• Title/Summary/Keyword: OFDM/FDD

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A Novel Two-step Channel Prediction Technique for Adaptive Transmission in OFDM/FDD System (OFDM/FDD 시스템에서 Target QoS 만족을 위한 다단계 적응전송 채널예측기법)

  • Heo Joo;Chang Kyung-Hi
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.8A
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    • pp.745-751
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    • 2006
  • The transmitter requires knowledge of the channel status information in order to adopt the adaptive modulation and coding scheme(AMC) for OFDM system. But in the outdoor environment which the users have high mobility, the channel status information from the users is outdated, so that it induces the degradation of system throughput and packet error rate(PER) performance. To solve this problem, researches about applying channel prediction technique to the AMC scheme have been proceeded. Most channel prediction techniques assume that there is no channel variation in the predefined time duration, e.g., a slot. As a result, those techniques cannot compensate the degradation of PER performance resulting from the rapid variation of channel during the slot duration. This paper introduces a novel channel prediction technique for OFDM/FDD system to support adaptive modulation and coding scheme over rapidly time-varying multipath fading channel. The proposed channel prediction technique considers the time-varying nature of channel during the slot duration. Simulation results show that the AMC scheme of OFDM/FDD system utilizing the proposed channel prediction technique can guarantee the target PER of 1% without any loss of system throughput compared with the case supported by the conventional channel prediction under ITU-R Veh A 30km/h.

A New Reduction Method of the Uplink Information for an Adaptive Modulation and Coding OFDM/FDD System (다중 사용자를 위한 적응형 OFDM/FDD 시스템의 상향링크 정보 축소 방안)

  • 장일순;유병한;조경록
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.29 no.2A
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    • pp.140-146
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    • 2004
  • In this paper we proposed the reducing method of feedback information for transmitting of adaptable data rate in multi-user OFDMA/FDD systems. In order to transmit downlink channel information to Base-Station(BS) through the limited uplink control channel, the proposed algorithm exploits the channel variation level which describes the similarity among the adjacent clusters and uses just one modulation and coding scheme(MCS) level representing channel information of all clusters'. We investigated the performance in single cell environment. It has a similar overhead for feedback information with conventional algorithm and has better performance in that bandwidth efficiency and outage probability than the conventional algorithms.

Implementation of OFDM Transceiver for Multiple Access at 18GHz (18GHz 다중통신을 위한 OFDM송수신 모듈 구현)

  • Jeong, Sang-Guk;An, Tae-Ki;Kim, Back-Hyun;Choi, Gab-Bong;Park, Jong-Chol
    • Proceedings of the KSR Conference
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    • 2011.05a
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    • pp.1155-1160
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    • 2011
  • The importance of broadband wireless communication implemented at subway tunnels is growing up. At 18GHz wireless video transmission system, the transmitter requires a digital modulation method. At subway tunnel, A 18GHz's influence of the multi-pass padding is strong. OFDM digital modulation that is strong for multi-pass padding is recommended. Duplexing methode uses FDD to transmit and receive broadband data at the same time. In the case of FDD we assign a private use channel each with the transmission at the receiving. In this paper, We implement multiple access wireless OFDM transceiver. We verified that one ground transceiver communicates with two car transceiver at the same time.

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A Test on Wireless Performance of OFDM Transceiver for Multiple Access at 18GHz (18GHz 다중통신을 위한 OFDM송수신 모듈의 데이터 전송특성 시험)

  • Park, Jong-Cheol;An, Tae-Ki;Kim, Sung-Nam;Lim, Min-Hyuk;Sim, Bo-Seog
    • Proceedings of the KSR Conference
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    • 2011.10a
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    • pp.1008-1013
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    • 2011
  • The importance of broadband wireless communication system at subway tunnels is growing up. At 18GHz wireless video transmission system, the transmitter requires a digital modulation method. At subway tunnel, A 18GHz's influence of the multi-pass padding is strong. OFDM digital modulation that is strong for multi-pass padding is recommended. Duplexing methode uses FDD to transmit and receive broadband data at the same time. In the case of FDD we assign a private use channel each with the transmission at the receiving. In this paper, We implement multiple access wireless OFDM transceiver. We verified that one ground transceiver communicates with two car transceiver at the same time.

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A Linear Precoding Technique for OFDM Systems with Cyclic Delay Diversity (순환 지연 다이버시티를 사용하는 OFDM 시스템을 위한 선형 프리코팅 기법)

  • Hui, Bing;Kim, Young-Bum;Chang, Kyung-Hi
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.34 no.3A
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    • pp.197-204
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    • 2009
  • 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 preceding technique can significantly improve the performance of communication systems by exploiting the channel state in formation (CSI). In order to achieve enhanced performance, we propose applying linear preceding 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 ass umed 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.

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.

A CP Detection Based SSS Detection Method for Initial Cell Search in 3GPP LTE FDD/TDD Dual Mode Downlink Receiver (3GPP LTE FDD/TDD 듀얼 모드 하향링크 수신기에서 초기 셀 탐색을 위한 CP 검출 기반의 SSS 검출 기법)

  • Kim, Jung-In;Jang, Jun-Hee;Choi, Hyung-Jin
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.35 no.1C
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    • pp.113-122
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    • 2010
  • In this paper, we propose a CP (Cyclic Prefix) detection based SSS (Secondary Synchronization Signal) detection method for initial cell search in 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) FDD/TDD (Frequency Division Duplex/Time Division Duplex) dual mode downlink receiver. In general, a blind coherent SSS detection method which can detect SSS without CP detection is applied. However, coherent detection method caused performance degradation by channel compensation error at high speed environment because it uses estimated CFR (Channel Frequency Response) at PSS (Primary Synchronization Signal), and it can be more serious problem in TDD mode due to increased distance between PSS and SSS. Also blind detectionhas the drawback of high computational complexity. Therefore, we proposed a CP type pre-decision structure with non-coherent SSS detection which has stable operation in high speed channel environments for 3GPP LTE TDD mode as well as FDD mode, and can reduce computational complexity by applying CP detection before SSS detection. Simulation results show that the proposed method has stable operation for 3GPP LTE TDD/FDD dual mode downlink receiver in various channel environments.

A Synchronous Digital Duplexing Technique for Wireless Transmission in Indoor Environments (옥내 환경에서 무선 전송을 위한 동기식 디지털 이중화 방식)

  • Park, Chang-Hwan;Ko, Yo-Han;Park, Kyung-Won;Jeon, Won-Gi;Paik, Jong-Ho;Lee, Seok-Pil;Cho, Yong-Soo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.33 no.12C
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    • pp.971-982
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    • 2008
  • In this paper, we propose a new digital duplexing scheme, called SDD(Synchronous Digital Duplexing), which can increase data efficiency and flexibility of resource by transmitting uplink signal and downlink signal simultaneously. In order to transmit uplink data and downlink data simultaneously, the proposed SDD obtains mutual informations between AP(access point) and each SSs(subscriber station), SS and other SSs by mutual ranging procedure. These informations are used for selection of transmission time, decision of CS insertion, setting of CS length, and FFT duration resetting, etc. It is shown that the proposed SDD is appropriate for duplexing scheme in indoor environments over the conventional TDD(Time Division Duplexing) and FDD(Frequency Division Duplexing).