Yiling Wu

Publications (2)0.92 Total impact

• Article: Sampling Frequency Offset Estimation for Pilot-Aided OFDM Systems in Mobile Environment

  Yiling Wu, Yuping Zhao, Dou Li
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  ABSTRACT: In orthogonal frequency division multiplexing (OFDM) systems, most of the conventional sampling frequency offset (SFO) estimation methods work under the assumption of time-invariant or slow time-variant channels. In mobile environment, the time-variant channel significantly degrades the accuracy of SFO estimation. To solve the problem, we first analyze the properties of time-variant channels. If terminal moves within some tens of the wavelength of radio frequency (RF) signal, channel path delay almost remains unchanged. For most practical OFDM systems, our analysis indicates that channel path delay can be regarded as unchanged during the interval of some tens of OFDM symbols in time-variant channels. Based on the analysis, we propose a novel SFO estimation method for pilot-aided OFDM systems. Different from the conventional methods, the proposed method estimates SFO by detecting the variation of the symbol timing error caused by SFO. The detection is finished by implementing correlation between the channel impulse responses (CIRs) estimated by different OFDM symbols. Performance of the proposed method is simulated and compared with that of two conventional post-FFT methods. Numerical results show that, the proposed SFO estimation method performs better than the conventional methods not only in time-variant channels, but also at low SNRs and large residual carrier frequency offsets (CFOs). KeywordsSampling frequency offset (SFO)–Pilot-aided OFDM–Time-varying channel–Low SNR–Large residual carrier frequency offset (CFO)
  Wireless Personal Communications 05/2012; 62(1):215-226. · 0.46 Impact Factor
• Article: Channel Estimation for Pilot-Aided OFDM Systems in Single Frequency Network

  Yiling Wu, Yuping Zhao, Dou Li
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  ABSTRACT: In single frequency network (SFN), there exist some special long delay spread channels as well as conventional multipath channels. For pilot-aided orthogonal frequency division multiplex (OFDM) systems, channel estimation is usually accomplished by interpolation with pilots. However, few pilot sub-carriers exist within the coherent bandwidth of the long delay spread channels in SFN. In this case, conventional frequency domain interpolation methods cannot work properly. In a narrowband channel, this paper indicates that both the real and the imaginary parts of channel frequency response can be accurately approximated as a sine-wave with DC offset. For many practical pilot-aided OFDM systems, the bandwidth of the narrowband channel mentioned before is comparable with the interval between several adjacent pilot sub-carriers. Then this paper proposes a sine-wave based frequency domain interpolation method for the channel estimation of pilot-aided OFDM systems in SFN. As simulation results show, the proposed method performs well in the long delay spread channel, whereas the mismatched Wiener interpolation filter (WIF) estimates channel response inaccurately. Moreover, the proposed method gives accurate channel estimation in conventional multipath channels, especially for the systems which adopt high order modulations. KeywordsChannel estimation–Pilot-aided OFDM–Single frequency network (SFN)–Sine-wave based interpolation
  Wireless Personal Communications 04/2012; 62(1):227-245. · 0.46 Impact Factor