Browsing by Author "Sheen, Wern-Ho"

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A GA-Based Optimization for Frequency-Selective Scheduling in Downlink OFDMA Systems with Cyclic-Delay Diversity
(2012)
Chen, Yu-Fan
;
Sheen, Wern-Ho
;
傳播研究所
;
Institute of Communication Studies
CDD (cyclic-delay diversity) aided frequency-selective scheduling has been known as an effective technique to increase system capacity of the OFDMA (orthogonal frequency-division multiple access) systems. By increasing the channels' frequency selectivity with cyclic delays, the merit of multi-user diversity can be exploited more effectively in the system. In this paper, we aim to optimize the design of the CDD-aided frequency-selective scheduling for downlink OFDMA systems. A genetic algorithm (GA)-based optimization is devised to obtain the cyclic-delay values which provides a higher system sum-rate than the multi-degree adaptive cyclic-delay diversity method and has a lower computational complexity than the exhaustive method with only a slight degradation in system sum-rate. The effectiveness of the proposed method is verified by extensive computer simulations.
A Lattice-Reduction Aided List Demapper for Coded MIMO Receiver
(2013)
Hsieh, Tung-Jung
;
Sheen, Wern-Ho
;
Chen, Sin-Horng
;
Hsu, Jen-Yuan
;
資訊工程學系
The max-log list demapper has been widely employed in the implementations of a coded multiple-input multiple-output (MIMO) receiver, where only a candidate-list of signal vectors is examined in the likelihood-ratio calculation to reduce complexity. Traditionally, the candidate-list is generated in the original-lattice domain which, unfortunately, results in a severe degradation in the performance of demapper if the channel is in ill-condition. In this paper, a new lattice-reduction aided max-log list demapper is proposed in which the candidate-list is generated after a successive cancellation of multi-layer interference in the lattice-reduced domain. Thanks to the newly designed metrics and search algorithms for the generation of the candidate-list, the proposed demapper provides significant gains over the existing methods, especially for the cases with a small list size and/or under a spatially-correlated channel.
A Lattice-Reduction Aided Max-Log List Demapper for Iterative Coded MIMO Receiver
(2014-01-01)
Hsieh, Tung-Jung
;
Sheen, Wern-Ho
;
Chen, Sin-Horng
;
Hsu, Jen-Yuan
;
資訊工程學系
The max-log list demapper has been widely employed in the implementation of a coded multiple-input multiple-output (MIMO) receiver, where only a candidate-list of signal vectors is examined in the likelihood-ratio calculation to reduce complexity. Traditionally, the candidate-list is generated in the original-lattice domain which, unfortunately, results in a severe degradation in the performance of demapper if the channel is in ill-condition. In this paper, a new lattice-reduction aided max-log list demapper is proposed for iterative receivers in which the candidate-list is generated after a successive cancellation of multi-layer interference in the lattice-reduced domain. Thanks to the newly designed metric and search algorithm for the generation of the candidate-list, the proposed demapper provides significant gains over the existing methods, especially for the cases with a small list size and/or under a spatially-correlated channel. The prior information coming out of the decoder is also exploited to lower the complexity of the demapper.
A Lattice-Reduction-Aided Max-Log List Demapper for Coded MIMO Receivers
(2014-02-01)
Hsieh, Tung-Jung
;
Sheen, Wern-Ho
;
電機資訊學士班
;
Undergraduate Honors Program of Electrical Engineering and Computer Science
The max-log list demapper has been widely employed in the implementations of a coded multiple-input-multiple-output (MIMO) receiver, where only a candidate list of signal vectors is examined in the likelihood-ratio calculation to reduce complexity. Traditionally, the candidate list is generated in the original-lattice domain, which, unfortunately, results in severe degradation in the performance of the demapper if the channel is in ill-condition. In this paper, two new lattice-reduction-aided max-log list demappers are proposed, i.e., one for an iterative receiver and the other for a noniterative receiver. With similar complexity, the proposed demappers provide significant gains over existing demappers, particularly for the cases with a small list size and/or under a spatially correlated channel, due to the new algorithms for the generation of the candidate list. In addition, for the iterative receiver, the prior information coming out of the decoder is exploited to lower the complexity of the demapper.
A Low-Complexity CDD-based Frequency Selective Scheduling with Efficient Feedback for Downlink OFDMA Systems
(2012)
Chen, Yu-Fan
;
Sheen, Wern-Ho
;
Wang, Li-Chun
;
傳播研究所
;
Institute of Communication Studies
Cyclic-delay diversity (CDD) based frequency-selective scheduling is an effective technique to increase system capacity with low complexity. By increasing the channels' frequency selectivity with cyclic delays, the merit of multi-user diversity can be exploited more effectively in the system. This paper aims to optimize the design of the CDD-aided frequency-selective scheduling for downlink OFDMA systems. First, a low-complexity search of CD-values is proposed that results in a higher system capacity than the existing methods. Second, a new feedback method is proposed based on the principle of proportional-fair, where users who currently enjoy more downlink source are allotted less uplink resource for feedback. The method is shown to provide a better tradeoff between system capacity and fairness than the traditional methods, under a fixed feedback overhead. The effectiveness of the proposed method is verified by extensive computer simulations.
A Low-complexity Power Allocation for Cooperative Bit-interleaved Coded Modulation Systems with Adaptive Decode-and-Forward Relaying
(2011)
Yu, Tsang-Wei
;
Sheen, Wern-Ho
;
Wang, Chung-Hsuan
;
電機工程學系
;
Department of Electrical and Computer Engineering
Transmit power allocation between source and relays is a critical design issue in a cooperative relaying system where source and relays are powered by batteries. In this paper, a low-complexity power allocation method is proposed for a 3-node cooperative bit-interleaved coded modulation system with adaptive decode-and-forward relaying, aiming to minimize the bit-error-rate at the destination. The key novelty of the method lies in transforming the power allocation into a max-min optimization problem which can be solved in a first-order equation with very low-complexity. Computer simulations show that the proposed method outperforms the equal gain power allocation with large margins in different channel conditions.
A New Self-Calibration Method for Transmitter and Receiver Radio Impairments in Direct-Conversion Architecture
(2010)
Hsu, Chen-Jui
;
Sheen, Wern-Ho
;
電機工程學系
;
Department of Electrical and Computer Engineering
Direct-conversion radio architecture is a low-cost, small-size design for the analog front-end subsystem in a wireless communication transceiver. This architecture, however, induces radio impairments such as I-Q imbalance and dc offset that incur severe degradation in communication performance. In this paper, a new time-domain method is proposed to self-calibrate simultaneously the transmitter and receiver impairments without a dedicated analog circuit in the feedback loop. Thanks to the time-domain approach, the method is applicable to all types of systems and is able to calibrate jointly the frequency-independent I-Q imbalance, frequency-dependent I-Q imbalance, and dc offset. In addition, training sequence design is investigated to optimize the performance of calibration. Analytical and simulation results confirm the effectiveness of the proposed method.
A Pragmatic Labeling Design of MIMO BICM-ID Systems Based on EXIT Chart
(2009)
Yu, Tsang-Wei
;
Wang, Chung-Hsuan
;
Sheen, Wern-Ho
;
電信工程研究所
;
Institute of Communications Engineering
We propose a pragmatic labeling design based on the extrinsic information transfer (EXIT) chart for bit-interleaved coded modulation with iterative decoding on multiple-input-multiple-output channels. In our design, the EXIT chart is used to determine a candidate set of labelings which have representative demapper transfer curves. Then, a procedure to generate these labelings is provided based on the genetic algorithm. Given fixed channel code and signal-to-noise ratio (SNR), we can search within this candidate set for a most-suitable labeling to minimize the bit-error-rate (BER) with low complexity. Simulation results show that the labeling chosen from the candidate set exhibits a controllable BER performance gap compared to the optimal labeling found through exhaustive search. Besides, even though the channel code or the SNR is changed, the same candidate set can still be directly adopted to reduce the time on re-searching a new labeling.
A tight BER upper bound for bit-interleaved coded modulation with square QAM and gray labeling
(2006-11-01)
Huang, Liang-Wei
;
Sheen, Wern-Ho
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Yiu, Tsang-Wei
;
交大名義發表
;
電信工程研究所
Bit-interleaved coded modulation (BICM) is a bandwidth-efficient coded system with diversity order higher than that of Ungerboeck's trellis-coded modulation on fading channels. In this paper, we investigate the BER (bit error rate) performance of BICM in the additive white Gaussian and Rayleigh fading channels. A new upper bound is given for the square QAM constellation with gray labeling, which constitutes a large portion of practical applications of BICM systems. The new upper bound is tighter than the well-known BICM union bound proposed in [4].
Address Generation Apparatus And Method For Quadratic Permutation Polynomial Interleaver De-Interleaver
(2011-03-17)
Lee, Shuenn-Gi
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Wang, Chung-Hsuan
;
Sheen, Wern-Ho
An address generation apparatus for a quadratic permutation polynomial (QPP) interleaver is provided. It comprises a basic recursive unit, and L recursive units represented by first recursive unit up to Lth recursive units. The apparatus inputs a plurality of configurable parameters according to a QPP function Π(i)=(f1i+f2i2) mod k, generates a plurality of interleaver addresses in serial via the basic recursive unit, and generates L groups of corresponding interleaver addresses via the first up to the Lth recursive units, wherein Π(i) is the i-th interleaver address generated by the apparatus, f1 and f2 are QPP coefficients, and k is information block length of an input sequence, 0≦i≦k−1.
An analysis on downlink capacity of multi-cell OFDMA systems under randomized inter-cell/sector interference
(2007)
Fu, I-Kang
;
Sheen, Wern-Ho
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電信工程研究所
;
Institute of Communications Engineering
An analysis on downlink capacity of multi-cell OFDMA (orthogonal frequency division multiple access) systems is presented in this paper under a model of randomized multiple access interference, which is a result of applying random sub-carrier allocation among different cells/sectors. The analysis shows that the system capacity is either in the bandwidth-limited or power-limited region and that optimum tradeoff between capacity and coverage is achievable in a sense that given a required capacity the maximum coverage can be determined. The capacity is evaluated for different system setups, which are characterized by cell radius, reuse factor and types of antenna system with and without spatial division multiple access (SDMA). Three types of antenna are considered including omni-directional antenna, 3-sector antenna and switched-beam smart antenna. Numerical results show that the use of 3-sector and switched-beam smart antenna can enlarge the bandwidth-limited region and achieves a better capacity and coverage tradeoff.
An SVD-aided List Demapper for Iterative Coded-MIMO Receivers
(2014-01-01)
Hsieh, Tung-Jung
;
Sheen, Wern-Ho
;
Chen, Sin-Horng
;
Hsu, Jen-Yuan
;
資訊工程學系
The list demapper has been widely implemented in a coded multiple-input multiple-output (MIMO) receiver, where only a part of total signal vectors are examined in the calculation of likelihood ratio for low complexity. Generally, the list is generated either in the original or the lattice-reduced domain. In the latter, thanks to the operation of lattice reduction (LR), a better-conditioned MIMO channel is obtained, and the adverse effect of noise enhancement is mitigated in the generation of list and thus can achieve a better performance. In this paper, a new singular-value-decomposition (SVD)-aided list demapper is proposed for the iterative coded-MIMO receiver. With SVD, the layer interference incurred in the operation of LR can be avoided, and that renders the SVD-aided list demapper a lower complexity. Computer simulations have confirmed that the proposed demapper has better performance-complexity tradeoffs as compared to the best-performed LR-aided methods in the literature.
Cell search in WCDMA under large-frequency and clock errors: Algorithms to hardware implementation
(2008-03-01)
Li, Chi-Fang
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Chu, Yuan-Sun
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Ho, Jan-Shin
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Sheen, Wern-Ho
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電信工程研究所
This paper proposes a complete cell-search solution for real-world handset operations in the wide-band code-division multiple-access system. Large-frequency and clock errors are induced at initial search due to an inaccuracy of crystal oscillators within handsets and could cause fatal performance degradation. In addition to a primary search algorithm for achieving essential pseudo-noise code acquisitions, an enhanced algorithm combining frequency offset compensation, random sample per frame, and sample point reordering is proposed to achieve fast initial search even while an inaccuracy is up to 12 ppm. After a series of trade-off between performance and complexity, two search bins in the first stage are adopted to mitigate possible errors in each bin and make the enhanced schemes become effective. In final, the complete solution is presented with alternative algorithms: a primary one and an enhanced one. The solution is implemented with the flexibility for switching algorithms in different searches and using low-power methods for the sake of handsets' working time. Its core area is 3.8 x 3.8-mm(2) in a 3.3-V 0.35-mm CMOS technology, and the power consumption is 35.6 and 67 mW for the primary and enhanced algorithms, respectively.
Coverage performance analysis of OFDM-based spatial multiplexing systems
(2007)
Wang, Li-Chun
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Chiu, Cheng-Wei
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Yeh, Chu-Jung
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Sheen, Wern-Ho
;
交大名義發表
Combining multi-input multi-output (MIMO) antenna techniques with orthogonal frequency division multiplexing (OFDM) modulation (MIMO-OFDM) becomes an attractive air-interface solution for the next generation high speed wireless systems. Nevertheless, because the total available transmit power is split uniformly across transmit antennas in MIMO-OFDM systems, increasing the number of transmit antennas leads to a smaller signal-to-noise ratio (SNR) per degree of freedom. Thus the coverage performance of this kind of MIMO-OFDM system becomes an essential issue. In this paper by means of order statistics and Glivenko-Cantelli theorem, we develop an analytical expressions for the link outage probability and cell coverage reliability of OFDM-based spatial multiplexing systems in a frequency selective fading channel, respectively.
Deployment and radio resource reuse in IEEE 802.16j multi-hop relay network in Manhattan-like environment
(2007)
Fu, I-Kang
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Sheen, Wern-Ho
;
Ren, Fang-Ching
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電信工程研究所
;
Institute of Communications Engineering
IEEE 802.16j is an amendment to the IEEE 802.16 broadband wireless access standard to enable the operation of multi-hop relay stations (RS). It aims to enhance the coverage, per user throughput and system capacity of IEEE 802.16e. Compared with base station (BS), RS does not need a wire-line backhaul and has much lower hardware complexity. Using RSs can significantly reduce the deployment cost of the system. In this paper, the RS deployment and radio-resource reuse strategies for IFEE 802.16j multi-hop relay (MR) networks are investigated. Simulation results show that the per-user throughput and system capacity of IEEE 802.16j MR network can be substantially improved by the proposed method.
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
;
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.
EXIT-chart based labeling design for bit-interleaved coded modulation with iterative decoding
(2007)
Yu, Tsang-Wei
;
Wang, Chu-Yan
;
Wang, Chung-Suan
;
Sheen, Wern-Ho
;
電信工程研究所
In this paper, labeling is jointly designed with the outer code by the EXIT chart based analysis to improve the performance of bit-interleaved coded modulation with iterative decoding. A systematic design methodology is proposed for regular modulation schemes which can easily obtain a set of labelings with various slopes. Given an outer code, the optimal labeling which has the steepest slope but still makes the tunnel between the decoder and demapper transfer curves open can then be chosen to optimize the BER performance. Verified by the simulation results, our design can provide remarkable SNR gain over the conventional ones.
Joint Calibration of Transmitter and Receiver Impairments in Direct-Conversion Radio Architecture
(2012-02-01)
Hsu, Chen-Jui
;
Sheen, Wern-Ho
;
電機工程學系
;
Department of Electrical and Computer Engineering
Direct-conversion radio architecture is a low-cost, low-power and small-size design that has been widely employed in today's wireless devices. This architecture, however, induces radio impairments such as I-Q imbalance and dc offset that may incur severe degradation in communication performance if left uncompensated. In this paper, a new method is proposed to calibrate simultaneously a transceiver's own transmitter and receiver radio impairments with no dedicated analog circuit in the feedback loop. Based on a unified time-domain approach, the proposed method is able to calibrate jointly the frequency-independent I-Q imbalance, frequency-dependent I-Q imbalance and dc offset and is applicable to any type of communication systems (single-carrier, multiple-carrier, etc.). The existing methods in the literature either need a dedicated analog circuit in the feedback loop and/or are applicable only to a particular type of systems with some radio impairments present. The issue of training sequence design is also investigated to optimize the calibration performance, and analytical and simulation results show that the performance loss due to radio impairments can be recovered by the proposed method.
JOINT ESTIMATION AND COMPENSATION OF FREQUENCY, DC-OFFSET, I-Q IMBALANCE AND CHANNEL IN MIMO RECEIVERS
(2009)
Hsu, Chen-Jiu
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Sheen, Wern-Ho
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Cheng, Racy
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電信工程研究所
;
Institute of Communications Engineering
Direct-conversion is a low-cost RF architecture that requires fewer external components in chip implementation. It introduces, however, extra RF impairments such as I-Q imbalance and DC-offset that degrade severely the receiver performance if left uncompensated. In this paper, a new method of joint estimation and compensation of frequency, DC-offset, I-Q imbalance and channel is developed for MIMO receivers. Numerical results show that the proposed method has a very good performance; less than 2 dB loss is observed at bit-error rate 10(-4), as compared to the ideal receiver. In addition, a new training sequence along with a low-complexity architecture is proposed to reduce largely the receiver complexity with negligible performance loss.
Joint Estimation and Compensation of Transmitter and Receiver Radio Impairments in MIMO-OFDM Receivers
(2009)
Hsu, Chen-Jiu
;
Sheen, Wern-Ho
;
電信工程研究所
;
Institute of Communications Engineering
This paper aims to improve the performance of estimation and compensation for both the transmitter and receiver radio impairments in the MIMO-OFDM (multiple-input, multiple-output orthogonal frequency-division multiplexing) systems. First, a joint least-squares estimation of channel and radio impairments is developed with a complete set of radio impairments being taken into consideration, including frequency-dependent and independent I-Q imbalances, dc-offsets and frequency-offset. Previously, only parts of the radio impairments were included and/or treated separately from the radio channel. Secood, a novel two-stage compensation scheme is proposed which is applicable to a general form of MIMO operations with any number of transmit and receive antennas. Numerical results show that the new design significantly outperforms the existing ones in error-rate performance and/or the number of training symbols required.