• Title/Summary/Keyword: Ofdm Signals

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Design and Performance Analysis of the Efficient Equalization Method for OFDM system using QAM in multipath fading channel (다중경로 페이딩 채널에서 QAM을 사용하는 OFDM시스템의 효율적인 등화기법 설계 및 성능분석)

  • 남성식;백인기;조성호
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.25 no.6B
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    • pp.1082-1091
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    • 2000
  • In this paper, the efficient equalization method for OFDM(Orthogonal Frequency Division Multiflexing) System using the QAM(Quadrature Amplitude Modulation) in multipath fading channel is proposed in order to faster and more efficiently equalize the received signals that are sent over real channel. In generally, the one-tap linear equalizers have been used in the frequency-domain as the existing equalization method for OFDM system. In this technique, if characteristics of the channel are changed fast, the one-tap linear equalizers cannot compensate for the distortion due to time variant multipath channels. Therefore, in this paper, we use one-tap non-linear equalizers instead of using one-tap linear equalizers in the frequency-domain, and also use the linear equalizer in the time-domain to compensate the rapid performance reduction at the low SNR(Signal-to-Noise Ratio) that is the disadvantage of the non-linear equalizer. In the frequency-domain, when QAM signals, consisting of in-phase components and quadrature (out-phase) components, are sent over the complex channel, the only in-phase and quadrature components of signals distorted by the multipath fading are changed the same as signals distorted by the noise. So the cross components are canceled in the frequency-domain equalizer. The time-domain equalizer and the adaptive algorithm that has lower-error probability and fast convergence speed are applied to compensate for the error that is caused by canceling the cross components in the frequency-domain equalizer. In the time-domain, To compensate for the performance of frequency-domain equalizer the time-domain equalizes the distorted signals at a frame by using the Gold-code as a training sequence in the receiver after the Gold-codes are inserted into the guard signal in the transmitter. By using the proposed equalization method, we can achieve faster and more efficient equalization method that has the reduced computational complexity and improved performance.

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Low-Power FFT Design for NC-OFDM in Cognitive Radio Systems (Cognitive Radio 시스템의 NC-OFDM을 위한 저전력 FFT 설계)

  • Jang, In-Gul;Chung, Jin-Gyun
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.48 no.6
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    • pp.28-33
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    • 2011
  • Recently, the investigation of the cognitive radio (CR) system is actively progressed as one of the methods for using the frequency resources more efficiently. In CR systems, when the frequency band allocated to the incumbent user is not used, the unused frequency band is assigned to the secondary user. Thus, the FFT input signals corresponding to the actually used frequency band by the incumbent user are assigned as '0'. In this paper, based on the fact that there are many '0' input signals in CR systems, a low-power FFT design method for NC-OFDM is proposed. An efficient zero flag generation technique for each stage is first presented. Then, to increase the utility of the zero flag signals, modified architectures for memory and arithmetic circuits are presented. To verify the performance of the proposed algorithm, 2048 point FFT with radix-24SDFstructureisdesignedusingVerilog HDL. The simulation results show that the power consumption of FFT is reduced considerably by the proposed algorithm.

A Novel Transmission Scheme with Spatial Modulation for Coded OFDM Systems (채널 부호화된 OFDM 시스템을 위한 공간 변조를 이용한 새로운 전송 기법)

  • Hwang, Soon-Up;Kim, Young-Ki;Jeon, Sung-Ho;Kang, Woo-Seok;Seo, Jong-Soo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.34 no.7A
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    • pp.515-522
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    • 2009
  • In this paper, a novel transmission scheme with spatial modulation is proposed for coded orthogonal frequency division multiplexing (OFDM). The multiple-input multiple-output (MIMO) technique, so-called spatial modulation (SM), divides input data into antenna index and data signals, transmitting data signals through the specific antenna chosen by the antenna index. In order to retrieve data stream at the receiver, SM needs to detect the antenna index which means that data signals are transmitted via a certain antenna. For this reason, it should be guaranteed that channel matrix is orthogonal. For the real environment, a MIMO channel has difficulty in maintaining orthogonality due to spatial correlation. Moreover, the receiver of the conventional SM is operated by hard decision, so that this scheme has a limit to be adopted for practical systems. Therefore, soft-output demappers for the conventional and proposed schemes are derived to detect antenna index and data stream by soft decision, and a novel transmission scheme combined with spatial modulation is proposed to improve the bit error rate (BER) performance of the conventional scheme.

English Performance of MIMO-OFDM Combing Bemaformer with Space-time Decoder in Multiuser Environments (다중 사용자 환경에서 빔 형성기와 결합된 Space-Time decoder을 가진 MIMO-OFDM 시스템의 성능)

  • Kim Chan-Kyu
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.8A
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    • pp.775-783
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    • 2006
  • In this paper, the new technique combining beamforming with space-time coding is proposed for an orthogonal frequency division multiplexing(OFDM) system with multi-input multi-output(MIMO). When MIMO-OFDM system is employing Nt(the number of transmitterantenna) beamfomers and one S-T decoder at Nr receiver antennas, Nt signals removed CCI are outputted at the beamformer and then diversity gain can be got through space-time decoding. As the proposed technique can reduce cochannel interference and get diversity gain in the multi-user environment, the performance of MIMO-OFDM system is very improved. BER performance improvement and convergence behavior of the proposed approach are investigated through computer simulation by applying it to MIMO-OFDM system in the multi-user environment.

A VHDL Implementation of Baseband Predistorter for the Compensation of Nonlinear Distortion in OFDM Systems (OFDM시스템에서 비선형 왜곡 보상을 위한 기저대역 사전왜곡기의 VHDL 구현)

  • 성시훈;김형호;최종희;신요안;임성빈
    • Proceedings of the IEEK Conference
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    • 2000.06a
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    • pp.256-259
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    • 2000
  • The OFDM (orthogonal frequency division multiplexing) systems are based en the transmission of a given set of signals on multiple orthogonal subcarriers, resulting in large variation in amplitude of transmit signals, and severe distortion by nonlinear characteristic of a high power amplifier (HPA) is unavoidable. We propose in this paper a computationally efficient structure of a baseband predistorter for compensation of nonlinear distortion by the HPA. Moreover, a predistorter which can be utilized in high speed transmission systems such as wireless ATM based on the proposed structure is designed using VHDL, and synthesized by the Synopsys tool.

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Performance of Cyclostationary Spectrum Sensing of Cognitive Radio Based for WiBro Systems (WiBro 시스템을 위한 인지무선 Cyclostationary 스펙트럼 센싱 성능)

  • Koo, Sung-Wan;Kim, Jin-Young
    • Journal of The Institute of Information and Telecommunication Facilities Engineering
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    • v.8 no.3
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    • pp.111-115
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    • 2009
  • Cognitive Radio (CR) technology is proposed for using the unused spectrum band efficiently because of the spectrum scarcity problems. Spectrum sensing is one of the most challenging issues in cognitive radio system. In this paper, we focus on the signal detection of WiBro system band. As most of the modulated signals can be treated as cyclostationary random process, we can detect the signal of the OFDM signals in WiBro system. OFDM symbols using WiBro system have several pilot subcarriers and periodic pilots have cyclostationary characteristic. To improve the detection performance, we get diversity gain using multiple antennas.

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Adaptive SLM Scheme Based on Peak Observation for PAPR Reduction of OFDM Signals (OFDM PAPR 감소를 위한 피크 신호 관찰 기반의 적응적 SLM 기법)

  • Yang, Suck-Chel;Shin, Yoan
    • Proceedings of the IEEK Conference
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    • 2006.06a
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    • pp.15-16
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    • 2006
  • In this paper, we propose an adaptive SLM scheme based on peak observation for PAPR reduction of OFDM signals. The proposed scheme is composed of three steps: peak scaling, sequence selection, and SLM procedures. In the first step, the peak signal samples in the IFFT outputs of the original input sequence are scaled down. In the second step, the sub-carrier positions where power difference between the original input sequence and the FFT outputs of the scaled signal is large, are identified. Then, the phase sequences which have the maximum number of phase-reversed sequence words only for these positions, are selected. Finally, only using the selected phase sequences, the generic SLM procedure is performed for the original input sequence. Simulation results reveal that the proposed adaptive SLM remarkably reduces the complexity in terms of IFFT and PAPR calculations than the conventional SLM, while maintaining the PAPR reduction performance.

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Sensing of OFDM Signals in Cognitive Radio Systems with Time Domain Cross-Correlation

  • Xu, Weiyang
    • ETRI Journal
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    • v.36 no.4
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    • pp.545-553
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    • 2014
  • This paper proposes an algorithm to sense orthogonal frequency-division multiplexing (OFDM) signals in cognitive radio (CR) systems. The basic idea behind this study is when a primary user is occupying a wireless channel, the covariance matrix is non-diagonal because of the time domain cross-correlation of the cyclic prefix (CP). In light of this property, a new decision metric that measures the power of the data found on two minor diagonals in the covariance matrix related to the CP is introduced. The impact of synchronization errors on the signal detection is analyzed. Besides this, a likelihood-ratio test is proposed according to the Neyman-Pearson criterion after deriving probability distribution functions of the decision metric under hypotheses of signal presence and absence. A threshold, subject to the requirement of probability of false alarm, is derived; also the probabilities of detection and false alarm are computed accordingly. Finally, numerical simulations are conducted to demonstrate the effectiveness of the proposed algorithm.

Spectrum Sensing of Cognitive Radio using Multiple Antennas in WiBro Systems (WiBro 시스템에서 다중 안테나를 이용한 인지 무선 스펙트럼 센싱)

  • Baek, Myung-Kie;Heo, Si-Young;Yang, Jae-Soo;Kim, Jin-Young;Kim, Yun-Hyeon
    • 한국정보통신설비학회:학술대회논문집
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    • 2008.08a
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    • pp.379-383
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    • 2008
  • Cognitive Radio (CR) technology is proposed for using the unused spectrum band efficiently because of the spectrum scarcity problems. Spectrum sensing is one of the most challenging issues in cognitive radio system. In this paper, we focus on the signal detection of WiBro system band. As most of the modulated signals can be treated as cyclostationary random process, we can detect the signal of the OFDM signals in WiBro system. OFDM symbols using WiBro system have several pilot subcarriers and periodic pilots have cyclostationary characteristic. To improve of the detection performance, we get diversity gain using multiple antennas.

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Timing Synchronization with Channel Impulse Response in OFDM Systems (채널 임펄스 응답을 이용한 OFDM 시스템 시간 동기)

  • Kang, Eun-Su;Han, Dong-Seog
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.44 no.7 s.361
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    • pp.53-58
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    • 2007
  • OFDM (orthogonal frequency division multiplexing) is an effective modulation technique for high speed transmission over fading channels. However, it has a high bit error rate in the receiver if there is an error on frame synchronization because of phase rotation. A coherent OFDM system has to acquire exact timing synchronization of fraction and integer sampling positions. When a sampling offset exist the performance of a receiver will be degraded severely. In this paper, we propose an algorithm that acquires the fractional sampling offset in OFDM systems. This scheme compares the channel impulse responses with the early and late sampled signals having 0.5 sample offset from the estimated sampling positions by correlation with the received and training samples. Its performance is verified by computer simulations in multipath channels.