• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.2
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• pp.141-150
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• 2002

In this paper, we composed orthogonal multi carrier FH/CDMA system using frequency hopping sequence. Considering hit possibilities by delayed other user's signals we searched the optimal number of user access carrier slots not to influence on performance deterioration with the variation of number of carrier slots according to the number of user access carrier slots. A]io, we evaluated the BER performance improvement due to TCM and Concatenated coding technique by computer simulation.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.12
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• pp.1886-1902
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• 1989

In this paper we discuss the generating algorithm of Kumar code sequences which are based on generalized bent sequences for FH-CDMA. The code sequence generator was constructed for the shift register stages n=4 over GF (5). Finally we analyze the characteristics fo Hamming correlation between two code sequences and the time-frequency correlatins of the complete waveform with the sinusoidal chips as the elemental waveforms.

• The KIPS Transactions:PartC
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• v.12C no.2 s.98
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• pp.223-228
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• 2005

The existing mobile communication system called DS/CDMA system, which is serviced widely nowadays, has some problems such as the severe ISI and multiple access interferences under the multi-path fading channel when applied to high-speed data transmission like multimedia transmission. To compensate these problems, we propose a sub-code multi-code hybrid DS/FH (Frequency Hopping) SS (Spread Spectrum) System by combining the multi-code system that restrains the multiple access interference with the hybrid DS/FH SS technique that reduces ISI(Intersymbol Interference) effect for high-speed transmission. Moreover, we implement and propose the sub-code technique to remedy the problems of the generic multi-code system. To verify the performance of the proposed system, the computer simulations are executed under the various channel environments.

• Journal of Communications and Networks
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• v.17 no.6
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• pp.622-633
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• 2015

The coexistence among different systems is a major problem in communications. Mutual interference between different systems should be analyzed and mitigated before their deployment. The paper focuses on two aspects that have an impact on the system performance. First, the coexistence analysis, i.e. evaluating the mutual interference. Second aspect is the coexistence techniques, i.e. appropriate system modifications that guarantee the simultaneous use of the spectrum by different technologies. In particular, the coexistence problem is analyzed between ultra-wide bandwidth (UWB) and narrow bandwidth (NB) systems emphasizing the role of spectrum sensing to identify and classify the NB interferers that mostly affect the performance of UWB system. A direct sequence (DS)-time hopping (TH) code design technique is used to mitigate the identified NB interference. Due to the severe effect of Narrowband Interference on UWB communications, we propose an UWB transceiver that utilizes spectrum-sensing techniques together with mitigation techniques. The proposed transceiver improves both the UWB and NB systems performance by adaptively reducing the mutual interference. Detection and avoidance method is used where spectrum is sensed every time duration to detect the NB interferer's frequency location and power avoiding it's effect by using the appropriate mitigation technique. Two scenarios are presented to identify, classify, and mitigate NB interferers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7C
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• pp.666-674
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• 2005

A hybrid multicarrier CDMA/FDM system with a truncated adaptive transmission scheme is analyzed in forward link based on the feedback information from the mobile station. In the single cell environment, the prop(mea scheme outperforms the adaptive FH/DS system as well as the MC DS/CDMA system when orthogonal signature sequences are used. In the multiple cell environment also, the proposed scheme has better performance characteristics than the adaptive FH/DS system when orthogonal and random codes are used as spreading sequences.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1149-1155
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• 2003

OFDM/SFH(orthogonal frequency division multiplexing/slow frequency hopping) system is the combination of OFDM communication system with frequency hopping(FH) method and OFDM/DS(orthogonal frequency division multiplexing/direct sequence) system combines the OFDM communication system with direct sequence(DS) method in terms of PN(pseudo noise) sequence. These two systems are also can be used for anti-jamming. In this study we analyze performances of OFDM/SFH system and OFDM/DS system with the equal information rate in partial band jamming and tone jamming channel. We find BER(bit error rate) in the variation of JFR(jamming fractional ratio) and JSR(jamming to signal power ratio) of the partial band jamming. Also, BER is found in the several JSR of the single tone or multi tone jamming. OFDM/DS system shows better performance than OFDM/SFH system in partial band jamming environment. OFDM/DS system has about 2.5 ㏈ SNR(signal to noise power ratio) gains than OFDM/SFH system when JFR=4/16 and JSR=0 ㏈ to meet BER=10$\^$-3/. However, OFDM/SFH system has about 3 ㏈ SNR gains than OFDM/DS system at single tone jamming of JSR=5 ㏈. In multi tone jamming, performance of OFDM/SFH system is considerably degraded than OFDM/DS system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2A
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• pp.127-132
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• 2011

This paper proposes a ranging and communicating system that uses the UWB frequency slope modulated chirp signal. Instead of using only the up-chirp and down-chirp with the same frequency sweeping rate, the proposed system uses several chirps that have different frequency sweeping rates with frequency hopping. This system performs better than the conventional communication and ranging schemes because it is capable of increasing the data transmission rate and at the same time decreasing the interference between sequences used by users. In this paper, we propose simulations of UWB communication system to show validity by using the MATLAB.

• 한국정보통신설비학회:학술대회논문집
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• 2009.08a
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• pp.242-247
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• 2009

In this paper, we investigate interference between short-range radiocommunication devices (SRDs) with frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS) methods when they are in the same frequency bands. In order to analyze interference from unwanted emission of SRD with DSSS to that of FHSS, Monte-Carlo (MC) simulation method is employed and interference probabilities are calculated. We simulate interference scenarios in accordance with several duty cycles and bandwidths. It is also assumed that the propagation model is free space The effect of distance between interfering transmitter and victim receiver is analyzed and bit error rate (BER) is simulated. From the interference analysis results, it is shown that duty cycle affects compatibility more than bandwidth does. Also, we can make sure of the separation distance which satisfies BER criterion when there are only one interfering transmitter and multiple interfering transmitters.

• 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.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.520-523
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• 2001

In this paper, a system that transmits ECG signals which get from hand baggage ECG is implemented by using Bluetooth technology. Bluetooth technology is a close range wireless communication used wireless frequency 2.4GHZ bandwidth. This technology consumes very small power and provides high reliability also self error correction with high speed frequency hopping. Because every device which uses Bluetooth protocol can communicate each other. These can connect between the system implemented and any devices such as mobile telephone with Bluetooth module, notebook, and the personal mobile device. Also, the paper proposes capability of transmission to the sever of hospital through each type of wireless communication device that acquired medical information signals in mobile medical machine. The system consists of hardware parts with Bluetooth module and host part, and software parts with bluetooth protocol stacks. The host precesses a connection with other device and transmits ECG signals with bluetooth frequency hopping sequence.