Projection wavelet weighted twin support vector regression for OFDM system channel estimation
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Projection wavelet weighted twin support vector regression for OFDM system channel estimation Lidong Wang1 · Yimei Ma1 · Xudong Chang1 · Chuang Gao1 · Qiang Qu1 · Xuebo Chen1
© The Author(s) 2020
Abstract In this paper, an efficient projection wavelet weighted twin support vector regression (PWWTSVR) based orthogonal frequency division multiplexing system (OFDM) system channel estimation algorithm is proposed. Most Channel estimation algorithms for OFDM systems are based on the linear assumption of channel model. In the proposed algorithm, the OFDM system channel is consumed to be nonlinear and fading in both time and frequency domains. The PWWTSVR utilizes pilot signals to estimate response of nonlinear wireless channel, which is the main work area of SVR. Projection axis in optimal objective function of PWWRSVR is sought to minimize the variance of the projected points due to the utilization of a priori information of training data. Different from traditional support vector regression algorithm, training samples in different positions in the proposed PWWTSVR model are given different penalty weights determined by the wavelet transform. The weights are applied to both the quadratic empirical risk term and the first-degree empirical risk term to reduce the influence of outliers. The final regressor can avoid the overfitting problem to a certain extent and yield great generalization ability for channel estimation. The results of numerical experiments show that the propose algorithm has better performance compared to the conventional pilot-aided channel estimation methods. Keywords Twin support vector regression · Wavelet transform · Unconstrained minimization · Channel estimation · OFDM
1 Introduction Recently, with the rapid development of wireless communication technology, the demand for high-speed data transmission has increased rapidly. Broadband communication is an effective technology to provide high data rate transmission. However, the increase of bandwidth will result in less sampling period than channel delay spread, especially in multipath scenarios, which gives rise to frequency-selective channels. Carrier frequency-offset due to the oscillators’ mismatch, together with high relative mobility between the transmitter * Lidong Wang [email protected] Extended author information available on the last page of the article
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and receiver cause the transmission channel to change rapidly in time, which is referred to as the time-selectivity of the channel. The channel with both the frequency-selectivity and the time-selectivity is called doubly-selective in wireless communications. Orthogonal frequency division multiplexing (OFDM) is an attractive multi-carrier modulation scheme, which divides the whole bandwidth into multiple overlapping narrowband subchannels to reduce the symbol rate. OFDM has the advantages of high spectral efficiency and simple structure of single tap equalizer. The bandwidth of each subcarrier in OFDM systems is small enough that each subcarrie
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