Browsing by Author "Lin, YP"

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A frequency-domain SIR maximizing time-domain equalizer for VDSL systems
(2005)
Lin, YP
;
Liang, LH
;
Chung, PJ
;
Phoong, SM
;
電控工程研究所
In this paper we propose a semi-blind time domain equalizer (TEQ) design method that maximize SIR (signal-to-interference ratio) in frequency domain for VDSL systems. The proposed method exploits the training symbols in VDSL initialization using an eigen approach. Unlike earlier eigen based TEQ designs, the proposed method does not require the channel impulse response. The TEQ can be obtained by computing an eigenvector of a positive definite matrix that depends only on the averaged received VDSL symbols. Examples will be given to demonstrate that the proposed TEQ design method can effectively shorten the channel impulse response, and achieve very good bit rates with only a small number of training symbols.
A kaiser window approach for the design of prototype filters of cosine modulated filterbanks
(1998-06-01)
Lin, YP
;
Vaidyanathan, PP
;
電控工程研究所
;
Institute of Electrical and Control Engineering
The traditional designs for the prototype filters of cosine modulated filterbanks usually involve nonlinear optimizations. We propose limiting the search of the prototype filters to the class of filters obtained using Kaiser windows. The design process is reduced to the optimization of a single parameter. An example will be given to show that very good designs can be obtained in spite of the limit of search.
A new class of optimal biorthogonal subband coder
(1999-01-01)
Phoong, SM
;
Lin, YP
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this letter, we introduce a novel two-channel biorthogonal subband coder. The new coder employs the ladder structure (or so-called wavelet with lifting scheme). The coding gain of the biorthogonal coder is always greater than or equal to unity, and it can be expressed in closed form. Moreover the proposed coder has a very low complexity and the perfect reconstruction property is structurally preserved. Given any filter order, the optimal solution can be found by the well-known Levinson fast algorithm. For both AR(1) process and MA(1) process, the proposed biorthogonal coder with 2 taps has a higher coding than the optimal orthonormal coder with infinite number of taps.
A switching predictor for lossless image coding
(2003)
Kau, LJ
;
Lin, YP
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we propose a switching adaptive predictor (SWAP) with automatic context modeling for lossless image coding. In the SWAP system, two predictors are used. For areas with edges, estimates of coding pixels are obtained using texture context matching (TCM). For all other areas, an adaptive neural predictor (ANP) is used. The SWAP encoder switches between the two predictors ANP and TCM depending on the neighborhood of the coding pixel. The switching predictor allows statistical redundancy to be removed effectively. On the other hand, it is known that prediction can be further refined using error compensation. For this, we propose the use of a modified fuzzy clustering, which leads to a modeling of errors that adapts itself to the input statistics. Experiments show that the proposed context clustering is very useful in modeling error for prediction refinement. Comparisons of the proposed system to existing state-of-the-art predictive coders will be given to demonstrate its coding efficiency.
Adaptive lossless image coding using least squares optimization with edge-look-ahead
(2005-11-01)
Kau, LJ
;
Lin, YP
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In predictive image coding, the least squares (LS)-based adaptive predictor is noted as an efficient method to improve prediction result around edges. However pixel-by-pixel optimization of the predictor coefficients leads to a high coding complexity. To reduce computational complexity, we activate the LS optimization process only when the coding pixel is around an edge or when the prediction error is large. We propose a simple yet effective edge detector using only causal pixels. The system can look ahead to determine if the coding pixel is around an edge and initiate the LS adaptation to prevent the occurrence of a large prediction error. Our experiments show that the proposed approach can achieve a noticeable reduction in complexity with only a minor degradation in the prediction results.
An approximately MAI-free multiaccess OFDM system in carrier frequency offset environment
(2005-11-01)
Tsai, SH
;
Lin, YP
;
Kuo, CCJ
;
電控工程研究所
;
Institute of Electrical and Control Engineering
The carrier frequency offset (CFO) effect of a new multiaccess orthogonal frequency division multiplexing (OFDM) transceiver is analyzed. We show that multiaccess interference (MAI) due to CFO can be mitigated by choosing a proper set of orthogonal codes. That is, if we use M/2 symmetric or antisymmetric codewords of the M Hadamard-Walsh codewords, MAI can be greatly reduced to a negligible amount. The new OFDM system has been shown to be approximately MAI-free when there is no CFO. The new result developed here shows that the system continues to be approximately MAI-free even in the presence of CFO. Furthermore, we derive a close form for the reduced MAI, which reveals an interesting property of the system. That is, when the number of users increases, the reduced MAI and the inter carrier interference (ICI) due to self-CFO will decrease. Finally, it is demonstrated by simulation that the proposed OFDM scheme with proper code selection outperforms the OFDMA and the multicarrier code division multiplexing access (MC-CDMA) systems in a CFO environment.
An semi-blind eigen approach to time-domain equalizer design for VDSL systems
(2005)
Lin, YP
;
Liang, LH
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper we propose a semi-blind time domain equalizer (TEQ) design method for VDSL system. In the VDSL system frequency division duplex is used to separate upstream and downstream signals. In downstream or upstream transmission, only half the tones carry data and the other half are null tones. The proposed semi-blind method exploits the null tones of VDSL training symbols. It does not require the channel impulse response nor the channel noise statistics, like all eigen approaches proposed earlier. Example will be given to demonstrate that proposed TEQ design method can effectively shorten the channel impulse responses for VDSL application.
Analog representation and digital implementation of OFDM systems
(2003)
Lin, YP
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Many existing results on the analysis of OFDM systems are based on an analog representation. The actual implementation of OFDM transmitters typically consists of a discrete DFT matrix and a digital-to-analog (DAC) converter. In this paper, we show that the analog representation admits the implementation of a DFT matrix followed by a DAC converter only in special cases. Necessary and sufficient conditions for such cases will be given. Analyses based on the analog representation, e.g., spectral roll-off of transmitter outputs and carrier frequency offset, may not be appropriate when digital implementation is employed.
Asymptotical optimality of DFT based DMT transceivers
(1999)
Lin, YP
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
The DMT (discrete multitone modulation) technique has been widely applied to data transmission over fading channels of twisted pairs. It has been shown that the DMT system with ideal filters can achieve within 8 to 9 dB of the channel capacity of ADSL. The DFT based DMT system is proposed as a practical DMT implementation but its optimality is never asserted. In this paper we will show that the DFT based DMT systems are asymptotically optimal although they are not optimal for finite number of channels. The DFT based DMT system and the DMT system with ideal filters achieve the same bound. However, for a modest number of channels the optimal transceiver can provide substantial gain over the DFT based system as will be demonstrated by examples.
BER minimized OFDM systems with channel independent precoders
(2003-09-01)
Lin, YP
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
We consider the minimization of uncoded bit error rate (BER) for the orthogonal frequency division multiplexing (OFDM) system with an orthogonal precoder. We analyze the BER performance of precoded OFDM systems with zero forcing and minimum mean squared error (MMSE) receivers. In the case of MMSE receivers, we show that for quadrature phase shift keying (QPSK), there exists a class of optimal precoders that are channel independent. Examples of this class include the discrete Fourier transform (DFT) matrix and the Hadamard matrix. When the precoder is the DFT matrix, the resulting optimal transceiver becomes the single carrier system with cyclic prefix (SC-CP) system. We also show that the worst solution corresponds to the conventional OFDM system; the conventional OFDM system has the largest BER. In the case of zero forcing receivers, the design of optimal transceiver depends on signal-to-noise ratio (SNR). For higher SNR, solutions of optimal precoders are the same as those of MMSE receivers.
BER optimized channel independent precoder for OFDM system
(2002)
Lin, YP
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
We consider the minimization of bit error rate (BER) for OFDM systems with orthogonal precoders. For low SNR, we show that the conventional OFDM system is the optimal solution and the optimal precoder is the identity matrix. For high SNR, corresponding to a relatively practical range of BER, there are channel independent solutions for optimal precoders. One such solution is the DFT matrix and the resulting optimal transceiver becomes the single carrier transmission system. Furthermore, in this case the conventional OFDM system has the largest BER among all OFDM systems with orthogonal precoders.
Blind watermarking using wavelet tree quantization
(2002)
Wang, SH
;
Lin, YP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper proposes a blind watermarking scheme using wavelet tree quantization. The wavelet coefficients of the host image are grouped into wavelet trees and each watermark bit is embedded using two trees. The trees are so quantized that they exhibit a large enough statistical difference; which will later be used for watermark extraction. Each watermark bit is embedded in all frequency bands, which renders the mark more resistant to attacks that remove certain frequency components. Also, the embedding is spread throughout a relatively large spatial region, which yields more robustness against spatial domain geometric attacks. Examples of various attacks will be given to demonstrate the robustness of the proposed technique.
Block based DMT systems with reduced redundancy
(2001)
Lin, YP
;
Weng, WL
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
There has been great interest in the design of DMT (discrete multitone) transceivers. An M-band DMT transceiver: is called block based if the transmitter and the receiver consist of constant matrices. The commonly used DMT systems are mostly block based, e.g., the DFT based system used in transmission over digital subscriber lines. For an FIR channel of order L, it is known that redundancy of length L enables the receiver to cancel ISI completely. Such a scheme allow us to trade bandwidth for ISI cancellation. In block based DMT (BDMT) systems, the redundancy K is typically chosen to be the same as the order of the channel L. In this paper we will consider BDMT transceiver with redundancy K less than or equal to L. With the reduced redundancy better bandwidth efficiency can be obtained as will be demonstrated by examples. Furthermore minimum redundancy for BDMT systems will be derived and the transceivers will be parameterized whenever ISI solutions exist.
Closed-form expression of smith forms for pseudo-circulants
(2002)
Lin, YP
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
The pseudo-circulant matrices arise naturally in the block filtering application of multirate systems. More recently, there has been considerable interests in pseudo-circulants for the applications of precoding and discrete multitone communications systems. In these systems, a scalar FIR channel P(z) is cast as a pseudo-circulant channel matrix. Many important channel properties have been derived from the Smith form and the decomposition of pseudo-circulants. In this paper, we will show that the Smith form of an FIR pseudo-circulant matrix can be given in terms of the zeros of the underlying scalar filter P(z). Once the zeros of P(z) are known, the Smith form of the corresponding pseudo-circulant matrix can be obtained in closed form.
Designing an optimal multivariate geostatistical groundwater quality monitoring network using factorial kriging and genetic algorithms
(2006-05-01)
Yeh, MS
;
Lin, YP
;
Chang, LC
;
土木工程學系
;
Department of Civil Engineering
The optimal selection of monitoring wells is a major task in designing an information-effective groundwater quality monitoring network which can provide sufficient and not redundant information of monitoring variables for delineating spatial distribution or variations of monitoring variables. This study develops a design approach for an optimal multivariate geostatistical groundwater quality network by proposing a network system to identify groundwater quality spatial variations by using factorial kriging with genetic algorithm. The proposed approach is applied in designing a groundwater quality monitoring network for nine variables (EC, TDS, Cl-, Na, Ca, Mg, SO42-, Mn and Fe) in the Pingtung Plain in Taiwan. The spatial structure results show that the variograms and cross-variograms of the nine variables can be modeled in two spatial structures: a Gaussian model with ranges 28.5 kin and a spherical model with 40 km for short and long spatial scale variations, respectively. Moreover, the nine variables can be grouped into two major components for both short and long scales. The proposed optimal monitoring design model successfully obtains different optimal network systems for delineating spatial variations of the nine groundwater quality variables by using 20, 25 and 30 monitoring wells in both short scale (28.5 km) and long scale (40 km). Finally, the study confirms that the proposed model can design an optimal groundwater monitoring network that not only considers multiple groundwater quality variables but also monitors variations of monitoring variables at various spatial scales in the study area.
DFT based transceivers with-windowing
(2004)
Lin, YP
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper we consider window designs for DFT (discrete Fourier transform) based multicarrier transceivers without using extra cyclic prefix. As in previous works of window designs for DFT based transceiver, a post processing matrix, generally channel dependent, is needed to have a zero-forcing receiver. We show that post processing is channel independent if and only if the window itself has the cyclic-prefixed property. We design optimal windows with minimum spectral leakage subject to the cyclic-prefixed condition. Moreover, we analyze how post processing affects SNR (signal to noise ratio) at the receiver, an aspect that is not considered in most of the earlier works. The resulting SNR can be given in a closed form. Join optimization of spectral leakage and SNR are also considered. Furthermore, examples demonstrate that we can have a significant reduction in spectral leakage at the cost of a small SNR penalty.
Discrete multitone modulation with principal component filter banks
(2002-10-01)
Vaidyanathan, PP
;
Lin, YP
;
Akkarakaran, S
;
Phoong, SM
;
電控工程研究所
Discrete multitone (DMT) modulation is an attractive method for communication over a nonflat channel with possibly colored noise. The uniform discrete Fourier transforn (DFT) filter bank and cosine modulated filter bank have in the past been used in this system because of low complexity. We show in this paper that principal component filter banks (PCFB) which are known to be optimal for data compression and denoising applications, are also optimal for a number of criteria in DMT modulation communication. For example, the PCFB of the effective channel noise power spectrum (noise psd weighted by the inverse of the channel gain) is optimal for DMT modulation in the sense of maximizing bit rate for fixed power and error probabilities. We also establish an optimality property of the PCFB when scalar prefilters and postfilters are used around the channel. The difference between the PCFB and a traditional filter bank such as the brickwall filter bank or DFT filter bank is significant for effective power spectra which depart considerably from monotonicity. The twisted pair channel with its bridged taps, next and fext noises, and AM interference, therefore appears to be a good candidate for the application of a PCFB. This will be demonstrated with the help of numerical results for the case of the ADSL channel.
ISI-free FIR filterbank transceivers for frequency-selective channels
(2001-11-01)
Lin, YP
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Discrete multitone modulation transceivers (DMTs) have been shown to be very useful for data transmission over frequency selective channels. The DMT scheme is realized by a transceiver that divides the channel into subbands. The efficiency of the scheme depends on the frequency selectivity of the transmitting and receiving filters. The receiving filters with good stopband attenuation are also desired for combating narrowband noise. The filterbank transceiver or discrete wavelet multitone (DWMT) system has been proposed as an implementation of the DMT transceiver that has better frequency band separation, but usually, inrtersymbol interference (IST) cannot be completely canceled in these filterbank transceivers, and additional equalization is required. In this paper, we show how to use over interpolated filterbanks to design IST-free FIR transceivers. A finite impulse response (FIR) transceiver with good frequency selectivity can be designed, as will be demonstrated by design examples.
Lapped unimodular transform and its factorization
(2002-11-01)
Phoong, SM
;
Lin, YP
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Two types of lapped transforms have been studied in detail in the literature, namely, the lapped orthogonal transform (LOT) and its extension, the biorthogonal lapped transform (BOLT). In this paper, we will study the lapped unimodular transform (LUT). All three transforms are first-order matrices with finite impulse response (FIR) inverses. We will show that like LOT and BOLT, all LUTs can be factorized into degree-one unimodular matrices. The factorization is both minimal and complete. We will also show that all first-order systems with FIR inverses can be minimally factorized as a cascade of degree-one LOT, BOLT, and LUT building blocks. Two examples will be given to demonstrate that despite having a very small system delay, the LUTs have a satisfactory performance in comparison with LOT and BOLT.
Lossless image coding using a switching predictor with run-length encodings
(2004)
Kau, LJ
;
Lin, YP
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we propose a switching adaptive predictor (FSWAP) with run-length encodings for lossless image coding. The proposed FSWAP system has two operation modes, run mode and regular mode. If the members in the texture context of the coding pixel have identical grey values, the run mode will be used; otherwise regular mode is used. The run mode using run-length coding with an arithmetic coder is very useful for image with flat regions. The regular mode borrows the switching predictor structure in SWAP [1] with some modifications. The SWAP coder, updating network weights on the fly and making automatic fuzzy context modeling, has been shown to provide very good results [1]. To make the proposed system more feasible for applications of limited resources, the dimension of ANP in SWAP [1] is simplified and the automatic fuzzy context modeling is replaced by a fixed context clustering. Experiments show that the simplified context clustering is very useful in modeling error for prediction refinement. Furthermore, the execution time of FSWAP can be accelerated with minor degradation in the bit rates associated with the modifications. Comparisons of the proposed system to existing state-of-the-art predictive coders will be given to demonstrate its coding efficiency.