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Yazar: Çırpan, Hakan Ali × WoS Q: Q3 ×

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  • Küçük Resim
    Yayın
    Maximum likelihood blind channel estimation for space-time coding systems
    (Hindawi Publishing Corporation, 2002-05) Çırpan, Hakan Ali; Panayırcı, Erdal; Çekli, Erdinç
    Sophisticated signal processing techniques have to be developed for capacity enhancement of future wireless communication systems, In recent years, space-time coding is proposed to provide significant capacity gains over the traditional communication systems in fading wireless channels. Space-time codes are obtained by combining channel coding, modulation, transmit diversity, and optional receive diversity in order to provide diversity at the receiver and coding gain without sacrificing the bandwidth. In this paper, we consider the problem of blind estimation of space-time coded signals along with the channel parameters. Both conditional and unconditional maximum likelihood approaches are developed and iterative solutions are proposed. The conditional maximum likelihood algorithm is based on iterative least squares with projection whereas the unconditional maximum likelihood approach is developed by means of finite state Markov process modelling. The performance analysis issues of the proposed methods are studied. Finally, some simulation results are presented.
  • Küçük Resim
    Yayın
    Maximum a posteriori multipath fading channel estimation for OFDM systems
    (Assoc Elettrotecnica Ed Elettronica Italiana, 2002-10) Panayırcı, Erdal; Çırpan, Hakan Ali
    In this paper, a non-data-aided maximum a posteriori (MAP) channel estimation technique for OFDM systems employing M-PSK modulation scheme is proposed. The technique requires a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve orthogonal expansion and estimates the complex channel parameters of each subcarriers iteratively in frequency domain using the Expectation-Maximization (EM) algorithm. Pilot symbols are employed to choose reliable initial values of the unknown channel parameters. An analytical expression is derived for the exact Cramer-Rao lower bound of the proposed MAP channel estimator. Moreover, robustness of estimator to changes in channel correlation and signal-to-noise ratio is also analyzed. The performance is presented in terms of the mean-square error and the uncoded symbol error rate for a system employing QPSK signaling. Computer simulations demonstrate that the performance of OFDM systems using coherent demodulation based on our channel estimation can be significantly improved.