• Journal of Communications and Networks
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• v.10 no.1
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• pp.44-54
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• 2008

In this paper, an iterative multiple symbol differential detection for turbo coded differential unitary space-time modulation using a posteriori probability (APP) demodulator is investigated. Two approaches of different complexity based on linear prediction are presented to utilize the temporal correlation of fading for the APP demodulator. The first approach intends to take account of all possible previous symbols for linear prediction, thus requiring an increase of the number of trellis states of the APP demodulator. In contrast, the second approach applies Viterbi algorithm to assist the APP demodulator in estimating the previous symbols, hence allowing much reduced decoding complexity. These two approaches are found to provide a trade-off between performance and complexity. It is shown through simulation that both approaches can offer significant BER performance improvement over the conventional differential detection under both correlated slow and fast Rayleigh flat-fading channels. In addition, when comparing the first approach to a modified bit-interleaved turbo coded differential space-time modulation counterpart of comparable decoding complexity, the proposed decoding structure can offer performance gain over 3 dB at BER of $10^{-5}$.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.6
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• pp.1-8
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• 1994

In this paper, in order to apply the idea MDPSK to TCM, we use signal set expansion and set partition by phase differences. Through this we propose the trellis-coded MDPSK. And the Viterbi decoder containing branch metrics of the squared Euclidean distance of the Lth order phase difference as well as the first order phase difference is introduced in order to improve the bit error rate(BER) in the differential detection of the trellis-coded MDPSK. The proposed Viterbi decoder is conceptually same to the sliding multiple symbol dection method which uses the branch metric with the first and Lth order phase differences. We investigate the performance of the uncoded DQPSK and the trallis-coded D8PSK in additive white Gaussian noise (AWGN) through the Monte Carlo simulation under the two cases of using and not using the Lth order phase difference metric. The study shows that trellis-coded 8DPSK is an attractive scheme for power and bandlimited systems while also improving the BER performance when the Viterbi decoder is employed to the Lth order phase order difference metric. This performance improvement has been obtained without sacrificing the bandwidth or the power efficiency.

• Journal of Advanced Navigation Technology
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• v.5 no.1
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• pp.62-73
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• 2001

In this paper, performance of DSRC systems is analyzed with considering the real roads and height of vehicles. The channels are modeled as 2-Ray and 4-Ray with a direct wave and reflected waves by a road and buildings in a physical layer because DSRC keeps LOS propagation characteristics, and the pass loss for each model is calculated respectively. Rician factor is obtained through the calculated path loss on two models for DSRC, and the performance of the systems is analyzed in AWGN and Rician fading channels, Impulsive noise and Rician fading channels respectively. As a result, in Rician fading channels with impulsive noise(A=0.2, ${\Gamma}^{\prime}=0.22$), BER is below $10^{-6}$ when the distance is farther than 80[m] and 40[m] in 2-Ray model and 4-Ray model respectively. For performance improvement, BCH coding scheme and MRC diversity scheme are adopted.

• 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.

• Current Optics and Photonics
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• v.3 no.6
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• pp.531-540
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• 2019

Spectral Amplitude Coding Optical Code Division Multiple Access (SAC OCDMA) is an advanced technique in asynchronous environments. This paper proposes design and implementation of a novel quantum logic gate (QLG) code, with code construction algorithm generated without following any code mapping procedures for SAC system. The proposed code has a unitary matrices property with maximum overlap of one chip for various clients and no overlaps in spectra for the rest of the subscribers. Results indicate that a single algorithm produces the same length increment for codes with weight greater than two and follows the same signal to noise ratio (SNR) and bit error rate (BER) calculations for a higher number of users. This paper further examines the performance of a QLG code based SAC-OCDMA system with NAND and direct detection techniques. BER analysis was carried out for the proposed code and results were compared with existing MDW, RD and GMP codes. We demonstrate that the QLG code based system performs better in terms of cardinality, which is followed by improved BER. Numerical analysis reveals that for error free transmission (10^-9), the suggested code supports approximately 170 users with code weight 4. Our results also conclude that the proposed code provides improvement in the code construction, cross-correlation and minimization of noises.

• Journal of information and communication convergence engineering
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• v.2 no.2
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• pp.71-75
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• 2004

In non-selective frequency environment, it is difficult to take the advantage of path diversity. In the literature, some methods have been proposed to solve the issue. This paper presents a new method to obtain the resolvable path in Indoor Multi-carrier Code Division Multiple Access (MC-CDMA) system by using downlink beam forming. With the aid of downlink beamforming, the most reliable path is found and chosen for the communication link. The new approach is evaluated in term of bit error rate (BER) and power consumption. The simulation results show that the new approach can get better BER performance. However, the cost of BER improvement is a small degradation in power reservation.

• ETRI Journal
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• v.35 no.3
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• pp.371-377
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• 2013

An effective signal detection algorithm with low complexity is presented for multiple-input multiple-output orthogonal frequency division multiplexing systems. The proposed technique, QR-MLD, combines the conventional maximum likelihood detection (MLD) algorithm and the QR algorithm, resulting in much lower complexity compared to MLD. The proposed technique is compared with a similar algorithm, showing that the complexity of the proposed technique with T=1 is a 95% improvement over that of MLD, at the expense of about a 2-dB signal-to-noise-ratio (SNR) degradation for a bit error rate (BER) of $10^{-3}$. Additionally, with T=2, the proposed technique reduces the complexity by 73% for multiplications and 80% for additions and enhances the SNR performance about 1 dB for a BER of $10^{-3}$.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.606-610
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• 2003

본 논문에서는 임펄스 잡음과 실내 무선 페이딩, 그리고 다중 사용자 간섭 환경에서 멀티코드 DS/CDMA-BPSK 통신 시스템의 BER 성능을 분석하였다. 분석 결과 멀티코드의 수가 증가함에 따라서 하나의 사용자에게 점유되는 채널의 수가 증가하여 시스템의 성능은 열화 되나 반면에 시스템에서 제공할 수 있는 서비스의 속도는 멀티코드의 수에 비례하여 증가함을 알 수 있었다. 또한, 성능개선기법으로 Turbo Code와 다이버시티 기법을 적용함으로써 전력선에서 방출되는 임펄스 잡음 파라미터인 A=0.2, $\Gamma$' =0.22에서 전송속도에 따라 5.5, 7, 16dB의 신호전력 이상에서 $10^{-5}$ 이하의 BER 성능을 얻을 수 있었다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.3
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• pp.510-515
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• 2005

Doppler spread can occur due to the relative movement of transmitter and receiver. The Doppler frequency shift varies as the relative location and the velocity of transceivers change. This Doppler spread may seriously degrade the performance of OFDM system which is considered to be very efficient for multimedia wireless communication. Therefore, applying the method of receiver diversity, we analyze the degree of BER improvement in Doppler spread environments to investigate the effectiveness of the chosen methods according to various wireless channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.9B
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• pp.1321-1328
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• 2001

터보 부호는 종료 알고리즘(termination algorithm)과 반복복호 알고리즘(iterative decoding algorithm)을 사용함으로써 AWGN 채널환경에서 BER 성능이 우수한 것으로 알려져 있다. 그러나 터보 부호는 복호과정에서 큰 복호지연을 요구하며 음성 신호를 전송할 때 프레임의 크기가 작아서 성능의 열화가 생긴다. 또한, 높은 SNR에서는 BER 성능의 개선이 없는 Error Floor 현상이 나타나기 때문에 오류정정 능력의 한계에 도달하는 큰 단점을 가진다. Flattening Effect는 종료 알고리즘을 사용하는 터보 부호(terminated conditions : TC)보다는 종료 알고리즘을 사용하지 않는 터보 부호(non terminated conditions : NTC)에서 상대적으로 많이 나타난다. 따라서 본 논문에서는 NTC 하에서 터보 부호의 Flattening Effect를 개선시키기 위한 새로운 블록 인터리빙 방법을 제시한다. 모의실험결과, 새로운 블록 인터리빙 방법을 적용함으로써 효과적으로 Flattening Effect를 제거할 수 있음을 알 수 있었다.