• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11C
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• pp.901-906
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• 2010

Low density parity check (LDPC) code, first introduced by Gallager and re-discovered by MacKay et al, has attracted researcher's interest mainly due to their performance and low decoding complexity. It was remarkable that the performance is very close to Shannon capacity limit under the assumption of having long codeword length and iterative decoder. However, comparing to turbo codes widely used in the current mobile communication, the encoding complexity of LDPC codes has been regarded as the drawback. This paper proposes a solution for DVB-S2 LDPC encoder to reduce the encoder latency. We use the fast IRA encoder that use the transformation of the parity check matrix into block-wise form and the partial parallel process to reduce the number of system clocks for the IRA code encoding. We compare the proposed encoder with the current DVB-S2 encoder to show that the performance of proposal is better than that of the current DVB-S2 encoder.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.3 s.345
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• pp.39-48
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• 2006

In this paper, we analyze the spectral efficiency of multicarrier-code division multiple access (MC-CDMA) scheme. First, we derive a generalized formula for the spectral efficiency according to the number of subcarriers involved in, code division multiplexing and the number of codes used (i.e., loading factor), under a given set of channel coefficients. Also, we derive a generalized formula for spectral efficiency of various reduced-complexity systems that divide the full sets of subcarriers into several groups of subcarriers for code division multiplexing. Then, through these derivations, we establish an inter-relationship between the frequency selectivity and diversity order according to the number of multipaths. From the results, we choose the smallest code length while maximizing the diversity effect, provide an optimum subcarrier allocation strategy, and finally suggest a system structure for capacity-maximizing under the smallest code length. Through numerical analyses under simulated environments, we analyze the properties of spectral efficiency of various systems with reduced complexity and choose a major contributing factors to system design and a better system design methodology. Finally, we compare the spectral efficiency of the MC-CDMA scheme and orthogonal frequency division multiplexing (OFDM) scheme to make a relationship between both schemes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10C
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• pp.597-604
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• 2011

In this paper, we propose group Manchester code (GM) modulation scheme for medical in-body wireless body area network (WBAN) systems. In IEEE, the WBAN system is assigned as 802.15. Task Group 6 (TG 6), and the related standardization is being progressed, Recently, in this Group, group pulse position modulation (GPPM), which can obtain data rate increase by grouping pulse position modulation (PPM) symbols, is proposed as a new modulation scheme for low-power operation of WBAN system. However, the conventional method suffers from BER performance degradation due to the absence of gray coding and its demodulation characteristics. Therefore, in this paper, we propose a modified GM scheme which groups Manchester code instead of PPM. In the proposed GM scheme, a low-complexity maximum likelihood (ML) demodulation method is employed in order to maximize the BER performances, Also, log likelihood ratio (LLR) decision method is proposed to employ the Turbo code as forward error correction (FEC), Finally, we verified that the proposed method has a good performance and is an appropriate scheme for in-body WBAN system through extensive performance evaluation.

• Journal of Information Processing Systems
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• v.16 no.4
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• pp.915-934
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• 2020

Software refactoring is a process to restructure an existing software code while keeping its external behavior the same. Currently, various refactoring techniques are being used to develop more readable and less complex codes by improving the non-functional attributes of software. Refactoring can further improve code maintainability by applying various techniques to the source code, which in turn preserves the behavior of code. Refactoring facilitates bug removal and extends the capabilities of the program. In this paper, an exhaustive review is conducted regarding bad smells present in source code, applications of specific refactoring methods to remove that bad smell and its effect on software quality. A total of 68 studies belonging to 32 journals, 31 conferences, and 5 other sources that were published between the years 2001 and 2019 were shortlisted. The studies were analyzed based on of bad smells identified, refactoring techniques used, and their effects on software metrics. We found that "long method", "feature envy", and "data class" bad smells were identified or corrected in the majority of studies. "Feature envy" smell was detected in 36.66% of the total shortlisted studies. Extract class refactoring approach was used in 38.77% of the total studies, followed by the move method and extract method techniques that were used in 34.69% and 30.61% of the total studies, respectively. The effects of refactoring on complexity and coupling metrics of software were also analyzed in the majority of studies, i.e., 29 studies each. Interestingly, the majority of selected studies (41%) used large open source datasets written in Java language instead of proprietary software. At the end, this study provides future guidelines for conducting research in the field of code refactoring.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.6
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• pp.63-69
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• 2008

In this paper, our goal is to find a power-effective protocol that improves the accuracy of transmission in sensor networks. Therefore we propose a cooperative communication protocol based on MRC(Maximal Ratio Combining) and cyclic code. In our proposal, one sensor node assists two others to communicate with a clusterhead that can get diversity effect and MRC can improve diversity effect also. The proposed protocol with cyclic code can correct error up to 3-bit and reduce decoding complexity compared with convolutional code. Simulation results reveal proposed protocol can save the network energy up to 6dB over single-hop protocol at BER(Bit Error Rate) of $10^{-2}$.

• Journal of KIISE
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• v.44 no.12
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• pp.1307-1312
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• 2017

Due to their convergence with state-of-the-art ICT technologies, the complexity and reliability demands of industrial automation systems have been rapidly increasing. In recent years, to cope with these demands, several research works have been carried out to adopt formal methods to the application development cycle at the early design stage. In this paper, we propose an automated code generation framework for industrial automation applications, based on a timed automata model. As a case study, we developed a formal model for a traffic light control system and verified the timing properties described in the specification. We finally demonstrated that the operation of a test-bed based on the auto-generated native code was identical to that of the model specification.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.3
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• pp.34-39
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• 2008

In this paper, we propose a bit-interleaved coded modulation (BICM) a lied to improved super-orthogonal space-time block code(SOSTBC). The proposed system achieves a greater diversity gain than that of super-orthogonal space-time trellis code (SOSTTC) with similar decoding complexity. Since, using the improved SOSTBC, the bit diversity carl be full diversity of SOSTBC. In contrast, BICM applied to Jafarkhani's SOSTBC is difficult to achieve a greater diversity gain than that of SOSTTC, because every bit diversity of the system is 1.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.7
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• pp.78-91
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• 1998

This paper presents modular design techniques of multiple-valued logic functions about the function decomposition method and input variable management method. The function decomposition method takes avantage of the property of the column multiplicity in a single-column variable partitioning. Due to the increased number of identical modules, we can achieve a simpler circuit design by using a single T-gate, which can eliminate some of the control functions in the module libraty types. The input variable management method is to reduce the complexity of the input variables by proposing the look up table which assign input variables to a code. In this case as the number of sub-functions increase the code-length and the size of the code-assignment table grow. We identify some situations where shard input variables among sub-functions can be further reduced by a simplicication technique. According to the result of adapting this method to a function, we have demonstrated the superiority of the proposed methods which is bing decreased to about 12% of interconnection and about 16% of T-gate numbers compare with th eexisting for th enon-symmetric and irregular function realization.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.3
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• pp.522-527
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• 2007

In this paper, we propose an error control coding scheme for constant-amplitude multicode-biorthogonal modulation. The product code is appropriate to the constant-amplitude multicode-biorthogonal modulation for the bit error rate performance improvement. In the constant-amplitude multicode-biorthogonal modulation, the vertical redundant bits are used for the constant amplitude coding. The proposed product code can be constructed by using the additional horizontal redundant bits. The hardware complexity of the encoder/decoder pair is very low. The simulation results show that the bit error rate performance of the proposed coding scheme is improve

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.1
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• pp.38-46
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• 1992

In this thesis, a high speed code synchronization circuit is implemented, which is applicable to frequency hopping FSK tranceiver within 68-88 MIBz band- width. synchronization Process consists of two steps, initial synchronization and tracking. A modified matched filter method using two channel passive correlators matched with short hopping frequencies, synchronization prcfix. is proposed for initial synchronization. To increase probability of initial synchronization, prefix are transmitted repeatedly. The outputs of correlators are sent to synchronization decision circuit, and code start time Is extracted by synchronizatlon decision circuit-Modified matched fitter method makes it possible to reduce complexity in hardware and obtain code acquisition rapidly.Clock recovery circuit regenerates PN code clock for tracking.