Search

Sixth generation (6G) wireless networks are envisioned to provide global coverage for the intelligent digital society of the near future, ranging from traditional terrestrial to non-terrestrial networks, where reliable communications in high-mobility scenarios at high carrier frequencies would play a vital role. In such scenarios, the conventional orthogonal frequency division multiplexing (OFDM) modulation, which has been widely used in both the fourth generation (4G) and the emerging fifth generation (5G) cellular systems, is vulnerable to severe Doppler spread. A new two-dimensional modulation technique called Orthogonal Time Frequency Space (OTFS) modulation designed in the delay-Doppler domain is introduced. Through this design, which exploits full diversity over time and frequency, OTFS coupled with equalization converts the fading, time-varying wireless channel experienced by modulated signals such as OFDM into a time-independent channel with a complex channel gain that is roughly constant for all symbols. In this paper, we evaluate and analyze the performance of the OTFS receiver using four data detection algorithms: Single-tap frequency domain equalizer, Linear minimum mean-square error detection (LMMSE), Message passing detection (MP), and Maximum-ratio combining detection (MRC). Further, we extend our study to the variants of OTFS, where the waveform is transmitted with a cyclic prefix (CP) or zero padding (ZP) added to each OTFS frame or block. The simulation results show that the MRC detector can be improved the detection of the OTFS receiver. [ABSTRACT FROM AUTHOR]

Filter bank multicarrier (FBMC) was proposed as an alternative approach to cyclic prefix - orthogonal frequency division multiplexing (CP-OFDM). FBMC is considered a promising non-orthogonal waveform due to its very low out of band radiation and high spectral efficiency. Nevertheless, the orthogonality constraint for FBMC/OQAM is relaxed being limited only to the real field which causes intrinsic interference. The presence of this interference leads to incompatibility between some well-known multiple-input and multiple-output (MIMO) schemes and FBMC/offset quadrature amplitude modulation (OQAM). From this perspective, we proposed in this paper an efficient implementation for FBMC/OQAM based on block spreading to restore the complex orthogonality to enable applying MIMO with FBMC/OQAM. The proposed scheme uses a discrete Haar transform (DHT) to enable low computational complexity. The performance of proposed approaches has been investigated and compared with CP-OFDM under three MIMO schemes, as space-time block coding (STBC) Alamuoti schemes, spatial multiplexing with zero-forcing (ZF), and maximum likelihood (ML) detection schemes. The simulation results show that the proposed schemes enable to apply of the MIMO schemes with FBMC with almost the same performance and complexity as CP-OFDM. [ABSTRACT FROM AUTHOR]