• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.10
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• pp.2100-2112
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• 2011

An orthogonal code hopping multiplexing (OCHM) technique has been proposed for accommodating a large number of users with low channel activities than the number of orthogonal codewords through statistical multiplexing in downlink cellular systems. In this paper, a multiple input multiple output (MIMO) antenna based OCHM system is proposed to improve the performance. Each modulated symbol is repeated N times and the N repeated symbols are transmitted simultaneously using N transmit antennas. Through repetitions, the effect of perforations that the OCHM system experiences is decentralized among the repeated symbols and the full perforation probability is significantly reduced. Each receiver detect the transmitted signal using its pre-assigned code hopping pattern. Simulation results show that the proposed scheme saves the required energy for a given frame error rate (FER).

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.407-412
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• 2014

In this paper, we propose an underwater acoustic communication of FH-MFSK(Frequency-Hopped Multiple Frequency Shift Keying) system with multiple orthogonal property. Generally, the processing of FSK(Frequency Shift Keying) method is simple, but it is vulnerable to ISI (Inter-Symbol Interference) caused by multipath transmission. In this paper, the orthogonal codes are generated with the same number of transmitting symbols, and these codes are corresponding to multiple frequencies. We used m-sequence to generate multiple orthogonal codes. We compared the performance of proposed method with conventional MFSK method via the experiment. As a result, we confirmed that the proposed method shows 6~10 % lower error rate at 100 bps than conventional method.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.9 s.339
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• pp.41-48
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• 2005

In this paper, we suggest the scheme combining long-term feedback and short-term feedback in MIMO multi-user system and analyze its system performance. At the beginning of communication, long-term feedback is fed back to transmitter such as the number of active antennas, constellations, and transmission powers which are determined to satisfy the given target symbol error and target data rate for each user. After this, short-term feedback of active antenna index is fed back periodically Simulation results show the proposed scheme outperforms better than long-term feedback or short-term feedback information scheme.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.2
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• pp.19-25
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• 2008

When there are numerous wireless communication systems co-existing in the limited available frequency resource, an unexpected time delay can be caused during the system switching. So, in order to reduce this time delay, a mode selection method is required. In this paper, we propose a mode selection method to minimize the time delay for multi-system wireless communication systems. For the sake of efficiency, the mode selection method is designed by analyzing the preamble characteristics of different standards. Instead of performing a full search, we propose the preamble partial search to reduce the time delay to a minimum. Simulated with Matlab in an additive white Gaussian noise(AWGN) environment with a signal to noise ratio(SNR) of 10dB and bit error rate(BER) of $10^{-6}$, we evaluated and showed the performance improvement gained by using our proposed mode selection method.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.4
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• pp.99-107
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• 2009

Visible Light Communication (VLC) is a promising wireless communication technology. It offers huge, worldwide available and free bandwidth without electro-magnetic interference, which makes it very attractive for RF-sensitive operating environments. We propose colored LED-based VLC system for hospital use which includes voice recognition system for operating the medical equipments. New Mr hlation Scheme based on the Light Color Space is suggested to overcome the effect of noise generated by background light. Different color space constellations for different symbol sizes are also suggested which would give better bit error rate performance. Finally, Slotted ALOHA or TDMA medium access control protocols are suggested for multi-user operations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.240-248
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• 2006

In this paper, we consider an OFDM receiver algorithm design for IEEE 802.11a/p system, which targeting large coverage area while keeping the transmission format unchanged. Particularly, taking into account the inter-symbol interference(ISI) and inter-carrier interference(ICI) that can be induced with large RMS delay spread, we employ channel shortening time-domain equalizer(TEQ) and evaluate the receiver performance in terms of SINR and packet error rate(PER). The preamble defined in IEEE802.11a/p is used to estimated the initial equalizer tap coefficients. Primary purpose of the paper is to give an answer to the question, though partially, whether or not 16-QAM constellation can be used in none line of sight environment at the boundary of a large coverage area. To this end, we first analyze the required TEQ parameters for the target channel environment and then perform simulation for PER performance evaluation in a generic frequency selective fading channel with exponential power-delay profile.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.164-167
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• 2005

Recently, STC techniques have been considered to be candidate to support multimedia services in the next generation mobile radio communications and have been developed the many communications systems in order to achieve the high data rates. In this paper, we propose the Trellis-Coded Differential Space Time Modulation system with multiple symbol detection. The Trellis-code performs the set partition with unitary group codes. The Viterbi decoder containing new branch metrics is introduced in order to improve the bit error rate (BER) in the differential detection of the unitary differential space time modulation. Also, we describe the Viterbi algorithm in order to use this branch metrics. Our study shows that such a Viterbi decoder improves BER performance without sacrificing bandwidth and power efficiency.

• The Transactions of the Korea Information Processing Society
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• v.5 no.8
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• pp.2061-2074
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• 1998

In pattern recognition and image analysis upplications, a graph is a useful tool for complex obect representation and recognition. However it takes much time to pair proper nodes between the prototype graph and an input data graph. Futhermore it is difficult to decide whether the two graphs in a class are the same hecause real images are degradd in general by noise and other distortions. In this paper we propose a matching algorithm using a matrix. The matrix is suiable for simple and easily understood representation and enables the ordering and matching process to be convenient due to its predefined matrix manipulation. The nodes which constitute a gaph are ordered in the matrix by their geometrical positions and this makes it possible to save much comparison time for finding proper node pairs. for the classification, we defined a distance measure thatreflects the symbo's structural aspect that is the sum of the mode distance and the relation distance; the fornet is from the parameters describing the node shapes, the latter from the relations with othes node in the matrix. We also introduced a subdivision operation to compensate node merging which is mainly due t the prepreocessing error. The proposed method is applied to the recognition of musteal symbols and the result is given. The result shows that almost all, except heavily degraded symbols are recognized, and the recognition rate is approximately 95 percent.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.901-906
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• 2019

UAV (Unmanned Aerial Vehicle) is widely used in various areas such as civil and military applications including entertainment industries. Among them, UAV based communication system is also one of the important application areas. Relays have been received much attention in communication system due to its benefits of performance enhancement and coverage extension. In this paper, we investigate UAVs as relays especially focusing on physical layer. First, we introduce the research on UAV application for the relays, then the basic performance of relay networks in dual-hop communication system is analyzed by adopting decode-and-forward (DF) relaying protocol. The performance is represented using symbol error rate (SER) and UAV channels are applied by assuming asymmetric environments. Based on the performance analysis, we discuss performance enhancement issues by considering physical layer.

• KSCI Review
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• v.2 no.1
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• pp.55-67
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• 1995

Recently, it is possible to high speed transmission of the non-voiced data, including voice, data, moving image instead of voice only in the past by changing the communication method to digital form from analog owing to the development of semiconductor and computer technology which for information transmission of the remote point. By doing so, we can get the improvement of the noise effect and low cost but the loss of transmission bandwidth. It is necessary to take some method in oreder to reducing the fading which is propotional to transmission bandwidth during the transmission of radio communication channel, especially. When we design the digital communication system, we must considered to the fading effect in order to determination of the transmitting power, modulation /demodulation method, transmission speed, bit error rate. This paper mainly concerns to the method to the channel simulator which descrives the fading effect during the transmission by computer model and digital filter modeling of the radio fading channel by unsing the transmitting and received signal. By taking the inverse of the characteristic of the modeled filter, it is possible to improvement of the communication system by reducing the distortion and inter-symbol interference which occurs in the channel.