• Journal of IKEEE
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• v.2 no.2 s.3
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• pp.212-224
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• 1998

There are two major factors of degrading the performance in the forward link of DS/CDMA systems. One is the multiple access interference (MAI) caused by using the same frequency bands simultaneously and the other is the multipath lading due to multipath propagation. PN codes which have minimum cross correlation properties among spread spectrum codes are necessary to reduce the MAI. In the conventional IS-95A system, the PN sequence has the period of $2^{15}$ and is of the length of 64 chips for spreading each data. In this case, since the length of PN code per bit is very short compared to the period of the PN code, the performance of the conventional system is not satisfied in view of suppressing the multipath interference. However, the correlation property of the PN codes at the demodulation can be improved by increasing the interval of Integration at the demodulation. This paper proposes a demodulation method to reduce the cross correlation among PN codes. The performance of the proposed demodulation method is investigated through computer simulations. We used multipath Ray lading channel and AWGN channel in the simulation. Our simulation results show the improved performance of $0.25{\sim}0.5dB$ SNR in a given BER compared to the conventional demodulation scheme.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.1
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• pp.71-82
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• 1996

In this paper, the Doppler phase error due to the relative velocity between a satellite and the earth station in communications using a low earth orbit mobile satellite is detected. The performance of BPSK system in the presence of Rician fading with Doppler phase error and interference, noise is compared with that of the system disturbed by Doppler phase error and noise only. The expression of error rate performance of BPSK system is derived as the type of complementary error function. The numerical calculation of the induced equation are performed in terms of satellite-height, orbit-eccentricity, the velocity of the earth, Rician fading parameter, signal to interference rateio (SIR), the ratio of carrier frequency and base band bit rate. The main conclusion that can be drawn from this analysis is that Rician fading channel environment with Doppler phase error and interference effect yields severe performance degradation than Do- ppler phase error and noise effect in satellite communication channel. And using the numerical calculation, we give a quantitative insight how much the satellite communication channel parameters degrade the system performance. Furthermore it is shown that an appropriate transmission power control for the performance enhancement is beneficial to the new satellite communication system planning.

• Journal of the Institute of Convergence Signal Processing
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• v.4 no.4
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• pp.73-80
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• 2003

In this paper, we propose a ETD-turbo code(Enhanced Time Diversity turbo code) which is a novel turbo code configuration to increase the time diversity effect and analyze the performance of ETD-turbo coded MC-CDMA system. The ETD-turbo code, which is added another interleaver to the conventional turbo code structure, is consisted. Time diversity effect of the ETD-turbo code is improved by every parity bits converted into interleaver pattern. In order to the performance of the ETD-turbo code, we conduct a computer simulation about interleaver type. And we make comparison between the performance of ETD-turbo coded MC-CDMA system and the conventional turbo coded MC-CDMA system. By the simulation results, ETD-turbo code has less BER than the conventional turbo code and time delay is decreased by reducing iteration numbers. Therefore, it is defined that the performance of ETD-turbo coded MC-CDMA system is improved than the conventional turbo coded MC-CDMA system.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.2
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• pp.137-144
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• 2009

This paper deals with the performance comparison of jammer signal's angle spreading in the beamforming after the estimation of direction of arrival using 3D array antenna basis of the GPS signal. After the estimation of direction of arrival using array antenna, the beamforming is need for the direction of arrival by spatial filtering and the other direction are nulling for reducing intererence signal, it is possible to improving the received signal strength and quality. But we obtains the degraded performance by the angle spreading due to the multi-jammer signal in this process. In this paper, the MUSIC and LCMV algorithms are applied for the estimating the direction of arrival and for beamforming using the 5 types of 3D array antenna. we performs the comparison of performance by calculating the bit error rate applying the BPSK modem and the varying the azimuth and elevation angle of incoming jammer signal. As a result of simulation, the Curved (B) type 3D array antenna has a more better performance compared to the other type antenna.

• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.295-300
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• 2002

We developed an optical transmitter and receiver for an electrical time division multiplexed (ETDM) 20 Gb/s optical transmission system, and experimentally investigated their characteristics. Especially, the clock extraction circuit, which is a key component in realizing broadband optical transmission receivers, was realized by using an NRZ-to-PRZ converter implemented with a half-period delay line and an EX-OR, a high-Q bandpass filter using a cylindrical dielectric resonator, and a microstrip coupled-line bandpass filter. Finally, the bit-error-rate of demultiplexed 10 Gb/s electrical signal after back to-back transmission was measured, and a high receiver sensitivity [-26.2 dBm for NRZ ($2^{7}-1$) pseudorandom binary sequence (PRBS)] was obtained

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.5
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• pp.489-498
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• 2003

Recently to introduce new services of ultra-high speed wireless access and systems beyond the 3rd generation mobile communication, 5 GHz band has been highly interested. As a way of getting the required frequency, it is considered that microwave relay bands below 6 GHz, which shows a slow decrease in demand and less cost-effectiveness, should be moved to other bands above 6 GHz. In this paper, as a tool for analyzing microwave link design and its service quality, the outage prediction based upon Vigants & Barnett＇s model is reviewed. To show outage and availability calculation, simulations are performed for the operating 4 GHz radio sites, and some results and features regarding frequency movement to 6.7 as well as 8 GHz are also discussed in terms of diversity techniques, bit error rate, and availability As the results, it is confirmed that only the diversity techniques of space or space and frequency can satisfy the annual objective of availability irrespective of frequency movement.

• Journal of Korea Multimedia Society
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• v.8 no.3
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• pp.362-371
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• 2005

This paper presents a digital video broadcasting - terrestrial (DVB-T) receiver system based on the orthogonal frequency division multiplexing (OFDM) modulation method, which has exhibited a good reception performance even with obstacles and a mobile reception. As such, an improved OFDM receiver is developed for a DVB-T system that also considers function expansion for further development. After manufacturing the DVB-T receiver system, the performance of the proposed system is compared with three other hardware systems, all of which are end products. The experimental results confirm the performance using the measured minimum required carrier-to-noise ratio and threshold of visibility signal for each system. In addition, a graphic user interface (GUI) and electronic program guide (EPG) are developed for the digital television user.

• Journal of Advanced Navigation Technology
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• v.15 no.6
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• pp.1053-1058
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• 2011

In this paper, we propose a concatenated single antenna diversity system to assure the data transmission reliability between flight type air nodes which move according to their atypical orbit, then analyze its performance. The proposed system achieve a diversity gain using single antenna and a coding gain from convolutional code simultaneously. Simulation result about the bit error rate(BER) of the proposed system shows that its BER performance is about 9.5dB greater than convolutional code at $10^{-4}$ and about 14dB greater than space time block code at $10^{-3}$ which has a full diversity gain. In addition, compared with space time trellis code with diversity gain and coding gain, the proposed system shows the better 4dB at a BER of $10^{-5}$. Therefore, it is necessary that concatenated single antenna diversity should be adopted to the reliable data transmission of flight type air nodes.

• The Journal of the Acoustical Society of Korea
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• v.10 no.4
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• pp.19-26
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• 1991

$GQ^2PSK$ which is a novel digital mobile communication modulation scheme has been introduced and described. $GQ^2PSK$ is a modulation scheme that bandlimits NRZ digital data with Gaussian filter and modulates it by $Q^2PSK$ scheme which uses two shaping pulses and two carriers which are pairwise quadrature. Thus transmission bit rate can be enhanced and available signal space dimensions are more efficiently utilized, with comparison to the already-existing GMSK, QPSK and OQPSK modulation methods. Via the computer simulation, bit error rate of $GQ^2PSK$ scheme which is bandlimited by gaussian filter to be suitable for digital mobil communication, is lower than that of $Q^2PSK$ by 1.4[dB] in case that the signal-to-noise ration is 0[dB], but we have confirmed that $GQ^2PSK$ modulation scheme is approximately equivalent to the GMSK in the respect of power efficiency, and transmission efficiency of $GQ^2PSK$ is improved to 1.5 times than that of GMSK.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.4
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• pp.649-659
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• 1994

The channel capacity of fadingchannel becomes less than that of Gaussian noise channel. Moreover, the channel capacity of system with modulated signal is expected to be much less than that of system with nonmodulated signal. It is very difficult to evaluate the capacity in fading channel with modulated signal. The channel capacity for M-ary PSK signal has already been derived in Gaussian noise channel but it is very complicate form composed of complex integral formula. In this paper, we have derived the simple form of channel capacity with M-ary PSK signal by using the average symbol error rate. And we also evaluate the capacity in Rician and m-distribution fading channels as well as Gaussian noise channel. We have verified that the channel capacity obtained are almost the same as in other literature. As a results, we show that the channel capacity of M-art PSK signal increases to converge to the number of bits per symbol (log M) as signal to-noise power ratio increases.