Browsing by Author "Lee, Ta-Sung"

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A closed-form phase-comparison ML DOA estimator for automotive radar with one single snapshot
(2013)
Huang, Chung-Jung
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Dai, Chia-Wei
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Tsai, Tsung-Yu
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Chung, Wei-Ho
;
Lee, Ta-Sung
In automotive radar systems, only a small number of snapshots are available for direction-of-arrival (DOA) estimation in high mobility scenarios. We here propose a closed-form single-snapshot maximum likelihood (ML) DOA estimator based on the phase-comparison technique. The estimator can be effective in a wide field-of-view (FOV) scenario and is robust to gain-mismatch effects among antenna elements. Computer simulations are conducted to confirm the effectiveness of the proposed method.
A Cooperative Multi-Group Priority MAC Protocol for Multi-Packet Reception Channels
(2009-11-01)
Yang, Wen-Fang
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Wu, Jwo-Yuh
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Wang, Li-Chun
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Lee, Ta-Sung
;
電子工程學系及電子研究所
Medium access control (MAC) protocol design for cooperative networks over multi-packet reception (MPR) channels is a challenging topic, but has not been addressed in the literature yet. In this paper, we propose a cooperative multi-group priority (CMGP) based MAC protocol to exploit the cooperation diversity for throughput enhancement over MPR channels. The proposed approach can bypass the computationally-intensive active user identification process. Moreover, our method can efficiently utilize the idle periods for packet relaying, and can thus effectively limit the throughput loss resulting from the relay phase. By means of a Markov chain model, the worst-case throughput analysis is conducted. The results allow us to investigate the throughput performance of the proposed CMGP protocol directly in terms of the MPR channel coefficients. Simulation results confirm the system-wide throughput advantage achieved by the proposed scheme, and also validate the analytic results.
A Distributed Cluster-Based Self-Organizing Approach to Resource Allocation in Femtocell Networks
(2012)
Lai, Wei-Sheng
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Lee, Ta-Sung
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電機工程學系
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Department of Electrical and Computer Engineering
Femtocell networks are an advantageous low-cost technology for providing indoor coverage and high-capacity solutions. Femtocell networks reuse the spectrum resources in co-channel environments due to its high geometric density. In this paper, a distributed algorithm is proposed, which uses a cluster-based self-organizing approach to managing the spectrum and power resources among femtocells. The aim of the proposed algorithm is to achieve an optimized throughput of the networks in a decentralized manner. The algorithm involves three phases: sensing phase, sniffer phase, and power control phase, and is performed in each femtocell. Simulation results indicate that the proposed algorithm improves the uplink throughput of the femtocell networks and effectively avoids interference with the conventional macro-cellular networks.
A geometry based efficient decoder for underdetermined MIMO systems
(2015-06-01)
Huang, Chung-Jung
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Lee, Chang-Shen
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Chung, Wei-Ho
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Lee, Ta-Sung
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電機資訊學士班
In this paper, a geometry based decoder with low decoding complexity and exact maximum-likelihood (ML) performance is proposed for underdetermined multiple-input multiple-output (MIMO) systems. In the proposed decoder, an underdetermined MIMO system can be divided into a multiple-input single-output (MISO) sub-system and a regular MIMO sub-system in which numbers of transmit and receive antennas are equal. An efficient slab search algorithm (ESSA) is adopted to efficiently obtain valid candidate points in the MISO sub-system. By adopting ESSA in the MISO sub-system and sphere decoding algorithm (SDA) in the MIMO sub-system, ML solution of underdetermined MIMO system can be obtained with low computational complexity. To further reduce the computational complexity, a near-ML SDA is proposed to more efficiently find the candidate points in the MIMO sub-system. In addition, an optimal preprocessing technique is proposed from the geometrical perspective and the comprehensive analysis on the complexity reduction is also provided. Simulation results indicate that the proposed approach significantly reduces the complexity as compared to existing ML decoders, particularly for systems with large number of antennas and/or high-order constellations. (C) 2015 Elsevier Inc. All rights reserved.
A hybrid multiuser detection technique based on interference cancellation knowledge in MIMO communications
(2007)
Pan, Chien-Hung
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Lee, Ta-Sung
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Li, Yiming
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電信工程研究所
;
Institute of Communications Engineering
In this paper, we propose a hybrid multiuser detection (MUD) technique, which is similar to the maximum likelihood detector (MLD) but with reduced complexity, for the application of multiple-input multiple-output (MIMO) communications. The proposed MUD technique avoids the exhaustive search required for the elimination of inter-antenna interference (IAI). Instead, the proposed method incorporates an efficient hybrid multiuser detection technique and consists of a two-stage procedure to achieve the performance of the ML detector with an acceptable level of computational complexity. The first stage performs interference cancellation by using the sorted QR decomposition (SQRD), and the second stage performs the genetic algorithm (GA). This two-stage procedure is thus called SQRD GA-MUD. The main advantage of the SQRD scheme is that it provides a "good initial setting knowledge" by eliminating IAI to improve the fitness of the population for GA. Simulation results obtained in this study demonstrate that SQRD GA-MUD achieves a gain of 6 dB to 15 dB compared to other well known detectors, with an acceptable number of iterations.
A Low Complexity Antenna Selection Algorithm for Energy Efficiency in Massive MIMO Systems
(2015)
Tai, Tzu-Hao
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Chung, Wei-Ho
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Lee, Ta-Sung
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電信工程研究所
;
Institute of Communications Engineering
Massive multi-input multi-output (MIMO) system adopting large amount of antennas is a promising technique to improve spectral efficiency and energy efficiency for next generation wireless communication systems. However, the power consumptions of the radio frequency (RF) chains can be huge, which poses great challenges. In this paper, we consider the problem of transmit RF chain configuration with the goal to maximize energy efficiency under total power constraint in massive MIMO systems. The RF chain configuration can be decided by applying antenna selection methods. Considering the trade-off between performance and complexity, we propose the norm-and-correlation-based selection algorithm with low complexity for energy efficiency maximization. Our selection metric considers the effect of the norm of each channel column and correlation between columns while attaining low computational complexity. Simulation results validate the advantages of the proposed algorithm.
A Low Complexity Configuration Selection Algorithm in IA-aided Uplink Coordinated Multipoint Systems
(2014-01-01)
Lee, Ming-Chun
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Huang, Chung-Jung
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Chung, Wei-Ho
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Lee, Ta-Sung
;
電機資訊學士班
This work investigates the configuration selection in IA-aided UL CoMP systems which pursues the maximal achievable sum rate. The configuration is defined by the number of data streams transmitted in each user. Intuitively, the solution can be found by exhaustively calculating the achievable sum rate for all the possible configurations, and select the configuration leading to the maximal achievable sum rate. The exhaustive search method is infeasible due to its high complexity. Based on the characteristics of IA-aided UL CoMP systems, an algorithm is proposed to obtain the configuration with extremely low complexity, and the proposed approach achieves comparable performance as in exhaustive method.
A Multi-Group Priority Based Cooperative MAC Protocol for Multi-Packet Reception Channels
(2009)
Yang, Wen-Fang
;
Wu, Jwo-Yuh
;
Wang, Li-Chun
;
Lee, Ta-Sung
;
電信工程研究所
Medium access control (MAC) protocol design for cooperative networks over multi-packet reception (MPR) channels is a challenging topic, but has not been addressed in the literature yet. In this paper, we propose a MAC protocol to exploit the cooperation diversity for throughput enhancement over MPR channels. The proposed approach can efficiently utilize the idle periods for packet relaying, and can thus effectively limit the throughput loss resulting from the relay phase. By means of a Markov chain model, the worst-case throughput analysis is conducted. Specifically, we derive (i) a closed-form upper bound for the throughput penalty of the direct link that is caused by the interference of concurrent packet relay transmission; (ii) a closed-form lower bound for the throughput gain that a user with packet transmission failure can benefit thanks to cooperative packet relaying. The results allow us to investigate the throughput performance of the proposed protocol directly in terms of the MPR channel coefficients. Simulation results confirm the system-wide throughput advantage achieved by the proposed scheme, and also validate the analytic results.
A multigroup priority queueing MAC protocol for wireless networks with multipacket reception
(2008)
Yang, Wen-Fang
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Wu, Jwo-Yuh
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Wang, Li-Chun
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Lee, Ta-Sung
;
電信工程研究所
Relying on a simple flag-assisted mechanism, a multigroup priority queueing (MGPQ) medium access control (MAC) protocol is proposed for the wireless networks with multipacket reception ( MPR). The proposed MGPQ scheme is capable of overcoming two major performance bottlenecks inherent in the existing MPR MAC protocols. First, the proposed solution can automatically produce the list of active users by observing the network traffic conditions, remove the need of active user estimation algorithm, and thus can largely reduce the algorithm complexity. Second, the packet blocking constraint imposed on the active users for keeping compliant with prediction is relaxed. As a result, the proposed MGPQ is not only applicable to both homogeneous and heterogeneous cases, but also outperforms the existing MPRMAC protocols. Simulation results show that the network throughput can be improved by 40% maximum and 14% average as compared with the well- known dynamic queue (DQ) MAC protocol.
A Survey on Deep Learning-Based Vehicular Communication Applications
(1970-01-01)
Lin, Chia-Hung
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Lin, Yu-Chien
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Wu, Yen-Jung
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Chung, Wei-Ho
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Lee, Ta-Sung
Besides the use of information transmission, vehicular communications also perform an essential role in intelligent transportation systems (ITS) for exchanging critical driving information among end users, vehicles, and infrastructures. Moreover, to enhance the understanding of the local environment, increasingly more data are collected by sensors, inducing an extensive use of deep learning (DL)-based algorithms in ITS. To further promote the development of DL-based algorithms in ITS, in this paper, we present a concise introduction of DL technologies. Then, we conduct an in-depth investigation on two popular DL-based applications used in ITS, traffic flow forecasting and trajectory prediction, focusing onwhenandhowthe authors employ different DL models and training schemes in these tasks. Finally, we raise two existing problems while employing DL-based algorithms in practical ITS and further discuss certain recent advances in DL-based research to tackle these challenges. To encourage more researchers to focus on the development of DL-based algorithms in ITS for a better world, we hope this paper can be treated as an informational material for prospective researchers, which contains the essential background knowledge of DL-based ITS applications; we also hope this paper will encourage experienced researchers to counter the open challenges and achieve a technical breakthrough to ITS.
A variable step-size sign algorithm for channel estimation
(2014-09-01)
Li, Yuan-Ping
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Lee, Ta-Sung
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Wu, Bing-Fei
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電機資訊學士班
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Undergraduate Honors Program of Electrical Engineering and Computer Science
This paper proposes a new variable step-size sign algorithm (VSSA) for unknown channel estimation or system identification, and applies this algorithm to an environment containing two-component Gaussian mixture observation noise. The step size is adjusted using the gradient-based weighted average of the sign algorithm. The proposed scheme exhibits a fast convergence rate and low misadjustment error, and provides robustness in environments with heavy-tailed impulsive interference. (C) 2014 Elsevier B.V. All rights reserved.
Achievable Throughput for Dual-Mode Limited-Feedback Transmit Beamforming over Temporally Correlated Wireless Channels
(2010)
Chang, Yi-Chieh
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Wu, Jwo-Yuh
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Lee, Ta-Sung
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電機工程學系
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Department of Electrical and Computer Engineering
Achieving high system throughput for limited-feedback communications against the time-varying channel effect is rather crucial in modern mobile system designs. Within the beamforming setup, this paper derives analytic throughput results for both the "more feedback less often" and "less feedback more often" scenarios. More specifically, under the assumptions that (i) the channels over two consecutive time slots follow the first-order Markov model and (ii) in each time slot, reliable feedback of a fixed amount of bits is allowed, the achievable system throughput over two consecutive time slots in both scenarios are characterized. In particular, while the exact throughput is in an integral form, we derive the associated closed-form approximate formulae which facilitate throughput evaluation without resorting to numerical integration. The analytic results also lead to a very low-complexity throughput-based mode selection scheme. Simulation study shows that: (1) the derived closed-form approximation is quite accurate; (2) with the aid of the proposed mode selection method, the throughput performance is robust against the channel temporal variation.
An efficient near-ML algorithm with SQRD for wireless MIMO communications in metro transportation systems
(2007)
Pan, Chien-Hung
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Lee, Ta-Sung
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Li, Yiming
;
電信工程研究所
;
Institute of Communications Engineering
A high-speed multiple input multiple output (NEMO) wireless communication system is proposed for metro transportation. In order to better mitigate the inter-antenna interference (LAI) which degrades the quality of the MIMO receiver, we propose an efficient hybrid multiuser detection (MUD) technique. This approach consists of a two-stage procedure to achieve the optimum multiuser detector (OMD) by an acceptable computational complexity. The first stage performs interference cancellation by using sorted QR decomposition (SQRD), and the second stage performs the genetic algorithm (GA). It has two significant advantages: 1) The SQRD scheme provides "good initial setting knowledge" to improve the fitness of the population for GA. 2) The effect of fitness calculation is obtained from the QR decomposition (QRD) of a MIMO channel. Simulation results demonstrate that the two-stage procedure obtains a gain of 3 dB to 25 dB than other well-known MUD schemes. The computational complexity of the two-stage procedure can be reduced by 30% with QRD than other fitness calculation scheme in GA-MUD.
An Enhanced Multi-Packet Reception MAC Protocol: Cooperative Approach
(2008)
Yang, Wen-Fang
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Wu, Jwo-Yuh
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Lee, Ta-Sung
;
電信工程研究所
;
Institute of Communications Engineering
An enhanced medium access control (MAC) protocol for wireless networks with multi-packet reception (MPR) capability is proposed. The proposed protocol is based on the dynamic multi-group priority queueing protocol recently introduced in [I] to exploit the cooperative diversity for improving the system throughput. Two kinds of throughput losses, i.e., over-loaded loss and under-loaded loss, are defined first to clarify the opportunity of improvement. it Markov chain analysis is provided as the theoretical background. It is shown that the under-loaded loss can be compensated by cooperation among users in light traffic environment, and the system throughput can be improved accordingly. Simulations further compare the delay and packet loss ratio with and without cooperation, it is found the average performance is improved too.
BER Analysis for Spatial Modulation in Multicast MIMO Systems
(2016-07)
Lee, Ming-Chun
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Chung, Wei-Ho
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Lee, Ta-Sung
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電機學院
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College of Electrical and Computer Engineering
In this paper, we investigate the bit error rate (BER) for multicast multiple-input multiple-output (MIMO) systems, employing spatial modulation (SM) and its variants, called multicast SM-type MIMO systems, in Rayleigh fading channels. The system BER, here, is derived by first attaining the BER of the worst receiver of each channel realization set, and then averaging over all possible sets. We first consider the uncorrelated channels. By exploiting the system statistics, a tight BER upper bound is proposed and the diversity is discussed for the systems. We then perform the asymptotic analysis, and show that the BER of the multicast SM-type MIMO system can be alternatively analyzed by analyzing the simple point-to-point SM-type MIMO system with Weibull fading channels. Through this property, a closed-form asymptotic BER upper bound is provided and the impact of the receiver number on BER is analyzed. Subsequently, our investigation is extended to correlated channels where all the receivers share the same correlation statistics. The BER analysis is performed again through the framework similar to the uncorrelated case. In the analysis, the tight upper bound is derived and the effect of correlations is analyzed. Moreover, we provide an explicit expression for the SNR degradation caused by the receive correlation through the analysis. Finally, simulations are exploited to evaluate the BER of the multicast SM-type MIMO systems and validate the analyses.
BER Improved Transmit Power Allocation for D-STTD Systems with QR-Based Successive Symbol Detection
(2009)
Wu, Jwo-Yuh
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Kuang, Jie-Gang
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Lee, Ta-Sung
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電信工程研究所
;
Institute of Communications Engineering
We propose a BER improved power allocation scheme for D-STTD systems over i.i.d. Rayleigh fading channels under the OR-based successive detection framework. Instead of relying on BER under a fixed channel realization, the adopted design criterion is the mean BER (assuming there is no inter-layer error propagation) averaged with respect to the channel distribution. Such a design metric has two-fold advantages: (i) It is analytically tractable and is closely related to a block error probability upper pound when inter-layer error propagation occurs, and (ii) There is no need for repeated feedback of the instantaneous channel information. By exploiting a distinctive channel matrix structure unique to D-STTD systems we derive a closed-form approximate tipper bound of the considered BER metric; through minimization (if this bound an optimal power allocation scheme is obtained. Numerical simulation is used to illustrate the performance of the proposed method.
BER minimized power allocation for quasi-orthogonal space-time block coded signals with QR-based successive detection
(2007)
Wu, Jwo-Yuh
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Fan, Sheng-Po
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Kuang, Jie-Gang
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Lee, Ta-Sung
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電信工程研究所
We propose a minimal BER power allocation scheme for a class of quasi-orthogonal space-time block coded transmission (the so-called ABBA system) over i.i.d. Rayleigh fading channels under the QR-based successive detection framework. Instead of relying on BER under a fixed channel realization, the design criterion we adopt is the overall mean BER averaged with respect to the channel distribution. By exploiting a distinctive channel matrix structure induced by the ABBA code we derive a closed-form upper bound of the considered BER metric and, through minimization of which, an optimal power allocation scheme is obtained. Numerical simulation shows that the resultant performance is almost identical to that of the joint maximum-likelihood decoding in the medium-to-high SNR regime.
Blind channel estimation for single-carrier space-time block coded transmission with frequency-domain equalization: A diagonal precoding based approach
(2006)
Wu, Jwo-Yuh
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Lee, Ta-Sung
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電信工程研究所
;
Institute of Communications Engineering
Relying on non-redundant diagonal precoding and i.i.d. source assumption, we propose a blind channel estimation scheme for single-carrier frequency-domain equalization based space-time block coded systems. The proposed method exploits the precoding-induced linear signal structure in the conjugate cross-correlation between the two temporal block receive signals as well as the circulant channel matrix property, and can yield exact solutions whenever the channel noise is circularly Gaussian and the receive data statistic is perfectly obtained. The channel estimation formulation builds on rearranging the set of linear equations relating the entries of conjugate cross-correlation matrix and products of channel impulse responses into one with a distinctive block-circulant with circulant-block (BCCB) structure. This allows a simple identifiability condition depending on precoder parameters alone, and also provides a natural yet effective optimal precoder design framework against imperfect data estimation. We consider the data mismatch as a deterministic perturbation and propose to minimize the condition number of the BCCB system matrix, leading to a simple closed-form optimal solution. Numerical examples are used to illustrate the performance of the proposed method.
Channel-Aware Decision Fusion With Unknown Local Sensor Detection Probability
(2010-03-01)
Wu, Jwo-Yuh
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Wu, Chan-Wei
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Wang, Tsang-Yi
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Lee, Ta-Sung
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電機工程學系
Existing channel-aware decision fusion schemes assume that the local detection probability is known at the fusion center (FC). However, this paradigm ignores the possibility of unknown sensor alarm responses to the occurrence of events. Accordingly, this correspondence examines the binary decision fusion problem under the assumption that the local detection probability is unknown. Treating the communication links between the nodes and the FC as binary symmetric channels and assuming that the sensor nodes transmit simple one-bit reports to the FC, the global fusion rule is formulated initially in terms of the generalized likelihood ratio test (GLRT). Adopting the assumption of a high SNR regime, an approximate maximum likelihood (ML) estimate is derived for the unknown parameter required to implement the GLRT that is affine in the received data. The GLRT-based formulation is intuitively straightforward, but does not permit a tractable performance analysis. Therefore, motivated by the affine nature of the approximate ML solution, a simple alternative fusion rule is proposed in which the test statistic remains affine in the received data. It is shown that the proposed fusion rule facilitates the analytic characterization of the channel effect on the global detection performance. In addition, given a reasonable range of the local detection probability, it is shown that the global detection probability can be improved by reducing the total link error. Thus, a sensor power allocation scheme is proposed for enhancing the detection performance by improving the link quality. Simulation results show that: 1) the alternative fusion rule outperforms the GLRT; and 2) the detection performance of the fusion rule is further improved when the proposed power loading method is applied.
Channel-Aware Quantization for Decentralized BLUE via Energy-Constrained Wireless Sensor Networks
(2009)
Wu, Jwo-Yuh
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Chen, Chiu-Ju
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Lee, Ta-Sung
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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
Bit assignment for local sensor data quantization in the decentralized best-linear-unbiased-estimation (BLUE) scenario is widely addressed in the signal processing research for wireless sensor networks. When the timely knowledge of the instantaneous sensor noise variance (for implementing the BLUE fusion rule) is too costly to obtain, one plausible alternative is to exploit the associated statistical characterization. Related such proposals, however, do not explicitly take into account the communication link impairments such as channel fading. In this paper we extend the current results to the more realistic case when signal transmission is subject to the fading effect. We show that the optimal bit allocation problem can be reformulated in the form of convex optimization, and then derive an analytical solution. Through numerical simulation the proposed solution is seen to outperform the uniform energy allocation scheme.