• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2C
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• pp.105-111
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• 2011

In this paper, we propose a novel Alamouti space-time transmission scheme for orthogonal frequency division multiplexing (OFDM) based asynchronous cooperative communication systems with low relay complexity. The conventional scheme requires an additional operation likes time-reversal at the relay nodes besides the simple multiplications at the relay nodes, which result in increasing the complexity of relay nodes. Unlike the conventional scheme, exploiting the simple combination of the symbols at the source node and the simple multiplications at the relay nodes, the proposed scheme achieves the second order diversity gain by obtaining the Alamouti code structure at the destination node. Simulation results show that the proposed scheme achieves the second order diversity gain and has the same bit error rate performance as the conventional scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6A
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• pp.438-449
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• 2012

This paper presents new CRC-p codes for VHF band maritime wireless communication system based on performance analysis of various CRC codes. For this purpose, we firstly describe the method of determination of undetected error probability and minimum Hamming distance according to variation of CRC codeword length. By using the fact that the dual code of cyclic Hamming code and primitive BCH code become maximum length codes, we present an algorithm for computation of undetected error probability and minimum Hamming distance where the concept of simple hardware that is consisted of linear feedback shift register is utilized to compute the weight distribution of CRC codes. We also present construction of transmit data frame of VHF band maritime wireless communication system and specification of major communication parameters. Finally, new optimal CRC-p codes are presented based on the simulation results of undetected error probability and minimum Hamming distance using the various generator polynomials of CRC codes, and their performances are evaluated with simulation results of bit error rate based on the Rician maritime channel model and ${\pi}$/4-DQPSK modulator.

• The KIPS Transactions:PartC
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• v.16C no.1
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• pp.57-64
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• 2009

In order to efficiently provide IP based Wireless Broadband services in Mobile WiMAX, schemes for more efficiently utilizing a limited bandwidth in radio links are needed. Robust Header Compression (ROHC), a standard header compression scheme proposed by IETF, Bi-directional Optimistic (O) mode provides higher compression efficiency and robustness compared with Payload Header Suppression (PHS) which is an optional header compression scheme for mobile WiMAX [1, 2]. However, if consecutive packet losses occur because of a Shadow Region of Mobile WiMAX or bit errors, header decompression failure rate of the ROHC O mode increases due to inconsistency of the compression information between the Compressor and the Decompressor. Therefore, a complementary mechanism is needed. In this paper, we propose an approach for the dynamic adjustment of an optimistic parameter, which has an effect on both the compression efficiency and the robustness, for improving the performance of ROHC O mode. We also analyze the performance of the proposed approach using an OPNET simulator.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.7
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• pp.580-591
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• 2013

The Orthogonal Frequency Division Multiple Access (OFDMA) is considered as a novel modulation and multiple access technique for 4th generation wireless systems. In this paper, we formulate a base station's power allocation algorithm for each user to maximize the user's sum rate, subject to constraints on total power, bit error rate, and rate proportionality among the users for a better proportional rate adaptive (RA) resource allocation method for OFDMA based system. We propose a novel power allocation method based on the proportion of subcarrier allocation and the user's normalized proportionality constant. We adapt a greedy algorithm and waterfilling technique for allocating the subcarriers among the users. In an end-to-end simulation, we validate that the proposed technique has higher system capacity and lower CPU execution times, while maintaining the acceptable rate proportionality among users.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.473-477
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• 2015

In this paper, a commercial phosphorescent white light-emitting diode (WLED) visible light communication (VLC) system with an equalization circuit to achieve the high modulation bandwidth was designed and demonstrated. An analytical method to examine the performance of the equalizer was carried out using a general circuit-simulator, PSpice. The equalization circuit was composed of two passive filters with resisters and a capacitor and an active filter with an op-amp. Utilizing our post-equalization technology, the ~3.5 MHz bandwidth of phosphor WLED could be extended to ~25 MHz without using an optical blue-filter. In this VLC system with a single round-type WLED and a single PIN photo-diode, ASK data transmission up to 35 Mbps at a 1m free space distance was obtained. The resulting bit-error-rate was $7.6{\times}10^{-4}$, which is less than the forward error correction (FEC) limit of $3.8{\times}10^{-3}$.

• Korean Journal of Optics and Photonics
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• v.19 no.5
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• pp.343-348
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• 2008

This study was carried out to commercialize FTTH by developing a burst mode optical receiver for E-PON. The optical receiver was manufactured by minimizing the capacitance of a photodiode to improve sensitivity for meeting 10, 20 km OLT Rx standard of E-PON at the transmission speed of 1.25 Gb/s. When bit-error ratio is $10^{-12}$ and PRBS is $2^5-1$, sensitivity is -26 dBm, loud/soft ratio is 23 dB. Both preamble time and guard time were set to 102.4 ns (128 bit). After comparing a photodiode whose capacitance is 0.53 pF with another photodiode whose capacitance has been minimized to 0.26 pF, we could see that sensitivity improved to 0.7 dBm and so did bandwidth to 190 MHz of burst mode for the optical receiver manufactured by the photodiode whose capacitance is 0.26 pF.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.187-192
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• 2015

Underwater acoustic communication channels have very complex channel characteristics caused by time-varying sea surface, submarine topography, sound speed, and geometry between transmitter and receiver. Especially, the channel has time-variance and doppler effect due to wind and sea current. We have to recognize the channel state and apply it to communication technique for increasing transmission efficiency in the underwater acoustic channel. In this paper, we present the frame recursive modulation and demodulation method using ambiguity function and autocorrelation function to estimate the doppler frequency. Furthermore, we conducted the simulation and sea experiment to evaluate the performance of the proposed method. When the channel coding technique was not used, the bit error rate performance of the proposed method was improved about 32 % compared with conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.3A
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• pp.223-231
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• 2011

It has been shown that the performance of multiple-input multiple-output (MIMO) spatial multiplexing systems is significantly degraded when spatial correlation exists between transmit and receive antenna pairs. In this paper, we investigate designs of a new statistical precoder for spatial multiplexing systems with maximum likelihood (ML) receiver which requires only correlation statistics at the transmitter. Two kinds of closed-form solution precoders based on rotation and power allocation are proposed by means of maximizing the minimum E tlidean distance of joint symbol constellations. In addition, we extend our results to linear receivers for correlated channels. We provide a method which yields the same profits from the proposed precoders based on a simple zero-forcing (ZF) receiver. The simulation shows that 2dB and 8dB gains are achieved for ML and ZF systems with two transmit antennas, respectively, compared to the conventional systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.7
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• pp.1118-1130
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• 1999

In this paper, error performance of DS/FH CDMA system has been analyzed in a radio channel which is characterized by near-far problem and multi-path fading. The DS/FH CDMA system adopts Maximum Ratio Combining(MRC) diversity and BCH(Bose-Chau dhuri-Hocquenghem) coding techniques to enhance system performance. Using the derived error probability equation, the error performance of DS/FH CDMA system has been evaluated and shown in figures to discuss as a function of PN code length(N), hopping rate(q), number of diversity branch(M), coding rate($\gamma$) and bit energy per noise power ratio ${E_b/N_o}$. The results show that DS/FH system is more effective to restrain the affection of near-far problem and multi-path fading than DS system. And there is a substantial enhancement in performance by employing an MRC diversity or BCH coding techniques. Consequently, we expected that proposed system structure is reliable to the voice communication system in near-far problem and multi-path fading channel.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.8
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• pp.1805-1811
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• 2005

We analyzed of the receiver which received OOK and the FSK transmission signal that were a general digital transmission technique in a WDM system. We expressed various error probability with the m which was bandwidth and a bit numerical function and carried out performance evaluation of a receiver in a performance evaluation way. When error probability was $10^{-4}$ which is m=10, as for the receive sensitivity of OOK, the $1.7{\times}10^2$, FSK got $2.2{\times}10^2$ through simulation. And the receive sensitivity of OOK and FSK was able to get each $2.15{\times}10^2$ and $3.07{\times}10^2$ when it was error probability of $10^{-9}$ which is m = 25. Transmission of 23Gb/S showed that it was possible when we does the $10^{-9}$ that was basis error probability of a light communication system with a basis through this, and a coding profit was with for and transmission capacity of 75Gb/s confirmed that it was possible if a code rate was with 0.8.