• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.5
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• pp.88-94
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• 2009

We propose a scheme which reduce the computational complexity of the lattice reduction (LR) aided detector in MIMO system. The performance of the ML detection algorithm is good but the computational complexity grows exponentially with the number of antenna elements and constellation points. LR aided detector shows the same diversity with the ML scheme with relatively less complexity. But the LR scheme still requires many computations since it involves several iterations of size reduction and column vector exchange. We notice that the LR process depends not on the received signal but only on the channel matrix so we can apply LR process offline and store the results in Look-Up Table (LUT). In this paper we propose an algorithm to generate the LUT which require less memory requirement and we evaluate the performance and complexity of the proposed system. We show that the proposed system requires less computational complexity with similar detection performance compared with the conventional LR aided detector.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.976-987
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• 1998

In this paper, the effect of nonllinear distortion, caused by a high-power amplifier(HPA) in an orthogonal frequency division multiplexing (OFDM) system, on the receiver part is analyzed. Since the HPA, which can be modeled by a memeoryless Volterra system, distorts OFDM signals in a nonlinear fashion, the received signal at each subchannel includes the multiplicative distortion of 1-st order as well as additive nonlinear distortion of high-order. the nonlinear distortion can be viewed as a nonlinear interchannel interference (NICI) since it consists of harmonic distortions and intermodulation distortions, produced by oother subchannels affecting the subchannel of interest. In this paper, we analytically derive the variance of NICI in terms of average input power using the volterra model for HPA, and then calculate the bit-effor rate(BER) performance of an OFDM system. Also, we propose a simple method to compensate for the phase distortion in OFDM system amplified by HPA, OFDM system employing 16-QAM constellation input.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.9
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• pp.1-8
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• 1999

In this paper, we propose and analyze a concatenated coding scheme for DS/CDMA systems in asynchronous channels. In the concatenated coding, bandwidth efficient $2^{2L-2}$-state ${\frac{L}{L+1}}$-rate 2-MTCM with biorthogonal signal constellation is used for the inner code, and $(2^{L-1},\;{\lceil}\frac{2^{L-1}}{L/2}{\rceil})$ RS code is use for the outer code. It is shown that we can get considerable performance gain over the uncoded system without sacrificing the data transmission rate. The proposed system can be used as a coding scheme for reliable and high speed integrated information services of mobile communication systems.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.10
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• pp.10-20
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• 1999

In this paper, we propose and analyze a multiuser receiver using a decorrelating filter and Viterbi decoders for trellis coded DS/CDMA systems with biorthgonal signal constellation in asynchronous channels. The biorthogonality is implemented by user signature waveforms and the decorrelating filter. The performance of the proposed system is investigated with emphasis on the asymptotic cases. It is shown that the proposed system can provide us with some coding gain and near-far resistance. We also analyze the performance of the proposed system with base-station antenna array.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.1
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• pp.24-31
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• 2007

DVB-T (Digital Video Broadcasting-Terrestrial) is an important multimedia broadcasting technology capable of high data-rate transmission and adopted by Europe. OFDM (Orthogonal Frequency Division Multiplexing) is the backbone technique employed in DVB-T to support multimedia services that have various bandwidths. Unfortunately, an OFDM signal has a large PAPR (Peak-to-Average Power Ratio). In this paper, we investigate the performance of a simple PAPR reduction scheme for the DVB-T system, which requires no change of a receiver structure or no additional information transmission. The approach we employed is clipping in the time and frequency domains. The time-domain clipping is carried out with a predetermined clipping level while the frequency-domain clipping is done within EVM (Error Vector Magnitude). This approach is suboptimal with lower computational complexity compared to the optimal method. The simulation results demonstrate that the proposed one is getting more effective at lower modulation levels and with more allowed constellation error.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.9
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• pp.1635-1641
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• 2017

In this paper, a trellis-coded 3-dimensional (3-D) orthogonal frequency division multiplexing (OFDM) system is presented and its performance is analyzed. Here, a set-partitioning technique for trellis coding with respect to a 3-D signal constellation is also presented. We show theoretically that the proposed system, which exploits a trellis coding scheme with recursive systematic convolutional codes (RSC) of code rate R = 1/3 and 2/3, can improve symbol error rate (SER) up to 7.8 dB as compared with the uncoded OFDM system in an additive white Gaussian noise (AWGN) channel. Computer simulation confirms that the theoretical analysis of the proposed system is very accurate. It is, therefore, considered that the proposed trellis-coded 3-D OFDM system is well suited for the high quality digital transmission system without increase in the available bandwidth.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.7A
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• pp.668-675
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• 2002

This paper proposes pre-distorter combined LUT with 2ιpartition interpolation method to reduce nonlinear distortion which was caused by high PAPR and to update LUT quickly. Pre-distorted gain and phase can be found by using LUT which consisted of AM/AM and AM/PM value, and OFDM signal amplitude. The proposed 2ιpartition interpolation can accurately find predistorted gain and phase using bit shift and add component instead of increasing size of LUT which requires increasing the amount of computation. The performance of the proposed method was measured by the difference between HPA input and output characteristics by the LUT size, constellation, SER performance by the HPA, and LUT update error by the HPA characteristic changes. As a result, it is shown that when the size of the LUT is 32 and 64 for 16-QAM and 64-QAM, nonlinear distortion nearly didn't occurred.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.3-8
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• 2006

The next decade promises drastic improvements and additions to global navigation satellite systems (GNSS). Plans for GPS modernization include a civilian code measurement on the L2 frequency and a new L5 signal at 1176.45 MHz. Current speculations indicate that a fully operational constellation with these improvements could be available by 2013. Simultaneously, the Galileo Joint Undertaking is in the development and validation stages of introducing a parallel GNSS called Galileo. Galileo will also transmit freely available satellite navigation signals on three frequencies and is scheduled to be fully operational as early as 2008. In other words, a dual system receiver (e.g., GPS+GALILEO) for general users can access six civil frequencies transmitted by at least fifty eights navigation satellites in space. The advent of GALILEO and the modernization of GPS raise a lot of attention to the study of the compatibility and interoperability of the two systems. A number of performance analyses have been conducted in a global scale with respect to availability, reliability, accuracy and integrity in different simulated scenarios (such as open sky and urban canyons) for the two systems individually and when integrated. Therefore, the scope of this article aims at providing the technical benefits analysis for Taiwan specifically in terms of the performance indices mentioned above in a local scale, especially in typical urban canyon scenarios. The conclusions gained by this study will be applied by the Land Survey Bureau of Taiwanese as the guideline for developing future GNSS tracking facilities and dual GNSS processing module for precise surveying applications in static and kinematic modes.

• Journal of Navigation and Port Research
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• v.42 no.1
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• pp.17-24
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• 2018

The Russian Global Navigation Satellite System (GLONASS) has been fully recovered since October 2011, and it has been significantly modernized. The recently launched GLONASS 752 was set for successful performance on October 16, 2017 and has resulted in 24-satellite constellation with 22 second-generation (GLONASS-M) satellites, and a third-generation (GLONASS-K) satellite. Therefore, this paper is focused on not only the identified navigation parameters, but also the performance analysis of the project based on its real data received from the studied satellites. It is verified that the 5-11 satellites are available for receiving navigation signal at this time. The obtained values of GDOP, PDOP, HDOP, VDOP, and TDOP are 2.790, 2.424, 1.169, 2.123, and 1.381, noted respectively in standard deviation. In fact, the level of positioning precision is about 1.4m in standard deviation. As a result, the positioning performances of the measured GLONASS and GPS are virtually identical. Therefore, we determine that the GLONASS is expected to be expanded for future applications.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.2
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• pp.267-273
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• 2021

Non-orthogonal multiple access is the promised candidates in the next generation wireless networks to improve the spectral efficiency by superposing multiple signals. In general, the superposition coding is performed using the difference in channel gain between users based on the user's power allocation. However, when user pairs have the similar channel gain problem, NOMA can not be allowed in the scenario. To overcome this problem, phase rotation based NOMA is presented to increase minimum distance between superposed signals in the constellation point. This paper proposed a novel non-orthogonal multiple access based index modulation using phase rotation. The additional bits can transfer using the index bits that is allocated according to the activated state of the phase rotation. Simulation results are shown that bit error rate and achievable sum rate are better than conventional NOMA.