Browsing by Author "Tan, TH"

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A hybrid strategy for Gilbert's channel characterization using gradient and annealing techniques
(1998-06-01)
Tan, TH
;
Chang, WW
;
電信工程研究所
;
Institute of Communications Engineering
This paper presents a hybrid algorithm for estimating Gilbert's channel model parameters from an experimental error-gap distribution. A stochastic simulated annealing algorithm is applied to determine automatically a set of good starting points, which are then used by the deterministic gradient algorithm for faster convergence to the global optimum. Simulation results indicate that, for channel characterization, this hybrid strategy provides an ideal compromise between modelling accuracy and convergence time.
Estimation of Gilbert's model parameters using the simulated annealing method
(1996)
Tan, TH
;
Chang, WW
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
Errors encountered in digital mobile radio channels are not independent but exhibit varying degrees of statistical dependencies. In many mobile applications, Gilbert's finite-state Markov chain model has been shown to adequately characterize the bursty-noise binary channels. An estimation method based on the simulated annealing algorithm is proposed for computing the model parameters from the sample error sequences. Experimental results indicate that the simulated annealing method yields more accurate identification at a faster convergence rate for comparison with the gradient iterative method.
Estimation of the Gilbert model parameters using the simulated annealing method
(1996-07-04)
Tan, TH
;
Chang, WW
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
An estimation method based on the simulated annealing algorithm is proposed for computing the Gilbert model parameters from sample error sequences. Experimental results indicate that the simulated annealing method yields estimates which more closely match the experimental error statistics.
Fuzzy neural systems for controlling sound localisation in stereophonic reproduction
(1998-07-01)
Chang, PR
;
Tan, TH
;
電信工程研究所
;
Institute of Communications Engineering
The paper presents a new fuzzy logic control (FLC) approach which leads to a stereophonic reproduction controller for localising an auditory image in the desired direction and at the expected distance. Since an auditory event is usually less precisely resolved than the physical sound space, the auditory event need not coincide with a physical sound source, and can occur at a position where nothing is visible to a listener. It turns out that controlling the auditory image is more difficult than the localisation of a sound image. Unlike the conventional sound image localisation approach, our fuzzy logic controller can take account of knowledge in human auditory perception. The ambiguous human auditory perception in conjunction with the spatial reverberation from the surrounding environment can be represented by a number of fuzzy-set values. From these fuzzy representations, the auditory image localisation controller characterises the function of how control outputs depend on control inputs as fuzzy implications or associations. Furthermore, the overall stereophonic reproduction controller can be realised by a 45-rule fuzzy associative memory (FAM) system. The performance of FLC-based auditory image localisation is verified in a number of experiments.
Robust vector quantization for wireless channels
(2001-07-01)
Chang, WW
;
Tan, TH
;
Wang, DY
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電信工程研究所
;
Institute of Communications Engineering
This study focuses on two issues: parametric modeling of the channel and index assignment of codevectors, to design a vector quantizer that achieves high robustness against channel errors. We first formulate the design of a robust zero-redundancy vector quantizer as a combinatorial optimization problem leading to a genetic search for a minimum-distortion index assignment. Performance is further enhanced by the use of the Fritchman channel model that more closely characterizes the statistical dependencies between error sequences. This study also presents an index assignment algorithm based on the Fritchman model with parameter values estimated using a real-coded genetic algorithm. Simulation results indicate that the global explorative properties of genetic algorithms make them very effective in estimating Fritchman model parameters, and use of this model can match index assignment to expected channel conditions.
Statistical characterization of error sequences and its applications to error control
(1996)
Chang, WW
;
Tan, TH
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
Average bit error rate is not a satisfactory descriptive feature required for code evaluation, because it can not precisely distinguish between random and bursty natures inherent in error occurrences. In this paper we report new results of exploiting the statistical characterization of error sequences in the design of error control for mobile radio communications. For tracking the nonstationary evolution of error sequences, Gilbert's model is considered here as a model representative of real channel behavior. We first employ the simulated annealing technique to extract the statistical parameters that are required for descriptive modeling the error sequences. To exploit this through adaptive coding system, we also construct a class of cyclic codes by using the least common multiple of the generator polynomials of both the BCH and Five codes.