Channel Estimation and Receiver Design for FBMC-OQAM and OTFS Modulation Schemes

Future generation wireless communication standards aim to have notable improvements upon the current communication standards. For example, the visions of 5th Generation (5G) and beyond communication systems include peak data transfer rate of 20 Gb/s, massive communication device capacity per unit area ( 10^6 per square km), end to end latency less than 1 ms, reliability and flexibility for supporting various applications when compared to the current systems. These critical visions should also be achieved in several complicated communication scenarios, including indoor, urban, dense urban, rural, and high-velocity scenarios. Many current systems utilize a multicarrier modulation technique called cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM). Although having multiple advantages, e.g., simple channel estimation and low-complexity channel equalization, the drawbacks of CP-OFDM, e.g., reduced spectral efficiency, problem of high out-of-band emissions, and degraded bit error rate (BER) performance in high-velocity communication scenarios makes it difficult for CP-OFDM to achieve future visions. As a result, several waveforms such as filterbank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) and orthogonal time frequency space (OTFS) are suggested in the literature to overcome CP-OFDM’s drawbacks. This thesis examines these OFDM alternative schemes with a particular focus on channel estimation, which in theory is not as straightforward as in OFDM. The notable contributions made to the literature through this thesis are: • An in-depth analysis of the FBMC-OQAM system’s intrinsic interference and its symmetry properties. • Proposal of a Generalized Least Squares based channel estimation technique which takes into account the correlated nature of noise-plus-interference of the FBMC-OQAM system. • Theoretical analysis of channel estimation mean squared error (CE-MSE) for conventional virtual symbol and Generalized Least Squares based channel estimation scheme. • Analysis of the OTFS received symbol’s variance, and proposal of a minimum mean squared error (MMSE) channel, estimator. • A low-complexity maximum likelihood (ML) channel path detector for the OTFS system is proposed. The proposed channel estimation (CE) schemes for FBMC-OQAM and OTFS systems are shown to outperform significantly compared to state of the art. The proposed schemes’ performance gains are demonstrated through theoretical CE-MSE analysis, bit error rate (BER), and CE-MSE simulations.