Frequency-Modulated OFDM: A New Waveform for High-Mobility Wireless Communications

Abstract

This paper introduces a novel waveform for wireless communication, denoted as Frequency-Modulated Orthogonal Frequency-Division Multiplexing (FM-OFDM). By frequencymodulating an OFDM signal and further defining a suitable cutoff subcarrier, the resulting constant-envelope waveform (ensuring a low Peak to Average Power Ratio) exhibits strong robustness not only to Doppler, but also to phase noise and carrier frequency offsets. These impairments introduce an additive error term at the information-bearing subcarriers that is mostly concentrated at the lowest part of the spectrum. No inter-carrier interference is thus present, and impairments can be easily overcome by mapping the information above a cutoff subcarrier. Theoretical expressions and numerical results prove the superiority of FM-OFDM over the state of the art, particularly in high-speed Rayleigh channels and/or high phase noise.

Overhead-Free Channel Estimation based on Phase-domain Injected Training for FM-OFDM

“…Recently, frequency modulated-OFDM (FM-OFDM) [4] is also proposed which is a variant of the existing CE-OFDM. The main advantage of FM-OFDM as compared to CE-OFDM corresponds to its high robustness against phase errors, i.e.…”

“…Consequently, the FM-OFDM inherits all the benefits of CE-OFDM. However, [4] also assumed that the channel impulse response is either perfectly known or estimated by transmitting a preamble-based pilot sequence at the transmitter, typically known as pilot symbol assisted modulation (PSAM). The channel is estimated in the frequency domain before performing the demodulation, similarly to the previous works on CE-OFDM [2], [3].…”

“…To the best knowledge of the authors, an efficient channel estimation method has never been proposed for FM-OFDM [4]. In this work, an overhead-free channel estimation method, namely phase-domain injected training (PIT), based on [5], is proposed for FM-OFDM which is capable of circumvent the excessive overhead induced by the transmission of preamble sequences.…”