Abstract
This study introduces extended-and-forward relaying for sub-terahertz (sub-THz) extended fronthaul link (EFL) via jointly implemented frequency division multiplexing at the fronthaul and wireless frequency extension for sub-THz relaying. EFL transmission and reception, phase noise (PN) induced symbol error probability, and operable frequency regions are modeled. Aggregated PN significance over distributedly synchronized (DS) and non-synchronized (NS) EFLs is compared. 180 GHz EFL on cascaded software-defined radio (SDR)-THz testbed is demonstrated with off-the-shelf SDRs, frequency extenders, and various radio frequency measurement tools. DS demonstration achieves 0 bit error rate over [Formula: see text] transmitted bits per user at measured signal-to-noise ratios between 11 and 13 dB, whereas NS shows 0.01 bit error floor with software controllable SDR clock aggregated 0.384 radian PN deviation at most. A digital post correction is proposed to suppress PN-related clock offset by dynamic phase correction, which achieves up to 0.088 BER decrement in NS, with the improvement varying by user and link distances.