• Title/Summary/Keyword: orthogonal frequency division multiplexing(OFDM)

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Adaptive beamforming for a PF-OFDM system using LMS algorithm (LMS기반 PF-OFDM에서의 적응 빔포밍 설계)

  • Yoo, Kyung-Rul;Oh, Jun-Suk
    • The Transactions of the Korean Institute of Electrical Engineers D
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    • v.55 no.3
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    • pp.119-123
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    • 2006
  • The orthogonal frequency-division multiplexing (OFDM) technique is well known to be robust against the frequency-selective fading in wireless channels. It is due to the exploitation of a guard interval that is inserted at beginning of each OFDM symbol. Based on the conventional OFDM and a polyphase filtered orthogonal frequency division multiplexing (PF-OFDM) technique, we developed an adaptive beamforming algorithm for antenna arrays. The proposed algorithm would lead to an efficient use of channel, since it is possible to eliminate a guard interval and also easily suppress interchannel interference at the same time. In this paper, a series of computer simulations have been provided to show the performance of the proposed system.

Pilot-Aided Iterative Frequency Offset Estimation for Digital Video Broadcasting Systems (디지털 비디오 방송 시스템에서의 파일럿을 이용한 반복적 주파수 옵셋 추정방법)

  • Lee, Kyung-Taek;Seo, Jong-Soo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.5A
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    • pp.484-489
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    • 2007
  • The main disadvantage of orthogonal frequency division multiplexing (OFDM) systems is its sensitivity to carrier frequency offset and timing offset. This paper proposes a simple way of improving the performance of the integer frequency offset (IFO) estimator in OFDM-based digital video broadcasting (DVB) system. By modifying the conventional maximum likelihood (ML) estimator to have multi-stage estimation strategy, IFO estimator is derived. Simulations indicate that the proposed IFO estimator works robustly with reduced computational burden when compared to ML estimator.

An Analysis of the HEMP Interference Effect in OFDM System (OFDM 시스템에 미치는 HEMP 간섭 영향 분석)

  • Seong, Yun-Hyeon;Chang, Eun-Young;Yoon, Seok-beom
    • Journal of Advanced Navigation Technology
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    • v.19 no.3
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    • pp.244-249
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    • 2015
  • High-altitude electromagnetic pulse (HEMP) is generated from a nuclear burst at high altitudes above the Earth, the electromagnetic fields reach the ground nearly simultaneously with regard to the operation time of systems. The aim of this analysis is to inquire about HEMP characteristics and to analyze about effect in orthogonal frequency division multiplexing (OFDM) system. Specifically, HEMP characteristics are classified field sources, spatial coverage, time domain behavior, frequency spectrum and field intensities in this study. Bits error rate (BER) of the receiver with the software simulation is confirmed for the HEMP effect. Q-factor made a difference about interference duration by transfer characteristics of system. When Q factor is smaller, the recovery time from HEMP interference is short. To the contrary, if the Q factor is larger, the recovery duration is lasted longer by 300-600%.

Linear Suppression of Intercarrier Interference in Time-Varying OFDM Systems: From the Viewpoint of Multiuser Detection

  • Li, Husheng
    • Journal of Communications and Networks
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    • v.12 no.6
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    • pp.605-615
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    • 2010
  • Intercarrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems, which causes substantial performance degradation in time-varying fading channels, is analyzed. An equivalent spreading code formulation is derived based on the analogy of OFDM and code division multiple access (CDMA) systems. Techniques as linear multiuser detection in CDMA systems are applied to suppress the ICI in OFDM systems. The performance of linear detection, measured using multiuser efficiency and asymptotic multiuser efficiency, is analyzed given the assumption of perfect channel state information (CSI), which serves as an upper bound for the performance of practical systems. For systems without CSI, time domain and frequency domain channel estimation based linear detectors are proposed. The performance gains and robustness of a linear minimum mean square error (LMMSE) filter over a traditional filter (TF) and matched filter (MF) in the high signal-to-noise ratio (SNR) regime are demonstrated with numerical simulation results.

Peformance Comparisons of CDMA, OFDM, and MC-CDMA with Inaccurate Channel Estimates and Low-SNR Environments (신호대잡음비가 낮고 부정확한 채널추정값을 가질 때의 CDMA, OFDM, MC-CDMA의 성능 비교)

  • Rim Minjoong
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.30 no.1A
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    • pp.55-61
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    • 2005
  • Mobile communication systems are required not only to support high-data-rate transmissions in favorable channel conditions but also to be able to tolerate hostile environments possibly encountered by cellular communications. This paper compares CDMA(Code Division Multiple Access), OFDM(Orthogonal Frequency Division Multiplexing), and MC-CDMA(Multi-Carrier CDMA)with inaccurate channel estimates and low SNR environments. The equations and simulation results show that the performance losses in CDMA systems due to imprecise channel estimates are not considerable while frequency-hopping of OFDM systems can result in more than l0dB SNR losses. Also, this paper show that frequency-spreading of MC-CDMA can be very helpful for channel compensation performances than frequency-hopping or time-spreading of OFDM.

A New Type of Complementary Code Keying Orthogonal frequency Division Multiplexing (CCK-OFDM) Wireless LAN Modem (새로운 방식의Complementary Code Keying Orthogonal Frequency Division Multiplexing (CCK-OFDM) 무선랜 모뎀에 관한 연구)

  • 정원정;박현철
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.29 no.8C
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    • pp.1069-1075
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    • 2004
  • In this paper, we show the equivalence between complementary code keying (CCK) codeword and coset of the first order Reed-Muller (RM) code with variables of three. The CCK codewords are Golay sequences which have peak-to-average power ratio (PAPR) of two at most and can correct one error. We propose a CCK-orthogonal frequency division multiplexing (OFDM) modem to reduce PAPR. Also, we present the performance improvement techniques by increasing the variables of four to correct three errors and reduce PAPR at least 9㏈ with this system. Although, two Fast Hadamard Transform (FHT) blocks of size 8 64 are required at the receiver, we reduce the complexity by using FHT blocks of size 8 64 and 2 4 without deteriorating the performance. We generalize our results that we may increase the variables of RM code to enhance the error correcting and PAPR reduction capabilities without increasing receiver's complexity.

Design of 3-Dimensional Orthogonal Frequency Division Multiplexing (3차원 직교 주파수분할다중화의 설계)

  • Kang, Seog-Geun
    • Journal of Broadcast Engineering
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    • v.13 no.5
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    • pp.677-680
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    • 2008
  • In this paper, a new orthogonal frequency division multiplexing (OFDM) with 3-dimensional (3-D) signal mapper is proposed. Here, the signal mapper consists of signals on the surface of Poincare sphere. If the signal points are uniformly distributed and normalized to have the same average power, the minimum Euclidean distance of a 3-D constellation is much larger than that of a 2-D constellation. Computer simulation shows that the proposed OFDM has much improved error performance as compared with the conventional system.

Adaptive beamforming for a PF-OFDM system using LMS algorithm (LMS기반 PF-OFDM엔서의 적응 빔포밍 설계)

  • Oh, Jun-Suk;Kim, Jae-Yun;Yoo, Kyung-Yul
    • Proceedings of the KIEE Conference
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    • 2005.07d
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    • pp.2998-3000
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    • 2005
  • The orthogonal frequency-division multiplexing (OFDM) technique is well known to be robust against the frequency-selective fading in wireless channels. It is due to the exploitation of a guard interval that is inserted at beginning of each OFDM symbol. Based or the conventional OFDM and a polyphase filtered orthogonal frequency division multiplexing (PF-OFDM) technique, we developed an adaptive beamforming algorithm for antenna arrays. The proposed algorithm would lead to an efficient use of channel, since it is possible to eliminate a guard interval and also easily suppress interchannel interference at the same time. In this paper, a series of computer simulations have been provided to show the performance of the proposed system.

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Implementation of Software Platform for STTC-OFDM based WiBro Systems (STTC-OFDM 기반의 WiBro 시스템 소프트웨어 플랫폼 구현)

  • Lee, Dong-Gi;Lee, Jong-Sik;Jun, Hwang-In;Lee, Seung-Hyun;Kim, Jin-Young
    • 한국정보통신설비학회:학술대회논문집
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    • 2008.08a
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    • pp.535-539
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    • 2008
  • Recently mobile devices can transmit mass data contained multi-media contents. According these flow, a demand for fast data transmission is being risen, so we acutely require remarkable technology that overcome mobile communication's poor environment and rise data transmission volume. Because it can be satisfied these needs, the OFDM(Orthogonal Frequency Division Multiplexing) that rise data transmission volume using efficient frequency, and MIMO(Multiple Input Multiple Output) that rise transmission confidence and data transmission volume using numbers of antenna is attended. Before design of MIMO-OFDM System we want to make an analysis for theory of its systems, and we want to design MIMO-OFDM simulator for verify an ability of modulation, data volume and numbers of antenna.

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Distributed Resource Allocation in Multimedia Ad Hoc Local Area Networks Based on OFDM-CDMA (OFDM-CDMA 기반 멀티미디어 무선 Ad Hoc LAN에서의 분산적 자원 할당 방식)

  • Yang, Hyun-ho;Jeon, Hee-jeong
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.5 no.7
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    • pp.1250-1256
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    • 2001
  • A resource management scheme for ad hoc wireless local area networks (AWLAN's) is presented. This scheme combines distributed resource management scheme and orthogonal frequency division multiplexing-code division multiple access(OFDM-CDMA) technique to support multimedia services with QoS guarantees. The performance evaluation has done in terms of blocking rates and QoS loss probability.

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