Yoon Hyun Kim

Scalable optical relay for LED-ID systems

LED-ID (light emitting diode - identification) system typically uses line of sight (LOS) channels to achieve high data rate and bright illumination. In LOS channel, however, the LED-ID system has very narrow coverage. In cellular networks, the relay station has been introduced to improve system throughput and coverage. Accordingly, new optical relay scheme is essential to support multi-hop transmission in relay-assisted LED-ID networks. In this paper, effects of shadow region problem are investigated for LED identification (LED-ID) system in a non-line of sight (NLOS) environment. A scenario on shadow region problem is proposed, and nominal interrogation range of a desired reader is derived from this model. In order to expand the coverage of LED-ID networks, an efficient optical relay scheme is proposed and simulated by employing cooperative communication methodology. It is confirmed that the proposed technique performs well both in terms of throughput and fairness by simulation results. Also, the proposed scheme is very effective to expand coverage of LED-ID communication networks.

Novel LBS technique based on visible light communications

In this paper, we propose novel location based service (LBS) technique using visible light communications (VLC) for indoor location service. As an indoor LBS technique, the VLC is employed due to its many advantages for location awareness and its performance is presented through simulations. The performance of location awareness is evaluated in terms of bit error rate and location awareness error. The results of the paper can be applicable to the indoor LBS technique with high accuracy.

Novel transmission algorithm of UWB signals for WBAN applications

Novel paradigm of medical service such as u-health service becomes the center of public attention. In u-health care area, the core technology is based on WBAN (Wireless Body Area Network). In this paper, we propose novel transmission algorithm of UWB signals based on watermarking scheme in WBAN. As watermarking sequence, Kasami sequence having good correlation property is applied. The performance of proposed scheme is analyzed in terms of detection probabilities. The results can be applied to design various applications based on WBAN.

Interference mitigation scheme of visible light communication systems for aircraft wireless applications

In this paper, we analyze and simulate the interference cancellation scheme for aircraft wireless communication environment with visible light communication (VLC) systems. We employ an interference cancellation scheme based on successive interference cancellation (SIC), and the performance is evaluated in term of bit error rate (BER). From the results, it is confirmed that the SIC with optimal ordering attains high performance compared with conventional algorithms. The results of the paper can be applied to the design and implementation of wireless aircraft communication systems.

Differential STBC MIMO-OFDM System with Cyclic Delay Diversity for Mobile Multimedia Communication Systems

In a conventional MIMO-OFDM system, it is well known that cyclic delay diversity (CDD) and space-time block coding (STBC) can increase data rate, capacity and bit error rate (BER) performance. However, a recent trend of research on the MIMO-OFDM system pays more attention to simplified implementation of receiver structure. In this paper, we propose differential STBC MIMO-OFDM system with CDD. This structure can provide a very close performance to that of the conventional diversity scheme with maximum likelihood (ML) detection without channel estimation block while the receiver structure is highly simplified. BER (bit error rate) performance of the proposed system is simulated for an AWGN channel by theoretical and simulated approaches. The results of this paper can be applicable to the 4G mobile multimedia communication systems.

Performance of Efficient Signal Detection for LED-ID Systems

In this paper, effects of reader-to-reader interference are investigated for LED identification (LED-ID) system in a multi-reader environment. The LED-ID readers typically use different channels to avoid collision between readers. However, in-channel collision usually happens in terms of interrogation range. A reader-to-reader interference scenario is proposed, and nominal interrogation range of a desired reader is derived from this model. In order to evaluate the LED-ID reader-to-reader interference quantitatively, an efficient detection scheme is proposed and simulated by employing spreading sequence. The spreading sequence is inserted between each user’s frame formats. In the receiver, the desired signal is detected by using correlation among inserted spreading sequences. From simulation results, it is confirmed that the proposed scheme is very effective to enhance reliability of LED-ID communication systems.

Performance comparison of 802.11n system with WLAN channel model

As the demand of high quality service in next generation wireless communication systems, a high performance of data transmission requires an increase of spectrum efficiency and an improvement of error performance in wireless communication systems. In this paper, we propose a multi-user multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system with cyclic delay diversity and block diagonalization procoding method to improve bit error rate (BER) performance with wireless local area network (WLAN) channel model C and D for 802.11n WLAN system. The results of mathlab simulation show the improvement of BER performance in 802.11n wireless indoor channel environment.

Transceiver Characteristics and Additional Data Transmission Scheme for LED-ID Systems

In this paper, characteristics of transmission and receive of RGB (Red/Green/Blue) light emitting diodes (LEDs) are analyzed for LED identification (LED-ID) systems. LED is considered as a future light technology because of advantages of LED such as the long life time, low power consumption and high power efficiency. Moreover, LED is used to lighting device also, it can be used a communication device, because LED has high frequency response of a few MHz. For LED communication systems, each red, green and blue LED has different transmission / receive characteristic. The red LED has good transmission characteristic in the transmission power and distance aspects. Similarly, the blue LED has good transmission characteristic in the data rate aspects. However, the green LED has low SNR (Signal-to-noise ratio) characteristic in comparison with red and blue LEDs. So, LED communication systems take in SNR to make the green LED. In this case, system performance such as data rate, transmission power and bit error rate (BER) are deteriorated for LED communication systems. For this reason, in this paper, we use optical filter to separate RGB colors and then, send the main data (image, video, etc.) using red and blue LEDs. And an additional data (simple text, location information, etc.) is transmitted by greed LEDs. Using this method, we obtain the SNR gain for main data transmission and receive, in additional, without increase of system complexity, we transmit additional data. From simulation results, it is confirmed that the proposed scheme is very effective to enhance system performance of LED-ID communication systems.

MIMO OFDM system with AMC and variable CP length for wireless communications

There are a few core technologies to enable high-performance 4th generation (4G) broadband wireless communication system. A multiple input multiple output (MIMO) provides high-rate transmission through expended channels by multiple array antennas in both sender and receiver side. Also orthogonal frequency division multiplexing (OFDM) is well-known as the most appropriate technique for high data rate transmission. Adaptive modulation and coding (AMC) changes a modulation order and coding rate according to channel conditions, so it is possible that the spectral efficiency is improved at the fixed error performance. Cyclic prefix (CP) is the one of the most important technique to OFDM system and is reducing inter-symbol interference (ISI) effects in high speed wireless mobile communication system. As consider the time varying channel condition, however, fixed CP length is not only increasing power consumption but also reducing data transmission rate. In this paper, we propose a multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system with AMC and adaptive CP length to improve system capacity with maintaining good error performance. The results of computer simulation show the improvement of system capacity in Rayleigh fading channel.

Performance of Detection Probability with Adaptive Threshold Algorithm for CR Based on Ad-Hoc Network

Ad-hoc networks can be used various environment, which it is difficult to construct infrastructures, such as shadowing areas, disaster areas, war area, and so on. In order to support to considerable and various wireless services, more spectrum resources are needed. However, efficient utilization of the frequency resource is difficult because of spectrum scarcity and the conventional frequency regulation. Ad-hoc networks employing cognitive radio(CR) system that guarantee high spectrum utilization provide effective way to increase the network capacity. In conventional CR based ad-hoc network, it uses constant threshold value to detect primary user signal, so the results become not reliable. In this paper, to solve this problem, we apply adaptive threshold value to the CR based ad-hoc network, and adaptive threshold is immediately changed by SNR(Signal to Noise Ratio). From the simulation results, we confirmed that proposed algorithm has the greatly better detection probabilities than conventional CR based ad-hoc network.