Earticle

We propose a novel cooperative space?time line code (C-STLC) scheme to improve performance of a relay-assisted internet of things (R-IoT). The proposed C-STLC operates with fully distributed manner, where each relay IoT device (RID) attempts to decode the received signal from a source IoT device at the first hop and the RIDs, that succeeded decoding, send the STLC encoded signal based on their local channel state information (CSI) to a single access point (AP) at the second hop. Then, the AP decodes the received signals without CSI. As a main result, we mathematically analyze the outage probability (OP) of the proposed C-STLC scheme. It is shown that the proposed C-STLC significantly outperforms conventional cooperative relaying techniques in terms of the OP.

In today's world, communication, the sharing of information, and money transactions are all possible to conduct via the Internet, but it is important that it these things are done by the actual person. It is possible via several means that an intruder can access user information. As such, several precautionary measures have to be taken to avoid such instances. The purpose of this paper is to introduce the idea of a one-time password (OTP), which makes unauthorized access difficult for unauthorized users. A OTP can be implemented using smart cards, time-based tokens, and short message service, but hardware based methodologies require maintenance costs and can be misplaced Therefore, the quick response code technique and personal assurance message has been added along with the OTP authentication.

Real-time embedded systems have become pervasive in general industry. They also began to be applied in such domains as avionics, automotive, aerospace, healthcare, and industrial Internet. However, the system failure of such domains could result in catastrophic consequences. Runtime software testing is required in such domains that demands very high accuracy. Traditional runtime software testing based on handwork is very inefficient and time consuming. Hence, test automation methodologies in runtime is demanding. In this paper, we introduce a software testing system that translates a real-time software into a monitorable real-time software. The monitorable real-time software means the software provides the monitoring information in runtime. The monitoring target are time constraints of the input real-time software. We anticipate that our system lessens the burden of runtime software testing.

Liquid crystal-polymer composite(LCPC) films promising new materials for both projection displays and vision product. LCPC films consist of a continous liquid crystal phase embedded in a three- dimensional network of polymer matrix. The liquid crystal in these LC phases can be elecrtrically switched giving rise to an opaque scattering off-stats and a transparent, non-scatting on- stats. In this work. a premixture is composed of LC, UV-curable monomer and photonitiator. LCPC films are formed by photopolymerization induced phase separation from this premixture. In conclusion, structure and electro-optical properties of LCPC films strongly depends on the selection of monomer, LC content and curing rate.

在國際航運業務中，按營運方式的不同可劃分爲班為班輪運和不定期船運輪。班輪運輪的特點是有固定航線, 有固定班期, 掛靠固定港口，按運费表結算運費, 主要適合運載小宗數量的貨物。但就世界海運貨量而言，以不定期船承運占了大部份。不定期船的特點是沒固定班期、航線和掛港，這種方式適合運載大宗貨物，如糧食、礦石、石油等。 不定期船按船舶租用方式可大致分為三種，即定期租船(期租)、航次租船(程租)和光船租賃(光租)，其中以定期租船最為普遍。船東船出租給承租人在一定期限(如一年)內使用，承租人可以根據約規定的允許航行區營運,如安排攬貨、掛港、載貨及調度等，船長要在經營方面服從承租人的命令。租金一般是以每天或每載重噸爲單位按月支付。 定期租船合同中承租人的責任問題是研究定期租船合同的核心問題之一。目前，國制上沒有關於定期租船的國際條約，僅是存在幾個標準合同格式，如NYPE租約和BALTIME租約。不管是普通法系國家還是大陸法系國家，都沒有對定期租船合同的強制性規定，並且國家對定期租船承租人的責任規定也有很大區别。文章眼球的重點是定期租船合同中承租人對船舶所有人(出租)應該承擔的義務和責任。以中國海商法中對定定租船承租人的責任規定爲重心，通過與國制標準租船合同中相關條款的對比和分析，從而為定期租船合同雙方當事人更好的簽訂合同提供一些建議。

실시간 시스템에서 시간적 제약의 불이행의 커다란 손실을 가져오며, 이를 위한 동적 스케쥴링은 유연성을 제공하는 대신 스케쥴링 오버헤드와 분석작업의 복잡성으로 인하여 스케쥴성을 예측하기 어려움이 있다. 반면, 정적 스케쥴링은 수행 중 오버헤드가 없으므로 정확한 시간을 예측할 수 있는 장점이 있다. 따라서 명령어 수준의 정적 스케쥴링과 시간 분석을 통하여 시스템의 시간적 정확도를 보장할 수 있다. 본 논문에서는 확정된 시간 분석을 위하여 befor와 after의 시간 제약을 고급 언어에 표현하고 이를 근거로 시간적 분석에 기반을 둔 컴파일러의 명령어 수준의 스케쥴링 알고리즘을 제안하였다. 이 스케쥴링의 특징은 명령어 수준의 스케쥴링을 위한 도메인이 지나치게 과대하므로 향상된 적합 유전자 알고리즘을 적용한 것이다.

In hard real-time systems, a timing fault may yield catastrophic results. Dynamic scheduling provides the flexibility to compensate for unexpected events at runtime; however, scheduling overhead at runtime is relatively large, constraining both the accuracy of the timing and the complexity of the scheduling analysis. In contrast, static scheduling need not have any runtime overhead. Thus, it has the potential to guarantee the precise time at which each instruction implementing a control action will execute. This paper presents a new approach to the problem of analyzing high-level language code, augmented by arbitrary before and after timing constraints, to provide a valid static schedule. Our technique is based on instruction-level complier code scheduling and timing analysis, and can ensure the timing of control operations to within a single instruction clock cycle. Because the search space for a valid static schedule is very large, a novel adaptive genetic search algorithm was developed.

원격 측정 시스템을 구성하는 장비들은 정확한 시간에 이벤트를 발생시키기 위해 GPS 수신기로부터 발생하는 절대 시간에 동기화가 되어야 한다. 이렇게 동기화된 시스템일수록 데이터의 일관성을 보장할 수 있기 때문에 시각동기화의 중요성은 더욱 중요시 되고 있다. 본 논문에서는 원격 측정 시스템에서 GPS 수신기로부터 발생되는 IRIG-B 표준의 시간 코드를 이용하여 NCO 기반의 동기화 클록을 생성하는 방법을 제안한다. 제안한 방법을 검증하기 위해 VHDL 로직으로 설계 및 구현하였으며, Modelsim을 이용해 시뮬레이션을 진행하였다. 또한 FPGA를 이용해 GPS 수신기로부터 IRIG-B 시간 코드를 수신하여 동기화된 클록 생성 여부에 대한 검증을 진행하였다. 제안한 방법은 원격 측정 시스템을 구성하는 각 장치에서 저가의 정밀도가 낮은 오실레이터를 사용하더라도 GPS의 절대 시간에 동기화된 클록을 생성하기 때문에 비용적인 측면에서 보다 도움이 될 것이다.

The equipment that constitutes a telemetry system must be synchronized to the absolute time generated by the GPS receiver in order to trigger events at precise times. The more synchronized the system, the better the consistency of the data can be ensured, making time synchronization increasingly important. In this paper, we propose a method for generating an NCO-based precise synchronized clock using the IRIG-B standard time code generated by a GPS receiver in a telemetry system. To validate the proposed method, we designed and implemented it using VHDL logic and conducted simulations with Modelsim. Additionally, we verified the generation of synchronized clocks by receiving IRIG-B time codes from a GPS receiver using FPGA. The proposed method will be beneficial in terms of cost, as it generates clocks synchronized to the GPS absolute time even when using low-cost oscillators with low precision in each device of the telemetry system.

본 논문에서는 SOSTTC를 다중 안테나 시스템에 적용하고 ST SF STF 복호화 기법을 통해 효과적으로 신호를 검출하는 방법을 연계하여 주파수 선택적인 채널에서 성능 평가를 한다. 또한 성능 향상을 위해 제안된 시스템에 OFDM을 적용한다. 먼저 기본적인 두 개의 전송 안테나를 가진 SOSTTC-OFDM 시스템을 설명하고 기존의 시 공간 부호화된 OFDM과 성능을 비교한다. 이 시스템을 네 개의 전송 안테나 시스템으로 확장하고 기존의 ST SF STF-OFDM 기법에 SOSTTC를 적용하여 SOSTTC ST SF STF-OFDM 시스템을 설계한다. 이 시스템에 적합한 복호화 기법을 사용하여 효과적으로 신호가 검출됨을 평가하고, 또한 주파수 선택적 채널에서 도플러 주파수가 변화함에 따라 제안된 시스템의 성능을 확인한다.

In this paper, we propose an efficient method to detect the signal and evaluate performance of the system in frequency selective fading channel. We combine proposed system with OFDM (Orthogonal Frequency Division Multiplexing) to improve performance of the system. First, we study the SOSTTC-OFDM system using two transmit antenna and one receive antenna, and compare performance of the proposed space-time coded OFDM with that of previous system. We expand this system to the system using four transmit antennas with the proposed decoding method. Simulation results show that the proposed decoding method can detect the signal efficiently, and we identify that the performance of the proposed system is shown with varying doppler frequency in frequency selective fading channel.

This paper shows the analysis results of time offsets using P1, P2 and P3 code in GPS time transfer. The r2cggtts program has been used in GNSS Time Transfer and use the P3 ionosphere free combination of P1 and P2 code measurements. We modified the r2cggtts program in order to calculate and write all kinds of time offsets P3 as well as P1 and P2. The result of the modified r2cggtts program shows that time offsets using P1 and P2 are of wide distribution comparing to time offsets using P3. In order to Figure out the error factors for wide distributions of P1 and P2, we analyze and present the relation between the elevation angle and time offsets in this paper.

Pseudolite is a contraction of the term pseudo-satellite, used to refer to something that is not a satellite which performs a function commonly in the domain of satellites. A pseudolite is installed on the ground, which sends the same waves as those from a GPS satellite to enable positioning in locations where it is difficult to receive the waves from GPS satellite, such as between tall buildings, underground, and indoors. The pseudo-range measurement accuracy of pseudolite depends on the performance of clock synchronization between pseudolite and GPS satellites. This paper proposes clock synchronization algorithm for pseudolite. It is a revision and improvement of the time comparison technique based on GPS code transfer in order to determine the UTC.

블록체인의 참여가 증가하면서 생태계 유지를 위한 거버넌스가 활성화되고 있다. 거버넌스는 블록체인을 유지하 고 발전시키기 위해 관리/감독이 이루어져야 한다. 하지만 블록체인의 사용량이 증가함에 따라 사람이 일일이 관리하기 엔 한계가 존재한다. 또한, 이더리움부터 적용된 스마트 컨트랙트라는 새로운 거래 형태가 가능함에 따라 상태 값에 따라 결정되는 거래에 대해 검증이 필요하다. 본 연구는 거버넌스의 블록체인 생태계 유지와 발전을 위한 도구로 블록체인 스마트 컨트랙트의 상태 모니터링을 기반으로 하는 관제시스템(Blockchain Watchdog)을 제안하며, 관제시스템의 구 현 및 실험을 진행하였다. 사례 연구로 Ropsten과 Ganache를 활용한 사설 네트워크에서 실험을 진행하였으며, 실시간 정보수집과 대시보드와 그래프, 차트를 활용한 시각화를 볼 수 있었다. 우리는 Blockchain Watchdog을 통해 블록체인 거버넌스의 생태계 유지와 발전에 기여할 것이라 기대한다.

As the participation of blockchain increases, governance to maintain the ecosystem is being activated. Governance must be managed/supervised to maintain and improve the blockchain. However, as the usage of blockchain increases, there is a limit for people to manage it individually. In addition, smart contracts applied from Ethereum need to be verified for trade that are determined according to status values, as new trade types are possible. This research proposes a surveillance system, Blockchain Watchdog, based on the state monitoring of the blockchain smart contract as a tool for maintaining and developing the blockchain ecosystem of governance, and implemented and tested the surveillance system. As a case study, we conducted experiments on Ropsten and Ganache, and were able to see real-time information collection and visualization using dashboards, graphs, and charts. We expect to contribute to the maintenance and development of the ecosystem of blockchain governance through Blockchain Watchdog.

공간-시간 부호(Space-Time Code)는 다중 안테나 시스템에서 기존의 기술에 비해서 부가적인 대역폭이 필요 없이 부호화 이득을 얻을 수 있다. 지금까지 공간-시간 부호(Space-Time Code)는 다이버시티 이득의 관점에서는 신호행렬들의 차가 완전-계수(Full-Rank)를 가져야 하고, 코딩 이득의 관점에서는 신호행렬들의 차의 determinant 값이 최소값을 가져야 한다. 본 논문에서는 공간-시간 블록 부호 디자인(Space-Time Block Code) 관점에서 직교-디자인(Orthogonal-design) 즉, 최소거리가 5이면서 완전-계수(Full-Rank)인 디자인을 비교대상으로 완전-계수(Full-Rank)가 아니면서 최소거리가 5와7인두 부호에 관하여 연구되어졌다.

공간-시간 블록 부호(STBC)는 다중안테나 시스템에서 기존 기술에 비해서 부가적인 대역폭 필요 없이 부호화 이득을 얻을 수 있다. STBC의 우수한 디자인 조건은 다이버시티 이득 관점에서는 신호 행렬들의 차가 완전 계수(Full-Rank)를 가져야 하고 코딩 이득의 관점에서는 신호 행렬들의 차의 determinant 값이 최소값을 가져야 한다. 본 논문에서는 STBC가 Full Rank 와 non-Full Rank 때 성능에 관하여 실험하였다. 시스템모델에 관하여 간략한 설명과 이 실험결과에 관하여 논의하였다. 본 논문의 실험 결과는 전송안테나와 수신안테나가 각각 4개씩, BPSK, QPSK, 8PSK 변조(modulation)을 사용하여 실험결과를 얻었다.

본 논문에서는 공간-시간 블록 부호디자인(Space-Time Block Code) 관점에서 직교-디자인(Orthogonal-design) 즉, 최소거리가 5이면서 완전-계수(Full-Rank)인 디자인을 비교대상으로 완전-계수(Full-Rank)가 아니면서 최소거리가 5와7인 두 부호에 관하여 연구되어졌다.

변형된 time mapped prime sequences를 time spreading pattern에 이용하여 다양한 wavelength-time codeword를 구현하는 방법을 연구하였다. 이 연구 결과 $P_t$ = 3 일 때는 autocorrelation sidelobe와 crosscorrelation을 1이하로 유지하며 사용하는 파장 수의 제곱에 해 당하는 wavelength-time codeword를 생성 할 수 있으며 $P_t$ = 5 와 $P_t$ = 7 일 때는 crosscorrelation을 1이하로 유지하면서 $P_w$개의 wavelength-time codeword에 대해서 autocorrelation sidelobe를 2이하로 제한하는 범위에서 역시 사용하는 파장 수의 제곱에 해당하는 wavelength-time codeword를 생성할 수 있다.

In this paper, a new family of wavelength-time codewords using modified time mapped prime sequences as a time spreading pattern is constructed. When $P_t$ = 3, we can construct $P_w^2$ wavelength-time codewords with low autocorrelation sidelobe and crosscorrelation of less than or equal to 1. When $P_t$ = 5 and $P_t$ = 7, the number of wavelength-time codewords of $P_w^2$ can be constructed with good crosscorrelation of 1 and autocorrelation of less than or equal to 2.

This paper presents a novel shore-to-sea maritime data transmission system based on time-code diversity, using visible light in maritime environments to overcome the limitations of conventional maritime wireless communications. The proposed system is primarily comprised of existing LED-based lighthouses and maritime transceivers (marine beacons, buoys, etc.), and thus is considered cost-effective in terms of implementation. We first analyze maritime visible-light communications on the basis of the unique properties of a maritime environment, i.e. sea states (wave height, wind speed, etc.), plus atmospheric turbulence, using the Pierson-Moskowitz (PM) and JONSWAP (JS) spectrum models. It is found that the JS model outperforms the PM model, and that the coverage distance depends on the LED power and sea states. To combat maritime fading conditions that significantly degrade performance and coverage distance, we propose a time-code diversity (TCD) scheme in which the delayed versions of the original data are retransmitted using orthogonal Walsh codes. This TCD scheme is found to be superior, in that it offers three orders of magnitude in terms of BER performance, compared to a conventional (non-TCD) transmission scheme. The proposed scheme is robust and efficient in overcoming the effect of impairments present in maritime environments with a BER of approximately $10^{-5}$and a data rate of 100 Kbps at a distance of 1 km.

Since the publication of Alamouti's famous space-time block code, various quasi-orthogonal space-time block codes (QSTBC) for multi-input multi-output (MIMO) fading channels for more than two transmit antennas have been proposed. It has been shown that these codes cannot achieve full diversity at full rate. In this paper, we present a simple feedback scheme for rich scattering (flat Rayleigh fading) MIMO channels that improves the coding gain and diversity of a QSTBC for 2$^n$ (n=3, 4, ${\cdots}$) transmit antennas. The relevant channel state information is sent back from the receiver to the transmitter quantized to one or two bits per code block. In this way, signal transmission with an improved coding gain and diversity near to the maximum diversity order is achieved. Such high diversity can be exploited with either a maximum-likelihood receiver or low-complexity zero-forcing receiver.