A Waveform for 5G: Guard Interval DFT-s-OFDM

Abstract

Delay spread can be detrimental to communication systems. Orthogonal Frequency Division Multiplexing (OFDM)/Discrete Fourier Transform-spread-OFDM (DFT-s- OFDM) based systems (for e.g., Long Term Evolution (LTE), WiFi, etc.) tackle delay spread by adding a cyclic prefix (CP) before the start of the OFDM symbol. The duration of the CP is pre-determined and is set according to channel delay spread characteristics or to fit a certain frame duration. Moreover, the CP does not carry any useful data and represents an overhead that needs to be minimized. In this paper, we propose the use of DFT-s-OFDM with flexible, configurable guard interval (GI) of variable size. We call the resulting waveform GI-DFT-s-OFDM. The length of the GI can be adjusted to accommodate the maximum delay spread in a given scenario or for a particular user (UE). Additionally, the GI may carry a sequence that can be used for time/frequency synchronization. We also discuss system design based on GI-DFT-s-OFDM, giving possible options for the GI sequence. The proposed waveform has good Peak-to- Average Power Ratio (PAPR) with out-of-band emissions similar to OFDM/DFT-s-OFDM.