A Generalized Spectral Shaping Method for OFDM Signals

TL;DR

This paper introduces a unified spectral shaping method for OFDM signals using generalized pulses, significantly reducing out-of-band emissions while maintaining data throughput and simplifying implementation.

Contribution

It proposes a novel generalized pulse design that unifies pulse-shaping and active interference cancellation, enabling analytical PSD calculation and improved spectral confinement.

Findings

Achieves compliance with strict PSD masks with less than 4% data loss.

Reduces out-of-band emissions compared to traditional methods.

Simplifies implementation through data-independent optimization.

Abstract

Orthogonal frequency division multiplexing (OFDM) signals with rectangularly windowed pulses exhibit low spectral confinement. Two approaches usually referred to as pulse-shaping and active interference cancellation (AIC) are classically employed to reduce the out-of-band emission (OOBE) without affecting the receiver. This paper proposes a spectral shaping method that generalizes and unifies these two strategies. To this end, the OFDM carriers are shaped with novel pulses, referred to as generalized pulses, that consist of the ones used in conventional OFDM systems plus a series of cancellation terms aimed at reducing the OOBE of the former. Hence, each generalized pulse embeds all the terms required to reduce its spectrum in the desired bands. This leads to a data-independent optimization problem that notably simplifies the implementation complexity and allows the analytical calculation of the resulting power spectral density (PSD), which in most methods found in the literature can only be estimated by means of simulations. As an example of its performance, the proposed technique allows complying with the stringent PSD mask imposed by the EN 50561-1 with a data carrier loss lower than 4%. By contrasts, 28% of the data carriers have to be nulled when pulse-shaping is employed in this scenario.