Blind Joint Estimation for OFDM Time-Frequency Parameters
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Blind Joint Estimation for OFDM Time-Frequency Parameters Mingqian Liu · Bingbing Li · Qinghai Yang · Ningjie Tang
Received: 27 April 2012 / Revised: 24 April 2013 © Springer Science+Business Media New York 2013
Abstract A novel blind joint estimation of orthogonal frequency division multiplexing (OFDM) time-frequency parameters is conceived in low signal-to-noise ratio (SNR) and multipath channel conditions. The oversampling factor is estimated by employing a new-designed cosine roll-off filter whose cut-off frequency is considered as the approximation of the sampling signal’s spectrum. The useful data length is estimated by means of the improved varying time-delay autocorrelation, and its final estimated value is defined as a power of 2, which has the minimum Euclidean distance with the peak position. The estimated useful data length is further utilized to refine the previous estimation of the oversampling factor. The bandwidth of OFDM signals is estimated by adopting the spectrum approximation method based on the estimated time-parameters. The simulation results demonstrate that the proposed method is robust to noise and multipath channel conditions without any requirement of a prior knowledge. Keywords OFDM · Parameters estimation · Oversampling factor · Useful data length · Bandwidth
M. Liu () · B. Li · Q. Yang · N. Tang State Key Laboratory of Integrated Service Networks, Xidian University, Xi’an 71007, China e-mail: [email protected] B. Li e-mail: [email protected] Q. Yang e-mail: [email protected] N. Tang e-mail: [email protected]
Circuits Syst Signal Process
1 Introduction Orthogonal frequency division multiplexing (OFDM) has been considered as one of the key transmission techniques for the fourth-generation mobile communication systems. The estimation of time-frequency parameters is the premier step for detection of OFDM signals in non-cooperative communication systems. The time-domain parameters of OFDM signals include the oversampling factor, the cyclic-prefix (CP) length, the useful data length and the whole signal duration. The frequency-domain parameters include the number of useful subcarriers and the bandwidth. Typically, the estimation of frequency-domain parameters is based on the prior time-domain parameters. The blind joint estimation of time-frequency-domain parameters is considered in this paper. Currently, a few approaches have been proposed to extract time-domain parameters of OFDM signals by virtue of the autocorrelation and the cyclic autocorrelation characteristics. The cyclic frequency detection method [10] and the spectrum approximation method with ideal low-pass filter [9] were proposed for estimating the oversampling factor. Based on the detection of the peak value or peak length, an autocorrelation method was proposed in [5] and [2]. However, the above results have poor performance under the low signal-to-noise ratio (SNR) and multipath fading channels conditions. In contrast to the autocorrelation method, the cyclic autocorrelation method has a better performanc
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