Browsing by Author "Tsai, Shang-Ho"

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A Bit Allocation Scheme for MIMO Equal Gain Precoders
(2010)
Chao, Chi-Liang
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Tsai, Shang-Ho
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Hsu, Terng-Yin
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資訊工程學系
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電機工程學系
We consider the design of the equal gain precoder in flat-fading and limited feedback multiple-input multiple-output (MIMO) systems. The advantage of the equal gain precoder based on the scalar quantization (SQ) is that it is easier to encode the feedback information and no need to construct codebook in advance. In the sort of precoder, the bit allocation methods will dominate the system performance. In this paper, we explore an efficient bit allocation algorithm for the scalar quantized equal gain precoder. The proposed bit allocation scheme can improve the performance of the straightforward scalar quantized equal gain precoder. Compared to the optimal bit allocation scheme with exhaustive search, the proposed algorithm greatly reduces the computational complexity while the performance is near to the optimal scheme.
A DIFFERENTIAL FEEDBACK SCHEME FOR EQUAL GAIN TRANSMISSION IN TEMPORALLY CORRELATED CHANNELS
(2012-01-01)
Chao, Chi-Liang
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Tsai, Shang-Ho
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Hsu, Terng-Yin
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資訊工程學系
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電機工程學系
The adoption of equal gain transmission (EGT) in MIMO systems can greatly reduce the computational complexity and the design effort of power amplifier. In a temporally correlated channel environment, the channel varies slowly and so does the corresponding beamforming vector. If the slowly varying channel condition can be taken into consideration while designing the feedback schemes of EGT, the computational complexity and feedback overhead of EGT are expected to be further diminished dramatically. In this paper, we propose a differential feedback scheme (DFS) with two algorithms to further improve the performance in EGT. Simulation results show the advantages of the proposed DFS in terms of the feedback overhead and the system performance.
A Joint Codebook Design for Beamforming Systems with Transmit Antenna Selection
(2011)
Chen, Yi-Chi
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Tsai, Shang-Ho
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Chuang, Gene C. H.
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電機工程學系
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Department of Electrical and Computer Engineering
This paper proposes a codebook design that considers transmit antenna selection and beamforming simultaneously. Under the same amount of feedback bits, the proposed codebook can reduce the number of RF units more than half while its performance is still maintained closely (within 0.1 dB loss) to the codebook designs that use all transmit antennas. Since RF units are expensive, the proposed codebook can greatly reduce the hardware implementational cost with slight performance degradation. Moreover, we analyze the proposed codebook and derive a lower bound of symbol error rate (SER). The derived SER lower bound generally matches the simulation results. Simulation results show the proposed codebook with around half active transmit antennas performs comparable to the Lloyd codebook design with full active antennas.
A K-BEST ORTHOGONAL MATCHING PURSUIT FOR COMPRESSIVE SENSING
(2013)
Lin, Pu-Hsuan
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Tsai, Shang-Ho
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Chuang, Gene C. -H.
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
This paper proposes an orthogonal matching pursuit (OMP-) based recovering algorithm for compressive sensing problems. This algorithm can significantly improve recovering performance while it can still maintain reasonable computational complexity. Complexity analysis and simulation results are provided for the proposed algorithm and compared with other popular recovering schemes. We observe that the proposed algorithm can significantly improve the exact recovering performance compared to the OMP scheme. Moreover, in the cases with high compressed ratio, the proposed algorithm can even outperform the benchmark performance achieved by the subspace programming and linear programming.
A Novel Multiuser Beamforming System With Reduced Complexity and Beam Optimizations
(2019-09-01)
Ho, Kuo-Chen
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Tsai, Shang-Ho
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Analog beamforming is widely used in the incoming 5G/B5C communications systems to leverage against power consumption by significantly reducing the number of RF chains. In this paper, we propose a new multiuser beamforming scheme that allows the number of RF chains to be smaller than the number of users. In addition, we propose the beamforming algorithms to minimize the transmit power and weighted symbol error rates for the proposed scheme. For both high- and low-SNR regimes, the proposed beamforming designs provide simple closed-form solutions. The simulation results show that with half the number of RF chains and, thus, lower hardware cost, the proposed scheme outperforms the conventional zero-forcing beamforming systems in several interested parameter settings. Meanwhile, the performance degradation due to the quantization effect of the proposed system is less pronounced than that of the conventional heamforming systems.
A Novel Sub-Nyquist Sampling of Sparse Wideband Signals
(2013)
Lin, Chia-Hua
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Tsai, Shang-Ho
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Chuang, Gene C. H.
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
We propose a Sub-Nyquist sampling scheme using only one mixer, one filter bank with M subfilters and M low rate ADCs. Compared to the MWC (Modulated Wideband Converter) system in [1], the proposed sampling system has several complexity advantages. First, due to the use of only one mixer, the hardware complexity for analog circuits is significantly reduced. Moreover, the system only needs one PN sequence and thus the search complexity for the best sequence is greatly reduced. The use of the best sequence enables the proposed system to achieve a smaller mean square error (MSE) between the original and the reconstructed signals than that of the MWC system. Simulation results are provided to show the performance superiority of the proposed system in terms of MSE and recovery percentage.
A Wearable Channel Selection-Based Brain-Computer Interface for Motor Imagery Detection
(2016-02-01)
Lo, Chi-Chun
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Chien, Tsung-Yi
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Chen, Yu-Chun
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Tsai, Shang-Ho
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Fang, Wai-Chi
Motor imagery-based brain-computer interface (BCI) is a communication interface between an external machine and the brain. Many kinds of spatial filters are used in BCIs to enhance the electroencephalography (EEG) features related to motor imagery. The approach of channel selection, developed to reserve meaningful EEG channels, is also an important technique for the development of BCIs. However, current BCI systems require a conventional EEG machine and EEG electrodes with conductive gel to acquire multi-channel EEG signals and then transmit these EEG signals to the back-end computer to perform the approach of channel selection. This reduces the convenience of use in daily life and increases the limitations of BCI applications. In order to improve the above issues, a novel wearable channel selection-based brain-computer interface is proposed. Here, retractable comb-shaped active dry electrodes are designed to measure the EEG signals on a hairy site, without conductive gel. By the design of analog CAR spatial filters and the firmware of EEG acquisition module, the function of spatial filters could be performed without any calculation, and channel selection could be performed in the front-end device to improve the practicability of detecting motor imagery in the wearable EEG device directly or in commercial mobile phones or tablets, which may have relatively low system specifications. Finally, the performance of the proposed BCI is investigated, and the experimental results show that the proposed system is a good wearable BCI system prototype.
An approximately MAI-Free multiaccess OFDM system in fast time-varying channels
(2007-07-01)
Tadjpour, Layla
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Tsai, Shang-Ho
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Kuo, C.-C. Jay
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電控工程研究所
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Institute of Electrical and Control Engineering
A new multiuser orthogonal frequency division multiplexing (OFDM) transceiver with preceding, called the precoded multiuser OFDM (PMU-OFDM) system, was recently introduced by Tsai et al (2005). The PMU-OFDM system can reduce multiaccess interference (MAI) due to the carrier frequency offset (CFO) to a negligible amount by preceding the data of each user with a codeword selected from either even or odd Hadamard-Walsh codes. The performance of the PMU-OFDM system in a mobile environment, where the channel response varies within one OFDM symbol due to the Doppler effect, is evaluated in this paper. It is shown by analysis and simulation that the use of even or odd Hadamard-Walsh codewords can greatly reduce the MAI effect due to the Doppler effect as well. Generally, all Hadamard-Walsh codewords except for the all-one codeword result in considerable suppression of intercarrier interference (ICI) induced by the Doppler effect. Furthermore, we discuss codeword priority schemes to minimize ICI as much as possible. Finally, simulations results are given to demonstrate the advantage of PMU-OFDM over OFDMA with a codeword priority scheme in the Doppler environment. We show that the PMU-OFDM system with odd Hadamard-Walsh codewords outperforms a half-loaded OFDMA system in a mobile environment.
An Interpretable Compression and Classification System: Theory and Applications
(2020-01-01)
Tseng, Tzu-Wei
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Yang, Kai-Jiun
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Kuo, C-C Jay
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Tsai, Shang-Ho
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電子工程學系及電子研究所
This study proposes a low-complexity interpretable classification system. The proposed system contains main modules including feature extraction, feature reduction, and classification. All of them are linear. Thanks to the linear property, the extracted and reduced features can be inversed to original data, like a linear transform such as Fourier transform, so that one can quantify and visualize the contribution of individual features towards the original data. Also, the reduced features and reversibility naturally endure the proposed system ability of data compression. This system can significantly compress data with a small percent deviation between the compressed and the original data. At the same time, when the compressed data is used for classification, it still achieves high testing accuracy. Furthermore, we observe that the extracted features of the proposed system can be approximated to uncorrelated Gaussian random variables. Hence, classical theory in estimation and detection can be applied for classification. This motivates us to propose using a MAP (maximum a posteriori) based classification method. As a result, the extracted features and the corresponding performance have statistical meaning and mathematically interpretable. Simulation results show that the proposed classification system not only enjoys significant reduced training and testing time but also high testing accuracy compared to the conventional schemes.
An LDPC Decoder with SNR Information
(2013-01-01)
Yang, Kai-Jiun
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Tsai, Shang-Ho
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Hsu, Heng-Chang
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電機工程學系
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Department of Electrical and Computer Engineering
In this work an LDPC decoder which complies with IEEE 802.11n is proposed and implemented. The code rate is 1/2 and the code length is 648. We used partially parallel structure to reduce the area. Additionally the SNR information is applied to improve the BER performance. Moreover the CNU and the BNU in the min-sum-correct algorithm were reordered so that the hardware complexity can be reduced, and early termination can be achieved at the first iteration. Furthermore the parity check matrix is reordered such that the latency of each iteration is reduced by 1/3. The proposed LDPC decoder can reach a throughput of 37 similar to 319Mbps with a core area of 5.3 mm(2) and power consumption 224mW in a TSMC 90nm process.
Bit Allocation Schemes for MIMO Equal Gain Precoding
(2011-05-01)
Chao, Chi-Liang
;
Tsai, Shang-Ho
;
Hsu, Terng-Yin
;
資訊工程學系
;
電機工程學系
We design equal gain precoders with scalar quantization in MIMO systems with limited feedback, which do not require the predefined codebook. In such precoders, bit allocation can be used to quantize the precoding vector/matrix to further improve the system performance. There are two conventional bit allocation schemes. One is the uniform bit allocation and the other is the optimal bit allocation obtained by using exhaustive search. The uniform bit allocation is simple but turns out to have obvious performance degradation. On the other hand, the exhaustive search method leads to the optimal performance. However, its computational complexity is extremely high and may be somewhat impractical to be realized. In this paper, we propose two bit allocation schemes for the MIMO equal gain precoder with scalar quantization. Both of the proposed methods are with low complexity and their performance is close to the optimal scheme. Consequently, the proposed bit allocations provide good trade-off between performance and complexity.
Codeword Design for Ultra-Wideband (UWB) Precoding
(2010-01-01)
Chang, Yu-Hao
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Tsai, Shang-Ho
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Yu, Xiaoli
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Kuo, C. -C. Jay
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電機工程學系
A precoding technique applied to symbols transmitted in an ultra-wideband (UWB) system can concentrate the signal power at the receiver for a higher data detection rate. The codeword design problem for optimal UWB precoding is investigated in this work. After the problem formulation, we examine its solution in the full-rank and the reduced-rank subspaces to obtain different tradeoffs between the detection performance and the amount of feedback messages. Furthermore, we propose two subspace selection schemes, each of which corresponds to a code design method. The resultant optimal codewords improve the performance of previous work significantly at the expense of a slightly increased amount of feedback messages. Finally, the performance of a precoded UWB system with various codewords is compared via computer simulation.
Compressed Sensing Recovery Algorithms and VLSI Implementation
(2013)
Lin, Kuan-Ting
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Yang, Kai-Jiun
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Lin, Pu-Hsuan
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Tsai, Shang-Ho
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電機工程學系
This paper proposes two recovery algorithms modified from subspace pursuit(SP) for compressed sensing problems. These algorithms can reduce the complexity of SP and maintain high recovery rate. Complexity analysis and simulation results are provided to demonstrate the improvements. Additionally this work has implemented the VLSI circuit APR of the proposed algorithm using TSMC 90 nm process. The target clock frequency is 100MHz, and the corresponding APR dimension is 11.69mm(2). Based on the post-layout simulation the average power consumption is 431 mW.
Decentralized Expectation Consistent Signal Recovery for Phase Retrieval
(2020-01-01)
Wang, Chang-Jen
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Wen, Chao-Kai
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Tsai, Shang-Ho
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Jin, Shi
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電子工程學系及電子研究所
In this study, we present a phase retrieval solution that aims to recover signals from noisy phaseless measurements. A recently proposed scheme known as generalized expectation consistent signal recovery (GEC-SR), has shown better accuracy, speed, and robustness than many existing methods. However, sensing high-resolution images with large transform matrices presents a computational burden for GEC-SR, thereby limiting its applications to areas, such as real-time implementation. Moreover, GEC-SR does not support distributed computing, which is an important requirement to modern computing. To address these issues, we propose a novel decentralized algorithm called & x201C;deGEC-SR & x201D; by leveraging the core framework of GEC-SR. deGEC-SR exhibits excellent performance similar to GEC-SR but runs tens to hundreds of times faster than GEC-SR. We derive the theoretical state evolution for deGEC-SR and demonstrate its accuracy using numerical results. Analysis allows quick generation of performance predictions and enriches our understanding on the proposed algorithm.
Design of applying FlexRay-bus to federated archiectecture for triple redundant reliable UAV flight control system
(2017-01-01)
Wu, Chang-Han
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Chen, Ti-Jui
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Hsu, Terng-Yin
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Tsai, Shang-Ho
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Chang, Hsung-Pin
For an Unmanned Aerial Vehicle (UAV) performing a mission, any failure of the flight control system can result in fatal disaster. Therefore, reliability requirement for UAV flight control system becomes increasingly important and then the redundancy technology is considered as a solution to enhance system reliability. This paper studies the designs of reliability, system architecture, and redundancy management logic for UAV flight control system. Therefore, a reliable federated architecture design for triple redundant UAV flight control system is introduced, in which the distributed hardware design combined with centralized software framework was adopted as well. The number of subsystems in the case study is more than that of centralized architecture and less for distributed architecture. Next, the fault detection and fault tolerant design can be achieved, and simultaneously the design problems associated with distributed software framework was reduced. Furthermore, by using the distributed hardware, system's reliability requirement of single hardware module was decreased. Consequently, the goal of high reliability for the entire system reached. Finally, FlexRay bus with time-trigger mechanism was chosen to simulate the communication of such a federated architecture designed. The experimental results show that the design is reasonable and satisfy the high reliability, high performance-price ratio and high expandability requirements of UAV flight control system.
Design of Low-Overhead Cooperative Beamforming for Information Relaying in Wireless Sensor Networks Under Imperfect Quantized SNR of Source-to-Relay Links
(2013-03-01)
Wu, Jwo-Yuh
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Hu, Chung-Hsuan
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Wang, Tsang-Yi
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Tsai, Shang-Ho
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電機資訊學士班
We consider a wireless sensor network employing cooperative beamforming for information relaying. To reduce the signaling overhead, each relay node quantizes the SNR of the source-to-relay (S-R) link into one bit, which is then transmitted through a binary symmetric channel (BSC) with a known crossover probability to the destination. Given the set of the error-corrupted one-bit messages received at the destination, the beamforming design criterion is the maximization of the expected receive SNR, averaged over the conditional bit-flipping distributions of BSCs. We derive an analytic expression for the considered SNR metric, which is a complicated function of the beamforming weights. To facilitate analysis, we further derive a tractable lower bound for the conditional average SNR. By conducting maximization with respect to this lower bound, a closed-form sub-optimal beamformer can be obtained as a solution to a generalized eigenvalue problem. Computer simulations are used to illustrate the performance of the proposed scheme.
Design of novel non-contact multimedia controller for disability by using visual stimulus
(2015-12-01)
Pan, Jeng-Shyang
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Lo, Chi-Chun
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Tsai, Shang-Ho
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Lin, Bor-Shyh
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影像與生醫光電研究所
The design of a novel non-contact multimedia controller is proposed in this study. Nowadays, multimedia controllers are generally used by patients and nursing assistants in the hospital. Conventional multimedia controllers usually involve in manual operation or other physical movements. However, it is more difficult for the disabled patients to operate the conventional multimedia controller by themselves; they might totally depend on others. Different from other multimedia controllers, the proposed system provides a novel concept of controlling multimedia via visual stimuli, without manual operation. The disabled patients can easily operate the proposed multimedia system by focusing on the control icons of a visual stimulus device, where a commercial tablet is used as the visual stimulus device. Moreover, a wearable and wireless electroencephalogram (EEG) acquisition device is also designed and implemented to easily monitor the user\'s EEG signals in daily life. Finally, the proposed system has been validated. The experimental result shows that the proposed system can effectively measure and extract the EEG feature related to visual stimuli, and its information transfer rate is also good. Therefore, the proposed non-contact multimedia controller exactly provides a good prototype of novel multimedia controlling scheme. (C) 2015 Elsevier Ireland Ltd. All rights reserved.
Economic dispatch of chiller plant by improved ripple bee swarm optimization algorithm for saving energy
(2016-05-05)
Lo, Chi-Chun
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Tsai, Shang-Ho
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Lin, Bor-Shyh
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影像與生醫光電研究所
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電控工程研究所
This paper presents an improved ripple bee swarm optimization (IRBSO) algorithm to solve the problem of the economic dispatch of chiller plants (EDCP). Using the characteristics of biological communities, different movement models are adopted to search within the feasible solution space. This paper uses nonlinear ripple weight factors and self-adaption repulsion factor to improve the BSO and proposes the influence of parameters on the IRBSO method to more effectively search the feasible space. For all bee swarms, the efficiency of searching movement in the solution space improves, and the capacity of information discovery and mining increases. This paper utilizes the test cases to verify the proposed IRBSO, including EDCP problems for a single day and a single week. Compared with other methods, the results of the proposed IRBSO exhibit higher accuracy and stability, making it suitable for the operation planning of multiple chiller systems. (C) 2016 Elsevier Ltd. All rights reserved.
Equal Gain Transmission with Antenna Selection in MIMO Communications
(2011-05-01)
Tsai, Shang-Ho
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電機工程學系
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Department of Electrical and Computer Engineering
The beamforming vectors of an equal gain transmission (EGT) contains phase information only and thereby enjoys several implementational advantages when compared to the optimal scheme, i.e. maximum ratio transmission (MRT). The implementational advantages make EGT a promising solution for simple transceiver design while offering a performance comparable to that of MRT. This solution motivates us to explore how close the performance can be between EGT and MRT. The maximum SNR loss between EGT and MRT is known to be 1.05 dB in MISO channels. However, little is known about the SNR loss in MIMO channels, since no closed-form solution is available for the best EGT in MIMO channels. In this work, a suboptimal closed-form EGT design for MIMO channels is proposed and its performance is analyzed. Interestingly, the maximum SNR loss between the proposed EGT and the MRT (both employing MRC in receiver) in MIMO channels is shown to be approximately 1.05 dB as well. Moreover, instead of applying conventional all transmit antennas, this study proposes to adopt antenna selection, to further improve the performance of EGT. Two antenna selection algorithms are proposed and the corresponding performance is analyzed. When the proposed antenna selection algorithms are applied to EGT, the SNR loss between EGT and MRT can be reduced to as low as 0.45-0.65 dB, with the numbers of transmit antennas ranging from 4 to 8. One of the proposals with fixed number of transmit antennas not only outperforms conventional EGT but also requires fewer number of RF (radio frequency) components; also, it employs constant power in each transmit antenna like EGT does. As a result, hardware complexity can be reduced by this proposal. Furthermore, design strategies to apply the proposed EGT and antenna selection algorithms in systems with limited feedback are also suggested.
Finite-Alphabet Precoding for Massive MU-MIMO With Low-Resolution DACs
(2018-07-01)
Wang, Chang-Jen
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Wen, Chao-Kai
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Jin, Shi
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Tsai, Shang-Ho
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電子工程學系及電子研究所
Massive multiuser multiple-input multiple-output (MU-MIMO) systems are expected to he the core technology in fifth-generation wireless systems because they significantly improve spectral efficiency. However, the requirement for a large number of radio frequency (RF) chains results in high hardware costs and power consumption, which obstruct the commercial deployment of massive MIMO systems. A potential solution is to use low-resolution digital-to-analog converters (DAC)/analogto-digital converters for each antenna and RF chain. However, using low-resolution DACs at the transmit side directly limits the degree of freedom of output signals and thus poses a challenge to the precoding design. In this paper, we develop efficient and universal algorithms for a downlink massive MU-MIMO system with finite-alphabet precodings. Our algorithms are developed based on the alternating direction method of multipliers (ADMM) framework. The original ADMM does not converge in a nonlinear discrete optimization problem. The primary cause of this problem is that the alternating (update) directions in ADMM on one side are biased, and those on the other side are unbiased. By making the two updates consistent in an unbiased manner, we develop two algorithms called iterative discrete estimation (IDE) and IDE2. IDE demonstrates excellent performance and IDE2 possesses a significantly low computational complexity. Compared with state-of-the-art techniques, the proposed preceding algorithms present significant advantages in performance and computational complexity.