Efficient Offline Waveform Design Using Quincunx/Hexagonal Time-Frequency Lattices For 5G Systems

TL;DR

This paper presents an optimized offline waveform design for FBMC systems with hexagonal time-frequency lattices, significantly improving robustness, SIR, and reducing out-of-band emissions in 5G channels with severe impairments.

Contribution

It introduces a novel offline waveform optimization method for hexagonal lattices in FBMC, enhancing performance over severe doubly dispersive channels compared to traditional OFDM.

Findings

Hexagonal POPS-FBMC improves SIR by 1dB over rectangular lattices.

Offers 10dB reduction in out-of-band emissions.

Provides increased robustness to frequency synchronization errors.

Abstract

Conventional OFDM, adopted in LTE-A systems, cannot provide the quality of service requirements sought in 5G systems because of extreme natural channel impairments caused by higher Doppler spreads and unexpected artificial impairments caused by multi-source transmission, to be brought by 5G, and by synchronization relaxation for closed-loop signaling overhead reduction in some 5G applications. These severe impairments induce a strong loss of orthogonality between subcarriers and OFDM symbols and, therefore, lead to a dramatic increase in ICI and ISI. To be well armed against these dramatic impairments, we, in the present paper, optimize the transmit/receive waveforms for FBMC systems, with hexagonal time-frequency lattices, operating over severe doubly dispersive channels, accounting for both natural and artificial impairments. For this, we exploit the POPS paradigm, recently proposed for rectangular time-frequency lattices, to design offline waveforms maximizing the SINR for hexagonal time-frequency lattices. We show that FBMC, with hexagonal lattices, offers a strong improvement in SIR with respect to conventional OFDM and an improvement of 1dB with respect to POPS-FBMC, with classical rectangular lattices. Furthermore, we show that the hexagonal POPS-FBMC brings more robustness to frequency synchronization errors and offers a 10dB reduction in OOB emissions with respect to rectangular POPS-FBMC.