• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 학술대회지
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• pp.653-657
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• 2004

The average bit error rate (HER) performance of a Gray coded arbitrary rectangular quadrature amplitude modulation (AR-QAM) signal with maximal ratio combining (MRC) diversity in an arbitrarily correlated Nakagami-m fading channel is derived and analyzed. The derived two types of general solutions are a simple closed-form and an integral form, depending on the types of the values (integer and non-integer) of the fading parameter. Using the derived equations in this paper, we analyzed the HER performances numerically based on the practical base station antenna configuration. The results show that MRC reception is a very effective scheme so far even though the combined signals are not independent each other because of the correlation values. The antenna height and separation of the MRC system relate to the correlation coefficient value between antennas, and go a long way with the diversity advantage. In particular, it is needed to be determined the antenna height that is carefully do for the diversity advantage because the correlation coefficient and the antenna height gain are contrary to each other from the aspect of the system performance. The expressions presented here can offer a convenient way to evaluate the exact HER performance of an arbitrary rectangular QAM signal with MRC diversity reception for various cases of practical interest on a correlated Nakagami fading channel.

• 한국전자파학회논문지
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• 제12권2호
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• pp.208-216
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• 2001

고속무선 이동통신에서 가장 문제가 되는 것이 전파의 다중경로에 의한 페이딩 잡음이며, 이러한 페이딩의 문제점을 이동성을 보장하면서도 효율적으로 해결할 수 있는 방법이 최근 제안된 STTD (Space Time Transmitter Diversity) 기법이다. STTD 방법은 2개의 송신 안테나와 1개의 수신안테나로 쉽게 2차 다이버시티를 제공할 수 있다. 본 논문에서는 상관된 레이레이 페이딩 채널환경에서 적용될 수 있는 확률 밀도함수를 유동하고 유도된 확률밀도함수를 이용하여 비동기 M-ray FSK, DPSK 및 ASK 송신 다이버시티 시스템의 정확한 오류확률을 유도하고 그 성능을 비교 분석한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권7호
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• pp.2992-3009
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• 2016

The performance of D-MIMO systems is not only affected by multipath fading but also from shadowing fading, as well as path loss. In this paper, we investigate the ergodic capacity of D-MIMO systems operating in non-correlated K fading (Rayleigh/Gamma) channels. With the aid of majorization and Minkowski theory, we derive analytical closed-form expressions of the upper and lower bounds on the ergodic capacity for D-MIMO systems over non-correlated K fading channels, which are quite general and applicable for arbitrary signal-to-noise ratio (SNR) and the number of transceiver antennas. To intuitively reveal the impacts of system and fading parameters on the ergodic capacity, we deduce asymptotic approximations in the high and low SNR regimes. Finally, we pursue the massive MIMO systems analysis for the lower bound and derive closed-form expressions when the number of antennas at BS grows large, and when the number of antennas at transceivers becomes large with a fixed and finite ratio. It is demonstrated that the proposed expressions on the ergodic capacity accurately match with the theoretical analysis.

• Journal of electromagnetic engineering and science
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• 제6권4호
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• pp.209-216
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• 2006

This paper investigates a distinct set of complex unitary matrices for QPSK differential space time coding. After properly selecting the initial transmission matrix and unitary matrices we find that the different combinations of them could lead different BER performance over slow/fast Rayleigh fading channels and antennas correlated channels. The numerical results show that the proper selection of the initial transmission matrix and the set of unitary matrices can efficiently improve the bit error rate performance, especially for the antennas correlated fading channel. The computer simulations are evaluated over slow and fast Rayleigh fading channels.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(1)
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• pp.117-120
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• 2001

In this paper, we propose a robust trellis coded modulation for a correlated Rayleigh fading channel. This method use only one transmit antenna, which can achieve superior performance compared to Space-Time Trellis Coded Modulation (STTC) over a wide channel correlation range among transmit antennas. The code is designed to have the largest Euclidean distance between faded signals at the receiver. Computer simulations are performed to evaluate the frame error rate (FER) performance and to compare the proposed code with the conventional one.

• 한국통신학회논문지
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• 제22권4호
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• pp.611-617
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• 1997

In this paper a new fading model is proposed, which is well consistent with the real environment of smart antenna applications since it is spatially and temporally correlated simultaneously. The new model(STCFM: Spatially and Temporally Correlated Fading Model) is derived statistically in spatio-temporal domain so that it can provide high accuracy in the evaluation of the smart antenna system. As will be seen, the simulation results agree well with the theory.

• Journal of information and communication convergence engineering
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• 제2권4호
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• pp.214-218
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• 2004

In this paper, we have analyzed TCP performance over wireless correlated fading links with and without Snoop protocol. For a given value of the packet error rate, TCP performance without Snoop protocol is degraded as the fading is getting fast (i.e. the user moves fast). When Snoop protocol is introduced in the base station, TCP performance is enhanced in most wireless environments. Especially the performance enhancement derived from using Snoop protocol is large in fast fading channel. This is because packet errors become random and sporadic in fast fading channel and these random packet errors (mostly single packet errors) can be compensated efficiently by Snoop protocol's local packet retransmissions. But Snoop protocol can't give a large performance improvement in slow fading environments where long bursts of packet errors occur. Concerning to packet error rate, Snoop protocol results in the highest performance enhancement in the channel with mid-high values of packet error rate. This means Snoop protocol cannot fully fulfill its ability under too low or too high packet error rate environments.

• Journal of Communications and Networks
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• 제8권2호
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• pp.212-219
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• 2006

In this paper, a new turbo codes-based hybrid automatic repeat request (TC-HARQ) scheme with segment selective repeat (SSR) is proposed. The main strategy is, upon retransmission, to repeat the data that are most important for the next round of decoding based on the distribution of residual errors after current decoding. The performance in terms of reliability and throughput is analyzed. To adapt to correlated fading channels where an inter-leaver is always employed before transmission, we further modify the SSR strategy so that data having experienced correlated deep fading are selected for retransmission. Finally, this proposed scheme is applied to the wideband code division multiple access (WCDMA) system under frequency selective fading channels. Simulation results demonstrate that in all single and multiple user cases, SSR-based TC-HARQ leads to significant throughput improvement with similar bit error rate (BER) performance as compared to type-I TC-HARQ.

• Journal of Communications and Networks
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• 제5권2호
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• pp.150-156
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• 2003

In this paper, an uplink MC-CDMA system incorporating multiuser detection and smart antennas has been considered. The performance of asynchronous as well as synchronous system is studied over a correlated Rayleigh multipath slow fading channel. A simplified array-processing algorithm suitable for slow fading situation is investigated to overcome the heavy computational complexity associated with Eigen solutions. The effect of variable data rate in the system performance is considered and effectiveness of antenna array to handle high data rate is discussed. A brief investigation on the system performance degradation due to correlated channel is also carried out. Based on the extensive simulation carried out, the performance of the asynchronous uplink system is found dramatically improved with antenna array and multiuser detection. Asynchronicity and channel correlation are found to affect the system performance significantly. The investigated simpli- fied algorithm produces similar results as Eigen solutions in slow fading situation with much reduced complexity.

• 한국정보통신학회논문지
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• 제10권5호
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• pp.910-920
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• 2006

본 논문에서는 평탄 페이딩과 근거리/원거리 현상이 존재할 때 안테나 어레이를 사용하는 DS-CDMA 신호의 코드 타이밍을 추정하는 문제를 다루고자 한다. 페이딩 과정의 시변 페이딩 특성을 보다 잘 활용할 수 있도록 DS-CDMA 시스템에 대한 희망하는 사용자의 코드 타이밍을 추정하는 최대가능성 알고리즘을 유도한다. 코드 타이밍 추정기의 개발에 있어서 주어진 관찰 비트들을 포함하는 윈도우를 각각의 부-윈도우가 충분히 큰 길이를 갖도록 나눈다. 제안된 방법은 채널 페이딩의 일관성 시간과 연관된 똑같은 크기를 가지는 부-윈도우들을 이용한다. 또한 페이딩 속도를 추정하지 않고 충분히 긴 관찰 비트들을 두 개의 연속적 인 부-윈도우로 나누는 방법을 대안으로 제시한다. 알고리즘의 유도과정은 공간적으로 상관성이 있는 다중안테나를 바탕으로 한다. 공간적인 페이딩 상관성이 제안된 알고리즘의 동기 획득 및 평균 동기 획득 성능에 미치는 영향을 분석한다.