Browsing by Author "Wu, Chia-Lung"

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A Self-Orthogonal Code and Its Maximum-Likelihood Decoder for Combined Channel Estimation and Error Protection
(2008)
Wu, Chia-Lung
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Chen, Po-Ning
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Han, Yunghsiang S.
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Wang, Shih-Wei
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電信工程研究所
Recent researches have confirmed that better system performance can be obtained by jointly considering channel equalization and channel estimation in the code design, when compared with the system with individually optimized devices. However, the existing codes are mostly searched by computers, and hence, exhibit no good structure for efficient decoding. In this paper, a systematic construction for the codes for combined channel estimation and error protection is proposed. Simulations show that it can yield codes of comparable performance to the computer-searched best codes. In addition, the structural codes can now be maximum-likelihoodly decodable in terms of a newly derived recursive metric for use of the priority-first search decoding algorithm. Thus, the decoding complexity reduces considerably when compared with that of the exhaustive decoder. In light of the rule-based construction, the feasible codeword length that was previously limited by the capability of code-search computers(1) can now be further extended, and therefore facilitates their applications.
A Systematic Space-Time Code Design and Its Maximum-Likelihood Decoding for Combined Channel Estimation and Error Correction
(2009)
Wu, Chia-Lung
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Skoglund, Mikael
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Chen, Po-Ning
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Han, Yunghsiang S.
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電信工程研究所
Several previous works have confirmed that a joint design that combines channel estimation, channel coding and space-time transmission can improve the system performance over that of a separate design. These conclusions are however in general based on unstructured solutions obtained using computer search. The coding gain of these joint designs is therefore limited by both the computer-searchable "short" code length and the compromise between "suboptimal" performance and "high" complexity of their optimal decoding. At this background, we propose a systematic space-time code construction for joint channel estimation and error correction for a two-transmit-antenna and half-rate system. Also proposed is its maximum-likelihood decoder that follows a priority-first search principle. Our systematic code construction, together with a fairly low-complexity optimal decoder, then allows one to work with longer codes with no sacrifice in performance. For codes of short block length, our simulations illustrate that the codes we propose have comparable performance to the best computer-searched codes. For codes of long block lengths that are almost beyond the searchable range of existing computer systems, our codes are still better than some reference designs based on separate channel estimation and error correction components.
A Two-Phase Maximum-Likelihood Sequence Estimation for Receivers with Partial CSI
(2013-01-01)
Wu, Chia-Lung
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Chen, Po-Ning
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Skoglund, Mikael
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Xiao, Ming
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Shieh, Shin-Lin
The optimality of the conventional maximum-likelihood sequence estimation (MLSE), also known as the Viterbi Algorithm (VA), relies on the assumption that the receiver has perfect knowledge of the channel coefficients or channel state information (CSI). However, in practical situations that fail the assumption, the MLSE method becomes suboptimal and then exhaustive checking is the only way to obtain the ML sequence. At this background, considering directly the ML criterion for partial CSI, we propose a two-phase low-complexity MLSE algorithm, in which the first phase performs the conventional MLSE algorithm in order to retain necessary information for the backward VA performed in the second phase. Simulations show that when the training sequence is moderately long in comparison with the entire data block such as 1/3 of the block, the proposed two-phase MLSE can approach the performance of the optimal exhaustive checking. In a normal case, where the training sequence consumes only 0.14 of the bandwidth, our proposed method still outperforms evidently the conventional MLSE.
Maximum-Likelihood Priority-First Search Decodable Codes for Combined Channel Estimation and Error Correction
(2009-09-01)
Wu, Chia-Lung
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Chen, Po-Ning
;
Han, Yunghsiang S.
;
Kuo, Ming-Hsin
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電信工程研究所
The coding technique that combines channel estimation and error correction has received attention recently, and has been regarded as a promising approach to counter the effects of multipath fading. It has been shown by simulation that a proper code design that jointly considers channel estimation can improve the system performance subject to a fixed code rate as compared to a conventional system which performs channel estimation and error correction separately. Nevertheless, the major obstacle that prevents the practice of such coding technique is that the existing codes are mostly searched by computers, and subsequently exhibit no apparent structure for efficient decoding. Hence, the operation-intensive exhaustive search becomes the only decoding option, and the decoding complexity increases dramatically with codeword length. In this paper, a systematic construction is derived for a class of structured codes that support joint channel estimation and error correction. It is confirmed by simulation that these codes have comparable performance to the best simulated-annealing-based computer-searched codes. Moreover, the systematically constructed codes can now be maximum-likelihoodly decoded with respect to the unknown-channel criterion in terms of a newly derived recursive metric for use by the priority-first search decoding algorithm. Thus, the decoding complexity is significantly reduced as compared with that of an exhaustive decoder.
On the Coding Scheme for Joint Channel Estimation and Error Correction over Block Fading Channels
(2009)
Wu, Chia-Lung
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Chen, Po-Ning
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Han, Yunghsiang S.
;
Zheng, Yan-Xiu
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電信工程研究所
In this work, we propose a novel systematic code construction scheme for joint channel estimation and error correction for channels with independently varying fading subblocks. Unlike the existing noncoherent codes that are designed with the help of computer search, a code of desired code length and code rate can be directly generated with our coding scheme. We then compare our codes with the three-times-repetitive (12, 6) code proposed by Xu et al. for use of channel quality indicator (CQI) in uplink control for IEEE 802.16m. Simulations show that our constructed (36, 6) code has comparable performance to Xu's code when channel coefficients changes randomly in every 12 symbols. If the channel taps remain constant in the entire coding block of length 36, our code outperforms Xu's code by 0.7 dB. This indicates that the new constructed code adapts more robustly to the two simulated scenarios. For frequency selective channels of unit memory order, our simulation results suggest that our code that takes in consideration the varying characteristic of channels can achieve better performance at median-to-high signal-to-noise ratio over the computer-searched, union-bound-minimized code of length less than the varying subblock size. A side advantage of our code construction scheme is that its systematic structure makes it maximum-likelihoodly decodable by the priority-first search algorithm. The decoding complexity is therefore significantly decreased in contrast to that of exhaustive decoder for the structureless computer-searched codes.