• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.10
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• pp.15-23
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• 2016

To support the telematics and infotainment services, vehicle-to-everything (V2X) communication requires a robust and reliable network. To do this, the 3rd Generation Partnership Project (3GPP) has recently developed V2X communication. For reliable communication, accurate channel estimation should be done. However, because vehicle speed is very fast, radio channel is rapidly changed with time. Therefore, it is difficult to accurately estimate the channel. In this paper, we propose the new linear minimum mean square error (LMMSE) channel interpolation scheme based on the Long Term Evolution (LTE) sidelink system in vehicle-to-vehicle (V2V) environments. In our proposed reduced decision error (RDE) channel estimation scheme, LMMSE channel estimation is applied in the pilot symbol, and then in the data symbol, smoothing and LMMSE channel interpolation scheme is applied. After that, time and frequency domain averaging are applied to obtain the whole channel frequency response. In addition, the LMMSE equalizer of the receiver side can reduce the error propagation due to the decision error. Therefore, it is possible to detect the reliable data. Analysis and simulation results demonstrate that the proposed scheme outperforms currently conventional schemes in normalized mean square error (NMSE) and bit error rate (BER).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.3
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• pp.319-325
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• 2004

FHMA(frequency hopping multiple access) communication system has good performance for the LPI and AJ(low probability of intercept and anti-jamming) application. However, high PAPR(peak to average power ratio) happens in the base-station or the repeater system because of a large number of users. In general, predistorter is used to complete the HPA(high power amplifier) nonlinear characteristics. This paper analyzes BER performance when magnitude of IBO(input back oft) and the number of user are considered as the system parameters. In case of the SSPA(solid state power amplifier), the predistorter does not always work as a complete nonlinear compensator. We find that there is a minimum value of IBO for the predistorter to compensate for the nonlinear SSP A, which is changed as the number of user. If IBO is lower than 6 ㏈ at the user number of 16 and p=1, the system with predistorter is poorer than the one without predistorter. Only when the IBO is over 6 ㏈, predistorter does work as a nonlinear compensator. We call it as cross-over IBO value. TWTA improves the more compensation performance than SSPA because characteristic AM/AM of TWTA has more nonlinear than SSPA. At the BER=10$\^$-3/, there are SNR power gains of about 2.5 ㏈ and 3 ㏈ due to the predistorter when the numbers of users are 16 and 32, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.1
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• pp.75-80
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• 2005

A new antenna shuffling scheme for double space time transmit diversity is proposed. The proposed method obtains the shuffling pattern directly from the estimated channel by maximizing minimum post-processing signal to noise ratio(SNR), while the conventional method minimizes channel correlation. Since the minimum post-processing SNR is directly related with error performance, the proposed method shows better bit error rate performance than the conventional method. Monte Carlo simulations showed that the proposed scheme has more 3 dB SNR gain than the conventional scheme for 10/sup -3/ bit error rate in spatially correlated fadingcaused by a single cluster model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.1034-1041
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• 2007

In this paper, we propose a FD USE (frequency domain minimum mean square error) equalizer algorithm for MBOK DS-UWB (M-ary bi-orthogonal keying direct sequence UWB) systems considered as a PHY proposal for high-speed wireless communication in IEEE 802.15.TG3a. The conventional FD MMSE equalization scheme has a structural limit due to insertion of the cyclic prefix (CP) in all transmit packets, but the proposed scheme is able to equalize the channel effect without CP. In order to overcome channel estimation error by multipath delay, we introduce a moving FFT and a moving average scheme. Compared with conventional FD MMSE equalizer and the traditional TD (time domain) MMSE-RAKE receiver, the proposed FD MMSE equalizer has better BER performance and we demonstrate this result by computer simulation.

• Journal of the Optical Society of Korea
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• v.19 no.4
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• pp.334-339
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• 2015

Terabit-per-second (Tb/s) transmission capacity for the next generation of long-haul communication networks can be achieved using multicarrier optical super-channel technology. In an elastic orthogonal frequency division multiplexing (OFDM) super-channel transmission system, demultiplexing a portion of an entire spectrum in the form of a subband with minimum power is critically required. A major obstacle to achieving this goal is the analog-to-digital converter (ADC), which is power-hungry and extremely expensive. Without a proper ADC that can work with low power, it is unrealistic to design a 100G coherent receiver suitable for a commercially deployable optical network. Discrete Fourier transform (DFT) is often seen as a primary technique for understanding partial demultiplexing, which can be attained either optically or electronically. If fairly comparable performance can be achieved with an all-optical DFT circuit, then a solution independent of data rate and modulation format can be obtained. In this paper, we investigate two distinct OFDM super-channel receiver models, based on electronic and all-optical DFT-technologies, for partial carrier demultiplexing in a multi-Tb/s transmission system. The performance comparison of the receivers is discussed in terms of bit-error-rate (BER) performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11A
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• pp.1095-1104
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• 2008

In multiuser OFDM systems, subcarrier and bit allocation plays an important role for the efficient resource use. However, in multiuser adaptive allocation as a non-linear problem, it is impractical to compute all to get the best solution because of the complexity. We set the goal of minimizing the transmit power while satisfying the BER and minimum bits required to transmit through the highest fitness combination of subcarriers and users. The proposed improved genetic algorithm employs the diversity of adaptive allocation more than existing genetic algorithm. Therefore, from the numerical simulation results, we find that the proposed heuristic algorithm has more performance than the existing algorithms.

• 한국정보통신설비학회:학술대회논문집
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• 2003.08a
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• pp.143-148
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• 2003

In this paper, we focused on the performance of reverse link in 1.8GHz CDMA 1x system including the Tower-Mount LNA in an urban environment. In order to study the benefit of TMLNA, Hata model is used and the effects of multiple cells are considered. Cell coverage extension ratio is proportional to the increased gain of TMLNA in CDMA cell site. However the cell coverage is not extended even if the noise figure of TMLNA is reduced in an urban area. When typical RSSI is between -70dBm and -80dBm, the increased gain and the reduced NF of TMLNA are not impact to the pole capacity of cell site. Namely, the benefit of TMLNA in an urban area is not the problem of capacity but the proble of sensitivity. The results are also shown that reverse link $E_b/N_o$ is improved by minimum 5dB and BER is lower than $10^{-6}$.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.8
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• pp.301-306
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• 2003

This paper proposes a novel detection scheme using a radial basis function (RBF) network in a multi-input multi-output (MIMO) environment. In order to evaluate the performance of the proposed MIMO-RBF receiver, simulations are performed over the rich-scattering fading channel. Simulation results confirm that the proposed scheme shows the similar bit-error rate (BER) performance of a maximum likelihood detection (MLD) and outperforms Vertical-Bell Laboratories Layered Space-Time using minimum-mean-square-error nulling (VBLAST-MMSE) as well as VBLAST using zero-forcing nulling (VBLAST-ZF). Moreover, we investigate the effect on the performance of the number of RBF center with two modulation formats (BPSK and QPSK) and different number of transmit and receive antennas. The performance of the proposed detector is verified with respect to an initialization-rate of RBF centers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.7
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• pp.2998-3017
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• 2018

Massive (large-scale) MIMO (multiple-input multiple-output) is one of the key technologies in next-generation wireless communication systems. This paper proposes a high-performance low-complexity turbo receiver for SC-FDMA (single-carrier frequency-division multiple access) based MMIMO (massive MIMO) systems. Because SC-FDMA technology has the desirable characteristics of OFDMA (orthogonal frequency division multiple access) and the low PAPR (peak-to-average power ratio) of SC transmission schemes, the 3GPP LTE (long-term evolution) has adopted it as the uplink transmission to meet the demand high data rate and low error rate performance. The complexity of computing will be increased greatly in base station with massive MIMO (MMIMO) system. In this paper, a low-complexity adaptive turbo equalization receiver based on normalized minimal symbol-error-rate for MMIMO SC-FDMA system is proposed. The proposed receiver is with low complexity than that of the conventional turbo MMSE (minimum mean square error) equalizer and is also with better bit error rate (BER) performance than that of the conventional adaptive turbo MMSE equalizer. Simulation results confirm the effectiveness of the proposed scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1A
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• pp.10-17
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• 2000

In this paper, we evaluate the correlation properties and the optimization of PN sequence phase for multi-media DS/CDMA system with variable spreading gain (VSG) scheme. In multi-media multi-rate DS/CDMA systems, the optimization of PN sequence phase is not a tractable problem, since the sequences should be optimized against both sequences of the same length and other sequences with different length. Hence, we verify the correlation properties of PN sequence phase in multi-rate system environment and furthermore, we propose the new phase criterion, MIN-AIP (minimum-average interference parameter), to minimize the bit error rate (BER). As the results of performance evaluations, it is shown that the performance of MIN-AIP criteria gives the best results.