• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.777-786
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• 2001

In this paper, as one of countermeasure techniques for a frequency selective fading, a digital slope equalizer(DSE) for 64-QAM digital radio relay system is analyzed in terms of principle, channel modeling, and digital implementation. Also computer simulations have been performed for DSE with a complex 13-tap adaptive time domain equalizer chip. It is shown that about 4.5 dB improvement in system signature can be obtained at the channel edge, and a variety of simulated results are reviewed in view of DSE modeling limit, operating frequency, control coefficient, signal constellation, and system signature. Finally, the functions of DSE chip confirmed up to 61 MHz clock operation are illustrated.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3C
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• pp.248-256
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• 2003

Space-time coding was designed for an efficient transmit diversity technique to improve performance of wireless communication. For the transmit diversity using space-time coding, the receiver requires to estimate channel parameters corresponding to each transmit antennas. In this paper, we propose an efficient channel estimation scheme based on trigonometric polynomial approximation in OFDM systems with transmit diversity using space-time coding. The proposed scheme is more efficient than the conventional scheme in terms of the computational complexity. For QAM modulation, when the size of FFH is 128, the conventional scheme with significant tap caching of 7 requires 9852 complex multiplications for TU, HT and BU channels. But the proposed scheme requires 2560, 7680 and 3584 complex multiplications for TU, HT and BU channels, respectively. Especially, for channels with smaller Doppler frequency and delay spreads, the proposed scheme has the improved BER performance and complexity. In addition, we evaluate the performance of maximum delay spread estimation in unknown channel. The performance of the proposed scheme is investigated by computer simulation in various multi-path fading environments.

• Journal of Advanced Navigation Technology
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• v.12 no.6
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• pp.634-639
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• 2008

In mobile communication networks, the main power consumption is due to the actual transmissions power. Therefore, power efficiency network structures have gained considerable importance in mobile multi-hop systems and networks in recent years. In this paper, the performance of mobile multi-hop wireless system with M-QAM signal and forward error control (FEC) technique are analyzed The FEC technique uses extra processing power related to encoding and decoding, it is need complex functions to be built into the communication node. The probability of receiving a correct bit and codeword for relaying a data frame over h hop relay station to the final station is evaluated as a function of channel parameter and number of hops, and the distance between the different station.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.11
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• pp.10-22
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• 1998

In this paper, as a way of improving the availability and spectral efficiency of radio relay system, a co-channel radio relay system based upon the synchronous digital hierarchy is developed and its performance measured by 64-QAM with a never-seen multi-purpose ASIC chip is illustrated. This system provides a couple of transmission capacity compared with alternative channel arrangement. By adopting a powerful complex 13-tap adaptive time domain equalizer and cross-pol interference canceller, improvement of more than 1.5 ~ 2.0 dB in signature is obtained in comparison to 9 or 11-tap adaptive time domain equalizer, and about 22.5 dB in improvement factor of cross-pol interference canceller is achieved at C/N of 24.5 dB. In addition, digital filter makes it possible to optimize the occupied bandwidth by selecting an appropriate roll-off factor externally. It is expected that co-channel radio relay system with the powerful multi-purpose ASIC chip plays a key role in creating a value-added product, reliability, and reducing the outage time.

• ETRI Journal
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• v.39 no.4
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• pp.514-524
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• 2017

In this paper, we propose a spatial modulation (SM) scheme referred to as complex quadrature SM (CQSM). In contrast to quadrature SM (QSM), CQSM transmits two complex signal constellation symbols on the real and quadrature spatial dimensions at each channel use, increasing the spectral efficiency. To achieve that, signal symbols transmitted at any given time instant are drawn from two different modulation sets. The first modulation set is any of the conventional QAM/PSK alphabets, while the second is a rotated version of it. The optimal rotation angle is obtained through simulations for several modulation schemes and analytically proven for the case of QPSK, where both results coincide. Simulation results showed that CQSM outperformed QSM and generalized SM by approximately 5 dB and 4.5 dB, respectively, for the same transmission rate. Its performance was similar to that of QSM; however, it achieved higher transmission rates. It was additionally shown numerically and analytically that CQSM outperformed QSM for a relatively large number of transmit antennas.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9C
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• pp.1279-1288
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• 2004

In this paper, the DMR(Digital Microwave Radio) system-based OFDM(Orthogonal Frequency Division Multiplexing) scheme in microwave channel environments has been proposed and system performances have been evaluated. The existing single carrier DMR system has a complex system structure due to using high-level QAM(Quadrature Amplitude Modulation) modulation scheme and so charmel capacity is limited by sensitive effects from fading. Therefore, in the proposed DMR system, it uses that the OFDM scheme for enhancement of fading distortion and also uses that the band-limited pulse shaping filter instead of windowing for no additional data such as GI/GB and for using efficient of IFFT/FFT block. The performance of OFDM/QPSK-DMR system and single carrier DMR system are analysed by computer simulation using two-ray model under the microwave channel environments The computer simulation results confirm that the fade margin of the proposed OFDM/QPSK-DMR system is highly increased as the number of sub-carriers is larger.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.3
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• pp.225-236
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• 2002

In this paper, to counteract a cross-polarization interference caused by co-channel dual polarization technique of digital radio relay system(DRRS), we analyze the theoretical model and digital design of cross-polarization interference canceller(XPIC). In addition a complex adaptive time domain equalizer(ATDE) is designed using a finite impulse response filter, and the structure of XPIC and its control method are also illustrated including ATDE. Our computer simulation shows that about 25 dB signature and more than 23 dB XPIC improvement factor can be obtained with XPIC and ATDE. In order to verify the operation of designed XPIC, we review the simulated results in view of tap number, algorithm convergence, system signature, and XPlC improvement factor in connection with 64-QAM DRRS with co-channel dual polarization.

• Journal of Communications and Networks
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• v.16 no.3
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• pp.280-292
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• 2014

This article presents a novel cooperative spectrum sharing (CSS) scheme. The primary transmitter transmits a complex Quadrature amplitude modulation (QAM) signal in the first phase, and CSS occurs in the second phase. The secondary transmitter with the largest forwarding channel gain among the nodes that successfully decode the primary signal in the first phase is selected for CSS. This selected node employs a pulse-amplitude modulation (PAM) signal for primary information message (IM) instead of the QAM signal, and it employs a modified PAM signal for the secondary IM. The proposed modified PAM signal depends on the amplitude of the primary PAM signal. This method results in no mutual interference and negligible primary interference constraint and allows a higher degree of exploitation of spatial diversity, thus enabling increase in secondary power to improve primary transmission. The outage performance is enhanced in both the primary and secondary systems. The critical region, in which the primary outage performance is enhanced with the proposed CSS scheme, can be adjusted and widened by varying either the modulation cooperation sharing factor or the number of secondary transmitters.

• Proceedings of the Korea Contents Association Conference
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• 2005.05a
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• pp.458-463
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• 2005

OFDM communication system is effective for the high data rate transmission in the frequency selective fading channel. Since OFDM has high PAPR, OFDM signal may be distorted by the nonlinear HPA. In this paper, we propose an combined SLM and PTS method for reducing the PAPR in OFDM communication system. Proposed method increased some system complex in comparison with exiting method. But we made sure of high efficiency in the case of reducing the PAPR. As a result of using the 16-QAM modulation and increasing the carrier number in the SLM, PTS method and the SLM-PTS combined method, SLM-PTS combined method is more an effective method of reducing 3.5 dB PAPR than exiting OFDM system when this method is M, L=3, D=128, 256 in 10-3 BER.