Browsing by Author "Lin, DW"

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A chip-interleaved synchronous DS-CDMA technique enabling MAI-free and reduced-ISI transmission with low complexity receiving
(2004)
Lin, YN
;
Lin, DW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The capacity of conventional direct-sequence code-division multiaccess (DS-CDMA) systems is limited by multiaccess interference (MAI) that arises from correlation among user signals, especially in multipath channels. While inducing an intersymbol-interference (ISI) problem, chip-interleaved DS-CDMA (CIDS-CDMA) can preserve the orthogonality among user signals and effect MAI-free transmission. We propose a multicode CIDS-CDMA (MCIDS-CDMA) technique which can also remove ISI in addition to MAI when a sufficient number of multicodes are assigned. This design facilitates a low complexity receiver structure. In addition, a low complexity ISI canceller can be used to deal with the residual ISI, should the number of codes be insufficient.
A family of low-complexity blind equalizers
(2004-03-01)
Hwang, CI
;
Lin, DW
;
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
Two important topics in equalizer design are its complexity and its training. We present a family of blind equalizers which, by incorporating a decomposition finite-impulse response filtering technique, can reduce the complexity of the convolution operation therein by about one half. The prototype algorithm in this equalizer family employs the prevalent Godard cost function. Several simplified algorithms are proposed, including a sign algorithm which eliminates multiplications in coefficient adaptation and a few delayed versions. We also study the convergence properties of the algorithms. For the prototype algorithm, we show that, in the limit of an infinitely long equalizer and under mild conditions on signal constellations and channel characteristics, there are only two sets of local minima on the performance surface. One of the sets is undesirable and is characterized by a null equalized channel response. The other corresponds to perfect equalization, which can be reached with proper equalizer initialization. For the simplified algorithms, corresponding cost functions may not exist. Some understanding of their convergence behaviors are obtained via examination of their adaptation equations. Simulation results are presented to demonstrate the performance of the algorithms.
A hybrid variable step-size adaptive blind equalization algorithm for QAM signals
(2005)
Hung, KC
;
Lin, DW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We develop an adaptive decision-feedback equalization algorithm that combines blind adaptation and decision-directed LMS in a dynamic manner according to the amount of equalizer output error. By observing how the mean-square blind equalization error depends on the adaptation step size, we obtain a way of continuously varying the adaptaion speed of the overall algorithm with the equalizer output error as well as a way to shift the relative emphasis between blind and decision-directed LMS operation. We also describe the way to estimate the amount of equalizer output error in the algorithm. Simulation results show that the proposed algorithm can achieve faster convergence at a lower complexity than some recently proposed hybrid adaptation algorithms.
A new charge-pumping technique for profiling the interface-states and oxide-trapped charges in MOSFET's
(2000-02-01)
Chu, YL
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Lin, DW
;
Wu, CY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A new charge-pumping method has been developed to characterize the hot-carrier induced local damages. By holding the rising and falling slopes of the gate pulse constant and then varying the high-level (V-GH) and base-level (V-GL) voltages, the lateral distribution of interface-states ( N-it (x)) and oxide-trapped charges (Q(ox) (x)) can be profiled. The experimental results show that during extracting Q(ox) (x) after hot-carrier stress, a contradictory result occurs between the extraction methods by varing the high-level (VGH) and base-level (V-GL) voltages. As a result, some modifications are made to eliminate the perturbation induced by the generated interface-states after hot-carrier stress for extracting Q(ox) (x).
Analysis of hardlimiting parallel interference cancellation (PIC) for synchronous CDMA communication
(2002)
Lin, YN
;
Lin, DW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Parallel interference cancellation (PIC) is a widely considered approach to multiuser detection in CDMA communication. While PIC receivers normally involve nonlinear functions, previous performance analyses mainly addressed linear PIC. We find that the performance of purely hardlimiting PIC may not improve after the second stage. In addition, for the two-user case, one stage usually suffices. Further, the performance of hardlimiting PIC does not approach the single-user limit. We also develop approximate expressions for numerical evaluation of the hardlimiting PIC performance. Simulation results agree well with the analysis.
Chip interleaving for performance improvement of coded DS-CDMA systems in Rayleigh fading channels
(2003)
Lin, YN
;
Lin, DW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In mobile wireless communication, signal is usually subject to fading. Gain-combining diversity is a common remedy for fading effects. Practical channel coded direct-sequence code-division-multiple-access (DS-CDMA) uses bit interleaving to effect gain-combining time diversity through the redundancy provided by the channel code. Recently, some have proposed chip-interleaved DS-CDMA (CIDS-CDMA). Simple CIDS-CDMA considers a set of bits at a time. Similarly indexed chips in the bits are grouped together for transmission. Such interleaving has been shown to yield diversity gain in uncoded transmission. This paper considers the performance of CIDS-CDMA with channel coding. For simplicity, synchronous DS-CDMA is considered. In addition to simple CIDS-CDMA, we also consider combined bit-and-chip interleaving (BODS-CDMA). We present theoretical analysis and simulation results for both cases under long-code and short-code spreading. It is concluded that the code period is vital for simple CIDS-CDMA but is of no importance for BCIDS-CDMA. Another conclusion is that BCIDS-CDMA yields the best performance for it provides the largest diversity gain.
Chip-interleaved WCDMA with parallel-interference-cancellation receiver in multipath Rayleigh fading channels
(2004)
Lin, YN
;
Lin, DW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Multiple access interference (MAI) is a major limiting factor of DS-CDMA system capacity. Parallel interference cancellation (PIC) is an effective means to mitigate MAI. However, if the initial decisions of which PIC is based on have high error probabilities, then PIC cannot perform well. To improve the performance of PIC, we propose chip-interleaving to provide intra-bit diversity. Then the initial decisions can be more accurate so as to enhance the PIC's performance. We design a chip-interleaving scheme based on some 3GPP WCDMA system features, such as the use of the Q-branch to transmit control bits and the I-branch to transmit data bits in a QPSK-like modulation scheme. Simulation results show that the proposed chip-interleaved WCDMA (CI-WCDMA) transmission can have significant performance advantage compared to simple WCDMA in transmission over fading multipath channels with MAI.
DSP implementation of successive interference cancellation (SIC) receiver for 3GPP WCDMA uplink transmission
(2003-09-01)
Chang, YJ
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Lin, YN
;
Lin, DW
;
電子工程學系及電子研究所
;
電信研究中心
The 3GPP WCDMA is a widely accepted third-generation cellular system standard. By using nonorthogonal codes for different users. the Multiple access interference (MAI) can be a limiting factor for system performance, as for other CDMA systems. Multiuser detection (MUD) is known to reduce MAI and improve CDMA system performance. but many Such techniques have high complexity. Successive interference cancellation (SIC) is an effective MUD technique with relatively low complexity. We consider the software implementation of an SIC receiver for WCDMA uplink transmission on a commercially available general-purpose multi digital signal processor (DSP) platform. This also goes in line with the recent interest in software-defined radio. Issues addressed in this work include job partitioning and signal routing for multiprocessor implementation, design of SIC components (especially the channel estimator and the si mal regenerator), determination of the precision of fixed-point computations. consideration of the receiver's error performance and analysis of the implementation's complexity and efficiency. These issues are tightly coupled with the 3GPP WCDMA specifications. Because the employed platform only contains four DSPs, the implementation only considers up to three users. But this is sufficient for Lis to appreciate various DSP implementation issues of an SIC receiver. Moreover, by the nature of SIC, it is easy to extend the implementation to handle more users with an enlarged platform. Our present implementation achieves real-time speed in the RAKE receiver part of the complete receiver. Due to the complexity in signal regeneration, the overall SIC receiver still falls short of the real-time requirement when interference cancellation is activated. In fact, the platform employed presently cannot support real-time processing when the number of multipaths is four or more, unless either the system architecture or the SIC algorithm is redesigned. Such and other ways of improvement are relegated to potential future work. Copyright (C) 2003 John Wiley Sons, Ltd.
Edge-and-motion-based semantic video object extraction and application to scene composition
(2004)
Jan, YH
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Lin, DW
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We consider automatic segmentation of natural video for content-based video applications. In particular, we present a segmentation algorithm employing both motion and edge information. It employs the edge-linking approach for accurate determination of object boundaries and bidirectional motion estimation for robust tracking of object motion and shape change. The algorithm is designed with computational complexity also in mind. We further consider scene composition using the segmented objects. We, describe and evaluate a method to enlarge or shrink objects for such purpose. The method is amenable to spatial-scalable coding.(1).
Edge-based morphological processing for efficient and accurate video object extraction
(2005-02-01)
Jan, YH
;
Lin, DW
;
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
We consider the edge-linking approach for accurate locating of moving object boundaries in video segmentation. We review the existing methods and propose a scheme designed for efficiency and better accuracy. The scheme first obtains a very rough outline of an object by a suitable means, e.g., change detection. It then forms a relatively compact image region that properly contains the object, through a procedure termed "mask sketch." Finally, the outermost edges in the region are found and linked via a shortest-path algorithm. Experiments show that the scheme yields good performance.
Efficient bit allocation under multiple constraints on cumulated rates for delayed video coding
(1997)
Lin, DW
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Chen, JJ
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交大名義發表
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電子工程學系及電子研究所
;
National Chiao Tung University
We consider optimal encoding of a sequence of video units under a given set of rate constraints which may arise from finite codec delay, finite channel capacity, and finite codec buffer sizes. A Lagrange-multiplier approach is employed and some useful properties of the optimal Lagrange-multiplier solution are obtained under the assumption that the allowed video data rates are continuous. Based on these properties, we derive two solution algorithms for discrete rate allocation. The algorithms are more efficient than that have been presented to date. The solution is optimal when the distortion-rate relations of the video units are convex and the selectable rates of the video units are uniformly spaced with the same granularity. When these conditions do not hold, the Lagrange-multiplier solution may be suboptimal, but can be improved or optimized by a search about the solution.
Efficient optimal rate-distortion coding of video sequences under multiple rate constraints
(1997)
Lin, DW
;
Chen, JJ
;
交大名義發表
;
電子工程學系及電子研究所
;
National Chiao Tung University
We consider optimal coding of video sequences in the sense of employing an optimal selection of quantization scales under buffer and channel constraints. As a result of the delayed-coding framework, multiple rate constraints emerge, leading to the appearance of multiple Lagrange multipliers in a Lagrangian solution approach. We review the applicable Lagrangian optimization theory developed to-date, and present an efficient new solution algorithm.
Error control for H.263 video transmission over wireless channels
(1998)
Chen, YL
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Lin, DW
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We consider ways to combat the error effects when transmitting H.263 video over a wireless channel. The error control measures consist of two "layers," namely, that of the coded bitstream and of the video information. At the bitstream layer, we employ error-resilient entropy coding (EREC), with pseudo-random block interleaving, to reduce the error propagation in decoding of variable-length codewords. At the information layer, we employ a DC recovery scheme to conceal the effects of corrupted DC coefficients. Corrupted motion vectors are detected and corrected using a motion-vector pairing technique in the encoder and a corresponding motion-vector checking and recovery algorithm in the decoder. By these methods, corrupted strips in the images caused by loss of synchronization are avoided. The annoying "green/pink block artifacts" caused by erroneous DC coefficients and the effects of incorrect motion compensation caused by corrupted motion vectors are also reduced.
Extraction of video objects by combined motion and edge analysis
(2002)
Jan, NH
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Lin, DW
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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
We present a mothod for automatic video region segmentation. The method is based, fundamentally, on motion analysis in image areas showing significant intensity variation. Since motion in these areas can be estimated more accurately than that in smoother areas, segmentation based on such motion information can be more reliable. A frequently encountered problem in automatic video segmentation is that the object boundaries may not be accurately identified: the identified boundaries may extend beyond the actual positions by some distance. We develop an edge delineation method, which combines edge detection and motion analysis, to deal with this problem. Some segmentation examples are provided.
Global motion parameter extraction and deformable block motion estimation
(1999-08-01)
Su, CH
;
Hang, HM
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Lin, DW
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A global motion parameter estimation method is proposed. The method can be used to segment an image sequence into regions of different moving objects. For any tao pixels belonging to the same moving object, their associated global motion components have a fixed relationship from the projection geometry of camera imaging. Therefore, by examining the measured motion vectors we are able to group pixels into objects and, at the same time, identify some global motion information. In the presence of camera zoom, the object shape is distorted and conventional translational motion estimation may not yield accurate motion modeling. A deformable block motion estimation scheme is thus proposed to estimate the local motion of an object in this situation. Some simulation results are reported. For an artificially generated sequence containing only zoom activity, we find that the maximum estimation error in the zoom factor is about 2.8%. Rather good moving object segmentation results are obtained using the proposed object local motion estimation method after zoom extraction. The deformable block motion compensation is also Seen to outperform conventional translational block motion compensation for video material containing zoom activity.
Image sequence segmentation via heuristic texture analysis and region tracking
(2002)
Jan, YH
;
Lin, DW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We develop a method for automatic segmentation of natural video sequences. The method is based on low-level spatial and temporal analyses. It features three designs to help facilitate good region segmentation while keeping the computational complexity at a reasonable level. Firstly, a preliminary seed-area identification and a final re-segmentation process are performed on each video frame to help region tracking. Secondly, a simple way to measure homogeneity of texture in a region is devised and the segmentation tries to locate object boundaries at where the texture shows significant changes. And thirdly, a reduced-complexity motion estimation technique is used, so that dense motion fields can be computed at a reasonable complexity. The overall method is organized into four tasks, namely, seed-area identification (for each frame), initial segmentation (only for the first frame in the sequence), motion-based segmentation (for all later frames), and region tracking and updating (also for all later frames). Some examples are provided to illustrate the performance of this method.
Joint carrier recovery and multimodulus blind decision-feedback equalization under high-order QAM
(2004)
Hung, KC
;
Lin, DW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The multimodulus algorithm (MMA) for blind equalization has good performance, but can only tolerate small carrier frequency offsets under high-order QAM. We propose a structure for joint carrier recovery (CR) and blind decision-feedback equalization (DFE), where the DFE is MMA-based. It turns out that a key point is the design and analysis of reduced-constellation phase detectors (PDs) that can facilitate a wide frequency lock range and make the CR loop converge in severe intersymbol interference and noise. Based on this, we design a multistage startup procedure for joint blind DFE and CR. Simulations show that the procedure can yield fast convergence in large carrier frequency errors under high-order QAM.
Joint low-complexity blind equalization, carrier recovery, and timing recovery with application to cable modem transmission
(1999-01-01)
Hwang, CI
;
Lin, DW
;
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
We present a receiver structure with joint blind equalization, carrier recovery, and timing recovery. The blind equalizer employs a decomposition transversal filtering technique which can reduce the complexity of convolution to about a half. We analyze the performance surface of the equalizer cost function and show that the global minima correspond to perfect equalization. We also derive proper initial tap settings of the equalizer for convergence to the global minima. We describe the timing recovery and the carrier recovery methods employed. And we describe a startup sequence to bring the receiver into full operation. The adaptation algorithms for equalization, carrier recovery, and timing recovery are relatively independent, resulting in good operational stability of the overall receiver. Some simulation results for cable-modem type of transmission are presented.
Joint rate-distortion coding of multiple videos
(1999-02-01)
Gu, WC
;
Lin, DW
;
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
Some communications applications involve the simultaneous transmission of multiple videos from one source location. We consider the optimal bandwidth allocation and coding of such co-located multiple videos for transmission over one constant bit rate channel. It turns out that a major issue consists in proper setting of target buffer levels, which arises due to the possibly large variation in the rate-distortion relations of the aggregate video material in a short time period. In fact, this is also an issue in MPEGx coding whose I, P, and B frames possess different rate-distortion characteristics. We outline an approach to optimal solutions under several common types of distortion measures. And we present two simplified techniques and some preliminary simulation results. The simulation results show that such joint bit allocation can significantly enhance the average coding performance over multiple videos.
Jointly optimal video coding and rate control for variable-bit-rate transmission
(1998)
Lin, DW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We consider the problem of optimal rate-distortion coding of video for variable-bit-rate transmission. We present some important properties of the optimal solution, under some conditions. And we outline a computational algorithm.