Browsing by Author "Huang, Chia-Chi"

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A Derivation on the Equivalence Between Newton's Method and DF DFT-Based Method for Channel Estimation in OFDM Systems
(2008-10-01)
Ku, Meng-Lin
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Huang, Chia-Chi
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電信工程研究所
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Institute of Communications Engineering
In this paper, we derive the decision-feedback (DF) discrete Fourier transform (DFT)-based channel estimation method from Newton's method for space-time block code (STBC)/orthogonal frequency division multiplexing (OFDM) systems. Through our derivation, the equivalence between Newton's method and the DF DFT-based method is established. Computer simulations are also used to demonstrate the equivalence of the two methods in terms of BER and normalized square error (NSE) performance. Finally, the results presented in this paper also hold for conventional OFDM systems.
A Differential Sliding Correlation Scheme for Symbol Timing Detection in Time Domain Synchronous OFDM Systems
(2009)
Sheu, Chorng-Ren
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Huang, Chia-Chi
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電信工程研究所
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Institute of Communications Engineering
In this paper, a new symbol timing detection scheme robust to carrier frequency offset is proposed for Time Domain Synchronous (TDS) OFDM systems. The proposed method computes the sliding correlation from both the differential received signal and the differential PN sequence. Rapid symbol timing detection can be obtained based on the correlation peaks. As differential operation is adopted before sliding correlation in the proposed method, the time-dependent linear phase effect caused by the carrier frequency offset will not influence the correlation peaks. Nevertheless, the incorrect correlation peaks caused by the cross terms of the multipath may be detected. An ambiguity protection module is added to validate the correlation peak detection results and further improve the system performance. Our simulation results show that the proposed scheme for symbol timing detection is accurate and simultaneously robust to carrier frequency offset for TDS-OFDM systems in both a time-varying TU6 channel and a fixed two-path channel.
A Hybrid Inter-Cell Interference Mitigation Scheme for an OFDMA Downlink System
(2010-01-01)
Chiu, Che-Sheng
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Huang, Chia-Chi
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電信工程研究所
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Institute of Communications Engineering
A number of inter-cell interference coordination schemes have been proposed to mitigate the inter-cell interference problem for orthogonal frequency division multiple access (OFDMA) systems and among them, partial frequency reuse is considered one of the most promising approaches. In this paper, we propose an inter-cell interference mitigation scheme for an OFDMA downlink system, which makes use of both partial frequency reuse and soft handover. The basic idea of this hybrid scheme is to dynamically select between a partial frequency reuse scheme and a soft handover scheme to provide better signal quality for cell edge users. Compared with the standard partial frequency reuse scheme, simulation results show that approximately one quarter of cell edge users can get improvements in signal quality as well as link spectral efficiency from using the proposed hybrid scheme. We also observe that by using our approach, there is a significant cell edge throughput gain over the standard partial frequency reuse scheme. Furthermore, based on a well defined data rate fairness criterion, we show that Our method achieves higher overall system capacity as compared with the standard partial frequency reuse scheme.
A Low Complexity Interference Suppression Scheme for High Mobility STBC-OFDM Systems
(2012)
Sheu, Chorng-Ren
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Liu, Jia-Wei
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Huang, Chuan-Yuan
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Huang, Chia-Chi
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電信工程研究所
A novel low complexity scheme based on received data symbol pair reordering and optimal selection, is proposed for space time block coded (STBC) OFDM systems to suppress co-channel interference (CCI) and inter-carrier interference (ICI) caused by time-varying channels. The proposed scheme reorders the conventional received data symbol pairs to produce extra received data symbol pairs. Then, the STBC decoding is performed on all the received data symbol pairs, and the STBC decoding output signals are used to obtain multiple combined signals. Finally, the optimal combined signal with minimum interference is selected to suppress CCI and ICI, and the system performance will be improved as long as the channels are mutually uncorrelated. Our computer simulation results verify that the proposed low complexity scheme achieves good performance for high mobility 2x2 STBC-OFDM systems in the ITU Vehicular A (VA) channels.
A modified DVB-T system architecture with multi-carrier multi-code transmission and MPIC based reception
(2008)
Jeng, You-Tsai
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Ku, Meng-Lin
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Huang, Chia-Chi
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電信工程研究所
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Institute of Communications Engineering
In this paper, we propose a modified DVB-T system architecture with a multi-carrier multi-code transmission format. The main techniques we use in the system include the orthogonal Walsh code spreading and soft multipath interference cancellation (soft MPIC). Both techniques are used to combat the system degradation caused by the multipath effect. With the spreading gain and the path diversity gain achievable from the used techniques, the proposed system architecture shows much better performance compared with the original DVB-T system.
A Novel 5G TDD Cellular System Proposal based on Multipath Division Multiple Access
(2017-01-01)
Hsiao, Wei-Han
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Huang, Chia-Chi
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資訊工程學系
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電機工程學系
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Department of Computer Science
Evolving from the 3G and the 4G communication systems, the 5G system demands both high system capacity and high data rate. A novel time division duplexing (TDD) cellular system based on multipath division multiple access (MDMA) with massive antennas in millimeter wave band is proposed in this paper. The system is built on multipath division multiple access which is a method to use massive antennas at BS along with the Rake receiver and the Pre-Rake transmitter to achieve a processing gain for suppressing multiple access interference. The system concept is demonstrated by computer simulations. In addition, the associated transceiver architecture and a TDD time slot structure are presented for practical system concerns. Moreover, it is shown through analysis that the total average data throughput equals 3.8 Gbps and the system can achieve a bandwidth efficiency of 19 bps/Hz/cell on 200 MHz transmission bandwidth.
A Novel Message Passing Based MIMO-OFDM Data Detector with a Progressive Parallel ICI Canceller
(2011-04-01)
Huang, Chao-Wang
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Ting, Pang-An
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Huang, Chia-Chi
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傳播研究所
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Institute of Communication Studies
A joint design of message passing MIMO data detector/decoder with progressive parallel inter-carrier interference canceller (PPIC) based on factor graph for OFDM-based wireless communication systems is proposed. By exchanging messages both in space domain and frequency domain, the proposed algorithm can suppress inter-antenna interferences and cancel inter-carrier interferences iteratively and progressively. With a proper designed message passing schedule and random inter-leaver, the short cycle problem is solved. Computer simulations show that the performance of the proposed message passing MIMO detector outperforms MMSE-SIC MIMO detector. The performances of PPIC, both in perfect channel estimation and imperfect channel estimation cases, are compared with the standard PIC architecture and the ICI self-canceller. The proposed PPIC is superior to PIC both in computational complexity and system architecture. The parallel structure of PPIC is similar to a systolic array. The proposed algorithm potentially leads to a very-high-speed detector/decoder. It is very suitable for VLSI implementation and it is a potential candidate for data detection/decoding in future high data rate, high mobility, wireless MIMO-OFDM communication systems.
A Refined Channel Estimation Method for STBC/OFDM Systems in High-Mobility Wireless Channels
(2008-11-01)
Ku, Meng-Lin
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Huang, Chia-Chi
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電信工程研究所
;
Institute of Communications Engineering
In this paper, we investigate channel estimation for orthogonal frequency division multiplexing (OFDM) systems with space-time block code (STBC) in mobile wireless channels. Our proposed method consists of two-stage processing and is developed on the basis of the classical discrete Fourier transform (DFT)-based channel estimation method. In the initialization stage, we employ a multipath interference cancellation technique to estimate multipath delays and multipath complex gains. In the tracking stage, we develop a refined decision-feedback (DF) DFT-based channel estimation method in which a few pilot tones inserted in OFDM data symbols are applied to form an optimal gradient vector at the first iteration such that the error propagation effect is mitigated. In order to reduce computational complexity, an approximate weighting matrix is adopted to avoid matrix inversion. We demonstrate the proposed method through computer simulation of an STBC/OFDM system with two transmit antennas and a single receive antenna. The results show that our method outperforms the classical DFT-based method, the STBC-based minimum mean square error (MMSE) method, and the Kalman filtering method as well, and that significant signal-to-noise ratio (SNR) performance improvement can be achieved, especially when a high-level modulation scheme, e.g. 16QAM, is adopted in high-mobility environments.
A Robust Channel Estimator for High-Mobility STBC-OFDM Systems
(2010-04-01)
Chen, Hsiao-Yun
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Ku, Meng-Lin
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Jou, Shyh-Jye
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Huang, Chia-Chi
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電機工程學系
In this paper, a robust channel estimator for high-mobility space-time block code-orthogonal frequency division multiplexing (STBC-OFDM) systems is proposed and applied in IEEE 802.16e systems. A high-performance two-stage channel estimation method is adopted. The proposed architecture reduces computational complexity effectively and improves 85.2% of the hardware implementation. The performances of the proposed design have been demonstrated through the simulation of an STBC-OFDM system with two transmit antennas and one receive antenna. At the vehicle speed of 120 and 240 km/hr for quadrature phase shift keying (QPSK) modulation, the proposed design can achieve the bit-error rate (BER) of about 10(-4) and 10(-3) without using channel coding. Moreover, it has significant performance improvement as compared with interpolation-based channel estimation methods. The proposed channel estimator implemented in 90 nm CMOS technology can support up to 29.03 Mbps (uncoded) downlink data transmission. The design only requires 859.6 K gates and dissipates 43.71 mW at 83.3 MHz operating frequency with 1 V power supply.
A Simple ICI Suppression Method Utilizing Cyclic Prefix for OFDM Systems in the Presence of Phase Noise
(2013-11-01)
Ma, Chun-Ying
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Wu, Chun-Yen
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Huang, Chia-Chi
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傳播研究所
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Institute of Communication Studies
An extremely low-complexity inter-carrier interference (ICI) suppression method for OFDM systems in the presence of phase noise is proposed in this paper. The core idea is to utilize the ISI-free part of cyclic prefix (CP), which is simply ignored in traditional methods. We linearly combine the ISI-free samples in CP with the corresponding samples in the OFDM symbol to suppress ICI, and this scheme is called 'CP combining' throughout this paper. In addition, the optimum combining coefficients, in the sense of ICI power minimization, are derived, and a set of near-optimum coefficients are proposed to reduce the complexity. Simulation results show that the proposed CP combining method improves the system performance by 0.5 - 1.5dB. Furthermore, the proposed method can be incorporated with other phase noise mitigation methods to further improve the system performance.
An Interference Coordination Scheme for Picocell Range Expansion in Heterogeneous Networks
(2012)
Chiu, Che-Sheng
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Huang, Chia-Chi
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電信工程研究所
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Institute of Communications Engineering
Through deploying additional low-power nodes (LPNs) under the coverage area of a macrocell, heterogeneous network (HetNet) or multi-layered network deployments could be critical for operators to boost system capacity (per unit area). In order to extent the coverage region of open access LPNs and hence offload more traffics from macrocells, cell range expansion (CRE) strategy is suggested to apply in HetNets. However, when macrocells and LPNs share the same spectrum, the total network throughput could actually decrease due to CRE if the inter-layer interference couldn\'t be effectively managed. In this paper, we propose an inter-layer interference coordination scheme on the downlink side for an OFDMA co-channel macro-pico HetNet that carries out CRE technique. The idea of the proposed method is to coordinate frequency and power resources among macrocells and picocells with a set of resource allocation rules. Simulation results show that the proposed method can bring a significant increase in overall system capacity as well as reduce the user outage rate in the system, especially when aggressive CRE is applied.
Analysis and simulation of MDMA-A spectrum efficient non-orthogonal multiple access scheme for 5G communication
(2017-12-01)
Hsiao, Wei-Han
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Huang, Chia-Chi
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資訊工程學系
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電機工程學系
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Department of Computer Science
In this paper, an analysis and simulation approach is used to verify the performance of a recently proposed non-orthogonal multiple access scheme called multipath division multiple access (MDMA). The spatial multipath channel (SMC), which is the distinct feature for each user, is introduced to model the matrix channel of each user, taking into account the multipath structure and massive antennas. The signal and interference powers are then derived. Thus, the corresponding bit error probability can be approximated in a closed form. Moreover, computer simulation results are shown to be consistent with the analysis results. Most importantly, it is revealed that theMDMAsystem can achieve the superior cellular spectrum efficiency of 25 bps/Hz/cell which fulfills the 5G cellular system requirement. (c) 2017 Elsevier B.V. All rights reserved.
Case study and performance evaluation of MDMA-A non-orthogonal multiple access scheme for 5G cellular systems
(2018-08-01)
Hsiao, Wei-Han
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Shih, Yung-Wen
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Huang, Chia-Chi
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電機工程學系
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Department of Electrical and Computer Engineering
Multipath division multiple access (MDMA) has recently been proposed as a non-orthogonal multiple access scheme which exploits multipath domain to separate its users [1]. It is claimed that both the system capacity and total data throughput can be enhanced to a large amount. Yet, it is at its early stage of developments and it needs to be further investigated and clarified for its real use. In this paper, the feasibility and realizability of the MDMA cellular system are demonstrated by computer simulation. The receiver operation is also described in detail. Besides, the system performance is compared with those claimed in the original paper [1]. In addition, practical considerations on implementing the MDMA cellular system are discussed as well. With considerable amount of channel estimation error, it is shown that the system can still achieve 16 bps/Hz/cell with 300 BS antennas in cellular spectrum efficiency, which is an order of magnitude larger than the currently used first-generation to fourth-generation multiple access schemes. Thus, the MDMA can be considered as an implementable and spectrum efficient non-orthogonal multiple access scheme for future 5G systems.
Case Study and Performance Evaluation of MDMA-A Non-orthogonal Multiple Access Scheme for 5G Cellular Systems (vol 23, pg 1035, 2018)
(2018-08-01)
Hsiao, Wei-Han
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Shih, Yung-Wen
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Huang, Chia-Chi
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電機工程學系
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Department of Electrical and Computer Engineering
Chunk-based Resource Allocation Under User Rate Constraints in Multiuser MIMO-OFDM Systems
(2012-01-01)
Chou, Po-Chien
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Ma, Chun-Ying
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Huang, Chia-Chi
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電信工程研究所
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Institute of Communications Engineering
In multiuser multiple-input multiple-output orthogonal frequency division multiplexing (MU MIMO-OFDM) systems, the communication resource needs to be efficiently allocated on subcarriers such that the quality-of-service (QoS) of each user can be satisfied. A low complexity chunk-based resource allocation algorithm with low signaling overhead is proposed to minimize the total transmit power under the constraint of each user's data rate. The channel estimation error is considered in the resource allocation problem. Simulation results show that the performance degradation with respect to subcarrier-based water-filling method is small and the effect of channel estimation error is negligible. Meanwhile, computation complexity is nearly in the same order and signaling overhead is reduced.
Combined partial reuse and soft handover in OFDMA downlink transmission
(2008)
Chiu, Che-Sheng
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Huang, Chia-Chi
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電信工程研究所
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Institute of Communications Engineering
The inter-cell interference problem is a key issue in a multi-cell OFDMA system. A number of inter-cell interference mitigation schemes have been suggested to address this problem and among them, partial reuse is considered a most promising one for emerging OFDMA systems. In this paper, we propose an inter-cell interference mitigation scheme for an OFDMA downlink system. The proposed scheme makes use of a combination of partial reuse and soft handover. The basic idea of the proposed scheme is to select the better signal quality among a partial reuse scheme and a soft handover scheme for the cell edge users. Compared to the conventional partial reuse scheme, simulation results show that the cell edge throughput can be significantly improved by using the proposed scheme. Furthermore, considering the data-rate fairness among the users, the results prove that our approach can give better average cell throughput as compared with the conventional partial reuse scheme, especially for a very fair system.
Design of Downlink Synchronization for Millimeter Wave Cellular System Based on Multipath Division Multiple Access
(2020-09-01)
Chiu, Kang-Lun
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Shen, Pai-Hsiang
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Lin, Bing-Ru
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Hsiao, Wei-Han
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Jou, Shyh-Jye Jerry
This work focuses on the design of downlink receiver for future generation cellular systems. In the multipath division multiple access (MDMA) system, the initial synchronization process includes timing and carrier frequency synchronization as well as home cell search. For the proposed system, the user data is transmitted in time domain and the cell search is based on control signals transmitted in frequency domain simultaneously. Firstly, this paper presents a novel architecture for the joint detection and estimation of both the coarse symbol boundary and the fractional carrier frequency offset based on cyclic prefix in time domain. Secondly, a robust integer carrier frequency offset detection is performed with the primary control tone in frequency domain. Moreover, the position of the secondary control tones is used to obtain the cell ID. Finally, the preamble sequence carried by the secondary control tones is used to detect frame header through differential detection. The simulation results show the proposed synchronization algorithms can achieve detection failure rate less than 1% and the normalized residual carrier frequency offset is less than 5% under the interference of user data. Furthermore, a hardware design targeted at 200 Mbps per-user data rate is realized with memory arbiter to share memory.
Downlink Optimization and Performance of Relay-Assisted Cellular Networks in Multicell Environments
(2010-06-01)
Sheen, Wern-Ho
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Lin, Shiang-Jiun
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Huang, Chia-Chi
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電信工程研究所
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Institute of Communications Engineering
Deploying fixed relay stations (RSs) in traditional mobile cellular networks is widely recognized as a promising technology to improve cell coverage, user throughput, and system capacity, to save the transmit power of a mobile station (MS) in the uplink, and to provide a low-cost deployment for coverage extension. One crucial step toward developing such a relay-assisted cellular network is to fully evaluate its performance from both theoretical and practical viewpoints. In the literature, however, the system has only been evaluated for very limited system configurations: with a fixed number of RSs and locations and/or a fixed frequency-reuse pattern. This paper aims to investigate the downlink performance limits of a general relay-assisted network with optimized system parameters in a multicell environment. A genetic algorithm (GA) is proposed for the joint optimization of system parameters, including the number of RSs and their locations, frequency-reuse pattern, path selection, and resource allocation to maximize the system spectral efficiency (SE). Two types of quality of end-user experience (QoE), i.e., 1) fixed-bandwidth allocation (FBA) and 2) fixed-throughput allocation (FTA), are investigated along with two path-selection methods, i.e., 1) SE based and 2) signal-to-interference-plus-noise ratio (SINR) based. Numerical results show that significant improvement on system performance can be achieved with the optimized system parameters.
EM-Based Iterative Receivers for OFDM and BICM/OFDM Systems in Doubly Selective Channels
(2011-05-01)
Ku, Meng-Lin
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Chen, Wen-Chuan
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Huang, Chia-Chi
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電機工程學系
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Department of Electrical and Computer Engineering
In this paper, we resort to the expectation-maximization (EM) algorithm to tackle the inter-carrier interference (ICI) problem, caused by time-variant multipath channels, for both orthogonal frequency division multiplexing (OFDM) systems and bit-interleaved coded modulation (BICM)/OFDM systems. We first analyze the ICI in frequency domain with a reduced set of parameters, and following this analysis, we derive an EM algorithm for maximum likelihood (ML) data detection. An ML-EM receiver for OFDM systems and a TURBO-EM receiver for BICM/OFDM systems are then developed to reduce computational complexity of the EM algorithm and to exploit temporal diversity, the main idea of which is to integrate the proposed EM algorithm with a groupwise ICI cancellation method. Compared with the ML-EM receiver, the TURBO-EM receiver further employs a soft-output Viterbi algorithm (SOVA) decoder to exchange information with a maximum a posteriori (MAP) EM detector through the turbo principle. Computer simulation demonstrates that the two proposed receivers clearly outperform the conventional one-tap equalizer, and the performance of the TURBO-EM receiver is close to the matched-filter bound even at a normalized maximum Doppler frequency (MDF) up to 0.2.
Energy-Efficient Power Loading Algorithms for Uniform-Rate OFDM Systems
(2014)
Ma, Chun-Ying
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Huang, Chia-Chi
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電信工程研究所
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Institute of Communications Engineering
In recent years, energy-efficiency has become one of the most critical issues in wireless communications. Although it is important and practical to design an energy-efficient power loading algorithms for uniform-rate orthogonal frequency division multiplexing (OFDM) systems, the problem has not been explored in literature. The terminology uniform-rate in this paper means that each subcarrier adopts the same modulation scheme. To this end, we propose an adaptive power-loading algorithm to maximize the energy-efficiency for a uniform-rate OFDM system in this paper. To reduce the complexity, a sub-optimum solution is proposed. The numerical results show that the sub-optimum solution is close to the optimum solution. We also show that by carefully determining the modulation scheme, energy efficiency can be extensively improved.