Multiplexing Scheme for Initial Access Control Signals Using Dedicated Frequency Bandwidth in Sub-THz Communications

This paper proposes a scheme that multiplexes control signals for initial access using a dedicated frequency bandwidth in the sub-Terahertz (THz) bands. We employ subcarrier spacings (SCSs) in a dedicated frequency bandwidth that are narrower than those for other frequency bandwidths that multiplex shared channels used to convey user data and control channels in the physical layer in both the downlink (DL) and uplink (UL). The estimation accuracy of fractional frequency offset (FFO) based on the autocorrelation using the cyclic prefix (CP) that is attached to each discrete Fourier transform-spread orthogonal frequency division multiplexing (DFT-S-OFDM) symbol is improved due to the increase in the CP power as the SCS becomes narrower. Accordingly, the narrower SCSs for the control signals in the initial access enable us to achieve a high physical layer cell ID detection probability by making effective use of the FFO estimation and joint estimation of the integer frequency offset (IFO) and primary synchronization signal (PSS) in the DL. Moreover, the narrow SCS achieves a relaxed round trip time delay measurement based on the physical random access channel (PRACH) with a low computational complexity in the UL. We also present a synchronization signal block structure in the DL and PRACH structure in the UL that are suitable for the sub-THz bands.