Multicarrier Waveform Design and Optimization for Doubly Dispersive Wireless Channels

Overview

Sixth-generation (6G) wireless networks and beyond must support reliable communication in high-mobility scenarios, such as aerial, vehicular, satellite, and high-speed train networks. The wireless channel in these scenarios is a linear time-varying (LTV) channel that imposes severe doubly-dispersive fading and asynchronous user access. Classical orthogonal frequency division multiplexing (OFDM) fails under these conditions because doubly-dispersive fading destroys subcarrier orthogonality, highlighting the need for alternative waveform designs. This thesis develops a structured approach to multicarrier waveform design for LTV channels. We construct a periodic table of waveforms to provide an interpretable design process for multicarrier waveforms using a three-parameter synthesis equation. We then optimize the joint transmit-receive pulse shape of filter-bank multicarrier (FBMC) waveforms for multiple-access LTV channels. We formulate the optimization problem as alternating generalized Rayleigh-quotient sub-problems with closed-form solutions. The resulting waveform tolerates 20 dB of power imbalance under fully asynchronous access and cuts guard-band overhead by 91%. Moreover, we show that using Zadoff-Chu (ZC) chirp modulation uniquely collapses the two-dimensional delay-Doppler dispersion onto a single chirp-domain delay. A pairwise error probability analysis reveals that the ZC root parameterizes a tunable diversity-complexity trade-off, yielding up to 10 dB gains over OFDM on the Extended Vehicular A channel at 540 km/h.