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    Low Complexity Equalization Method for ZP-OFDM under Highly Mobile Environments
    (2020-02-01)
    Tanangsanakool, Saha
    ;
    Reangsuntea, Pongsathorn
    ;
    Mori, Kazuo
    ;
    Boonsrimuang, Pisit
    Many Interferences from multipath fading channels in the mobile channels, there are many types of research trying to compensate for such interferences. The Zero-padded OFDM (ZP-OFDM) is a popular method that has much attention as an efficient technique to improve the performances. In the high-speed mobile channel, the Doppler frequency destroyed orthogonality among subcarriers and inter-carrier interference (ICI), It would degrade the bit error rate (BER) performance. We proposed both equalization (TDE) method and CIR estimation with less computation complexity for the ZP-OFDM signal that can solve this problem. The salient feature of our proposed method is using a training sequence (TS) instead of using Zero-padded which enables for estimation of CIR. And we show that the proposed method shows the less computational complexity when compared with the conventional frequency-domain equalization, the proposed TDE method employs an iterative solution instead of using the direct inverse matrix method. We validate the proposed methods presented by computer simulations under highly mobile environments. The simulation results show a comparison of the effectiveness of the proposed TDE method and conventional TDE methods.
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    Low-complexity based TDE Method for OFDM signal in higher time-varying fading channels
    (2020-01-01)
    Tanangsanakool, Saha
    ;
    Reangsuntea, Pongsathorn
    ;
    Mori, Kazuo
    ;
    Boonsrimuang, Pisit
    Orthogonal Frequency Division Multiplexing (OFDM) signal would be damaged significantly by inter-carrier interference (ICI) in higher time-varying fading channels. The ICI leads to fatal degradation of bit error rate (BER) performance due to the loss of orthogonality among subcarriers. To solve this problem, this paper proposes a high accuracy time-domain channel impulse response (CIR) estimation method and low-complexity based time-domain equalization (TDE) method for solving the simultaneous equations instead of using an inverse matrix calculation which can achieve better BER performance and lower computation complexity even in higher time-varying fading channels. The salient features of proposed method are to employ a time-domain training sequence (TS) in the estimation of channel impulse response (CIR) instead of using pilot subcarriers in the frequency domain and to employ the time domain equalization (TDE) method with maximum likelihood (ML) estimation instead of using a conventional frequency domain equalization (FDE) method. This paper also proposes a low-complexity iterative method for solving the simultaneous equations instead of using an inverse matrix calculation, which remains the computation complexity up to 7.8% of inverse matrix calculation with the same BER performance but achieves the BER performance when compared with the conventional method. This paper presents various simulation results in higher time-varying fading channels (vehicle speed ≈ 381 km/hrs) to demonstrate the effectiveness of the proposed method as compared with conventional FDE and TDE methods.
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    Channel Estimation and Equalization Methods for ZP-OFDM under Highly Mobile Environments
    (2019-04-29)
    Tanangsanakool, Saha
    ;
    Reangsuntea, Pongsathorn
    ;
    Mori, Kazuo
    ;
    Boonsrimuang, Pisit
    Zero-Padded OFDM (ZP-OFDM) has been attracted a lot of attention as an efficient technique to improve the performance in severe multipath fading channels. Many works were devoted to the equalization method for ZP-OFDM in quasi-static channel model. However, an inter-carrier interference (ICI) which occurred under highly mobile environments would be destroyed orthogonality among subcarriers and causes the degradation of bit error rate (BER) performance due to the time domain channel impulse responses (CIRs) are assumed to be constant over one OFDM symbol. The time domain equalization (TDE) method in conjunction with a time domain CIR estimation method is proposed to solve this problem for the ZP-OFDM signal in the time domain. The advantage of the proposed method is to apply a training sequence (TS) instead of using ZP which enables for estimation of CIR. And also to reduce computational complexity, the proposed method is employed time domain equalization based on the minimum mean squared error (MMSE-TDE) instead of using the conventional frequency domain equalization based on MMSE (MMSE-FDE) method. This paper presents various simulation results under highly mobile environments to demonstrate the effectiveness of proposed TDE method as compared with conventional demodulation methods.
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    Iterative based ML demodulation method for OFDM signal under higher mobile environments
    (2015-07-01)
    Reangsuntea, Pongsathorn
    ;
    Hourai, Mio
    ;
    Mori, Kazuo
    ;
    Boonsrimuang, Pisit
    ;
    Kobayashi, Hideo
    Orthogonal Frequency Division Multiplexing (OFDM) signal would be damaged significantly by inter- carrier interference (ICI) in higher time-varying fading channels which leads fatal degradation of bit error rate (BER) performance due to the loss of orthogonality among subcarriers. To solve this problem, this paper proposes an iterative based maximum likelihood demodulation (MLD) method which can achieve better BER performance with lower computation complexity even in higher time-varying fading channels. The features of proposed method are to employ a time domain training sequence (TS) in the estimation of channel impulse response (CIR) instead of using pilot subcarriers in the frequency domain and to employ a time domain equalization (TDE) method with a maximum likelihood (ML) estimation instead of using a conventional frequency domain equalization (FDE) method. This paper also proposes a low-complexity iterative method for solving the simultaneous equations in the MLD method instead of using an inverse matrix calculation. This paper presents various simulation results in higher time-varying fading channels to demonstrate the effectiveness of proposed method as comparing with the conventional frequency domain equalization method.