• Title/Summary/Keyword: Multiple Carrier Frequency Offset

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A Robust OFDMA Channel Estimation Against Imperfect Synchronization (불완전 동기 환경에 강인한 OFDMA 채널 추정기법)

  • Chae Soo-Jin;Kim Eun-Ju;Kim Nak-Myeong
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.30 no.8A
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    • pp.649-655
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    • 2005
  • We propose a robust channel estimation method against imperfect synchronization in orthogonal frequency division multiple access (OFDMA) downlink systems. We address time and frequency synchronization, and the channel estimation at the same time, and try to minimize the error propagation from the time and frequency synchronization steps into the chailnel estimation. The simulation results show that the proposed channel estimation method outperforms the conventional algorithms by about 3dB, and circumvents the problem of mismatch among the synchronization tasks.

Uplink Frequency Offset Compensation Scheme for High-Speed Moving Terminals (고속 이동체를 위한 상향링크 주파수 옵셋 보상 방법)

  • Choi, Sung-woo;Kim, Ilgyu;Ahn, Jae Min
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.40 no.9
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    • pp.1699-1709
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    • 2015
  • Moving terminals like high-speed-train undergo high Doppler frequency shift, and this leads to carrier frequency offsets that have to be compensated to avoid degradation of communication performance. In multiple access mechanism like OFDMA, base-stations need complex hardware to compensate the uplink frequency offset. In this paper, we propose a method, which can reduce burden of the base-station and makes frequency offset estimation and compensation simple. This method contains transmitting new synchronization signal, estimating frequency offsets in base-station, transmitting feedback information to terminal, and compensating the offset in uplink transmission. Simulation results show the proposed method operates well in high Doppler frequency shift conditions of 500 km/h which is the requirements of 5G mobile communication.

An Enhanced Scheme with CFO and SFO in OFDMA system (OFDMA 시스템에서 SFO와 CFO 저감 기법에 관한 연구)

  • Lee, Young-Gwang;Lee, Kyu-Seop;Choi, Gin-Kyu
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.14 no.1
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    • pp.1-6
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    • 2014
  • Recently, orthogonal frequency-division multiplexing(OFDM), with clusters of subcarriers allocated to different subscribers(often referred to as OFDMA), has gained much attention for its ability in enabling multiple-access wireless multimedia communications. In such systems, carrier frequency offsets (CFOs) can destroy the orthogonality among subcarriers. And the mismatch in sampling frequencies between transmitter and receiver can lead to serious degradation due to the loss of orthogonality between the subcarriers. As a result, multiuser interference (MUI) along with significant performance degradation can be induced. In this paper, we present a scheme to compensate for the SFOs and CFOs at the base station of an OFDMA system. A novel sampling frequency offset estimation algorithm is proposed, which is based on the repetition of a symbol at the communication start-up. Then, circular convolutions are employed to generate the interference after the discrete Fourier transform processing, which is then removed from the original received signal to increase the signal to interference power ratio(SIR). Simulation result shows that the proposed scheme can improve system performance.

Turbo MIMO-OFDM Receiver in Time-Varying Channels

  • Chang, Yu-Kuan;Ueng, Fang-Biau;Jhang, Yi-Wei
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.12 no.8
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    • pp.3704-3724
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    • 2018
  • This paper proposes an advanced turbo receiver with joint inter-carrier interference (ICI) self cancellation and channel equalization for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems over rapidly time-varying channel environment. The ICI caused by impairment of local oscillators and carrier frequency offset (CFO) is the major problem for MIMO-OFDM communication systems. The existing schemes (conjugate cancellation (CC) and phase rotated conjugate cancellation (PRCC)) that deal with the ICI cancellation and channel equalization can't provide satisfactory performance over time-varying channels. In term of error rate performance and low computational complexity, ICI self cancellation is the best choice. So, this paper proposes a turbo receiver to deal with the problem of joint ICI self cancellation and channel equalization. We employ the adaptive phase rotations in the receiver to effectively track the CFO variations without feeding back the CFO estimate to the transmitter as required in traditional existing scheme. We also give some simulations to verify the proposed scheme. The proposed schene outperforms the existing schemes.

Mitigating Techniques for OFDMA System Based on SDD (SDD 기반 OFDMA 시스템을 위한 간섭 완화 기법)

  • Park, Chang-Hwan;Ko, Yo-Han;Kim, Moo-Chul;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.34 no.8C
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    • pp.742-749
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    • 2009
  • In this paper, we propose mitigation techniques using time-domain shortening filter (TSF) and frequency-domain shortening filter (FSF) to overcome inter-block interference (IBn and inter-carrier interference (ICn due to the time difference of arrival (TDoA) and carrier frequency offset (CFO) between downlink and uplink signals from access point (AP) and subscriber station (SS) in synchronous digital duplexing (SDD)/orthogonal frequency division multiple access (OFDMA) systems for indoor wireless communication. The proposed TSF and FSF maximize SIR for shortening in time (SIRST) and SINR for shortening in frequency (SINRSF), respectively, by using channel impulse responses and timing information among stations, obtained from mutual ranging procedure. It is verified by computer simulation that the proposed TSF and FSF reduce effectively the effects of IBI and ICI in the SDD/OFDMA systems.

ICI and Compensation Algorithm against Frequency Offset and Phase Noise in SC-FDMA System with Comb Type Pilot (Comb Type 파일럿을 갖는 SC-FDMA에서 주파수 옵셋과 위상 잡음에 의한 ICI와 보상 알고리즘)

  • Ryu, Sang-Burm;Ryu, Heung-Gyoon
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.21 no.4
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    • pp.399-407
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    • 2010
  • SC-FDMA system uses DFT-spreading method for reducing the PAPR of OFDM signal, which improves the power efficiency. Block type pilot is used in SC-FDMA system. However, there are ICI due to the inevitable phase noise and frequency offset that can be generated from the Doppler frequency and inaccuracy between the transceiver oscillators. This ICI definitely degrades the BER performance. To overcome this problem and estimate the channel efficiently, we like to propose ICI compensation algorithm for the SC-FDMA system with comb type pilot. SLM method is additionally included for the PAPR reduction when pilot is assigned in comb type. Finally, it is confirmed that the ICI due to the phase noise and frequency offset is efficiently compensated by the suggested algorithm.

A Multicarrier CDMA System for Multipath and Doppler Diversity (다중경로 및 도플러 다이버시티를 위한 멀티캐리어 CDMA 시스템)

  • Park Hyung-Kun
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.42 no.1
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    • pp.29-37
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    • 2005
  • One of the principal disadvantages of multicarrier modulation technique is the sensitivity to the frequency offset introduced by Doppler shift. This frequency offset introduces inter-carrier interference (ICI) among the multiplicity of carriers in the multicarrier modulated signal. However, Doppler spread induced by temporal channel variations can Provide another means for diversity. In this paper, we propose a modified multicarrier code division multiple access (CDMA) system to exploit Doppler diversity as well as multipath diversity. The key work of our framework is a canonical time-frequency-based decomposition of the mobile wireless channel into series of independent fading channel. The decomposition naturally leads to a time-frequency generalization of the Rake receiver that exploits both multipath and Doppler diversity.

A Distributed Frequency Synchronization Technique for OFDMA-Based Mesh Networks Using Bio-Inspired Algorithm (Bio-inspired 알고리즘을 이용한 OFDMA 기반 메쉬 네트워크의 분산 주파수 동기화 기법)

  • Yoo, Hyun-Jong;Lee, Mi-Na;Cho, Yong-Soo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.37B no.11
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    • pp.1022-1032
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    • 2012
  • In OFDMA-based wireless mesh networks, synchronization of carrier frequencies among adjacent nodes is known to be difficult. In this paper, a distributed synchronization technique is proposed to solve the synchronization problem in OFDMA-based wireless mesh networks by using the bio-inspired algorithm. In the proposed approach, carrier frequencies of all nodes in a mesh network are converged into one frequency by locally synchronizing the frequencies of adjacent nodes. It may take a long time to be converged in some topologies since the convergence characteristic of carrier frequencies in a mesh network may vary depending on the size of the network and deployment of nodes. It is shown that fast frequency synchronization, not heavily depending on the topology, can be achieved through the proposed algorithm with an adjustable weight.

Analysis and Compensation of STO Effects in the Multi-band OFDM Communication System of TDM Reception Method (TDM 수신 방식의 멀티 대역 OFDM 통신 시스템에서 STO 특성 분석 및 보상)

  • Lee, Hui-Kyu;Ryu, Heung-Gyoon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.5A
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    • pp.432-440
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    • 2011
  • For the 4th generation mobile communication, LTE-advanced system needs the broad frequency band up to 100MHz for providing the data rate of maximum 1Gpbs. However, it is very difficult to secure the broad frequency band in the current frequency allocation situation. So, carrier aggregation was proposed as the solution, in which several fragmented frequency bands are used at the same time. Basically, multiple parallel receivers are required to get the information data from the different frequency bands but this conventional multi-chain receiver system is very inefficient. Therefore, in this paper, we like to study the single chain system that is able to receive the multi-band signals in a single receiver based on the time division multiplexing (TDM) reception method. This proposed TDM receiver efficiently manage to receive the multi-band signals in time domain and handle the baseband signals with one DSP board. However, the serious distortion could be generated by the sampling timing offset (STO) in the TDM-based system. Therefore, we like to analyze STO effects in the TDM-based system and propose a compensation method using estimated STO. Finally, it is shown by simulation that the proposed method is appropriate for the single chain receiver and show good compensation performance.

Joint Blind Parameter Estimation of Non-cooperative High-Order Modulated PCMA Signals

  • Guo, Yiming;Peng, Hua;Fu, Jun
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.12 no.10
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    • pp.4873-4888
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    • 2018
  • A joint blind parameter estimation algorithm based on minimum channel stability function aimed at the non-cooperative high-order modulated paired carrier multiple access (PCMA) signals is proposed. The method, which uses hierarchical search to estimate time delay, amplitude and frequency offset and the estimation of phase offset, including finite ambiguity, is presented simultaneously based on the derivation of the channel stability function. In this work, the structure of hierarchical iterative processing is used to enhance the performance of the algorithm, and the improved algorithm is used to reduce complexity. Compared with existing data-aided algorithms, this algorithm does not require a priori information. Therefore, it has significant advantage in solving the problem of blind parameter estimation of non-cooperative high-order modulated PCMA signals. Simulation results show the performance of the proposed algorithm is similar to the modified Cramer-Rao bound (MCRB) when the signal-to-noise ratio is larger than 16 dB. The simulation results also verify the practicality of the proposed algorithm.