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Yayın Maximum likelihood blind channel estimation for space-time coding systems(Hindawi Publishing Corporation, 2002-05) Çırpan, Hakan Ali; Panayırcı, Erdal; Çekli, ErdinçSophisticated 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.Yayın Adaptive identification and equalization of magnetic recording channels(Wiley-Blackwell, 1998-03) Özden, Mehmet Tahir; Kayran, Ahmet Hamdi; Panayırcı, ErdalA new RLS adaptive Volterra filter is presented. The nonlinear filtering problem is transformed into an equivalent multichannel, but linear, filtering problem. The multichannel input signal is completely orthogonalized using sequential processing multichannel lattice stages. Thus, a fast convergent, highly modular and, simple filter with good numerical properties is designed. In the identification of magnetic recording channels, the filter identifies the channels directly and parameters for the channel nonlinearity are quantified simultaneously. In the equalization of magnetic channels, the most effective equalizer length can be assigned dynamically.Yayın Maximum a posteriori multipath fading channel estimation for OFDM systems(Assoc Elettrotecnica Ed Elettronica Italiana, 2002-10) Panayırcı, Erdal; Çırpan, Hakan AliIn 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.Yayın Non-data-aided ML carrier frequency and phase synchronization in OFDM systems(Wiley-Blackwell, 2001-04) Panayırcı, Erdal; Georghiades, Costas N.; Huq, Ayesha T.In this paper non-data-aided(NDA), maximum likelihood(ML) algorithms are derived for the carrier frequency and phase offset, separately, for OFDM systems employing M-PSK modulation scheme. NDA ML estimation algorithm for frequency offset estimation exploits the redundant information contained in the cyclic prefix preceeding the OFDM symbols, thus reducing the need for pilots. Its mean-squared performance is obtained analytically and compared with simulation results. It is observed that the resulting algorithm generates very accurate estimation even when the offset is high. It is also shown that the frequency estimator may be used in a tracking mode. The ML algorithm derived for the carrier phase estimation is also a non-data-aided(NDA) and maximizes the low SNR limit of the likelihood function averaged over M-PSK signal constellation. It is shown that for sufficiently small SNR the ML phase estimator obtained reduces to the familiar Mth order power synchronizer which belongs to the class of NDA feedforward carrier synchronizers introduced earlier in the literature. Its mean-squared performance is obtained analytically and compared with simulation results. We observe that the resulting algorithm generates very accurate estimation even when the phase offset is high, that the self noise is absent and the performance of the algorithm is basically the same as the Cramer-Rao bound for moderate to high SNR. Finally we note that the error variance derived for the mean-squared performance of this NDA ML synchronizer is an extension of the approximate variance formula appeared in Reference 20,equation(14) for M-PSK.Yayın Adaptive Volterra channel equalisation with lattice orthogonalisation(Institution of Engineering and Technology, 1998-04) Özden, Mehmet Tahir; Kayran, Ahmet Hamdi; Panayırcı, ErdalThe authors present a new recursive least-squares adaptive nonlinear equaliser based on Volterra series expansion. The main approach is to transform the nonlinear equalisation problem into an equivalent multichannel, but linear, equalisation problem. Then the multichannel input signal is completely orthogonalised using sequential processing multichannel lattice stages. With the complete orthogonalisation of the input signal, only scalar operations are required, instability problems owing to matrix inversion are avoided, and good numerical properties are achieved. Avoidance of matrix inversion and vector operations reduce the complexity considerably, and make the filter highly modular and suitable for VLSI implementation. Several experiments demonstrating the performance under different channel distortion and channel noise conditions are also included in the paper.Yayın Analysis of self-noise in a clock recovery system with a high-order nonlinearity(IEEE-INST Electrical Electronics Engineers Inc, 2003-11) Panayırcı, ErdalThis correspondence presents a new technique to compute efficiently the spectra of the in-phase (I) and quadrature (Q) components as well as the cross-spectrum of the in-phase and quadrature (I-Q) components of self-noise appearing at the output of the zero-memory, high-order nonlinear (NL) device employed in a clock recovery system. It is known that these spectra play an important role in the phase jitter performance of the clock regenerator. The results are very general and applicable to many cases of practical interest. Numerical examples and computer simulations provided show that the new approach yields very accurate results and is much faster than the usual computer simulation method. in addition, we give a theorem to show that for the signal shapes having linear phase, the cross-power spectrum of self-noise is zero. We also provide a general expression for the jitter variance of the generated clock signal in terms of the power spectra of self-noise in-phase and quadrature components. It is shown that the cross-power spectrum will also contribute to timing jitter if the selected signaling shape does not have any symmetry in time domain. The optimal periodic sampling instants Eire determined by the axis crossings of the clock signal in the positive direction. The axis is set at a level whereby the jitter variance takes on a minimum value. It is concluded that when the cross-power spectrum is zero for all frequencies then the optimal sampling instants occur at the positive zero crossings of the clock signal and only the Q noise contributes to the timing jitter performance.Yayın On the performance of trellis coded M-PSK systems over Rician fading channels with phase jitter(Assoc Elettrotecnica Ed Elettronica Italiana, 2001-02) Uysal, Murat; Aygölü, Hasan Ümit; Panayırcı, ErdalIn this paper, the performance of trellis coded M-PSK systems is investigated operating over Rician fading channels with phase jitter. Thus the results reflect not only the degradation due to the effect of fading on the amplitude of the received signal, but also the impairment caused by the noisy carrier reference, which is usually neglected by the assumption of perfect phase tracking at the receiver. Analytical upper bounds on pairwise error probability for Rician fading with phase jitter are derived using Chernoff bounding technique in both cases where channel state information is available or not. The bit error probability performances are evaluated based on the modified transfer function approach. The numerical examples clearly demonstrate the error performance degradation due to both amplitude fading and phase noise process.
