Performance of OFDM and DFT-s-OFDM in the THz-Band Communications Channels




Khorram, Erfan

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The terahertz (THz) band is a promising frequency band that ranges from 300 GHz to 10 THz and being considered for the next generation of wireless networks due to the large available bandwidth and achievable ultra fast data rates. The first step in studying every wireless system is to accurately characterize the propagation channel. Therefore, in this thesis, a channel model is proposed with unique terahertz propagation characteristics that can be used to study candidate waveforms in the THz band. The next step is to study the candidate waveform designs. In this work, orthogonal frequency-division multiplexing (OFDM) and discrete Fourier transform-spread-OFDM (DFT-s-OFDM) are examined waveform candidates in the THz band. As OFDM is widely used in industry and thoroughly studied in the past couple of decades, it can be used as a benchmark for multi-carrier waveform designs. This study helps us to understand if OFDM can still be a reliable waveform in higher frequencies and how it compares with single carrier DFT-s-OFDM. In the first part of the thesis, the multi-ray communication channel is modeled based on ray tracing methods which consists of line-of-sight (LoS), reflected, and scattered paths. This model is a modified version of an existing multi-ray channel model with improvement. The coded OFDM and DFT-s-OFDM systems are studied by simulation in terms of spectral efficiency, CP length, peak-to-average power ratio (PAPR), phase noise, etc. DFT-s-OFDM is shown to possess advantages over OFDM in scattering rich THz channels with better PAPR, error performance and tolerance to phase noise, making it a preferred candidate over OFDM.



OFDM, DFT-s-OFDM, Terahertz, Phase noise