• Title/Summary/Keyword: Fading Time

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Design and Performance of Space-Time Trellis Codes for Rapid Rayleigh Fading Channels

  • Zummo, Salam A.;Al-Semari, Saud A.
    • Journal of Communications and Networks
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    • v.5 no.2
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    • pp.174-183
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    • 2003
  • Space-Time (ST) codes are known to provide high transmission rates, diversity and coding gains. In this paper, a tight upper bound on the error probability of ST codes over rapid fading channels is presented. Moreover, ST codes suitable for rapid fading channels are presented. These codes are designed using the QPSK and 16-QAM signal constellations. The proposed codes are based on two different encoding schemes. The first scheme uses a single trellis encoder, whereas the second scheme uses the I-Q encoding technique. Code design is achieved via partitioning the signal space such that the design criteria are maximized. As a solution for the decoding problem of I-Q ST codes, the paper introduces a low-complexity decoding algorithm. Results show that the I-Q ST codes using the proposed decoding algorithm outperform singleencoder ST codes with equal complexity. The proposed codes are tested over fading channels with different interleaving conditions, where it is shown that the new codes are robust under such imperfect interleaving conditions.

A Study On the Rayleigh Fading Channel Model (Rayleigh Fading Channel Model에 관한 연구)

  • 원인재;박재현;김창희
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2004.05b
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    • pp.486-488
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    • 2004
  • Rayleigh signal fading phenomena due to multipath propagation in wireless communication can be simulated using the sum-of-sinusoids channel model. Jakes' fading model is very simple simulator based on the sum-of-sinusoids and has been widely used. However, It has some short-comings. Its time correlation properties based on the simulated waveform do not correspond to the statistical ones. In this paper, the difference between statistical and time properties of Jakes' fading channel model is examined and new simulator is proposed.

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Sum rate and Energy Efficiency of Massive MIMO Downlink with Channel Aging in Time Varying Ricean Fading Channel

  • Yang, Lihua;Yang, Longxiang;Zhu, Hongbo;Liang, Yan
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.12 no.3
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    • pp.1098-1112
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    • 2018
  • Achievable sum rate and energy efficiency (EE) are investigated for the massive multiple-input multiple-output (Massive MIMO) downlink with channel aging in the time varying Ricean fading channel. Specifically, the expression of the achievable sum rate of the system for the maximum ratio transmission (MRT) precoder with aged channel state information (CSI) in the time varying Ricean fading channel is first presented. Based on the expression, the effect of both channel aging and the Ricean factor on the power scaling law are studied. It is found that the transmit power of base station (BS) is scaled down by $1/{\sqrt{M}}$(where M is the number of the BS antennas) when the Ricean factor K is equal to zero (i.e., time varying Rayleigh fading channel), indicating that aged CSI does not affect the power scaling law. However, the transmit power of the BS is scaled down by 1/M for the time varying Ricean fading channel (where $K{\neq}0$) indicating that the Ricean factor affects the power scaling law and sum rate, and channel aging only leads to a reduction of the sum rate. Second, the EE of the system is analyzed based on the general power consumption model. Both the theoretical analysis and the simulations show that the channel aging could degrade the sum rate and the EE of the system, and it does not affect the power scaling law.

Improved Code Timing Estimator for DS-CDMA Systems Using Correlated Antennas in Time-Varying Fading Channels (시변 페이딩 채널에서 상관관계가 있는 안테나를 사용하는 DS-CDMA 통신 시스템을 위한 개선된 최대가능도 코드 타이밍 추정기)

  • Kim Sang-Choon;Jeong Bong-Sik
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.10 no.5
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    • pp.910-920
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    • 2006
  • We consider the problem of estimating a code-timing of DS-CDMA signal in antenna array systems in the presence of flat fading channels and near-far environments. We derive an approximate maximum likelihood algorithm of estimating the code-timing of a desired user for DS-CDMA systems to better utilize the time-varying characteristics of the fading process. In the development of code timing estimator, the given observation bits are divided into many sets of sub-windows with each sufficiently large. The proposed method uses sub-windows with equal size associated with the coherence time of channel fading. The alternative approach is that without the estimation of the fading rate, the sufficiently given observation bits are simply separated into two consecutive sets of sub-windows. The derivation of the proposed algorithms is based on multiple antennas partially correlated in space. The impacts of spatial fading correlation on acquisition and men acquisition time performance of the proposed algorithms are also examined.

Inter-carrier Interference of Multicarrier-CDMA System in Time Selective Fading Channel (시간선택적 페이딩 환경에서 멀티캐리어-CDMA 시스템의 서브캐리어간 간섭)

  • 김명진;김성필;하경민
    • Proceedings of the IEEK Conference
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    • 2000.06a
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    • pp.53-56
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    • 2000
  • In MC-CDMA systems effects of delay spread of the channel are reduced with increased symbol duration by simultaneously transmitting data symbols on the parallel subcarriers. However, the increased symbol duration causes the system to be more vulnerable to time selective fading. In other words, although MC-CDMA systems are robust against frequency selective fading in a multipath environment, they are sensitive to Doppler spread and hence inter-carrier interference is increased. In this paper, we investigate the effects of time selective fading characteristics of the mobile channel from the viewpoint of desired signal power to inter-carrier interference power ratio at the combiner output of the MC-CDMA receiver.

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Differential Space Time Coding based on Different Unitary Matrices Sets

  • Lee, Kwang-Jae;Kim, Chang-Joo;Yoo, Hyun-Seok;Kim, Sung-Hun;Lee, Moon-Ho
    • Journal of electromagnetic engineering and science
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    • v.6 no.4
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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.

Performance Analysis of Noncoherent Transmit Diversity System over Correlated Rayleigh Fading Channel (상관된 레일레이 페이딩 채널에서 비동기 송신 다이버시티 시스템 성능해석)

  • 여민기;한영열
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.12 no.2
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    • pp.208-216
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    • 2001
  • Signal Fading due to multipath propagation severely impairs the performance of high-speed mobile communication systems. Effective diversity scheme for fading channel is STTD (Space Time Transmitter Diversity) method. This scheme is very simple and using 2 transmit antennas and 1 receive antenna provides a diversity order of two[1],[2]. In this paper, we derive the new probability density function of the envelope of the received signal over correlated Rayleigh fading channel. Using the new pdf of the envelope we analyze the performance of noncoherent M-ary FSK, DPSK and ASKSTTD (Space Time Transmitter Diversity) a system on correlated Rayleigh fading channel.

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Performance Analysis of FH/MFSK systems with Fading and Multitone Jamming using Time Diversity (페이딩과 멀티톤 재밍하에서 시간 다이버시티를 이용한 FH/MFSK 시스템의 성능 분석)

  • 오영석;조형래;강창언
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.17 no.3
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    • pp.260-267
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    • 1992
  • In this paper, the performance of frequency hopped(FH) M-ary frequency shift keyed(MFSK)system is analyzed with the fading channel and the multione famming. In general, the performance degradation of FH/MFSK system is due to the Rayleigh fading and the multitone jamming environment. In order to improve the system performance. the time diversity is used. When the time diversity is applied to the Rayleigh fading and the mulitone jamming, we get around 18dB and 19dB improvements. respectively. And when it is applied to both the Rayleigh fading and the multitone jamming, we get around 4 dB improvement.

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The Performance Analysis of the Initial Synchronization for the Direct Sequence Spread Spectrum Communication under the Rician Fading Channel (Rician Fading Channel에서의 직접대역확산통신용 초기동기 성능분석)

  • Lim, Myoung-Seob
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.9 no.1
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    • pp.43-51
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    • 1998
  • In this paper, the performance about the CDMA inital synchronization under the Rician fading channel, which is actively studied as a CAI for IMT2000(FPLMTS) is analyzed. Through the performance analysis with the double dwell serial search code acquisition, the minimum mean initial synchronization acquisition time vs signal detection threshold value and first dwell duration time respectively with parameters of false alarm probability, detection probability and test PN chips is presented and the results show the mean initial synchronization acquisition time is increased with lower slope than Rayleigh fading as the threshold value of the initial synchronization acquisition decision is increased.

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A Time-Varying Modified MMSE Detector for Multirate CDMA Signals in Fast Rayleigh Fading Channels

  • Jeong, Kil-Soo;Yokoyama, Mitsuo;Uehara, Hideyuki
    • ETRI Journal
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    • v.29 no.2
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    • pp.143-152
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    • 2007
  • In this paper, we propose a time-varying modified minimum mean-squared error (MMSE) detector for the detection of higher data rate signals in a multirate asynchronous code-division multiple-access (CDMA) system which is signaled in a fast Rayleigh fading channel. The interference viewed by a higher data rate symbol will be periodic due to the presence of a lower data rate symbol which spans multiple higher data rate symbols. The detection is carried out on the basis of a modified MMSE criterion which incorporates differential detection and the ratio of channel coefficients in two consecutive observation intervals inherently compensating the fast variation of the channel due to fading. The numerical results obtained by the MMSE detector with time-varying detection show around 3 dB (M=2) and 6 dB (M=4) performance improvement at a BER of $10^{-3}$ in the AWGN channel, while introducing more computational complexity than the MMSE detector without time-varying detection. At a higher $E_b/N_0$, the proposed scheme can achieve a BER of approximately $10^{-3}$ in the presence of fast channel variation which is an improvement over other schemes.

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