• Journal of electromagnetic engineering and science
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• v.1 no.2
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• pp.113-119
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• 2001

Conventional channel estimation methods for orthogonal frequency division multiplexing (OFDM) system don't show the good characteristics in terms of fast fading channels. To solve this drawback in conventional methods, we propose the channel estimation method fur OFDM, assisted pilot for improvement and convergence in mobile system (APIM), which has a good performance and computational complexity in consideration of other methods. APIM uses the more developed concept of conventional methods and a block frame structure within a whole channel. This concept prevents overall performance from diverging or showing a poor one. The simulation results demonstrate the APIM outperforms pilot symbol assisted modulation (PSAM) and extended symbol aided estimation (ESAE) in terms of mean square error (MSE) and bit error rate (BER) performance under all Rayleigh fading environment. Considering the simulation performance and computational complexity, we can see APIM shows better characteristics than conventional methods for OFDM and has not any error floor even in a fast Rayleigh fading environment.

• Journal of Communications and Networks
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• v.11 no.1
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• pp.47-56
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• 2009

We investigate the connectivity of fading wireless ad-hoc networks with a pair of novel connectivity metrics. Our first metric looks at the problem of connectivity relying on the outage capacity of MIMO channels. Our second metric relies on a probabilistic treatment of the symbol error rates for such channels. We relate both capacity and symbol error rates to the characteristics of the underlying communication system such as antenna configuration, modulation, coding, and signal strength measured in terms of signal-to-interference-noise-ratio. For each metric of connectivity, we also provide a simplified treatment in the case of ergodic fading channels. In each case, we assume a pair of nodes are connected if their bi-directional measure of connectivity is better than a given threshold. Our analysis relies on the central limit theorem to approximate the distribution of the combined undesired signal affecting each link of an ad-hoc network as Gaussian. Supported by our simulation results, our analysis shows that (1) a measure of connectivity purely based on signal strength is not capable of accurately capturing the connectivity phenomenon, and (2) employing multiple antenna mobile nodes improves the connectivity of fading ad-hoc networks.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.5
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• pp.27-33
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• 2011

In digital communication system that the Modified Constant Modulus Algorithm (MCMA) reduced the use of the adaptive equalization algorithm to combat the Inter-symbol Interference (ISI). MCMA is relatively brief operation. The major point of MCMA that it only achieves moderate convergence rate and steady state mean square error (MSE). In this paper suggest, MCMA equalization improve the performance with parallel structure. It combines Modified Constant Modulus Algorithm(MCMA) and Modified Decision Directed(MDD) algorithm. By exploiting the inherent structural relationship between the 4-QAM signal's coordinates and 16-QAM signal's coordinates, another style of cost function for Modified Constant Modulus Algorithm(MCMA) is defined and If it happen to offset of received signals and MCMA is poor performance in order to overcome this because the paper combines apply for MCMA and MDD(Modified Decision Direct) algorithm. By computer simulation, we confirmed that the proposed PMCMA-MDD algorithm has the fater convergence rate and steady mean square error than the conventional MCMA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.351-363
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• 2006

The 8-VSB modulation, the transmission standard for the terrestrial digital television(DTV) of the Advanced Television Systems Committee(ATSC), suffers from multipath fading because it conveys information on the amplitude. To solve this problem, decision feedback equalizers(DFE's) have been commonly used in terrestrial DTV receivers. However, under severe channels, such as a 0 dB ghost channel or a single frequency network (SFN) channel, the DFE shows unstable convergence due to the error propagation caused by decision errors. Instead of unstable time-domain DFE schemes, by proposing a frequency-domain direct-inversion equalization method, we try to guarantee stable equalization and achieve low symbol error rates. To secure the existence of a channel inverse, channel-matched filtering and noncausal filtering are carried out prior to equalization. Simulation results show that the proposed method performs much better than existing DFE schemes in terms of both the stability and the symbol error rate.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.184-191
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• 2022

Underwater acoustic wave in shallow water is propagated through multipath that has a large delay spread causing Inter-Symbol Interference (ISI) and these characteristics deteriorate the performance in the communication system. In order to analyze the communication performance and investigate the correlation with multipath delay spread in a reverberant environment, an underwater acoustic communication experiment using Binary Phase-Shift Keying (BPSK) signals with symbol rates from 100 sym/s to 8000 sym/s was conducted in a 5 × 5 × 5 m³ water tank. The acoustic channels in a well-controlled tank environment had the characteristics of dense multipath delay spread due to multiple reflections from the interfaces and walls within the tank and showed the maximum excess delay of 40 ms or less, and the Root Mean Squared (RMS) delay spread of 8 ms or less. In this paper, the performances of Bit Error Rate (BER) and output Signal-to-Noise Ratio (SNR) were analyzed using four types of communication demodulation techniques. And the parameter, Symbol interval to Delay spread Ratio in reverberant environment (SDR_rev), which is the ratio of symbol interval to RMS delay spread in the reverberant environment is defined. Finally, the SDR_rev was compared to the BER and the output SNR. The results present the reference symbol rate in which high communication performance can be guaranteed.

• The Journal of the Acoustical Society of Korea
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• v.24 no.2E
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• pp.61-66
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• 2005

Experimental work in underwater acoustic communications using passive phase conjugation has shown that the demodulation error depends on the relative drift rate between the source and receiver [Rouseff et al., IEEE J. Oceanic Eng. 26, 821-831 (2001)]. The observed effect involves the mismatch between the initial impulse response and the subsequent response after the source or receiver has changed locations. In the present work, the effect of drifting source is analyzed by numerical simulations and compared to the experimental results. The communications bit error rate is qualified as a function of drift rate, drifting direction, and source-receiver range.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.9
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• pp.1633-1637
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• 2008

A protocol is proposed to control the rate of each subcarrier in OFDM-based wireless network systems. The proposed protocol adds an OFDM symbol in CTS frame defined in IEEE 802.11 standard. A receiver determines the rate of its subcarrier after it receives the RTS frame. The determined rate is added to OFDM symbol in CTS frame. In order to synchronize the rate information between the sender and the receiver, error recovery process is proposed. The performance improvement of the proposed method is shown by numerical results.

• Information and Communications Magazine
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• v.18 no.6
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• pp.46-57
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• 2001

본 논문은 IMT-2000 이동통신 표준인 cdma2000 환경에서 라그랑제(Lagrange)승수를 이용한 알고리즘을 이용하여 설계한 스마트안테나 시스템을 성능 분석하였다. 본 논문에 적용한 수신안테나 시스템은 기존의 2 안테나 다이버시티(2-antenna diversity) 시스템과는 달리 선형배열안테나를 이용하여 각 안테나 소자에 대한 위상보정을 통해 최적의 수신이득을 얻는 시스템이다[1]. 본 논문에서는 안테나위상의 보정을 위해 수신신호의 자기상관행렬의 최대 고유치에 해당하는 고유벡터를 계산하는 절차를 거치며 이를 위해 라그랑제승수(Laglange Multiplier)에 기초한 알고리즘을 사용하였다[2]. 이렇게 구현된 스마트안테나 시스템을 변조심볼(Mudulation Symbol)의 SER(symbol error rate)에 대한 성능분석을 통해 cdma2000 데이터채널의 수용용량을 제시함으로써 시스템의 성능을 분석하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.5
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• pp.887-892
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• 2003

In this paper, we propose a simple scaling algorithm for CDMA mobile communications where a voice traffic signals are transmitted by individual one of several data rates at every frames. The traditional method is based on using look-up table called SMT(symbol metric table), but the proposed algorithm is real-time direct scaling method through simple bit manipulations without lookup table. The bit error rate performance is calculated by computer simulation over AWGN and Rayleigh fading channels. From the results, it is shown that the proposed algorithm outperforms the traditional SMT method on Rayleigh channel by 0.3∼0.8dB, while achieving the less H/W complexity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.6
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• pp.1606-1626
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• 2012

This paper investigates the performance of an amplify-and-forward (AF) two-way relaying system with antenna correlation. The system consists of two multiple-antenna sources, which exchange information via the aid of a single-antenna relay. In particular, we derive the exact outage probability expression. Furthermore, we provide a simple, tight closed-form lower bound for the outage probability. Based on the lower bound, we obtain the closed-form asymptotic outage probability and the average symbol error rate expressions at high signal-to-noise ratio (SNR), which reveal the system's diversity order and coding gain with antenna correlation. To investigate the system's throughput performance with antenna correlation, we also derive a closed-form lower bound for the average sum-rate, which is quite tight from medium to high SNR regime. The analytical results readily enable us to obtain insight into the effect of antenna correlation on the system's performance. Extensive Monte Carlo simulations are conducted to verify the analytical results.