Abstract
In higher time-varying fading channels, the signal quality of orthogonal frequency division multiplexing (OFDM) technique would be degraded relatively due to the occurrence of inter-carrier interference (ICI). To solve this problem, this paper firstly proposes a new design of time domain training sequence (TS) in the estimation of channel impulse response (CIR) for the TS-OFDM signal which can reduce the leakage of power spectrum density (PSD) at the outside of OFDM allocated frequency bandwidth with keeping higher CIR estimation accuracy. Secondly, this paper proposes a time domain equalization (TDE) method which can achieve better bit error rate (BER) performance with keeping lower computation complexity even in higher time-varying fading channels. The salient feature of the proposed TDE method is to employ a partial differentiation for the time domain CIR matrix for solving the maximum likelihood (ML) equation in which the time domain CIR matrix becomes a symmetric banded matrix. From this feature, a low-complexity parallel block inverse matrix algorithm can be employed in the calculation of inverse matrix in keeping the same accuracy as that of the direct inverse matrix calculation. This paper presents various computer simulation results to demonstrate the effectiveness of the proposed TDE method for the TS-OFDM signal as compared with conventional frequency domain equalization (FDE) methods under higher mobile environments.
Highlights
Orthogonal frequency division multiplexing (OFDM) has been employed as an efficient transmission technique in various wireless communications systems which require the reliable high data rate communications in the frequency-selective multipath fading channels [1]
OFDM has been adopted as the standard transmission technique in the digital audio broadcasting (DAB), digital video broadcasting (DVB), wireless local area network (WLAN), and the fourth-generation (4G) cellular systems [2]
In the proposed time domain equalization (TDE) method for the training sequence (TS)-OFDM with the parallel block inverse matrix algorithm, the removal of intersymbol interference (ISI) incurred both ends of data symbol from the TS given in (12) requires the complexity O[S2 − S]
Summary
Orthogonal frequency division multiplexing (OFDM) has been employed as an efficient transmission technique in various wireless communications systems which require the reliable high data rate communications in the frequency-selective multipath fading channels [1]. The salient feature of OFDM technique is to employ the guard interval (GI) for avoiding the intersymbol interference (ISI) with keeping the orthogonality among OFDM subcarriers even in multipath fading channels. In the OFDM signal under the static or lower mobile environments, the channel impulse response (CIR) can be assumed to be the time-invariant within one OFDM symbol period. From this fact, the simple frequency domain equalization (FDE) method with one-tap filter can be used to compensate the distortion of multipath fading. The CIR is no more constant even within one OFDM symbol period in higher time-varying fading channels which are experienced by the users on the high speed
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