Browsing by Author "Lin, Yuan-Pei"

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A Filterbank Approach to Window Designs for Multicarrier Systems
(2007)
Lin, Yuan-Pei
;
Li, Chien-Chang
;
Phoong, See-May
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Windowing is often applied to multicarrier systems to improve frequency separation among the subcarriers. At the transmitter side better frequency separation leads to a smaller out-of-band spectral leakage and also less interference to radio frequency transmission. At the receiver side better separation gives more suppression of radio frequency interference. As these are frequency based characteristics, a filterbank representation presents a natural and useful framework for formulating the problem. In this work, we propose a unified filterbank approach to the design of windows for multicarrier systems. The filterbank viewpoint provides an additional insight into the transmitter design for spectral leakage reduction as well as to the receiver design for interference suppression. A better frequency separation among the subchannels can be achieved.
A frequency domain based TEQ design for DSL systems
(2006)
Lin, Yuan-Pei
;
Lin, Yu-Pin
;
Phoong, See-May
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we propose a frequency domain based design method for designing TEQ (time domain equalizer) for DSL (digital subscriber loops) applications. In DSL applications, usually frequency division multiplexing is used to separate the upstream and downstream signals. In either direction of transmission, some of the frequency bands are not used for transmission. Interference is formulated and minimized in the frequency domain to take advantage of the unused frequency bands. The frequency domain approach allows us to have a more direct control over the frequency response of the resulting TEQ, which is crucial in the final achievable transmission bit rates. The simulation examples demonstrate that the proposed method shortens the channel effectively and very good transmission bit rates can be achieved.
A Fuzzy Neural Network Based Adaptive Predictor with P-Controller Compensation for Lossless Compression of Images
(2009)
Lee, Ching-Hung
;
Kau, Lih-Jen
;
Lin, Yuan-Pei
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Predictively encoded techniques are commonly used for lossless compression of images for its effectiveness of removing statistical redundancy between pixels. However, there can be large prediction errors for pixels around boundaries. In this paper, we introduce techniques commonly used in control systems to enhance the coding efficiency of predictive coding. Actually, the predictive coding system behaves just like a multi-input single-output system with the predictor itself can be taken as the system model. When compared with the purpose of a control system, which is to follow the system command as precisely as possible, we find the objective of both systems are the same. Moreover, an edge or a boundary among image pixels can be regarded as a step command in control systems. These observations lead to the idea of using control technologies to improve prediction result for pixels around boundaries. To realize this idea, we use an adaptive Takagi-Sugeno fuzzy neural network (TS-FNN) as the predictor. Furthermore, the widely used proportional controller in control system is implemented implicitly in the consequent part of the network so that the prediction error can be further compensated for pixels around boundaries. We find in experiments that the proposed approach can have a very good prediction result even without using any online training area for network adaptation process. This makes the proposed system more feasible under limited resources. Finally, comparisons to existing state-of-theart lossless predictors and coders will be given to highlight the advantages of the proposed novel approach.
A New Iterative Algorithm for Finding the Minimum Sampling Frequency of MultiBand Signals
(2010-10-01)
Lin, Yuan-Pei
;
Liu, Yi-De
;
Phoong, See-May
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this correspondence, we propose a new iterative algorithm for finding the minimum sampling frequency of a signal that consists of multiple bandpass signals. This finds important application in software radio where it is desirable to downconvert multiple bandpass signals simultaneously. We will derive a new set of conditions for alias-free sampling. The minimum sampling frequency can be found by iteratively increasing the sampling frequency to meet the alias-free conditions. We will show how the algorithm can be generalized to find alias-free sampling frequency intervals. Simulations will be given to demonstrate the usefulness of the proposed method.
A New Iterative Algorithm for Finding the Minimum Sampling Frequency of MultiBand Signals
(2010-10-01)
Lin, Yuan-Pei
;
Liu, Yi-De
;
Phoong, See-May
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this correspondence, we propose a new iterative algorithm for finding the minimum sampling frequency of a signal that consists of multiple bandpass signals. This finds important application in software radio where it is desirable to downconvert multiple bandpass signals simultaneously. We will derive a new set of conditions for alias-free sampling. The minimum sampling frequency can be found by iteratively increasing the sampling frequency to meet the alias-free conditions. We will show how the algorithm can be generalized to find alias-free sampling frequency intervals. Simulations will be given to demonstrate the usefulness of the proposed method.
An eigren-based TEQ design for VDSL systems
(2007-01-01)
Lin, Yuan-Pei
;
Liang, Li-Han
;
Chung, Pei-Ju
;
Phoong, See-May
;
電信工程研究所
In this paper, we propose an eigen-based semiblind time-domain equalizer (TEQ) design method for VDSL systems. We exploit the fact that the VDSL system is frequency-division duplexing and maximize signal-to-interference ratio in the frequency domain. Unlike earlier eigen-based TEQ designs, the proposed method does not require the channel impulse response nor channel noise statistics. Using properties of the training symbols in VDSL initialization, the TEQ can be obtained by computing an eigenvector of a positive definite matrix that depends only on the averaged received VDSL symbols. The proposed method is referred to as semiblind, as properties of the training symbols are used but the channel impulse response is not known. 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.
An Improved ESPRIT-Based Blind CFO Estimation Algorithm In OFDM Systems
(2014)
Pan, Yen-Chang
;
Phoong, See-May
;
Lin, Yuan-Pei
;
電機學院
;
College of Electrical and Computer Engineering
Carrier frequency offset (CFO) is an important issue in orthogonal frequency division multiplexing (OFDM) systems. It destroys the orthogonality between subcarriers and causes degradation in system performance. This paper presents an improved algorithm for the existing ESPRIT-based CFO estimation method. The proposed method estimates the CFO by taking the determinant of a matrix within the ESPRIT algorithm. It is a simple modification to the original ESPRIT-based method and its computational overhead is low. The performance analysis shows that the proposed method can achieve a lower mean square error.
AN ITERATIVE ALGORITHM FOR FINDING THE MINIMUM SAMPLING FREQUENCY FOR TWO BANDPASS SIGNALS
(2009)
Lin, Yuan-Pei
;
Liu, Yi-De
;
Phoong, See-May
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we propose an efficient algorithm for finding the minimum sampling frequency for a signal that consists of two bandpass signals. This has important application in software radio where it is desirable to downconvert multiple bandpass signals simultaneously. We will derive a new set of conditions for alias-free sampling that can be checked with few computations. The minimum sampling frequency can be found by iteratively increasing the sampling frequency to meet the alias-free conditions. We will demonstrate that the proposed method has a much lower complexity than previously reported algorithms.
Beamforming with no instantaneous feedback for mmWave transmission
(2017-01-01)
Lin, Yuan-Pei
;
Tsai, Shang-Ho (Lawrence)
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this paper we consider statistical beamforming for millimeter wave (mmWave) channels. For a commonly used geometry channel model of uniform planar array (UPA), we show that the average channel Gram matrix can be approximated in a closed form, which allows the statistical beamformer to be computed directly. The sparse nature of the mmWave channel lends itself to statistical beamforming as the optimal beamformer that uses full channel information is typically steered in some spatial frequency determined by the statistics. Simulations are given to show that the performance of the proposed statistical beamformer that needs no instantaneous feedback is comparable to a limited feedback system with 1/8 feedback bits per antenna.
Beamforming with no instantaneous feedback for mmWave transmission
(2017-01-01)
Lin, Yuan-Pei
;
Tsai, Shang-Ho (Lawrence)
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this paper we consider statistical beamforming for millimeter wave (mmWave) channels. For a commonly used geometry channel model of uniform planar array (UPA), we show that the average channel Gram matrix can be approximated in a closed form, which allows the statistical beamformer to be computed directly. The sparse nature of the mmWave channel lends itself to statistical beamforming as the optimal beamformer that uses full channel information is typically steered in some spatial frequency determined by the statistics. Simulations are given to show that the performance of the proposed statistical beamformer that needs no instantaneous feedback is comparable to a limited feedback system with 1/8 feedback bits per antenna.
Bit Allocation and Statistical Precoding for Correlated MIMO Channels With Limited Feedback
(2012-02-01)
Lin, Yuan-Pei
;
Chen, Hung-Chun
;
Jeng, Panna
;
電機工程學系
;
Department of Electrical and Computer Engineering
In this paper, we jointly consider statistical precoding and feedback of bit allocation (BA) for multiple-input-multiple-ouput (MIMO) systems over correlated channels. The proposed system will be termed a BA system. We assume that the statistics of the channel is known to the transmitter and a reverse link of very low rate is available so that the receiver can send back the quantized BA. Based on the statistics of the channel, we derive the statistical precoder so that bounds of the error rate averaged over the random correlated channel are minimized. Due to statistical precoding, the distribution of the BA is highly nonuniform. Treating BA as a vector signal, we quantize it using vector quantization (VQ), which is known to be particularly useful for quantizing signals with nonuniform distributions. As the distribution of BA is taken into consideration in the codebook design, a good tradeoff between performance and feedback rate can be achieved. Simulations show that the combination of statistical precoding and VQ-based quantization for BA leads to good performance with a small number of feedback bits.
Compensation of IQ imbalance and DC offset for OFDM transmission over frequency selective channels
(2008)
Tseng, Hsien-Yu
;
Cho, Wen-Jen
;
Chang, Ting-Kang
;
Phoong, See-May
;
Lin, Yuan-Pei
In this paper a time-domain method for joint estimation of in-phase and quadrature-phase (IQ) imbalance, direct current (DC) offset and channel response for orthogonal frequency division multiplexing (OFDM) system is proposed. Using the fact that in an OFDM system the block size is usually much larger than the cyclic prefix length, we show that without knowing the channel impulse response, we are able to accurately estimate the IQ mismatch and DC offset, from which the channel response can be obtained. Only one OFDM block is needed for training. Simulation results demonstrate that the performance of the proposed method is very close to the ideal case when IQ mismatch, DC offset and channel response are perfectly known at the receiver.
Design of nonuniform filter bank transceivers for frequency selective channels
(2007)
Chiang, Han-Ting
;
Phoong, See-May
;
Lin, Yuan-Pei
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In recent years, there has been considerable interest in the theory and design of filter bank transceivers due to their superior frequency response. In many applications, it is desired to have transceivers that can support multiple services with different incoming data rates and different quality-of-service requirements. To meet these requirements, we can either do resource allocation or design transceivers with a nonuniform bandwidth partition. In this paper, we propose a method for the design of nonuniform filter bank transceivers for frequency selective channels. Both frequency response and signal-to-interference ratio (SIR) can be incorporated in the transceiver design. Moreover, the technique can be extended to the case of nonuniform filter bank transceivers with rational sampling factors. Simulation results show that nonuniform filter bank transceivers with good filter responses as well as high SIR can be obtained by the proposed design method. Copyright (c) 2007 Hindawi Publishing Corporation. All rights reserved.
Design of time domain equalizers incorporating radio frequency interference suppression
(2006)
Wu, Ya-Wen
;
Lin, Yuan-Pei
;
Li, Chien-Chang
;
Phoong, See-May
;
電控工程研究所
It is known that radio frequency interference (RFI) degrades the performance of DMT systems for digital subscriber loops. The RFI signal, though narrowband in nature, may be spread to subchannels around the RFI frequencies due to the large sidelobes of the receiving rectangular window. In this paper, we propose a joint consideration of channel shortening and RFI suppression in the design of time domain equalizers (TEQ). We will design the TEQ by minimizing ISI, channel noise and RFI interference. Simulation results are given to show that the proposed method can considerably reduce interference around the RFI frequencies and increase the transmission rate.
Differential Feedback of Geometrical Mean Decomposition Precoder for Time-Correlated MIMO Systems
(2017-07-15)
Chen, Hung-Chun
;
Lin, Yuan-Pei
;
電機工程學系
;
Department of Electrical and Computer Engineering
For a time-correlated channel, we consider the differential feedback of the geometrical mean decomposition (GMD) precoder, which is known to be optimal for a number of criteria. When the channel varies slowly, we can expect the optimal GMD precoders of consecutive channel uses to be close. We consider the feedback of the so-called differential precoder and show that it lies in a neighborhood of the identity matrix using matrix perturbation theory. Furthermore, the radius of the neighborhood is shown to be proportional to a time-correlation parameter. Such a characterization allows for subsequent efficient quantization of the differential precoder. We show how to design codewords for the prescribed radius by perturbing the identity matrix and applying QR decomposition on the perturbed matrix. Simulations are given to demonstrate that, with a small feedback rate, the performance of the proposed differential GMD comes close to the case when perfect channel state information is available to the transmitter for slowly time-varying channels like those in indoor and microcellular environments.
EFFICIENT FEEDBACK FOR MIMO CHANNELS WITH TIME AND SPATIAL CORRELATION
(2015)
Lin, Yuan-Pei
;
Tsai, Sz-Kai
;
電機工程學系
;
Department of Electrical and Computer Engineering
In this paper, we consider limited feedback for MEMO channels that have time and spatial correlation. The bit loading is dynamically assigned according to the channel condition and fed hack to the transmitter to achieve an adaptive rate. To take advantage of the time correlation of the channel, the bit loading is predictively coded for feedback. The precoder is designed according to the statistics of the channel and it requires no feedback. We derive the optimal predictor of bit loading that minimizes the mean squared prediction error in this case and present a practical feedback scheme based on the optimal predictor. With a small feedback rate the proposed statistical preceding and predictive quantization of bit loading can achieve a performance very close to the case when there is no quantization on bit loading.
FEEDBACK FOR TIME-CORRELATED MIMO-OFDM SYSTEM USING PREDICTIVE QUANTIZATION OF BIT LOADING AND SUBCARRIER CLUSTERING
(2015)
Lin, Yuan-Pei
;
Chou, Tzu-Hsuan
;
Phoong, See-May
;
電機工程學系
;
Department of Electrical and Computer Engineering
In the paper, we consider limited feedback for a MIMO-OFDM system over a time-correlated multipath fading channel. Due to time correlation, the subcarriers are correlated in both time and frequency. We propose the use of predictive quantization of bit loading (PQB) and subcarrier clustering (SC). Applying PQB on the subcarriers allows us to exploit the time correlation of the channel and adapt the transmission rate according to the channel condition while SC enables us to take advantage of the frequency correlation of the channel. Simulation results are given to demonstrate that the proposed feedback scheme can achieve a good performance due to the exploitation of both time and frequency correlation.
FEEDBACK OF DIFFERENTIAL PRECODER FOR GEOMETRICAL MEAN DECOMPOSITION SYSTEMS
(2016)
Chen, Hung-Chun
;
Lin, Yuan-Pei
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
For a time-correlated channel, we consider the differential feedback of the geometrical mean decomposition (GMD) precoder, which is known to be optimal for a number of criteria. When the channel varies slowly, we can expect the optimal GMD precoders of consecutive channel uses to be close. We consider the feedback of the so-called differential precoder and show that it lies in a neighborhood of the identity matrix using matrix perturbation theory. Furthermore the radius of the neighborhood is proportional to a time-correlation parameter. Such a characterization is crucial for efficient quantization of the differential precoder. Simulations are given to demonstrate that, with a small feedback rate, the performance of the proposed differential GMD comes close to the case when perfect channel state information is available to the transmitter.
FEEDBACK RATE ALLOCATION OF PRECODER AND BIT LOADING FOR MIMO SYSTEMS WITH LIMITED FEEDBACK
(2013)
Chen, Hung-Chun
;
Lin, Yuan-Pei
;
電機學院
;
College of Electrical and Computer Engineering
In this paper we consider feedback rate allocation for MIMO systems with limited feedback of both bit loading and precoder. Allocation of feedback rate is an essential problem when there are two or more kinds of feedback information. We address this issue by analyzing the performance loss due to quantization of precoder and bit loading. We first derive the increase in transmission power when precoder is quantized, and then the additional penalty when bit loading is also quantized. The analysis allows us to find the optimal feedback rate allocation that minimizes the power penalty. Simulations show that the system with proper feedback rate allocation can achieve a very good performance compared with systems that do not consider the feedback of precoder and bit loading jointly.
Filterbank framework for multicarrier systems with improved subcarrier separation
(2006)
Lin, Yuan-Pei
;
Li, Chien-Chang
;
Phoong, See-May
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Frequency separation among the subcarriers is of great importance for multicarrier systems. At the transmitter side better frequency separation leads to a smaller out-of-band spectral leakage and also less interference to radio frequency transmission. At the receiver side better separation gives more suppression of radio frequency interference. As these are frequency based characteristics, a filterbank representation renders a natural tool for formulating the problem. In this work, we will consider a filterbank framework for designing multicarrier systems with improved subcarrier separation.