者： HAJELA, DJ SALEHI, JA BELL COMMUN RES INC DIV SYST PRINCIPLES RESMORRISTOWNNJ

In this paper we obtain lower and upper bounds on the peak intensity of a spectrally phase encoded ultrashort light pulse as a function of the length of spectral phase encoding. We show that using random phase codes for spectral encoding of ultrashort light pulses in a coherent ultrashort light pulse code-division multiple-access (CDMA) system is almost optimal. Furthermore, simple upper bounds and an asymptotic approximation on the bit error rate (BER) for a wide class of ultrashort light pulse CDMA systems are obtained. It is shown that, sin spite of being simple, these upperbounds can be used to evaluate the performance of a coherent ultrashort light pulse CDMA system.

关键词： random phase phase coding spectrum coding Code division multiple access Upper bound coding ultrashort light pulse CDMA mobile communications

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Power Series Quantization for Noisy Channels

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IEEE TRANSACTIONS ON COMMUNICATIONS 2010年第5期58卷 1405-1414页

作者： Persson, Daniel Eriksson, Thomas Linkoping Univ Dept Elect Engn S-58183 Linkoping Sweden Chalmers Univ Technol Dept Signals & Syst S-41296 Gothenburg Sweden

A recently proposed method for transmission of correlated sources under noise-free conditions, power series quantization (PSQ), uses a separate linear or nonlinear predictor for each quantizer region, and has shown to increase performance compared to several common quantization schemes for sources with memory. In this paper, it is shown how to apply PSQ for transmission of a source with memory over a noisy channel. A channel-optimized PSQ (COPSQ) encoder and codebook optimization algorithms are derived. The suggested scheme is shown to increase performance compared with previous state-of-the-art methods.

关键词： Channel-optimized quantization noisy channels memory-based quantization spectrum coding

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Interframe LSF quantization for noisy channels

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IEEE TRANSACTIONS ON SPEECH AND AUDIO PROCESSING 1999年第5期7卷 495-509页

作者： Eriksson, T Lindén, J Skoglund, J Chalmers Univ Technol Dept Informat Theory SE-41296 Gothenburg Sweden

In linear predictive speech coding algorithms, transmission of linear predictive coding (LPC) parameters-often transformed to the line spectrum frequencies (LSF) representation-consumes' a large part of the total bit rate of the coder. Typically, the LSF parameters are highly correlated from one frame to the next, and a considerable reduction in bit rate can be achieved by exploiting this interframe correlation. However, interframe coding leads to error propagation if the channel is noisy, which possibly cancels the achievable gain. In this paper, several algorithms for exploiting interframe correlation of LSF parameters are compared. Especially, performance for transmission over noisy channels is examined, and methods to improve noisy channel performance are proposed, By combining an interframe quantizer and a memoryless "safety-net" quantizer, we demonstrate that the advantages of both quantization strategies can be utilized, and the performance for both noiseless and noisy channels improves. The results indicate that the best interframe method performs as good as a memoryless quantizing scheme, with 4 bits less per frame. Subjective listening tests have been employed that verify the results from the objective measurements.

关键词： interframe coding memory-based vector quantization robust coding spectrum coding speech coding vector quantization

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ADAPTIVE PARAMETER-ESTIMATION USING PARALLEL KALMAN FILTERING FOR SPREAD-spectrum CODE AND DOPPLER TRACKING

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IEEE TRANSACTIONS ON COMMUNICATIONS 1994年第6期42卷 2227-2230页

作者： FUXJAEGER, AW ILTIS, RA Department of Electrical and Computer Engineering Center for Information Processing Research University of California Santa Barbara CA 93106

We present a new digital direct-sequence (DS) receiver with joint estimation of code delay, multipath gains and Doppler shift. A parameter estimator consisting of a parallel bank of extended Kalman filters (EKF's) extracts estimates of the timing, tau and the multipath coefficients, f(l) distorting the received signal. A ''detected'' estimate of the Doppler shift, v(r) distorting the received signal is also provided by the estimator. We compute the bit error rate that results when a RAKE matched filter uses the estimated parameters to detect the DPSK encoded binary data in the received signal. The bit-error rate (BER) is evaluated, and successful performance of the proposed receiver in the presence of Doppler shift distortion is observed in many cases. We demonstrate that the receiver can operate when the multipath coefficients vary in time (Doppler spread).

关键词： received signal rakes Kalman filtering binary data spectrum coding Receivers Doppler tracking Doppler effect Parameter estimation differential phase shift keying joint estimation

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100 kHz Mueller polarimeter in reflection configuration

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OPTICS LETTERS 2015年第4期40卷 645-648页

作者： Le Gratiet, Aymeric Rivet, Sylvain Dubreuil, Matthieu Le Grand, Yann Univ Brest EA Lab Spectrometrie & Opt Laser 938 SFR Scinbios F-29238 Brest 3 France

A new setup is proposed to perform high-speed Mueller polarimetry by spectral coding of polarization in a reflection configuration. The system uses a swept laser source and a photodiode, which results in a simple optical setup that allows measurement of Mueller matrices at 100 kHz repetition rate. A special focus is made on the influence of the cube beam splitter polarimetric response, which is essential to measurements in a reflection configuration. The instrument is first validated on reference samples for single-point measurements, and the effect of a proper system calibration is also demonstrated on polarimetric images. The device is intended to be implemented within a laser scanning microscope to perform multimodal imaging (confocal/multiphoton and Mueller polarimetry). c 2015 Optical Society of America

关键词： CONFOCAL LASER SCANNING MICROSCOPY Reflection spectrum coding Photodiodes Polarization calibration system Repetition rate polarimetry Laser Source beam splitters

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