Performance of NR Physical Random Access Channel in the Presence of Carrier Frequency Offset in Millimeter-Wave Bands

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This paper presents the miss-detection probability (MDP) of the Physical Random Access Channel (PRACH) with a short sequence for the 3GPP New Radio specifications in the presence of carrier frequency offset (CFO) in millimeter-wave bands. At a base-station receiver, the correlation of every repetition unit of the PRACH-preamble sequence between the received PRACH signal and the PRACH-preamble sequence candidates is computed using a matched filter in the frequency domain. This is followed by combining the correlations of the repeated PRACH-preamble sequences that correspond to the fast Fourier transform blocks in the time domain. The multiple correlations of the repeated PRACH sequences are combined by coherent combining with in-phase and quadrature components or by combining in squared form in the power domain, followed by the detection of the sequence and received timing of the desired PRACH. This paper first investigates the effect of the repetition of the PRACH-preamble sequence on reducing the MDP for various 3GPP Tapped Delay Line channel models in non-line-of-sight (NLOS) and LOS environments. Next, we establish the best combining method for the correlations of the repeated PRACH sequences from two candidates based on the PRACH MDP for various types of PRACH formats and for various subcarrier spacings (SCSs) from 120 kHz to 960 kHz in the presence of CFO based on extensive simulations. We also show that a wide SCS of up to 960 kHz is effective in reducing the PRACH MDP in the presence of CFO for the frequency stability of a set of user equipment of up to 3 ppm at the carrier frequency of 60 GHz.