• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12A
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• pp.1122-1127
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• 2010

In this paper, we propose a relay-based DF cooperative communication scheme using repetitive transmission algorithm for wireless LAN environments on D-STBC. Additional transmission diversity gain can be obtained by repetitive transmission algorithm. However, in comparison with conventional schemes, data rate is decreased in half. We consider data modulation constellation twice higher than conventional schemes. Further, system complexity is decreased and performance degradation is minimized because repetitive transmission algorithm is adapted between source and relay node. We show the uncoded BER performance of the proposed algorithm over HiperLAN/2 Rayleigh fading channel.

• Journal of Satellite, Information and Communications
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• v.3 no.2
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• pp.18-25
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• 2008

A major drawback of Orthogonal Frequency Division Multiplexing (OFDM) system is high peak-to-average power ratio (PAPR) of the transmitted signal which introduces inevitable non-linear distortion in the transmission due to the amplifier non-linear property. This causes both in-band distortion and out of band spectrum re-growth. A polynomial based pre-distortion is estimated using the non-linear and inverse non-linear polynomial achieved through the Least Square Error (LSE) method. A new technique of PAPR reduction called 'Phase Realignment' (PR) is proposed which has a optimal effect in improving the BER performance as well as considerable reduction in the PAPR. In this paper we used the PR method along with the 'Peak Clipping' (PC) method is used before the pre-distortion to remove the high peak present in the non constant amplitude of the OFDM signal responsible to drive the amplifier in near saturation region for better performance of the system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10C
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• pp.927-932
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• 2006

We Propose a partial response maximum likelihood(PRML) detection method that improves the performance of the high-density optical storage system. It concurrently adjusts the coefficient of equalizer and reference values of branches in Viterbi detector. For the estimation of asymmetric channel characteristics by the tangential tilt, we exploit sync patterns in each data frame. The simulation result shows it improves the Performance up to 4dB at 10-6 BER compared to conventional adaptive PRML.

• Journal of information and communication convergence engineering
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• v.6 no.2
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• pp.150-153
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• 2008

In the blind Maximum-likelihood (ML) detection for Orthogonal Space-Time Block Codes (OSTBC), the problem of ambiguity in determining the symbols has been a great concern. A possible solution to this problem is to apply semi-blind ML detection, i.e. the blind ML decoding with pilot symbols or training sequence. In order to increase the performance, the number of pilot symbols or length of training sequence should be increased. Unfortunately, this leads to a significantly decrease in system spectral efficiency. This work presents an approach to resolve the aforementioned issue by introducing a new method for constructing transmitted information symbols, in which transmitting information symbols drawn form different modulation constellations. Therefore, the ambiguity can be easily eliminated. In addition, computer simulation is implemented to verify the performance of the proposed approach.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9C
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• pp.1219-1226
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• 2004

The objective of this paper is to proposed a new Hybrid Interference Cancellation(HlC) receiver to cancel MAI in a multirate DS-CDMA system based on multiple processing gain(MPG). We propose a new improved HIC scheme that divides the active users with different data rates split into a number of groups for effectives cancellation Between each group, GW-PIC is performed to cancel other group signals and within them, SIC is carried out to remove multiple access interference in group. We analyze the performance of the proposed receiver in terms of the bit error rate(BER) and examine its performance. As a conclusion, computer simulations show that the proposed schemes outperforms adaptive multistage PIC and conventional SIC receiver over AWGN channel.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.3
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• pp.307-316
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• 2016

Reversible data hiding is a technique to hide any data without affecting the original image. Zhang proposed the encryption of original image and a data hiding scheme in encrypted image. First, the encrypted image is decrypted and uses the fluctuation function which exploits the spatial correlation property of decrypted image to extract hidden data. In this paper, the new fluctuation function is proposed to reduce errors which arise from the process extracting hidden data and the performance is verified by simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.11
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• pp.53-59
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• 2011

We propose an adaptive resource allocation algorithm with generalized triangular decomposition scheme in downlink multi-user multiple-input-multiple-output channel to maximize the system throughput when we adopt the modulation scheme such as BPSK, QPSK, 16QAM, and 64QAM. The proposed scheme also considers an bit-error-rate performance as well as system throughput while performing resource allocation. We present simulation results to show that the proposed scheme achieves the system throughput up to 2bit difference by capacity and has better BER performance than SVD based resource allocation scheme in all SNR regions.

• IEIE Transactions on Smart Processing and Computing
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• v.3 no.3
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• pp.142-152
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• 2014

Vehicular Ad-hoc Networks (VANETs) are comprised of wireless mobile nodes characterized by a randomly changing topology, high mobility, availability of geographic position, and fewer power constraints. Orthogonal Frequency Division Multiplexing (OFDM) is a promising candidate for the physical layer of VANET because of the inherent characteristics of the spectral efficiency and robustness to channel impairments. The susceptibility of OFDM to Inter-Carrier Interference (ICI) is a challenging issue. The high mobility of nodes in VANET causes higher Doppler shifts, which results in ICI in the OFDM system. In this paper, a frequency domain com-btype channel estimation was used to cancel out ICI. The channel frequency response at the pilot tones was estimated using a Least Square (LS) estimator. An efficient interpolation technique is required to estimate the channel at the data tones with low interpolation error. This paper proposes a robust interpolation technique to estimate the channel frequency response at the data subcarriers. The channel induced noise tended to degrade the Bit Error Rate (BER) performance of the system. Parallel concatenated Convolutional codes were used for error correction. At the decoding end, different decoding algorithms were considered for the component decoders of the iterative Turbo decoder. A performance and complexity comparison among the various decoding algorithms was also carried out.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.9
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• pp.2470-2480
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• 1996

The energy efficiency and bandwidth efficiency are two important criterion in designing a modulation scheme Especially the constant envelope property must be considered as in the non-linear channel tht exit, for example in the nonlinear amplifiers for satellite repeater. The Q$^{2}$AM(Quadrature Quadrature Amplitude Modulation) is a new modulation scheme which combines the Q$^{2}$PSK(Quadrature Quadrature Phase Shift Keying) scheme which increases the signal space dimension and the QAM scheme which increases the bandwidth efficiency using the multi-level signal. The Q$^{2}$AM scheme has by far superior spectrum efficiency compared with the existing modulation schemes. Applying this scheme in the non-linear communication system increses the bandwidth efficiency but cannot envelop property. In this paper, a new system architecture is suggested which satisfies the large spectrum efficiency and constant envelope property by implementing the linear block coding prior to the Q$^{2}$AM modulation. the system has improved in performance by gaining the constant envelope and the additional coding gain. We able to observe the performance improvement of the suggested system(at BER=10$^{-5}$ ) of 4.4 dB for the 16-QAM and 0.7 dB for the Q$^{2}$PSK under the exact spectrum efficiency.