Browsing by Author "Hwang, HC"

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A new blind adaptive interference suppression scheme for acquisition and MMSE demodulation of DS/CDMA signals
(2000-05-01)
Hwang, HC
;
Wei, CH
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this paper, we present an efficient blind algorithm for estimating the code timing of a desired user in an asynchronous direct-sequence code-division multiple-access (DS/CDMA) system over frequency-nonselective-fading channels. The proposed algorithm acquires the code timing explicitly and results in a near-far resistant minimum mean-squared error (MMSE) demodulation without requiring the knowledge of the timing information, amplitudes, and transmitted symbols of all transmissions, The only required knowledge is the information of the signature sequence used by the desired transmission. Several computer simulations are done for additive white Gaussian channels, Rayleigh fading channels, and two-ray Rayleigh fading multipath channels, respectively. Numerical results show that the new algorithm is near-far resistant to the multiple-access interference (MAI) in the DS/CDMA system.
Adaptive receiver for DS/CDMA communications over impulsive noise channels
(1998-03-05)
Hwang, HC
;
Wei, CH
;
電子工程學系及電子研究所
;
電信研究中心
;
Department of Electronics Engineering and Institute of Electronics
A new adaptive algorithm is proposed for training soft-limiter based correlation receiver in which the direct sequence code division multiple access signals corrupted by impulsive symmetric a-stable noise are demodulated. The new adaptation algorithm allows simpler implementation and faster convergence speed in comparison with the traditional adaptive stochastic gradient-based algorithms.
Adaptive variable step-size Griffiths' algorithm for blind demodulation of DS/CDMA signals
(1999-10-01)
Hwang, HC
;
Wei, CH
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The minimum mean-squared error (MMSE) linear detector [1], [2] has been proposed to successfully suppress the multiple access interference and mitigate the near-far problem in direct-sequence code-division multiple access communication systems. In the presence of unknown or time-varying channel parameters, the MMSE linear detector can be implemented by the blind Griffiths' algorithm [3], which uses the desired signal vector instead of a training sequence of symbols for initial adaptation. In this paper, a variable step-size (VSS) Griffiths' algorithm is proposed for accelerating the convergence speed, especially in the presence of strong interference. Numerical results show that the convergence properties of the VSS Griffiths' algorithm are robust against the wide eigenvalue-spread problem of the correlation matrix associated with the received signal vector compared to the Griffiths' algorithm using a fixed step-size.
Blind adaptive algorithm for demodulation of DS/CDMA signals with mismatch
(1999-02-01)
Hwang, HC
;
Wei, CH
;
電子工程學系及電子研究所
;
電信研究中心
;
Department of Electronics Engineering and Institute of Electronics
The minimum mean-squared error (MMSE) linear detector is known to be a near-far resistant strategy for direct-sequence code-division multiple access systems. The MMSE linear detector can be implemented adaptively by the MOE adaptation algorithm or the Griffiths' adaptation algorithm, which utilises the desired signal vector for initial adaptation instead of training sequences, The performance loss caused by the imprecise knowledge of the desired signal vector is investigated. A new blind adaptive algorithm is presented to mitigate the effect of the mismatch caused by the timing error in acquisition. Several;numerical results show that the new algorithm can provide a resistance to the effect of mismatch compared to the MOE and Griffiths' algorithms.
Performance of linear detectors for DS/CDMA in impulsive noise channel
(1996)
Hwang, HC
;
Wei, CH
;
交大名義發表
;
電子工程學系及電子研究所
;
National Chiao Tung University
Minimum mean-squared error(MMSE) linear correlation receiver has been presented to efficiently suppress the multiple access interference(MAI) for direct-sequence code-division multiple-access (DS/CDMA) systems in Gaussian channels [1]. The MMSE linear receiver is near-far resistant so as to reduce the requirement of perfect power control. However, additive non-Gaussian impulsive noise bursts in the realistic communication channels. In this paper, we analyze the performance of a linear correlation receiver operating in the presence of the MAI and the ambient noise modeled as a symmetric stable process. We also use the Fourier-Bessel series expansion to approximate the exact form of performance analysis. The learning curves of an adaptive linear correlation receiver with different training methods are then examined by computer simulations.