• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.7
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• pp.3583-3598
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• 2019

In order to improve the reliability and repair efficiency of distributed storage systems, minimum bandwidth regenerating (MBR) codes based on cyclic variable fractional repetition (VFR) codes are constructed in this thesis, which can repair failed nodes accurately. Specifically, in order to consider the imbalance of data accessed by the users, cyclic VFR codes are constructed according to that data with different heat degrees are copied in different repetition degrees. Moreover, we divide the storage nodes into groups, and construct MBR codes based on cyclic VFR codes to improve the file download speed. Performance analysis and simulation results show that, the repair locality of a single node failure is always 2 when MBR codes based on cyclic VFR codes are adopted in distributed storage systems, which is obviously superior to the traditional MBR codes. Compared with RS codes and simple regenerating codes, the proposed MBR codes based on cyclic VFR codes have lower repair locality, repair complexity and bandwidth overhead, as well as higher repair efficiency. Moreover, relative to FR codes, the MBR codes based on cyclic VFR codes can be applicable to more storage systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.11
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• pp.5335-5353
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• 2019

The definition of the bandwidth efficiency (BE) of cognitive cooperative network (CCN) is the ratio between a number of the licensed slot(s) or sub-channel(s) used by the unlicensed users to transmit a single data packet from the unlicensed transmitter to unlicensed destination, and from unlicensed relay(s) to unlicensed destination. This paper analyzes and improves the BE in the underlay CCN with a new reactive relay selection under interference and power constraints. In other words, this paper studies how unlicensed cooperative users use the licensed network slot(s) or sub-channel(s) efficiently. To this end, a reactive relay selection method named as Relay Automatic Repeat Request (RARQ) is proposed and utilized with a CCN under interference and power constraints. It is shown that the BE of CCN is higher than that of cooperative transmission (CT) due to the interference and power constraint. Furthermore, the BE of CCN is affected by the distance of the interference links which are between the unlicensed transmitter to the licensed destination and unlicensed relay to the licensed destination. In addition, the BE for multiple relays selection over a CCN under interference and power constraints is also analyzed and studied, and it is shown that the BE of CCN decreases as the number of relays increases.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.1
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• pp.493-499
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• 2011

To improve the bandwidth efficiency of conventional orthogonal modulation, the MCTO(Multi-Code Trans-Orthogonal) modulation, which is modified orthogonal modulation, was proposed. However, the RF(Radio Frequency) power amplifier for the MCTO modulation is too complex to reject the amplitude distortion due to the non-constant amplitude property of the MCTO. Therefore, in this paper, CAMCTO(constant-amplitude multi-code trans-orthogonal) modulation is proposed by using the constant-amplitude encoding algorithm for multi-code signal. Additionally, the performance of the proposed CAMCTO modulation is compared with those of the orthogonal modulation and the MCTO modulation by using the computer simulation. The computer simulations show that the bandwidth efficiency of the proposed CAMCTO modulation is better than that of the conventional orthogonal modulation.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.01a
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• pp.258-262
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• 2009

In this paper, we propose an effective memory reduction algorithm to reduce the amount of reference frame buffer and memory bandwidth in video encoder and decoder. In general video codecs, decoded previous frames should be stored and referred to reduce temporal redundancy. Recently, reference frames are recompressed for memory efficiency and bandwidth reduction between a main processor and external memory. However, these algorithms could hurt coding efficiency. Several algorithms have been proposed to reduce the amount of reference memory with minimum quality degradation. They still suffer from quality degradation with fixed-bit allocation. In this paper, we propose an adaptive block-based min-max quantization that considers local characteristics of image. In the proposed algorithm, basic process unit is $8{\times}8$ for memory alignment and apply an adaptive quantization to each $4{\times}4$ block for minimizing quality degradation. We found that the proposed algorithm could improve approximately 37.5% in coding efficiency, compared with an existing memory reduction algorithm, at the same memory reduction rate.

• 한국정보통신설비학회:학술대회논문집
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• 2005.08a
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• pp.427-430
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• 2005

A multi-code biorthogonal code keying (MBCK) system consists of multiple waveform coding blocks, and the sum of output codewords is transmitted. Drawback of MBCK is that it requires amplifier with high linearity because its output symbol is multi-level. MBCK with constant amplitude precoding block (CA-MBCK) has been proposed, which guarantees sum of orthogonal codes to have constant amplitude. The precoding block in CA-MBCK is a redundant waveform coder whose input bits are generated by processing the information bits. Redundant bits of constant amplitude coded CA-MBCK are not only used to make constant amplitude signal but also used to improve the BER performance at the receiver. In this paper, we proposed a transmission scheme which combines CA-MBCK with $Q^2PSK$ modulation to improve bandwidth efficiency of CA-MBCK and also uses chip interleaving to maintain a constant amplitude feature of CA-MBCK. bandwidth efficiency of a proposed transmission scheme is increased fourfold. And the BER performance of the scheme is same as that of CA-MBCK.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.10
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• pp.951-959
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• 2011

The low power consumption modulation is required for short range communication. In this paper, we analyze performance of low power consumption modulation scheme such as PSPM, PSSK and QAPM using OFDM transmission in AWGN channel. A PSPM, PSSK and QAPM modulation scheme are decrease in bandwidth efficiency but improved power efficiency than existing PSK and QAM. These modulation schemes can achieve power efficiency because every symbol of modulations has a zero-envelope period like PPM techniques. The OFDM system is high bandwidth efficiency than single carrier system. In this paper, we are propose the frequency domain mapping method for OFDM transmission using low power consumption modulation method. Also, we compare low power OFDM communication system regard to BER performance, throughput and PAPR.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.12
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• pp.1394-1400
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• 2010

In this paper, we analyze performance of PSPM(Phase Shift Position Modulation) modulation scheme in multi-path channel. A PSPM modulation method transmits the information data by both PSK symbol data and symbol position data, so that we can significantly improve the power efficiency. The bandwidth efficiency of PSPM is quarter than PSK but improve BER performance, because increasing symbol hamming distance. In this results, a PSPM scheme is bandwidth efficiency better than FSK and power efficiency better than PSK. This characteristic can be useful in WBAN and wireless sensor networks also PSPM modulation method can be expected high throughput than existing FSK. In this paper, we compare PSPM, PSSK and PSK regard to BER performance and throughput in multi-path channel.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.19-27
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• 1991

A new bandwidth reduction algorithm is developed by combining the two-step approach and the frontal ordering scheme. In the two-step approach, finite elements are numbered first, followed by nodal numbering based on the graph theory. The concept of wave front is incorporated into it to control the cardinality of the set of adjacent nodes and the bandwidth to be achieved. They are controlled systematically by rational selection of next candidates with the purpose of getting the smaller bandwidth efficiently. Eighteen meshes are renumbered and the results are compared with those of well-known algorithms. The results demonstrate the efficiency and the reliability of the proposed algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.12
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• pp.4293-4304
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• 2014

In order to ensure the wireless connectivity and seamless service to mobile users, the next generation network system will be an integration of multiple wireless access networks. In a heterogeneous wireless access system, bandwidth allocation becomes crucial for load balancing to avoid network congestion and improve system utilization efficiency. In this article, we propose a new dynamic bandwidth allocation scheme for hierarchical wireless network systems. First, we derive a multi-objective decision criterion for each access point. Second, a bargaining strategy selection algorithm is developed for the dynamic bandwidth re-allocation. Based on the intervenient Stackelberg game model, the proposed scheme effectively formulates the competitive interaction situation between several access points. The system performance of proposed scheme is evaluated by using extensive simulations. With a simulation study, it is confirmed that the proposed scheme can achieve better performance than other existing schemes under widely diverse network environments.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1145-1150
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• 2008

In this paper, We studied efficient design of wireless transmission system for unified data transmission in a subway and railway. It is increased that need of broadband multimedia service to make useful environment for user and to support the operation of railway system. High bandwidth is better if we need more services. But, high bandwidth requires more cost at tunnel of subway. More bandwidth make receive sensitivity to bad. So it need more wireless Station. We deduced best bandwidth of subway wireless transmission system reflecting the cost of installation and efficiency of system. Consequently, we decide efficient service model of broadband wireless system at a subway. Subway broadband wireless transmission system is tested in this year, and it is to be extended to province subway. Cost of subway broadband wireless transmission system is saved, because the system can be efficiently designed. Therefore, the effectiveness is expected to be very big.