Time-asymmetric and subcarrier-specific pulse shaping in ofdm-based waveforms

Abstract

In orthogonal frequency-division multiplexing (OFDM) systems, suppressing the out-of-band (OOB) emission with pulse shaping comes with a price. The expense emerges in designing the transition between consecutive symbols. The price can be either the reduction of spectral efficiency (SE) with symbol extension for better transition or the introduction of intersymbol and intercarrier interference (ISI and ICI) due to reduced cyclic prefix (CP) size. In this paper, we propose a time-asymmetric and per-subcarrier (per-SC) pulse-shaping method to minimize the introduced interference without sacrificing SE and OOB performances. Although time-asymmetric pulse reduces the interference due to shortened CP by exploiting the asymmetry in channel delay profile, it causes spectral growth. Thus, the time asymmetry of the pulse-shaping function is gradually increased for the inner SCs that have wider spectral room to the OOB region. A generalized Kaiser window with adjustable time asymmetry is introduced to the provided framework. Theoretical and simulation results showed that the proposed technique achieves superior BER performance while achieving the same level of OOB suppression of pulse shaping and SE of plain OFDM.