Spectral Properties of Multicarrier Signals Under Broadband Signal Alignment

Broadband signal alignment (BSA) is a recently proposed scheme that introduces frequency-domain repetition coding in multicarrier transmission. Combined with canonical correlation analysis (CCA) at the multiantenna receiver, this approach provides robustness against strong interference. We derive an analytical expression for the power spectral density (PSD) of BSA-encoded multicarrier signals and show that the original scheme generally degrades out-of-band sidelobes. We then propose a modified BSA approach that unlocks additional degrees of freedom to be exploited for sidelobe reduction while preserving the interference resilience of the original scheme. Our analysis reveals that the frequency-domain data repetition pattern is a critical design parameter, as it significantly impacts both spectral characteristics and error-rate performance.