This work proposes a novel pilot structure (PS) to improve channel estimation (CE) in massive multiple-input multiple-output filter bank multi-carrier (mMIMO-FBMC) communications using offset quadrature amplitude modulation (OQAM). Accurate CE is essential to fully benefit from the corresponding spectral efficiency (SE) advantages and robustness against dispersive channels. Unlike orthogonal frequency division multiplexing (OFDM), FBMC/OQAM shows only real-field orthogonality. Therefore, corresponding signals suffer from intrinsic interference, motivating the use of alternative CE techniques. Furthermore, typical CE methods for mMIMO-FBMC systems require large training overheads, particularly for a large number of users or for flat-fading channel conditions over each subcarrier band. To address these issues, this paper proposes a PS that reduces the training overhead by interleaving user pilots in frequency while using conventional OFDM CE techniques, particularly the least squares (LS) method in the context of single-user (SU) and multi-user (MU) scenarios. Analytical expressions for the mean square error (MSE) and the Cramer-Rao lower bound (CRLB) are derived for the estimation technique considering the proposed PSs. Furthermore, performed simulations over the 5G QuaDRiga channel show that the proposed PS improves SE while delivering optimal performance in both preamble-based MU-mMIMO and SU systems.

Massive multiple-input multiple-output (mMIMO) systems and filtered multi-carrier waveforms have recently emerged as hot research topics in next-generation wireless networks. This paper extends the use of Overlap-Save Filter Bank Multi-Carrier (FBMC) receivers to mMIMO communication systems and investigates the corresponding FBMC transceiver advantages over OFDM. To this aim, we derived the signal-to-interference ratio (SIR) expressions analytically under several channel impairments such as timing offsets and carrier frequency offsets. Furthermore, we conducted an asymptotic study on the performance of FBMC augmented with our proposed receivers in the context of massive MIMO systems. While still outperforming OFDM, results for FBMC show that increasing the number of base station (BS) antennas does not increase the SINR unboundedly. We have validated the proposed analytical study by comparing its results with those obtained from Monte Carlo simulations and confirmed the superiority of the proposed receivers over those in mMIMO literature. Moreover, analytical and simulation results confirm that the Overlap-Save FBMC receiver can support asynchronous communications in the context of mMIMO, a cornerstone for grant-free communications and massive access.

A crucial element of cellular communication networks is the achievable spectral efficiency (SE). Indeed, motivated by the continuous growth in mobile data traffic in wireless networks, improving SE has represented one of the key goals of the 3rd Generation Partner Project (3GPP) along several generations of communication standards. In this paper, we propose a novel transmission scheme based on intentionally overlapping the subcarriers of adjacent users considering two state-of-the-art waveforms: the orthogonal frequency division multiplexing (OFDM) and the filter bank multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM). We investigate the achievable spectral efficiency improvement of the proposed transmission scheme in the presence and absence of timing offset impairments under the tapped delay line B (TDL-B) multipath 3GPP model of the 5G QuaDRiGa channel. According to the test results, the proposed transmission technique achieves up to 20% SE improvement for FBMC/OQAM when associated to the overlap-save FBMC receiver and 12% for OFDM.

Massive MIMO and filtered multi-carrier waveforms are considered as key enabling technologies for next-generation wireless networks. In this work, the Filter Bank Multi-Carrier (FBMC) waveform solution applying our previously proposed short filter and advanced receivers is extended to massive MIMO systems and evaluated in comparison to OFDM. Simulation results are presented for the non-line of sight (NLOS) 3D Urban-Macrocell (UMa) model of the 5G QuaDRiGa channel. Results show that the solution applying the proposed Overlap-Save (OS) and Overlap-Save-Block FBMC (OSB) receivers out-performs OFDM under timing offsets, carrier frequency offsets and Doppler spreads. Moreover, they confirm that the Overlap-Save FBMC receiver can support asynchronous communications in the context of massive MIMO, a cornerstone for grant-free communications and massive access.