Utsaw Kumar

A comparison of waveform candidates for 5G millimeter wave systems

Fifth generation wireless systems will heavily rely on available bandwidth in millimeter wave frequencies to achieve the very ambitious data rate targets that have been set forth. Besides overcoming challenging propagation conditions with reasonable implementation complexity and power consumption, careful system design is needed. In this paper we address a fundamental component, the waveform. We first characterize the requirements, and then explore possible multi-carrier and single carrier waveforms. Our analysis shows that design tradeoffs for millimeter wave are different from lower frequency bands, and that DFT-spread waveforms may represent a balanced solution between spectral efficiency and robustness to implementation impairments. Furthermore, we propose a newly introduced waveform, GI-DFT-s-OFDM, as a suitable candidate.

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

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.