BER for QAM Schemes and LDPC Coding Rates in the Presence of Strong Phase Noise in Sub-THz Bands

This paper presents the bit error rate (BER) performance for various quadrature amplitude modulation (QAM) schemes with low-density parity-check (LDPC) coding using pilot symbol assisted (PSA) - extended Kalman filter (EKF) phase-noise compensation (PNC) in the presence of strong phase noise (PN) for orthogonal frequency division multiplexing (OFDM) waveforms in sub-terahertz (sub-THz) bands. In the sub-THz bands, PN is a significant hardware impairment and comprises random Wiener PN and uncorrelated Gaussian PN. Hence, in this paper, we propose a compensation method for the correlated Wiener PN by using PSA-EKF PNC and to make use of the large coding gain from the LDPC code to mitigate the effect of the uncorrelated Gaussian PN in the sub-THz bands. Based on computer simulations, we show that the loss in the required received signal-to-noise ratio (SNR) at the BER of $10^{-6}$ compared to the case without PN is suppressed to less than 1.0 dB for both QPSK and 16QAM with the LDPC coding rate of $R=8 / 9$ for the power spectral density level of an uncorrelated Gaussian PN of $-105 \mathrm{dBc} / \mathrm{Hz}$ or lower. We also show that the 64QAM scheme achieves the BER of $10^{-6}$ by utilizing the LDPC coding gain at the cost of an increase in the required received SNR in the presence of strong PN in the sub-THz bands.