• Title/Summary/Keyword: frequency diversity gain

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Analysis of BER According to Spatial and Frequency Diversity Gain in Uplink SC-FDMA with SIMO Systems (상향링크 SIMO 시스템에서 공간 및 주파수 다이버시티 이득에 따른 SC-FDMA의 BER 성능 분석)

  • Lee, Jin-Hui;Choi, Kwonhue
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.39A no.9
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    • pp.535-547
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    • 2014
  • We investigate BER (Bit Error Ratio) performance according to the gain of spatial and frequency diversities in uplink SC-FDMA of SIMO (Single Input Multiple Output) systems. The main results of the analysis in this paper are as follows. First, we prove that performance of integrated system for considering spatial and frequency diversity combining in parallel is equivalent with the performance of sequential system for performing diversity combining in sequence. By signal modeling, it is demonstrated that the performances of both systems are the same when the frequency diversity combining technique of the sequential system is equal to diversity combining technique of the integrated system, and spatial diversity combining technique of the sequential system is performed as MRC in advance of frequency diversity combining. Secondly, it is found that effect on the BER performance is different according to the gain of spatial and frequency diversities, respectively. The frequency diversity gain increases by increasing the number of subcarrier. It might affect the performance improvement of high SNR(Signal to Noise Ratio) while it maintains gap between performances of ZF(Zero Forcing) and MMSE(Minimum Mean Square Error) in frequency diversity combining schemes. Also, spatial diversity gain increases as the number of receiving antennas increases. It means that it can reduce performance gap between ZF and MMSE in frequency diversity combining schemes by increasing the number of receiving antennas. In addition, it might affect the performance improvement of the whole SNR. Finally, through the analysis of performance according to the spatial diversity gain, the performance of ZF in frequency diversity combining is equal to the MMSE if the number of receiving antennas is 6 or more.

Delay Determination of Cyclic Delay Diversity for Multi-user Scheduling in OFDMA Systems (OFDMA 시스템의 다중 사용자 스케줄링을 위한 순환지연 다이버시티의 지연값 결정)

  • Rim, Min-Joong;Hur, Seong-Ho;Song, Hyun-Joo;Lim, Dae-Woon;Jeong, Byung-Jang;Noh, Tae-Gyun
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.33 no.3A
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    • pp.248-255
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    • 2008
  • In an OFDMA system the performance of multi-user scheduling in the frequency domain is affected by the frequency selectivity of the channel. If the channel is too flat in the frequency domain, the multi-user scheduling gain might be degraded. On the contrary, if the frequency selectivity is too high and the magnitude of the frequency response severely fluctuates on the allocation bandwidth, it is also hard to get sufficient scheduling gain. For maximizing the multi-user scheduling gain, a cyclic delay diversity technique can be used to adjust the frequency selectivity of the channel. This paper proposes a method to determine the optimal delay value of cyclic delay diversity according to the allocation bandwidth and the channel characteristics.

STF-OFDM Transmission Scheme via Preceding in Frequency Domain (주파수 영역에서의 사전 부호화를 이용한 STF-OFDM 전송 기법)

  • 박상순;김한경;백흥기
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.29 no.7C
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    • pp.954-961
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    • 2004
  • In this paper, we propose a STF(Space-Time-Frequency) coded OFDM(Orthogonal Frequency Division Multiplexing) transmission scheme as an attractive solution for high bit rate data transmission in a multipath fading environment. The STF-OFDM transmission scheme that we propose in this paper is a simple transmission cheme for achieving frequency diversity gain with low complexity. Using preceding in frequency domain, we obtain frequency diversity gain and improve the SER performance of conventional ST-OFDM. The preceding scheme proposed in this paper is a very simple method that can be encoded and decoded with low complexity.

Adaptive Channel-Matched Extended Alamouti Space-Time Code Exploiting Partial Feedback

  • Badic, Biljana;Rupp, Markus;Weinrichter, Hans
    • ETRI Journal
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    • v.26 no.5
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    • pp.443-451
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    • 2004
  • Since the publication of Alamouti's famous space-time block code, various quasi-orthogonal space-time block codes (QSTBC) for multi-input multi-output (MIMO) fading channels for more than two transmit antennas have been proposed. It has been shown that these codes cannot achieve full diversity at full rate. In this paper, we present a simple feedback scheme for rich scattering (flat Rayleigh fading) MIMO channels that improves the coding gain and diversity of a QSTBC for 2$^n$ (n=3, 4, ${\cdots}$) transmit antennas. The relevant channel state information is sent back from the receiver to the transmitter quantized to one or two bits per code block. In this way, signal transmission with an improved coding gain and diversity near to the maximum diversity order is achieved. Such high diversity can be exploited with either a maximum-likelihood receiver or low-complexity zero-forcing receiver.

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Non-Pilot-Aided Timing Offset Estimation for OFDM Systems with Frequency Diversity

  • Yang, Hyun;You, Young-Hwan
    • Proceedings of the Korean Society of Broadcast Engineers Conference
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    • 2006.11a
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    • pp.175-177
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    • 2006
  • This letter deals with non-pilot-aided symbol timing estimation methods in an orthogonal frequency division multiplexing (OFDM) system. To do this, OFDM system uses a frequency diversity scheme over two consecutive data symbols. Our approach can be viewed as an expansion of Schmidl's and Minn's correlation methods. Using the OFDM signal equipped with frequency diversity, however, symbol timing is accurately estimated without additional training symbol and a second-order diversity gain is achieved.

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A Study on the Relation Between Frequency Diversity and Inter Code Interference in the Multi-rate MC-CDMA system (Multi-rate MC-CDMA시스템에서의 코드 간 간섭과 주파수 다이버시티와의 관계에 대한 연구)

  • Lee, Kyu-Jin;Lee, Kye-San;Kim, Jin-Young
    • The Journal of The Korea Institute of Intelligent Transport Systems
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    • v.7 no.5
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    • pp.131-138
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    • 2008
  • The channel parameters such as RMS delay spread and Doppler frequency have an effect on performance of system. This paper investigates the effect between the Inter-Code Interference (ICI) and the frequency diversity gain in the multi-rate MC-CDMA system. The multi-rate MC-CDMA system has achieved the more variable data rate than the MC-CDMA and moreover it has the better performance than the OFDMA system, because it has achieved the frquency diversity gain. However, the frequency diversity gain and ICI have a trade-off relationship by using the spreading code. Therefore, we have improved the system performance by efficient choice of system parameters. In order to evaluate the effectiveness of the frequency diversify gain and the ICI effect, we perform simulations by altering the Doppler frequency and RMS delay spread.

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On Maximum Diversity Order over Doubly-Selective MIMO-OFDM Channes

  • Yang Qinghai;Kwak Kyung Sup
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.30 no.7A
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    • pp.628-638
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    • 2005
  • The analysis of maximum diversity order and coding gain for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems over time-and frequency-selective (or doubly-selective) channels is addressed in this paper. A novel channel time-space correlation function is developed given the spatially correlated doubly-selective Rayleigh fading channel model. Based on this channel-model assumption, the upper-bound of pairwise error probability (PEP) for MIMO-OFDM systems is derived under the maximum likelihood (ML) detection. For a certain space-frequency code, we quantify the maximum diversity order and deduce the expression of coding gain. In this wort the impact of channel time selectivity is especially studied and a new definition of time diversity is illustrated correspondingly

Spatial and Frequency Diversity Combining Order in Uplink SC-FDMA with SIMO Systems (상향링크 SIMO 시스템에서 공간 및 주파수 다이버시티 컴바이닝 순서에 따른 SC-FDMA 성능 분석)

  • Lee, Jin-Hui;Choi, Kwonhue
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.40 no.3
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    • pp.432-440
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    • 2015
  • We investigate BER performance according to the order of spatial and frequency diversity combining in uplink SC-FDMA of SIMO systems. It is found that frequency diversity combining (FDC) after spatial diversity combining (SDC) is better than the reverse order combing in all SNR (Signal to Noise Ratio) range. Also, it is shown that FDC after SDC requires less computational complexity than the reverse order combining.

A Linear Precoding Technique for OFDM Systems with Cyclic Delay Diversity

  • Hui, Bing;Chang, Kyung-Hi
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.2 no.5
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    • pp.253-264
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    • 2008
  • Cyclic delay diversity (CDD) is considered a simple approach to exploit the frequency diversity, to improve the system performance in orthogonal frequency division multiplexing (OFDM) systems. Also, the linear precoding technique can significantly improve the performance of communication systems by exploiting the channel state information (CSI). In order to achieve enhanced performance, we propose applying linear precoding to the conventional CDD-OFDM transmit diversity schemes over Rayleigh fading channels. The proposed scheme works effectively with the accurate CSI in time-division-duplex (TDD) OFDM systems with CDD, where the reciprocity is assumed instead of channel state feedback. For a BER of $10^{-4}$ and the mobility of 3 km/h, simulation results show that a gain of 6 dB is achieved by the proposed scheme over both flat fading and Pedestrian A (Ped A) channels, compared to the conventional CDD-OFDM system. On the other hand, for a mobility of 120 km/h, a gain of 2.7 dB and 3.8 dB is achieved in flat fading and Vehicular A (Veh A) channels, respectively.

Novel Technique for Obtaining Diversity Gain Using Symbol Share In OFDM Systems (OFDM 시스템에서의 심볼 공유를 이용한 다이버시티 이득 획득 기법)

  • Kang, Jae-Won;Park, Jin-Bae;Hwang, Hae-Gwang;Kim, Kwang-Soon
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.47 no.12
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    • pp.1-7
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    • 2010
  • In this paper, the technique for obtaining diversity gain without increasing the antenna is proposed using symbol share in the OFDM systems. Proposed technique groups symbols which are mapped into different sub-carriers and these symbols are modulated by proposed constellation. Proposed constellation has the identical minimum distance with QPSK modulation constellation and obtain more frequency diversity gain. Also, proposed modulation scheme make it possible to increase data rate using subcarriers allocated symbols.