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    Item type:Publication,
    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.
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    Time domain channel estimation method for uplink OFDMA system
    (2015-06-16)
    Mata, Tanairat
    ;
    Hourai, Mio
    ;
    Mori, Kazuo
    ;
    Kobayashi, Hideo
    ;
    Boonsrimuang, Pisit
    Orthogonal Frequency Division Multiple Access (OFDMA) is considered as one of promising wireless access techniques which can accommodate multiple users flexibly and efficiently. In the uplink OFDMA system, it is required to estimate all users' channel frequency responses (CFRs) simultaneously which are used in the equalization for the data information at the base station (BS). To realize this requirement, the Discrete Fourier Transform interpolation based channel estimation (DFTI-CE) method was proposed in which all users transmit one scattered pilot symbol to the BS at the same time. The DFTI-CE method can achieve higher estimation accuracy for all users' CFRs only when the number of FFT points is equal to the number of data subcarriers which corresponds to the Nyquist rate. However the CFR estimation accuracy would be degraded in the actual OFDM system at the non-Nyquist rate in which null subcarriers (zero padding) are added at both ends of OFDM data subcarrier to reject the aliasing occurring at the output of digital to analogue (D/A) converter. To solve this problem, this paper proposes a time domain channel estimation (TD-CE) method which can achieve higher estimation accuracy even at the non-Nyquist rate. This paper presents various simulation results for the uplink OFDMA system in the time-varying fading channels to demonstrate the effectiveness of proposed estimation method.