• Title/Summary/Keyword: OFDM System

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Improvement of Power Efficiency of HPA by the PAPR Reduction and Predistorter in MIMO-OFDM (MIMO-OFDM에서 PAPR 저감 및 사전 왜곡기에 의한 HPA의 전력 효율 개선)

  • Trang Ngo Thi Thu;Kim Nam;Han Tae-Young
    • The Journal of the Korea Contents Association
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    • v.5 no.1
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    • pp.201-208
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    • 2005
  • Tn this paper, we evaluate the peak-to-average power ratio (PAPR) performance in a space-time block code (STBC) multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system using selected mapping (SLM) and partial transmit sequences (PTS) approaches. SLM and PTS methods are used to decrease the nonlinear distortion and to improve the power efficiency of the nonlinear high power amplifier(HPA) in the MIMO-OFDM system. In simulation result, when compared with the existing MIMO-OFDM system using QPSK, the PTS method reduces the PAPR about 5dB while the SLM method can reduce about 3.5 dB. Also, we find the BER performance of the MIMO-OFDM system with and without the predistorter in front of the HPA. When the predistorter is used, the input back-off (IBO) of 4 dB is required in the PTS method, and IBO of 6 dB in the SLM method to closely conform to the linear amplifier. If the method of improving the PAPR is not used, the value of IBO of 8 dB is required.

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Channel Modeling for UWB MB-OFDM System Considering RF Frequency Hopping (RF 주파수 호핑을 고려한 UWB Multi-Band OFDM 시스템 채널 모델 성형)

  • Noh, JungHo;Heo, Joo;Chang, KyungHi
    • Journal of Advanced Navigation Technology
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    • v.8 no.1
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    • pp.73-80
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    • 2004
  • In the case of Non-Line-of-Sight (NLOS), common telecommunication systems typically have Rayleigh distributed amplitude characteristics. However measurement result of Ultra Wideband (UWB) Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) system which is proposed as one of candidate standard in IEEE 802. 15. 3a for Wireless Personal Area Network (WPAN) shows that it has independent log normal fading in each cluster as well as in each ray within the cluster. Based on this clustering phenomenon observed, MB-OFDM channel model derived from Saleh-Valenzuela model with a couple of slight modifications. In this paper, channel remodeling for RF frequency hopping in MB-OFDM system is achieved, and performances of MB-OFDM system for each channel mode and data rate are verified using modified channel model.

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Nonlinear Characteristics Evaluation of the FBMC and UFMC System for the 5G Mobile Communication (5세대 이동통신을 위한 FBMC와 UFMC 시스템의 비선형 특성 평가)

  • An, Changyoung;Ryu, Heung-Gyoon
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.27 no.8
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    • pp.725-734
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    • 2016
  • Recently, novel candidate waveform techniques for spectral efficiency improvement was proposed in order to satisfy key performance indicators(KPIs) of 5th generation(5G) mobile communication. Multi-carrier based universal filtered multi-carrier(UFMC) and filter bank multi-carrier(FBMC) are very famous as 5G candidate waveform techniques. Also, weighted orthogonal frequency division multiplexing (W-OFDM) that has low-complexity is receiving the spotlight slowly. In this paper, firstly, we describe a basic OFDM system. And then, we also describe UFMC, FBMC, and W-OFDM system. Next, we evaluate and analyze spectrum and BER performance of these systems under the nonlinear high power amplifier(HPA) environment. As simulation results, spectrum characteristic and BER performance of UFMC, FBMC, and W-OFDM are similar to each other. Therefore, under the nonlinear HPA environment, W-OFDM system is more advantageous because W-OFDM system uses a simple time-domain windowing technique and has similar characteristics to the others.

OFDM system using adaptive code-rate for each sub-carrier (적응부호율 기법을 부반송파별로 적용한 OFDM 시스템)

  • Park Dong chan;Kim Suk chan
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.30 no.4C
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    • pp.200-206
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    • 2005
  • Adaptive transmission techniques can improve the performance of wireless communication system by adaptively changing the transmission parameter such as modulation, code-rate, and power according to the channel state. For orthogonal frequency division multiplexing (OFDM) system, the adaptive transmission techniques can be applied to each subcarrier unit. In this paper, we consider the adaptive code-rate OFDM system in which optimal code-rate is applied to each subcarrier according to the subchannel state. Performance analysis show that $3\sim6$dB gain of SNR or up to $30\sim50\%$ increase of data rate are achieved in the condition of bit error rate $10^{-6}$.

A Comparative Study on the Impulsive Noise Mitigation Algorithms for Orthogonal Frequency Division Multiplexing Systems (직교 주파수분할다중화 시스템을 위한 충격성 잡음 완화 알고리즘에 대한 비교 연구)

  • Ma, Shuang;Kang, Seog Geun
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.18 no.5
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    • pp.1051-1060
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    • 2014
  • In this paper, performance of an orthogonal frequency division multiplexing (OFDM) system in an impulsive noise environment is analyzed. Here, it is verified that performance of the OFDM system with window nonlinearity, which is one of the impulsive noise mitigation algorithms, is dependent on the over-sampling rate and the size of window. With respect to the variation of those parameters, we also provide an appropriate region of threshold values that control amplitudes of the sampled waveform of received signals. As a result, a new combination of parameters which improves error performance of OFDM system in an impulsive noise environment as compared to the previously reported parameters is presented.

An Analysis of Trellis-Coded Orthogonal Frequency Division Multiplex over Frequency-Selective Fading Channel (주파수선택성 페이딩을 갖는 통신로에 격자부호 직교주파수분할 다중통신방식의 성능 분석)

  • Suh, Heejong;Zhang, Ke
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.41 no.11
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    • pp.33-38
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    • 2004
  • In this paper, we review a trellis-coded orthogonal frequency division multiplex (TC-OFDM) system, which combines OFDM with trellis-coded modulation, for overcoming the frequency selective and multipath fading of time dispersive channels. We simulate and analyse the BER performance of rate 2/3 trellis coded 8DPSK-OFDM over time dispersive channels. Design of the trellis codes at different carrier numbers of OFDM is discussed. Results show that TC-OFDM system can provide 6 dB coding gain at a BER of 10$^{-3}$ compared with OFDM system without coding.

Performance analysis of MIMO-OFDM systems with adaptive beamformer (다중 사용자 환경에서 적응 빔 형성기를 가진 MIMO-OFDM 시스템의 성능 분석)

  • Kim, Chan-Kyu
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.44 no.9
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    • pp.1-8
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    • 2007
  • In this paper, the new beamforming is proposed for an orthogonal frequency division multiplexing(OFDM) system with multi-input multi-output(MIMO). Through the proposed Pre-FFT beamforming technique for MIMO-OFDM, the multibeams are formed toward each multi-transmitter antenna of the desired user. The proposed beamforming for MIMO-OFDM can reduce cochannel interference and get diversity gain in the multi-user environment. Therefore, the performance of MIMO-OFDM system is very improved. BER performance improvement of the proposed approach is investigated through computer simulation by applying it to MIMO-OFDM system in the multi-user environment.

IS-OFDM performance analysis for narrow band interference channel (협대역 간섭 채널환경에서 IS-OFDM 성능 분석)

  • 강현정;이정재
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • pp.119-123
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    • 2003
  • In this paper, a new OFDM scheme, IS-OFDM(Interference Suppressing Orthogonal Frequency Division Multiplexing), which has the capabilities of suppressing narrow-band interference for wide-band wireless communication systems, is introduced. This IS-OFDM system is composed of the parallel stages of ordinary OFDM, and each sub-carrier contains all of the transmitted symbols. Using Hadamard sequences, the transmitted information symbols in the same sub-carriers are separated from the other sub-carriers in the receiver. After analyzing and evaluating the performance of IS-OFDM system using Monte-Carlo simulation, the effective improvements of performance in IS-OFDM compare favorably with that of a conventional OFDM system in a narrow-band channel, is shown.

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PAPR reduction effects in the OFDM by the modified QPSK signal mapping method (OFDM 시스템에서 변형된 QPSK 신호 매핑 방법에 의한 PAPR 감소 효과)

  • 성백민;이우재;주창복
    • Journal of the Institute of Convergence Signal Processing
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    • v.3 no.2
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    • pp.58-63
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    • 2002
  • One of the important problems of OFDM system is the large PAPR of the output signal, which can result the significant signal distortion in presence of nonlinear amplifiers. To reduce the PAPR, we use fundamentally the level clipping and propose the modified mapping/demapping method for effective reducing the PAPR of the OFDM signals with level clipping. We can significantly improve the BER performance characteristics for the OFDM system. We discussed, through extensive computer simulations, the effects of level clipping and modified mapping/demapping method on the performance of OFDM system including the trade off between bandwidth expansion and BER performance and between bandwidth efficiency and BER performance.

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Linearization of OFDM signal using Predistorter (OFDM 신호의 사전 왜곡제거기를 이용한 비선형 왜곡보상)

  • 신은영;방성일
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.41 no.2
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    • pp.9-18
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    • 2004
  • OFDM is a special case of multicarrier transmission, where a high-rate datastream is transmitted over a number of lower rate subcarriers. In this paper, the structure of ORM system is studied, and causes of inter carrier interference (ICI) are analyzed. Based on analysis, this paper shows a technique to prevent a distortion due to nonlinearity of high power amplifier. The proposed scheme is a predistorter(PD) for high power amplifier linearization in OFDM system. This is verified by comparing BER characteristics of OFDM system, between used PD and not used PD, and superiority is shown by comparing BER characteristics of OFDM system, between used the proposed PD and used some other PDs.