• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.4
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• pp.1-9
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• 2003

Many CDMA systems provide pilot channels in order to help channel estimation process. Especially in wideband CDMA systems, the number of receive diversity paths can be large due to small chip duration and high multi-path resolution capability. Hence, the received signal power of each path is small for a given total SNR (signal-to-noise ratio) and the pilot power of each path may not be sufficiently large for accurate channel estimation. When the pilot power is small, one can use decision-directed channel estimation to utilize more energy of the received data. However, the decision errors can deteriorate the quality of decision-directed channel estimation. This paper proposes a novel channel estimation method that optimally utilizes receiver decisions as well as pilot symbols with the help of estimated SER (symbol error rate) and SNR. The proposed method computes two channel estimates using the pilot and the data channel filters and optimally combines them. The simulation results show that the proposed method is robust and outperforms the conventional pilot-symbol-aided channel estimation method.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.3
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• pp.41-50
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• 2010

In this paper, an area-efficient symbol detector is proposed for MIMO communication systems with two transmit and two receive antennas. The proposed symbol detector can support both the spatial multiplexing mode and spatial diversity mode for MIMO transmission technique, and shows the optimal maximum likelihood (ML) performance. Also, by sharing the hardware block with multi-stage pipeline structure and using the complex multiplier based on polar-coordinate，the complexity of the proposed architecture is dramatically decreased. The proposed symbol detector was designed in hardware description language (HDL) and implemented with Xilinx Virtex-5 FPGA. With the proposed architecture, the number of logic slices for the proposed symbol detection is 52490 and the number of DSP48s (dedicated multiplier) is 52, which are reduced by 35.3% and 85.3%, respectively, compared with the conventional architecture.

• Journal of Advanced Navigation Technology
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• v.14 no.2
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• pp.220-226
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• 2010

In this paper, an low power symbol detector is proposed for MIMO communication system with two transmit and two receive antennas. The proposed symbol detector can support both the spatial multiplexing (SM) mode and spatial diversity (SD) mode for MIMO transmission technique, and shows the optimal maximum likelihood (ML) performance. Also, by sharing the hardware block and using the dedicated clock MIMO modes, the power of the proposed architecture is dramatically decreased. The proposed symbol detector was designed in hardware description language (HDL) and synthesized to logic gates using a $0.13-{\mu}m$ CMOS standard cell library. The power consumption was estimated by using Synopsys Power CompilerTM, which is reduced by maximum 85%, compared with the conventional architecture.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.8
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• pp.1773-1779
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• 2015

Shore-to-sea visible light communication using color clustered multiple-input and multiple-output (MIMO) is presented. The proposed maritime visible light communication (MVLC) offers a low-cost, high-speed wireless link for shore-to-sea maritime communications. Each color cluster is comprised of 50 red, green and blue (RGB) light emitting diodes (LEDs) and is modulated using on-off-keying (OOK). Selection combining is performed at the receiver, producing diversity effect within that color cluster. In this paper, we employ sea states (wave height, wind speed, etc.) data from both Pierson-Moskowitz and JONSWAP spectrum models under atmospheric turbulence conditions. Based on the simulation model, the maritime link quality is analysed in terms of coverage distance and bit error rate performance. The results show that the proposed system provides an efficient MVLC, while satisfying International Association of Lighthouse Authorities (IALA) requirements for maritime buoyage system and also offering sufficient illumination from high power LEDs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2A
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• pp.202-213
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• 2004

In this paper, we propose a preamble structure and synchronization/channel estimation methods for OFDM-based multiple antenna WLAN systems that have 200Mbps transmit rate. With the proposed preamble structure, multiple antenna WLAN systems are backward-compatible with IEEE 802.11a systems which use the same 5㎓ band and synchronization performance is better than that of single antenna OFDM systems. For channel estimation, the preamble overhead is small and performance degradation by timing synchronization error that causes the critical problem of conventional comb-type multiple antenna channel estimation method also can be minimized by frequency domain phase recovery. Synchronizer and channel estimator for proposed preamble structure are implemented and verified using Verilog HDL. For the system with 4 transmit antennas and 4 receive antennas, about 150K gates are needed for synchronizer and 12K gates for channel estimator.

• Journal of the Institute of Convergence Signal Processing
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• v.8 no.4
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• pp.266-271
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• 2007

In mobile channel environments, the effect of the multi-path fading reduces the performance of the mobile communication severely. Previous studies on the effect of the multi-path fading show that, only the channel between fixed base stations and mobile terminals are considered. However, the future mobile communication service such as telematics may use the communication between moving mobile terminals, so called mobile ad-hoc communication, the studies on the channel is required for such situations. In this paper we have measured the mobile channel and analyzed the fading characteristics when using the linear array antennas. In the data measurements, we sent the QPSK modulated signal with carrier frequency of 2GHz band and received the signal using the array antennas equipped on moving vehicles. We have analyzed the fading characteristics and the effects of the fading reduction using the CDF of fading depth using data collected from two moving vehicles. The simulation results show that the beamforming technique adds 6 or 7dB to the fading margin than that of the selection diversity depending on channel environments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.1
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• pp.22-34
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• 1997

In LEO system, the signal degradation is mainly due to fading and Doppler shift, so that the analysis of the signal degradation and compensation techniques are very important. As the Doppler shift compensator, the block demodulator has been known to be useful in compensating for the time-varing Doppler shift, but its compensating ability is about several hundreds Hz in 32 ksymbols / s QAM (QPSK) signal transmission. Therefore, in this paper, to compensate for severe fading and Doppler shift more than several kHz, we use a conventional pilot symbol-aided fading compensator, and propose the Doppler shift compensator. It is shown that the proposed compensator is able to compensate for Doppler shift more than several kHz. And a pilot symbol-aided fading compensator is shown to be a suitable scheme for severe Rician fading ($K{\leq}10 dB$) as well as Rayleigh fading. Also, it is shown that the equal gain combiner improves greatly the QAM performance even if the fading or Doppler shift becomes deeper or larger.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.2 no.2
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• pp.36-45
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• 2003

This paper presents a way to maximize transmission efficiency and reception ability through transmission diversity technology, which can be adapted to wireless multimedia OFDM (orthogonal FDM) system. The presented method gives a comparative analysis between a case where parameter a for time average is 0.3, i with consideration of channel presumption and two types of rms delayed proliferation, which is 50nsec, 150nsec, for the performance analysis of STTC (Space-Time Trellis Code) using time-space code method which is appropriate for MIMO channel, and performance, in the case, where presumed channel value from long training column section is applied to the according frame in a single frame. The result shows that BER brought SNR improvement of 1.0dB in $10^{-3}$ when a was 0.3 than using only the long training column, and shows an increasement of general performance improvement when the time average factor is used.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4C
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• pp.241-253
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• 2011

In this paper, a CFNC (Complex Field Network Coding) scheme is presented, which focuses on improving transmission efficiency by reducing time slots that are needed to exchange data frames. Conventional CFNC scheme has the advantage of minimizing the number of time slots required for information exchanges. However, there exists serious performance deterioration because the transmit signals are interfered with each other. Moreover, when CFNC scheme is applied, the estimation and compensation performance of fine frequency offset severely deteriorates due to the multiple frequency offsets in received signal of relay node. In order to overcome these critical problems, we propose an improved CFNC scheme with modified maximum likelihood decision method which uses uplink transmit diversity. Also, we propose an enhanced fine frequency offset estimation method and a corresponding compensation method to deal with the multiple frequency offsets. Corresponding simulation results verify that the proposed methods are able to effectively solve the problems of CFNC scheme.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.211-218
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• 2000

This paper describes the improvement of broadband radio channel characteristics using a MMSE adaptive equalization technique as a fundamental study of high transmission rates in indoor radio channel. First, the performance of 16-QAM system that employs a MMSE linear adaptive equalizer in Rayleigh fading channel is analyzed. Next, in order to improve broadband radio channel characteristics, we apply an adaptive equalization technique employing the MMSE algorithm to the radio channel measured by using circularly polarized antenna under indoor NLOS(non-line-of sight) environment. Consequently, for 16-QAM with adaptive equalizer, we can achieve the improvement of about 13 dB at $10^{-3}$ error rate as compared with general 16-QAM. Moreover, it was found that the adaptive equalization technique could improve broadband radio channel characteristics over the all measured areas. Also, it was found that the employing both adaptive equalization and polarization diversity technique together could improve broadband radio channel characteristics and reduce fading more effectively.