Earticle

본 논문에서는 해양 환경에서 기후에 따른 가시광 무선통신 시스템에 대해 연구한다. 해양 환경에 적합한 대기 채널 모델인 Kim 모델을 이용하여 가시광 선명도에 따른 기후 조건을 맑음, 비, 폭풍, 안개로 구분하였고, OOK-NRZ 변조기법을 적용한 모의실험을통해 기후 조건에 따른 BER 성능을 비교하였다. 또한 현장실험을 통해 실제로 가시광 통신에서 에러 비트를 측정하고 모의실험과비교 분석을 통하여 해양 환경에서의 가시광 통신 유효성을 입증하였다.

In this paper, visible light wireless communication system according to the climate is studied in the marine environment. The light visibility can be determined by the different weather conditions (clear air, rain, storm, fog) in Kim’s atmospheric channel model. By simulating the OOK-NRZ modulation technique, the BER performances are compared in the different weather conditions. In the field test, the error bit is measured in the visible-light communication. The effectiveness of visible light communication in the marine environment is confirmed by comparing the analysis of simulations and field experiments.

Free Space Optical Communication has been developed to cover the longer distances with the growing needs of high speed. It is a data transmission technology from one point to another point by using laser beam carrying information in free space. Multiple transmitters/receivers (TX/RX) are used to improve the performance and quality of Free Space Optics (FSO) communication system under different weather conditions. This paper analyzes the performance of multiple transceivers system by the received power level (PR), Q factor and bit error rate (BER) under clear, fog and haze conditions. From the measured data is possible to calculate visibility which is the main factor for quality and estimation for the availability and reliability of FSO link. The Free Space Optical link was modelled and simulated using a commercial optical system simulator named OptiSystem by Optiwave.

Recently, the density of Flash memory has dramatically increased by moving to smaller geometries and storing more bits per cell with enhanced memory technologies. However, with the density increasing rapidly, the error rate of Flash memory is also increasing rapidly. To improve the reliability issue of upcoming flash memory, usually, redundancy techniques were adopted in both of architecture and operations for flash memory based systems. For outside the flash memory page, several reliability schemes were proposed which employ Redundant Array of Inexpensive Disks (RAID). In this paper, we propose in-block level redundancy scheme for providing reliability of flash memory while minimizing maintaining overhead of the redundancy. In the proposed scheme, the redundancy is generated in a flash memory block level. During the programming stage of a flash block, the redundancy is kept in Dram memory. If a block is exhausted with last-1 page to record incoming data, the in-keeping redundancy is flushed to last page of the block. By doing this, block level redundancy is maintained with minimal overhead.

Nonlinear optical effects in fibers occur via ultrafast Kerr nonlinearity, offers a flexible framework within which numerous signal-processing functions can be accomplished. When high power launched in optical fiber, several nonlinear transmission impairment such as amplitude noise, phase noise, power spectral losses, that degrades the performance of optical communication system. All optical regeneration is one of the solution to mitigate transmission impairments instead of optical to electrical conversion. In this paper, all optical regeneration is demonstrated for 10Gb/s DPSK system using 3R regeneration and Phase sensitive amplification to mitigate amplitude and nonlinear phase noise form 10G noisy DPSK transmission system. Bit error rate of 10-11 is achieved at power penalty of 6 dB. The system is developed and tested using optisystem. The developed all optical regeneration system is very demanding for long distance transmission in high-speed communication systems.

The demands for high speed applications are growing at a faster rate. To meet theserequirements, 4G technologies are being used nowadays. COFDM based WiMax is the outcome in this direction which promises to cater these high speed and high quality applications. Worldwide Interoperability for Microwave Access (WiMax) is an IEEE 802.16 standard-based broadband wireless access (BWA) technology which employsCoded orthogonal frequency division multiplexing access (COFDM). This paper analyses Bit Error Rate for WiMax based COFDM system with QPSK modulation scheme under various channel conditions like AWGN, Rayleigh, Rician and Nakagami-m. It has been observed that performance of Nakagami fading channel is better than other fading channels.

This paper presents the conventional and multiband Orthogonal Frequency Division Multiplexing (OFDM) simulation software named Signal Modulation Simulator (SiMiSIM). A simulation system was built with a Graphical User Interface (GUI) to provide a more user friendly interface than contemporary or command line interfaces. Three basic frequency modulation techniques were made available in SiMiSIM: Binary Phase Shift Keying (BPSK), Quadrature Phase-Shift Keying (QPSK) and Quadrature Amplitude Modulation (QAM). Each of the signals had to face Forward Error Correction (FEC) encoder to enhance the signal robustness at the receiver end. The simulation was able to simulate Bit Error Rate (BER) and Power Spectral Density (PSD) for research purposes as well as educational purposes.

Collaborative communication produces significant (N2 where N is number of nodes used for collaboration) power gain and overcomes the effect of fading. With imperfect frequency synchronization significant but slightly less than N2 power can be achieved. As the N increases more power gain can be achieved at the expense of more circuit power. In this paper an energy consumption model for collaborative communication system with imperfect frequency synchronization is proposed. The model to calculate the energy consumed by the sensor network for local communication and communication with base station is presented. Energy efficiency model for collaborative communication for the off-the shell products (CC2420 and AT86RF212) are presented. It is also shown that significant energy can be saved using collaborative communication as compared to traditional SISO (Single input single output) for products. The break-even distance where the energy consumed by SISO and collaborative communication is also calculated. From results it is revealed that collaborative communication

본 논문에서는 한 쌍의 1차 사용자 송․수신단(PT-PR)과 한 쌍의 2차 사용자 송․수신단(ST-SR)을 가지는 무선 인지 통신 시스템을 고려한다. 첫 번째 시간 슬롯(1 Phase)에서 1차 사용자 송신단(Primary Transmitter : PT)은 1차 사용자 수신단(Primary Receiver : PR), 2차 사용자 송신단(Secondary Transmitter : ST) 및 2차 사용자 수신단(Secondary Receiver : SR)에 자신의 신호 를 브로드캐스트하며, 각각의 수신단(PR, ST, SR)에서는 수신된 신호를 복호한다. 두 번째 시간 슬롯(2 Phase)에서 ST는 수신 후 복호한 와 자신이 전송하고자하는 신호 를 결합하여 PR과 SR에 브로드캐스트하고, 각 수신단(PR, SR)에서는 수신한 신호를 복호한다. 이 때 PR은 첫 번째 시간 슬롯에 수신한 와 두 번째 시간 슬롯에 수신한 + 신호 중 를 검출하여 최대 비 결합(Maximal Ratio Combining) 기법을 이용하여 결합한다. 이 때 PR에서는 다이버시티 이득을 얻을 수 있다. SR은 첫 번째 시간 슬롯에 수신한 와 두 번째 시간 슬롯에 수신한 신호를 가지고 선형결합을 통해 를 얻는다.

In this paper, the considered cognitive radio system has a pair of PT-PR and a pair of ST-SR. In first time slot(1 Phase), PT broadcast signal to PR, ST and SR. Then, each receivers(PR, ST, SR) decode received signal . In second time slot(2 Phase), ST combine decoded signal and signal , and it broadcast combined signal to PR and SR. PR and SR decode combined signal. At this time, PR can achieve diversity gain, due to using MRC, it combine 'received and decoded signal at 1 phase' and 'detected signal at 2 phase'. SR use linear combining technique and it can obtain .

Optical code division multiple access system (OCDMA) has been important with increasing demands of high capacity and speed for communication in optical networks. Due to OCDMA technique high efficiency is achieved, hence fiber bandwidth is fully used. In this paper we will focus on different codes i.e MD (Multi Diagonal) FCC (Flexible cross correlation), DCS (Dynamic cyclic shift) code with BER parameter. Due to this codes we will eliminated MAI (multiple access interference) and improve BER (bit error rate), PIIN (Phase induced intensity noise) and make orthogonality between users in the system .We will use AND subtraction detection technique to implement these codes with technique of OCDMA using optiwave system design tool.

Recently, positively asymmetric binary pulse amplitude modulation (2PAM) has been proposed to improve the bit error rate (BER) performance of the weak channel gain user, with a tolerable BER loss of the strong channel gain user, for non-orthogonal multiple access (NOMA). However, the BER loss of the stronger channel gain user is inevitable in such positively asymmetric 2PAM NOMA scheme. Thus, we propose the negatively asymmetric 2PAM NOMA scheme. First, we derive closed-form expressions for the BERs of the negatively asymmetric 2PAM NOMA. Then, simulations demonstrate that for the stronger channel gain user, the BER of the proposed negatively asymmetric 2PAM NOMA improves, compared to that of the conventional positively asymmetric 2PAM NOMA. Moreover, we also show that for the weaker channel gain user, the BER of the proposed negatively asymmetric 2PAM NOMA is comparable to that of the conventional positively asymmetric 2PAM NOMA, over the power allocation range less than about 10 %.

In this paper a DPLL circuit realizable by digital IC's is propose and the principles of general DPLL are described. An all Digital phase locked loop is designed, analyzed, and tested. In particular, the approach of invoking Gaussian assumption on the decision variable and based on S.O.Rices theory is used. As a performance of the above PLL detector operating on low data rate FSK is given and demonsrtated to be FSK reception.

Bit error rate (BER) monitoring is the ultimate goal of performance monitoring in all digital transmission systems as well as optical fiber transmission systems. To achieve this goal, optimization of the decision threshold must also be considered because BER is dependent on the level of decision threshold. In this paper, we analyze a pseudo-error counting scheme and propose an algorithm to achieve both BER monitoring and adaptive decision threshold optimization in optical fiber transmission systems. To verify the effectiveness of the proposed algorithm, we conduct computer simulations in both Gaussian and non-Gaussian distribution cases. According to the simulation results, BER and the optimum decision threshold can be estimated with the errors of < 20% and < 10 mV, respectively, within 0.1-s processing time in > 40-Gb/s transmission systems.

Uplink multicarrier code-division multiple-access (MC-CDMA) with equal gain combining (EGC) over Nakagami fading channels is considered. An improved expression which is a feasible alternative for the bit error rate (BER) performance evaluation of MC-CDMA signals is proposed. Simulated annealing algorithm is employed to obtain the optimum value of the coefficients belonging to the proposed expression. Numerical examples show that the performance curves computed by the improved expression are in good agreement with the results obtained by the exact expression. Thus, the proposed expression can improve the accuracy of BER performance evaluation that has been realized by the approximate expression.

This paper presents closed-form expressions for exact bit error rate of MSK and OQPSK systems employing an adaptive antenna array at base station to eliminate co-channel interference. The channels under consideration are AWGN and one-path flat Rayleigh fading with AWGN. Computer simulation is carried out to confirm the theoretical results.

Wear leveling techniques have been studied to prolong the lifetime of NAND flash memory. Most of studies have used Program/Erase(P/E) cycles as wear index for wear leveling. Unfortunately, P/E cycles could not predict the real lifetime of NAND flash blocks. Therefore, these algorithms have the limited performance from prolonging the lifetime when applied to the SSD. In order to apply the real lifetime, wear leveling algorithms, which use raw Bit Error Rate(rBER) as wear index, have been studied in recent years. In this paper, we propose CrEWL(Cold data identification using raw Bit error rate in Wear Leveling), which uses rBER as wear index to apply to the real lifetime. The proposed wear leveling reduces an overhead of garbage collections by using HBSQ(Hot Block Sequence Queue) which identifies hot data. In order to reduce overhead of wear leveling, CrEWL does not perform wear leveling until rBER of the some blocks reaches a threshold value. We evaluate CrEWL in comparison with the previous studies under the traces having the different Hot/Cold rate, and the experimental results show that our wear leveling technique can reduce the overhead up to 41% and prolong the lifetime up to 72% compared with previous wear leveling techniques.

Cooperative transmission is an effective solution to improve the performance of wireless communications over fading channels without the need for physical co-located antenna arrays. In this paper, selection combining is used at the destination instead of maximal ratio combing to optimize the structure of destination and to reduce power consumption in selective decode-and-forward relaying networks. For an arbitrary number of relays, an exact and closed-form expression of the bit error rate (BER) is derived for M-PAM, M-QAM, and M-PSK, respectively, in both independent identically distributed and independent but not identically distributed Rayleigh fading channels. A variety of simulations are performed and show that they match exactly with analytic ones. In addition, our results show that the optimum number of relays depend not only on channel conditions (operating SNRs) but also on modulation schemes which to be used.