Browsing by Author "Chao, Chi-Chao"

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Complete Complementary Codes and Generalized Reed-Muller Codes
(2008-11-01)
Chen, Chao-Yu
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Wang, Chung-Hsuan
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Chao, Chi-Chao
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電信工程研究所
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Institute of Communications Engineering
Due to ideal autocorrelation and cross-correlation properties, complete complementary codes (CCCs) can be employed in CDMA systems to eliminate the multiple-access interference. In this letter, we propose a direct general construction of CCCs from cosets; of the first-order Reed-Muller codes, which includes previous results as a special case. The larger number of CCCs constructed by our method can provide advantages in applications to cellular CDMA systems.
Feedback-Aided Pilot Placement and Subcarrier Pairing for AF OFDM Relay Channels
(2013-02-01)
Sung, Kuang-Yu
;
Hong, Y. -W. Peter
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Chao, Chi-Chao
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傳播研究所
;
Institute of Communication Studies
This paper examines the use of channel feedback to adaptively determine pilot placement among subcarriers in amplify-and-forward (AF) orthogonal frequency-division multiplexing (OFDM) relay systems. With feedback of the previous channel estimate, pilot subcarriers at the source and relay can be reassigned to reduce channel estimation error and ensure that good subcarriers are made available for data transmission. The minimum effective signal-to-noise ratio (SNR) among data subcarriers is utilized as the performance metric for the optimization of the pilot locations. The effective SNR is defined as the receive SNR at the destination, taking into consideration the source-to-relay (SR) and relay-to-destination (RD) channels, as well as their respective channel estimation errors. The feedback gain, which is defined as the ratio between the minimum effective SNR achieved with the optimal feedback-aided pilot placement and that achieved with the equal-spaced pilot placement, is used to measure the gains achieved through feedback. In this paper, we first derive an analytic lower bound on the optimal feedback gain and show its rate of increase with respect to the number of subcarriers. These studies are performed for systems both without and with subcarrier pairing (SP) at the relay. Specifically, in systems without SP, the relay forwards each datum on the same subcarrier on which it is received. In systems with SP, the relay is allowed to reassign the subcarriers used to forward the data received from the source. With the goal of maximizing the minimum effective SNR, the optimal SP scheme is shown to be an inverse mapping between the SR and RD subcarriers with respect to their channel gains. Due to the complexity of finding the optimal placement, a suboptimal but efficient algorithm called the iterative pilot relocation (IterPR) scheme is then proposed. The effectiveness of the proposed IterPR schemes is demonstrated through numerical simulations.
New Construction of LDPC Convolutional Codes
(2008)
Wu, Chi-Jen
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Chou, Yi-Chun
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Wang, Chung-Hsuan
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Chao, Chi-Chao
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電信工程研究所
In this paper, we propose a new construction of (3,t)-regular low-density parity-check convolutional codes by properly including binomial entries in the parity-check matrices. Both of the upper and lower bounds on free distance are derived for the new codes. Compared with previous constructions, our design can not only avoid codes of girth less than 8 but also provide enlarged free distances for some code rates. Simulation results show that the codes based on the new construction can achieve better bit-error-rate performance and lower error floor.
On Unequal Error Protection of Convolutional Codes From an Algebraic Perspective
(2010-01-01)
Wang, Chung-Hsuan
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Chiu, Mao-Ching
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Chao, Chi-Chao
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傳播研究所
;
電機工程學系
In this paper, convolutional codes are studied for unequal error protection (UEP) from an algebraic theoretical viewpoint. We first show that for every convolutional code there exists at least one optimal generator matrix with respect to UEP. The UEP optimality of convolutional encoders is then combined with several algebraic properties, e.g., systematic, basic, canonical, and minimal, to establish the fundamentals of convolutional codes for UEP. In addition, a generic lower bound on the length of a UEP convolutional code is proposed. Good UEP codes with their lengths equal to the derived lower bound are obtained by computer search.
UWB communications with under-sampled receivers
(2006)
Wu, Wei-De
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Wang, Chung-Hsuan
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Chiu, Mao-Ching
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Chao, Chi-Chao
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電子工程學系及電子研究所
In this paper, we investigate a novel coding idea proposed previously to enable under-sampled receivers. An under-sampled receiver can sample the received baseband signals at only a fraction of the Nyquist rate and turns out to be an effective solution to the bottleneck of high-rate sampling and processing in ultra-wideband (UWB) communications. The spectrum aliasing problem can be solved by an analogy between an under-sampled system and a multiple-antenna one. However, underlying differences between the two systems exist and motivate the study of the fundamental limits of a coded under-sampled system. The study is carried out by characterizing the optimal coding structures with and without channel state information at transmitter (CSIT). A practical selective coding structure is also developed to provide satisfactory performance with reduced CSIT requirement. Finally, simulations are conducted to verify the theoretical characterization. Our results indicate that an under-sampled UWB system can benefit from power-saving, cost reduction, and full multipath diversity at the expanse of little or confined performance degradation.