• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.2
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• pp.246-252
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• 2012

STBC is a technique where a multiple antenna signals are transmitted. With this technique, antenna diversity can be achieved. The performance of STBC OFDM system using pilot symbol for the channel estimation is analyzed. IEEE 802.16e standards suggest that the BER performance of STBC system can be improved using channel state information. Pilot symbol is used for the channel estimation in OFDM systems. However, imperfect channel estimates in this systems degrade the performance. The performance of this STBC OFDM systems using channel state information, gauged by the average bit error rate, is analyzed considering the channel estimation error.

• Journal of Industrial Technology
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• v.21 no.B
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• pp.99-105
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• 2001

In this paper, the selective normalized constant modulus algorithm(SNCMA) is applied to a fractionally spaced equalizer. The fractionally spaced equalizer is insensitive to the sampling timing because it processes received signals with the sampling rate larger than the symbol rate. The SNCMA improves the convergence rate by using the large step size for the most outer covering symbol belonging to the trust-level. This blind equalizer exhibits a fast start-up convergence rate as well as a reduced steady-state residual error compared to the fractionally spaced blind equalizer and the T-spaced blind equalizer using conventional blind algorithms.

• Journal of Communications and Networks
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• v.12 no.5
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• pp.442-448
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• 2010

Cooperative relaying methods have attracted a lot of interest in the past few years. A conventional cooperative relaying scheme has a source, a destination, and a single relay. This cooperative scheme can support one symbol transmission per time slot, and is caned full rate transmission. However, existing fun rate cooperative relay approaches provide asymmetrical gain for different transmitted symbols. In this paper, we propose a cooperative relaying scheme that is assisted with dual relays and provides full transmission rate with the same macro-diversity to each symbol. We also address equalization for the dual relay transmission system in addition to addressing the issues concerning the improvement of system performance in terms of optimal power allocations.

• Journal of Communications and Networks
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• v.12 no.5
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• pp.433-441
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• 2010

Multihop transmission is a promising technique that helps in achieving broader coverage (excellent network connectivity) and preventing the impairment of wireless channels. This paper proposes a cluster-based multihop wireless network that makes use of the advantages of multihop relaying, i.e., path loss gain, and partial relay selection in each hop, i.e., spatial diversity. In this partial relay selection, the node with the maximum instantaneous channel gain will serve as the sender for the next hop. With the proposed protocol, the transmit power and spectral efficiency can be improved over those in the case of direct transmission and conventional multihop transmission. Moreover, at a high signal-to-noise ratio (SNR), the performance of the system with at least two nodes in each cluster is dependent only on the last hop and not on any of the intermediate hops. For a practically feasible decode-and-forward relay strategy, a compact expression for the probability density function of the end-to-end SNR at the destination is derived. This expression is then used to derive closed-form expressions for the outage probability, average symbol error rate, and average bit error rate for M-ary square quadrature amplitude modulation as well as to determine the spectral efficiency of the system. In addition, the probability of SNR gain over direct transmission is investigated for different environments. The mathematical analysis is verified by various simulation results for demonstrating the accuracy of the theoretical approach.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6B
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• pp.1024-1031
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• 1999

In order to transmit high-speed wide band signals efficiently in multipath fading environments, M-ary QAM signalling combined with OFDM transmission technique is applied. In this paper, the effect of synchronization error caused by carrier frequency offset and SER(Symbol Error Rate) performance of OFDM-16QAM and OFDM-64QAM are theoretically analyzed. Our result shows that as the number of sub-carrier in OFDM system increases the frequency-offset caused inter-channel interference(ICI) increases significantly, and that an error floor occurs even at high SNR of OFDM system. For OFDM-64QAM, the error floor occurs at SER=1$\times$10-7 when a normalized frequency-offset is 0.001, in which the SNR degradation is much greater than that of OFDM-16QAM. From this study the maximum allowable frequency-offset of OFDM-16QAM and OFDM-64QAM systems can be determined to meet the specific SER requirement.

• ETRI Journal
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• v.42 no.6
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• pp.859-871
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• 2020

A spectrally encapsulated (SE) orthogonal frequency-division multiplexing (OFDM) precoding scheme for wireless short packet transmission, which can suppress the out-of-band emission (OoBE) while maintaining the advantage of the cyclic prefix (CP)-OFDM, is proposed. The SE-OFDM symbol consists of a prefix, an inverse fast Fourier transform (IFFT) symbol, and a suffix generated by the head, center, and tail matrices, respectively. The prefix and suffix play the roles of a guard interval and suppress the OoBE, and the IFFT symbol has the same size as the discrete Fourier transform symbol in the CP-OFDM symbol and serves as an information field. Specifically, as the center matrix generating the IFFT symbol is orthogonal, data and pilot symbols can be allocated to any subcarrier without distinction. Even if the proposed precoder is required to generate OFDM symbols with spectral efficiency in the transmitter, a corresponding decoder is not required in the receiver. The proposed scheme is compared with CP-OFDM in terms of spectrum, OoBE, and bit-error rate.

• Journal of Broadcast Engineering
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• v.15 no.6
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• pp.803-814
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• 2010

In this paper, we propose a frame structure for modified ATSC transmission systems which is used for a terrestrial 3D HDTV broadcasting. The modified ATSC transmission systems [2] see the potential of increasing a transmission capacity at reasonable TOV (Threshold of Visibility) by modifying channel codes of conventional ATSC systems and varying modulations. We use PN symbols (Pseudorandom Noise) in a guard interval which is used for avoiding the ISI (Inter Symbol Interference) to estimate and compensate the time-varying multi path channel effectively with a maximum transmission payload. With PN symbols in the guard interval, a CIR (Channel Impulse Response) in a time domain can be estimated and a compensation in a frequency domain can be achieved for the accurate channel estimation and compensation. The prosed frame structure is applied to the modified ATSC systems and computer simulations are performed for SER (Symbol Error Rate) performances in TU (Typical Urban)-6 Channel.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.486-492
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• 2002

In this paper. we presented 1 & 2 dimensional minimum mean-squared-error (MMSE) equalization scheme in a digital holographic data storage system to improve bit-error-rate (BER) and to mitigate inter-symbol interference (ISI) which were generated during the data storage and retrieval processes. We showed experimentally for ten data pages retrieved from the holographic storage system that BER and signal-to-noise ratio (SNR) were improved by adopting MMSE equalization.

• Journal of the Korea Institute of Military Science and Technology
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• v.19 no.1
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• pp.50-56
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• 2016

This paper is about the implementation of the OFDM-based border guard/reconnaissance communication terminal systems. We have implemented Real-time Dynamic DL/UL symbol rate control function using the DL-MAP message, and proposed error detection method caused by malfunctioning and timing optimization method. The proposed scheme detects the variable rate symbol decoding timing without increasing additional physical layer logic, and also provides a wide variety of DL/UL data transfer rate. Furthermore, the proposed scheme applies to the current border guard/reconnaissance equipment and confirms a operation performance through field tests and demonstration at home and abroad.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.10
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• pp.75-82
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• 2008

In this paper, we propose an efficient symbol detection algorithm for multiple-input multiple-output spatial multiplexing (MIMO-SM) systems and present its design and implementation results. By enhancing the performance of the first detected symbol which causes error propagation, the proposed algorithm achieves a considerable performance gain as compared to the conventional sorted QR decomposition (SQRD) based detection and the ordered successive detection (OSD) algorithms. The bit error rate (BER) performance of the proposed detection algorithm is evaluated by the simulation. In case of 16QAM MIMO-SM system with 4 transmit and 4 receive ($4{\times}4$) antennas, at $BER=10^{-3}$ the proposed algorithm obtains the gai improvement of about 2.5-13.5 dB over the conventional algorithms. The proposed detection algorithm was designed in a hardware description language (HDL) and synthesized to gate-level circuits using 0.18um 1.8V CMOS standard cell library. The results show that the proposed algorithm can be implemented without increasing the hardware costs significantly.