We consider a practical cell-free massive multiple-input-multiple-output (MIMO) system with multi-antenna access points (APs) and spatially correlated Rician fading channels. The significant phase-shift of the line-of-sight component induced by user equipment movement is modeled randomly. Furthermore, we investigate uplink spectral efficiency (SE) maximum ratio (MR)/local minimum mean squared e...

We consider the problem of estimating, in the presence of model uncertainties, a random vector x that is observed through a linear transformation H and corrupted by additive noise. We first assume that both the covariance of x and the transformation H are not completely specified, and develop the linear estimator that minimizes the worst-case mean-squared error (MSE) across all possible covaria...

Signal to Noise Ratio (SNR) estimation of a received signal is an important and essential information for Orthogonal Frequency Division Multiplexing (OFDM) system. This is because in OFDM system, robustness in frequency selective channels can be achieved using adaptable transmission parameters. Therefore, to reckon these parameters, knowledge of SNR estimates obtained by channel state informati...

In this paper, we describe the channel estimation based on time domain channel statistics. Using a general model for a slowly fading channel, we present the MMSE and LS estimators. The mean square error and symbol error rate for a BPSK system is presented by means of simulation results. Depending upon estimator complexity, up to 4 dB in SNR can be gained over the LS estimator.

MMSE-FDE can improve the transmission performance of OFDM combined with time division multiplexing (OFDM/TDM), but knowledge of the channel state information and the noise variance is required to compute the MMSE weight. In this paper, a performance evaluation of OFDM/TDM using MMSE-FDE with pilot-assisted channel estimation over a fast fading channel is presented. To improve the tracking abili...

Cooperative networking plays an important role in wireless adhoc and sensor networks, in which the information from the source to the destination is relayed by intermediate nodes. In this paper, we propose OFDM-based all subcarrier and per subcarrier basis relay selection schemes. The relay selection is based on average signal to noise ratio (SNR) estimation. Data aided (DA) preamble based MMSE...