• Title/Summary/Keyword: Frequency Diversity

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Performance Analysis of Frequency Diversity Scheme for OFDM Systems Using Sub-channel Correlation Characteristics (부채별 상관 특성을 이용한 OFDM 시스템의 주파수 다이버시티 기법 성능 분석)

  • 이종식;김장욱;오창헌;조성준
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.29 no.6A
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    • pp.614-622
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    • 2004
  • In this paper, we propose the frequency diversity scheme for performance improvement of a OFDM system without decreasing the spectral efficiency. In the proposed scheme, information bit is encoded to symbol by a simple procedure, and the encoded symbol is transmitted through the two lowest correlated sub-channels with the particular phase difference. At the receiver, a frequency diversity gain is obtained by a simple signal processing. We also suggest optimum phase difference value to minimize the performance degradation which resulted from a phase difference estimation error and bit/symbol mapping method to minimize BER. As results, at the point of performance improvement, the proposed scheme is excellent even though it requires a little increase of system complexity because of an additional encoding and decoding. In particular, we confirmed through computer simulation that on the same channel environment and bandwidth efficiency, the 27x/1Rx STBC-OFDM system adopting the proposed frequency diversity scheme outperforms the conventional 27x/1Rx STBC-OFDM system performance

Performance of MIMO-OFDM Systems using The Relay With Multi-Antennas for Cooperative Diversity (Put English Title Here) (다중 안테나의 relay를 가진 MIMO-OFDM시스템의 Cooperative diversity에 따른 성능)

  • Kim, Chan-Kyu;Kim, Young-Il
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.45 no.6
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    • pp.13-19
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    • 2008
  • In this paper, the new cooperative communication techniques is proposed for multi-input multi-output(MIMO)-orthogonal frequency division multiplexing (OFDM) system using the relay with multiple antenna. As the MIMO channel is formed by space time coding at the MS(mobile station)-RS(relay station) and RS-BS(base station), we can get the cooperative diversity and MIMO diversity gain simultaneously. Therefore, the performance of MIMO-OFDM system using the relay with multiple-antennas is very improved. And the simple power allocation technique is Proposed for the transmitting power of the mobile station and the relay.

Turbo Equalization and Decoding with Diversity Reception on the Frequency-Selective Fading Channel (주파수 선택적 페이딩 채널에서의 다이버시티 수신 터보 등화 및 복호화)

  • 임동민
    • Proceedings of the IEEK Conference
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    • 1999.11a
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    • pp.39-42
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    • 1999
  • In this paper, a method based on the turbo principle is presented which combines diversity reception, equalization, and channel decoding, to combat the high transmission losses over the frequency-selective fading channel. The simulation results show that with the method presented, the BER performance within 0.3 ㏈ from that on the AWGN channel can be obtained over the frequency-selective fading channel in the investigated scenarios.

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Integer Frequency Offset Estimation by Pilot Subset Selection for DRM+ Systems with CDD (순환 지연 다이버시티를 갖는 DRM+ 시스템에서 파일럿 집합 선택을 이용한 정수배 주파수 오차 추정 기법)

  • Kwon, Ki-Won;Cho, Yong-Soo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.7C
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    • pp.481-487
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    • 2011
  • Cyclic delay diversity (CDD) is a simple transmit diversity technique for an OFDM system using multiple transmit antennas. However, the performance of post-FFT estimation, i.e., integer frequency offset (lFO) is deteriorated by high frequency selectivity introduced by CDD. In this paper, the IFO estimation scheme is proposed for OFDM-based DRM+ system with CDD. Based on the pilot subset partitioning, the proposed IFO estimation scheme reduces the effect of performance degradation caused by frequency selectivity in OFDM systems with CDD . The simulation results show that the performance of the proposed IFO estimator is significantly improved when compared to that of the conventional IFO estimator.

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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A Full Rate Quasi-orthogonal STF-OFDM with DAC-ZF Decoder over Wireless Fading Channels

  • Jin, Ji-Yu;Ryu, Kwan-Woong;Park, Yong-Wan
    • ETRI Journal
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    • v.28 no.1
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    • pp.87-90
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    • 2006
  • In this letter, we propose a quasi-orthogonal space-time-frequency (QOSTF) block coded orthogonal frequency division multiplexing (OFDM) that can achieve full symbol rate with four transmit antennas. Since the proposed QOSTF-OFDM cannot achieve full diversity, we use a diversity advantage collection with zero forcing (DAC-ZF) decoder to compensate the diversity loss at the receiving side. Due to modulation advantage and collected diversity advantage, the proposed scheme exhibits a better bit-error rate performance than other orthogonal schemes.

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A Study on Effects of Antenna Diversity in Doppler Spread Environments (도플러 확산 환경에서의 안테나 다이버시티 효과에 관한 연구)

  • Lee Jong-Gil
    • 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.

Improving the Performance of OFDM-Based Vehicular Systems through Diversity Coding

  • Arrobo, Gabriel E.;Gitlin, Richard D.
    • Journal of Communications and Networks
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    • v.15 no.2
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    • pp.132-141
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    • 2013
  • In this paper, we present diversity coded orthogonal frequency division multiplexing (DC-OFDM), an approach to maximize the probability of successful reception and increase the reliability of OFDM-based systems through diversity coding. We focus on the application of DC-OFDM to vehicular networks based on IEEE 802.11p technology and analyze the performance improvement using this new technology. It is shown that DC-OFDM significantly improves the performance of vehicular ad hoc networks in terms of throughput and the expected number of correctly received symbols.

A Study on Polarization Diversity for the Next Generation Mobile Radio Communications

  • Jung, Hee-Chang;Park, Seung-Keun;Ha, Deock-Ho
    • Journal of Electrical Engineering and information Science
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    • v.3 no.1
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    • pp.117-125
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    • 1998
  • In this paper, in order to investigate the fading reduction effect of narrowband and broadband signals in an indoor multipath propagation environment, both the received narrowband signal while a vehicle unit in motion and the frequency sweeped broadband signal received by vertical polarized antenna, horizontal polarized antenna and circularly polarized antenna are analyzed. Specifically, in order to evaluate polarization diversity effect, we examined the difference of fading reduction effect between the polarization diversity reception and the space diversity reception. Using the correlation coefficient and correlation graph for the polarization diversity branches, the diversity effect is evaluated. And also, using the cumulative distribution for the received signal strength simulated by diversity reception, the diversity effect is also estimated. From the evaluation results it was found that the polarization diversity which use a circularly polarized antenna at the transmitting end and the vertical and horizontal polarized antenna branches at the receiving end is markedly excellent.

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Receive Diversity for OFDM Systems with Cochannel Interference (동일 채널 간섭을 고려한 OFDM 시스템의 수신 다이버시티 기법)

  • Seo Bo-Seok
    • Journal of Broadcast Engineering
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    • v.11 no.2 s.31
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    • pp.222-228
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    • 2006
  • In this paper, we propose a receive diversity method for orthogonal frequency division multiplexing (OFDM) systems with cochannel interference. In the method, combining is done in the frequency domain by using the subcarrier based maximum ratio combining (MRC) method. For MRC, we exploit the power of cochannel interference as well as the power of channel noise. The accuracy of the power estimate of interference plus noise is enhanced by averaging the initial estimates over the correlated subchannels where the coherency between the subchannel gains comes from the limited delay spread of the channel. Simulation results show that the proposed method yields 2-3.5dB gain of signal to noise ratio compared to the conventional MRC method and less than 1 dB difference to the ideal case.