• Journal of Satellite, Information and Communications
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• v.11 no.3
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• pp.104-109
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• 2016

A technology of GEO satellite communications starts from Koreasat program in Korea. Payload equipment of EQM Ku and Ka band transponders had been developed and space-qualified Ka band payload in COMS was successfully launched in June, 2010. For the purpose of military communications, Dehop-Rehop transponder was developed in Koreasat5 as ANASIS system and DAT(Digital Active Transponder) and DCAMP(Digital Channel AMPlifier) transponders are now under development. In this paper, from the study of military satellite communications trend, a direction of military communication satellite is suggested based on the current GEO SATCOM technologies in Korea. Considering the limit of frequency resources, a technology of battlefield adaptive transponder with medium capacity against high moveable jamming tactics would be efficient for the future military SATCOM system. Mid-sized military satellites with frequency hopping and mid-capacity transponders can be a solution of vitalizing the GEO satellite programs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.7
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• pp.796-804
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• 2010

It is important to use the comb type pilot allocation for the continuous channel and efficient processing. And DFT-spreading OFDM is used a lot to solve high PAPR problem of OFDM system. However, PAPR is increased again when comb type pilot is used to estimate channel characteristics. So, in this paper, we employ a new SLM method to DFT-spreading OFDM system to reduce increased high PAPR. And we suggest an effective method to transmit side information without additional bandwidth. Pilot and side information must be preserved from jamming or intentional interferences since those are very important in DFT spread OFDM system using SLM. So, in this paper, we like to analyze and simulate the performance of DFT spread OFDM system based on SLM against jamming signal. To remedy the vulnerable shortcomings of DFT spread OFDM about jamming or intentional interferences, we employ FH(Frequency Hopping) method and analyze system performance under the several jamming conditions such as MTJ(Multi Tone Jamming) and PBJ(Partial Band Jamming).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.2
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• pp.168-180
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• 1992

Commumication technology has been continuously developed to overcome the distance and time for the transmission of information to the human society. Wireless mobile communication, which had been used mostly in the military and police is widely used these days for enterprise and individuals. Therefore the domestic usage of the advanced mobile phone service are progressively gaining wide popularity. The modulation techniques used usually in mobile communications were the analog techniques such as AM and FM, but they are getting replaced by the digital techniques, However, the major disadvantage of the digital communications is the increase of the transmission bandwidth. Therefore, it is very important to use efficiently the limited frequency bandwidth. The domestic research and development on the subject seems quite limited and in order to establish the technology of the digital mobile communications. This thesis presents the design of the frequency hopping synthesizer providing 124 channels with a channel spcing of 200KHz. VCD used in the synthesizer employs a semi-rigid cable for higher purity of signal spectrum, and a hybrid pgase detector is realized with a sample hold phase detector in conjuction with a tri-state phase detedctor.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1A
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• pp.1-12
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• 2002

Ultra Wideband (UWB) system uses wide band signal, which power spectral density likes as a noise floor, so UWB system can be used high speed communication without interfering with other communication system. As this system doesn't use radio frequency carrier. Its structure would be very simple and consume very low power. For the first time, we adopted Rayleigh monopulse multiple access system. And under the AWGN, we analysis and compare error probability, the number of user and data rate of the two methods that pulse position modulation and antipodal. In the result, We concluded that the antipodal method had much better probability of error, the number of user and data rate than PPM.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.8
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• pp.8-16
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• 1999

In this paper, the performance of a hybrid DS/SFH-SS(direct-sequence/slow-frequency-hopped spread-spectrum) system with coherent BPSK modulation over Nakagami fading channel in the presence of multiple tone jamming is analyzed. Because the Nakagami m-distribution can describe not only Rayleigh fading but also more general fluctuations involving a specular component by adjusting the value of the fading index m. It is known that for m=1 corresponds to Rayleigh fading, for $1/2{\le}m{\le}1$ corresponds to the worst case fading condition, for m>1 corresponds to Rician fading, and for $m{\to}{\infty}$ corresponds to the nonfading condition. The bit error probability is derived over Nakagami model and numerical evaluations are presented for some combinations of system parameters. The results show that as m increases, the bit error probability is better. Also, at a low JSR(jamming-to-signal power ratio), a pure DS-SS system can achieve lower bit error probability than a hybrid DS/SFH-SS system. But at a high JSR, a hybrid DS/SFH-SS system is shown to be superior to a pure DS-SS system. Therefore, it is demonstrated that without increasing the total system bandwidth, the performance of a hybrid DS/SFH-SS is superior to that of a pure DS-SS system in the presence of multiple tone jamming.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.4
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• pp.28-34
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• 2000

In this paper, a continuous-time filter for low voltage and high frequency applications using fully-balanced current integrators is presented. As the balanced structure of integrator circuits, the designed filter has improved noise characteristics and wide dynamic range since even-order harmonics are cancelled and the input signal range is doubled. Using complementary current mirrors, bias circuits are simplified and the cutoff frequency of filters can be controlled easily by a single DC bias current. As a design example, the 3rd-order lowpass Butterworth filter with a leapfrog realization is designed. The designed fully-balanced current-mode filter is simulated and examined by SPICE using 0.65${\mu}{\textrm}{m}$ CMOS n-well process parameters. The simulation results show 50MHz cutoff frequency, 69㏈ dynamic range with 1% total harmonic distortion(THD), and 4㎽ power dissipation with a 3V supply voltage.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10A
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• pp.1462-1470
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• 1999

In this paper, the performance of packet radio networks using the ALOHA protocol in Rayleigh fading channels is analyzed in terms of the capture probability and the throughput. We consider capture effect in order to increase the probability of the channel access and to include cellular environment we assume that the traffic is a truncated bell-shaped distribution. The packet proposed in this paper consists of a competition part and a data part to decrease the probability of collision in the channel access. In the competition part, DS system with common spreading code is used and in the data, hybrid DS/FH system is used. We consider the linear correlation receiver and the hard-limiting correlation receiver as the receiver model. BPSK modulation is also employed. Because hybrid DS/FH systems are not sensitive to variation of the interference power, as we choose a proper chip number N and a frequency hopping number q, we can obtain a steady system performance even though the variation of interference power is severe fading channels such as Rayleigh fading.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.8
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• pp.1629-1637
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• 2003

In this paper, we analyzed the performance of a hybird DS/SFH(Direct­Sequency­Slow Frequency­Hopping) Spread Spectrum system with BFSK modulation over Nakagami­m fading channel with multitone jamming. The performance of the system was improved when a frequency bowing rate increased. In case that process gain of hybrid DS/SFH Spread Spectrum system to be fixed, the hybrid DS/SFH Spread Spectrum takes the low bit error probability than a DS Spread Spectrum system. Also, when the fading index m increases, the fading effect decrease, when the JSR(jamming to signal power ratio) increases ,the performance of a hybrid DS/SFH Spread Spectrum system improved than DS Spread Spectrum system. The result, we have been proved that performance of a hybrid DS/SFH Spread Spectrum was superior to DS Spend Spectrum system over Nakagami­m fading with tome jamming.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.8
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• pp.1-10
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• 2000

Performance analyses of hybrid DS-SFH spread-spectrum systems using coherent MSK and QPSK modulation techniques are considered over Rayleigh fading channel in the presence of multi-tone jamming. The BER equations for MSK and QPSK systems with non-diversity reception in the receiver are derived as the concept of average signal-to-noise power ratio E$\_$b//N$\_$0/ and jamming-to-signal power ratio JSR, and the performances is evaluated for various system parameters. The evaluation of performance is done between fading and nonfading system, and between MSK and QPSK system. Results show that the performances of two systems are similar in low JSR. However, MSK system outperforms QPSK system as JSR increases. Overall performances of two systems are a little improved as the DS spreading gain increases for the total spread-spectrum bandwidth fixed. The performance difference between fading system and nonfading system is similar in low E$\_$b//N$\_$0/, however, it becomes very largewith increase of E$\_$b//N$\_$0/..

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2A
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• pp.159-166
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• 2008

In this paper, we proposed an algorithm to solve the problem that can't maintain hop synchronization using only early-late gate tracking loop due to the drift of geo-stationary satellite in frequency hopping satellite communication system. When the signal is transferred to downlink through DRT(Dehop-Rebop Transponder), the problem with synchronization loss is occurred periodically when using only early-late gate tracking loop, because of energy loss in each side portion of hop due to orbital variation of the satellite. To solve this problem, we have developed Anti-Shrink synchronization tracking algorithm which uses the prediction value of transmission timing and the structure of inner-outer gate instead of early-late gate with the ranging information. Through simulations, we showed that the performance of the Anti-Shrink algorithm is better than that of simple inner-outer energy ratio algorithm and similar to that of conventional early-late tracking loop algorithm with ranging information. No synchronization failure in the proposed algorithm was occurred because of less energy loss and robustness without the ranging information.