Robust Doppler Spread Estimation in the Presence of a Residual Carrier Frequency Offset

Abstract

Abstract-In high data-rate transmission systems, accurate Doppler spread estimation is a critical task for not only mobile velocity estimation, but also for optimal adaptive processing. It is known that the residual carrier frequency offset (CFO) which is inherent to the asynchrony between the communicating ends in a wireless link has a detrimental effect on the Doppler spread estimation. In this correspondence, we propose a new simple and accurate approach that copes with this issue by explicitly taking the CFO into account when estimating the Doppler spread. This new approach stems from the fact that the cross-correlation of the channel is a weighted summation of monochromatic plane waves (or an inverse Fourier transform of its power spectral density). It turns out that these plane waves are locally (as compared to the sampling rate) distributed around a main frequency which is nothing but the CFO. Using this property, we base our analysis on Taylor series expansions in addition to an observation temporal aperture to develop a two-ray spectrum approximate model for the Doppler spread estimation. We find that the Doppler spread is half of the frequency spacing between both rays which are located symmetrically around the CFO. Finally, we deduce new closed-form estimators for the Doppler spread and also for the CFO. These estimators are accurate and practical in environments with isotropic scattering where the channel power spectrum density (PSD) is symmetric. Simulations are provided to illustrate the advantages of the proposed method and its robustness to the CFO.Index Terms-Carrier frequency offset, Doppler spread, Doppler spread factor, maximum Doppler frequency, two-ray spectrum approximation.

Joint mean angle of arrival, angular and Doppler spreads estimation in macrocell environments

“…For the DS estimators, the temporal correlation function is exploited as in [3,8,13] and is defined by…”

“…The mean AoA is then obtained as for the Gaussian case (13). Using all the cross-correlation coefficients defined in (19) for two antenna couples (k, l) and (k, j), we obtain the following AS estimate:…”

“…As one can notice, only the cross-correlation matrix is used to jointly estimate the three parameters. Contrarily to the methods developed in [1,13], the proposed algorithm does not require the additive noise power estimation nor the eigenvalue decomposition of the correlation matrix, which reduces considerably the overall computational complexity. In the next section, we study both performance and complexity of our joint estimator.…”

“…The second one considers the ambiguity function [11], while the proposed algorithm in [12] uses the instantaneous frequency of the received signal. The two-ray (TR) approximation proposed in [13] offers a robust maximum DS estimation. It offers a closed-form expression and considers the presence of residual carrier frequency offset (CFO), which is closer to real-life scenarios.…”

“…In this work, we consider as benchmarks the TS approach [1] and the SRM algorithm [7] for the mean AoA and AS estimation, and the TR approach [13] and the ACF-based algorithm [8] for the maximum DS estimation. These recent works were chosen because they currently offer best trade-off between estimation accuracy and computational complexity.…”